RepRap: Builders

Been a while, but I am still going

2011-12-26T13:41:00.001-08:00

Hi all, it has been a long time, but I have something to show.

I have the 3 axes working now. I connected a pen and drew some lines and made a 5 x 5 inch square approximately (that is right about 127 mm for the metric crowd). I found that my Gen 3 electronics now reside on deprecated electronics pages? I was thoroughly disturbed till I found out that is someones opinion. Mostly I fixed that by ordering a stepper carrier for the stepper motor, I don't want that whining from enabling stepper drivers from the dc designed controls.

Boot-strappable Open Laser Cutter: Part 2

2011-09-17T18:00:00.000-07:00

Hi folks,

I thought I'd post a quick update to my Open 3D-Printable Boot-strappable laser cutter) project. While some of the finishing touches or aesthetic details (such as side panels, or a top) are still incomplete, the machine moves fantastically under EMC2, and I've had much of the design built for some time. The main issue that I'm encountering right now is in aligning the laser beam to be accurate over the course of the 1m x 1m travel area, which I'm finding is not easy (but more on that later). Here's a tour of the printed parts, so far:

The system uses linear rails and pillow block bearings for linear travel on each axis. Upon each of the pillow blocks mounts a carriage -- in the case of the bottom axis, these carriages contain (1) two shaft holders, for the shafts on the top axis, (2) a pinch mechanism to hold onto a timing belt, and (3) either a mirror holder/idler mount (on the left side), or a NEMA 17 motor mount (on the right side). This is the mirror mount version, with the idler for the top axis also visible.

The timing belt goes through a pinch loop to keep it taught and transfer its motion to the pillow block. This pinch loop has an open center, so one can use large loops of timing belt without having to cut the belt and break the loop (I think this is a handy feature, incase you plan on making a larger machine, or using the belts for something else later).

The carriage for the NEMA 17 stepper motor that drives the top axis sits on the right hand side of the lower axis. I'm using the NEMA 17 motors from Adafruit ( [link] ) since they're relatively inexpensive at only $14.

The top carriage slides on the two shafts held by the lower axis, and also contains a mount for the Z-mirror and focusing lens. These optics are relatively inexpensive, and are from Light Object's build-your-own bundle ( [link] ) that a lot of folks on buildlog.net are using to build their own laser cutters.

The NEMA 17 stepper motor brackets for the bottom axis are much as they were in the last post, and have worked out pretty well so far. They mount to the aluminum extrusion with standard M5 bolts, and are reversible -- so they can face either left, or right. These are the same Adafruit steppers as used above, and there are two used on the bottom axis (one to drive each side).

The idler pulley brackets for the bottom axis are much as they were in the first iteration, only I've added a little more support to the design so they can take a bit more stress. They mount to the standard 20mm Misumi aluminum extrusion using the same standard M5 bolts that everything else uses. I've also added in a nylon bushing between the timing pulley and the M3 bolt that it's spinning on, which makes it glide fantastically better. All in all, I estimate that each idler mount with the hardware (minus the pulley) is only a dollar or two -- so very inxpensive. (Thanks to everyone who posted suggestions in the comments of the last post!)

The static mirror mount holds a mirror that deflects the beam at a right angle, from the CO2 laser, down the bottom axis. It then deflects off the mirror held on the bottom axis carriage toward the Z mirror on the top axis carriage, and onto the work piece.

This piece went through a bunch of iterations, largely because it's about 80mm high and needed to be rigid enough to not jiggle while the machine was moving. The hitch to this is that there are a bunch of bolts for mounting the mirror (top) or mounting the whole thing to the aluminum extrusion (bottom), so it can't easily be made solid. In the end this design works out pretty well, and is fairly rigid.

The laser mount was a fun and challenging part to design. The laser is about 2" in diameter, and also needs adjustment screws with another half inch or so of travel on either side. In my design, the laser also sits up 3 or 4 inches off the height of the aluminum extrusion. This is to allow a lot of depth to the cut chamber, and potentially enable some SLS experiments with a broader spectrum of materials than the Open Selective Laser Sintering project was able to use.

In the end, while I had designed some single piece holders, they were too large to print on anything but a RepRap, and so not too useful to the Makerbot folks. They also used a fantastic amount of plastic, so I decided to rethink the design. In the end I settled on using these 3D printable mounts, and mounting the laser tube itself into a piece of ABS pipe. While I was definitely into a "print everything you can" mindset, in this case I decided that a quick trip to the hardware store and $10 was more than worth the 10 hours of printing custom holders. I was also a little more comfortable with tapping the ABS pipe, and believing in its rigidity to hold the CO2 laser at exactly the right level. Even being off by a few millimeters could mean the beam hitting something it shouldn't (like a printed mount), and causing a catastrophic (and undoubtedly spectacular) failure.

This mount I'm actually very happy with, and it fits the CO2 laser wonderfully. Rather than use the CO2 laser for testing, for safety reasons I'm using a laser pointer that I've placed into a long ABS tube for alignment.

The CO2 laser tube tends to arrive in a fantastically large package to keep it safe (here, with a 3D printer and ikea desk for comparison ;) ).

The tube itself is about 70cm long, and about 2 inches in diameter.

The laser mount tube has a bunch of large nylon bolts placed at 120° angles to help adjust the laser path.

Here's the complete optical path, with both axes near their home positions. The total travel is quite large (about 1 meter by 1 meter).

For the controller, I'm using Bart Dring's Laser Interface Driver board. Honestly, I'd considered making my own board, but for just under $150 with the Pololu stepper controllers and connectors for something that's predesigned, it's really not that bad. I figured that the parts and a run of boards would cost me about the same to make, and this has already had the bugs worked out and has run quite well with EMC2 out of the box. I have had nothing but positive experiences using it, and it's even worked out well with the 2 steppers for the bottom axis plugged into a single driver. My only complaint is that it's a bit tricky to calibrate the voltages in on the stepper drivers, but that's more an issue with the spot Pololu's chosen to place the test point, and really you only have to do it once.

With the lights off, it's much easier to see the test beam in this picture. I'm having some issues aligning the optical path, and so I'm at a bit of an impasse. The beam seems to be at the same height at either end of the bottom axis, but in the middle it appears to move up a few millimeters (which corresponds to the entire carriage moving down a few millimeters). This isn't great, appears to get amplified as it moves down the +1meter on the final optical path before being sent to the workpiece. By the time the beam hits the Z mirror when the top carriage is at the far end (all the way to the right), it can wander quite a bit -- say up to 5mm or more. The beam width of the CO2 laser should be about 6-7mm by the time it reaches that distance, and the aperture to the Z mirror is only about 9mm wide -- so any divergence from being true really isn't okay.

As near as I can tell, this dip is coming from a bit of a sag with the rods. Placing a little bit of upward pressure on the bottom of the pillow bearings tends to level the optical path out, and so the rods appear to be sagging -- likely from a combination of their own weight, and the weight of the top axis. The rods are fairly large in diameter -- 12mm, or 1/2 inch -- so I didn't expect any sag, but I've also never constructed a machine that has a meter of travel before. It's not clear to me whether there's a quick hack I could do to help support the axis (perhaps sticking another piece of aluminum extrusion under the pillow bearings, along with some tiny wheels for it to travel on and keep the distance constant) -- or whether there's a better and inexpensive solution, like moving towards something like Bart's Makerslide v-rail based aluminum extrusion. I've noticed that the lasersaur folks seem to be using aluminum extrusion too, and are also dealing with similar distances to my design (I think their travel is about 2x4 feet, which is about the same as this design at 3x3 feet). That being said, I've noticed they've been in beta for quite some time, and haven't seen a video of their system cutting at full travel, so I'm not sure if they're also having issues with sag in their aluminum extrusion system at those large distances. Doing a couple of quick sag tests with some spare extrusion, it looks like it definitely sags less than the rods -- so it definitely has the potential to be a replacement if it comes to that. I'd just feel safer if there was an existance proof out there first for such large travels.

That's my quick update! Because this is an open project, I've posted the Google Sketchup and STL files to Thingiverse (available here: [link]), though there are still a few bugs left with alignment and such. Still, there are a bunch of interesting design elements that might be useful for other projects.

Thanks for reading, and please feel free to send along your comments or suggestions!
~peter
[Laser Cutter part 1] [OpenSLS Part 8] [http://cogsci.mcmaster.ca/~peter/]

Hot Plastic

2011-08-04T13:55:00.000-07:00

Hot plastic. My extruder was running on the hot side, Nophead suggested this was due to the difference between the internal and external temperatures and he was spot on. Whilst I had originally constructed my Thermistor lookup table using a temperature probe clipped to the outside of the nozzle the inside was running a good 40 to 50 Deg C hotter. The problem is fixed now and a new thermistor table is in place all with the help of an Arduino based tool to help the process along.

Boot-strappable Open Laser Cutter

2011-05-30T13:33:00.000-07:00

Hi folks,

I thought I'd take a second to make a quick post about a bootstrappable open laser cutter design that I've been working on. I know I haven't posted relating to the Open Selective Laser Sintering (SLS) Project much after the Reciprocating Laser Cutter. Much of my lack of work on the project was due to our local hackerspace moving over the course of several months (when I had to help construct the new space), before quickly having to finish my PhD and begin a postdoc.

I love having access to a laser cutter. One can construct rather large items fairly quickly, and the materials available (like acrylic) mean that not only will one's creations be structurally sound, but they'll often look wonderful too. While my dad and I have been tinkering with our own 3d printers for a couple of years now, I still feel very much a beginner in constructing 3d models, unless using a tool more geared towards programmers (such as OpenSCAD). That being said, when I was introduced to laser cutting, the relative ease of designing and working in 2.5D as well as the (even more rapid) time to go from design to physical prototype simply made my creative self very happy. I remember several times waiting impatiently at the laser cutter for it to cut out the next sheet of some design I'd made that afternoon -- and upon assembling it, realizing how silly it was to be impatient that I could design, fabricate, and assemble some fantastic machine in only a few short hours. Not only for the OpenSLS project, but also for other creative projects, art, and tinkering, I greatly miss having access to a laser cutter, and decided to investigate how expensive it would be to construct one.

Several other folks have already been in this exact place, including the lasersaur folks ( http://labs.nortd.com/lasersaur/ ), who aim to create a fairly large format open laser cutter, as well as Bart Dring's excellent work on the open buildlog 2X laser ( http://www.buildlog.net ), a smaller format cutter that uses mostly off-the-shelf components combined with a few custom CNC-made parts. When I started thinking about this a month or two ago, Bart had just released his new design and had begin shipping the first kits to folks, and had quite a waiting list built up. I decided to get on his waiting list, but that I'd also get ahold of some of the parts that I could (such as the laser and power supply) to get a head start.

When the laser arrived, I ended up realizing just how big the tube is. With a tube approximately 70cm long (not including the mirrors to steer the beam), I learned that most of the length of most laser cutter designs is taken up by the tube. For example, with the Buildlog 2X design, the tube sits along the entire back of the machine, while the front includes both the x/y axis in the cut chamber (about 2/3 of the volume), as well as a separate area on the right that holds the electronics (about the remaining 1/3 of the volume). This is similar to a bunch of other designs, including the Chinese laser cutter we were using at my old hackerspace. I decided that while the ~20x12" cut area of the Buildlog 2X laser was great and much larger than what I had used before, that if the tube plus optics was nearly a meter long, I might as well make the cut area as much of that space as I could, and just stuff the electronics (which are relatively small) somewhere else -- say, under the tube. Making one axis a meter long meant the other might as well be a meter long too, so that the cut area would be square. (Put another way, I realized that from a cost standpoint, increasing the size of the machine doesn't really add a great deal of expense -- but it increases the utility by expanding the size of what you can build. I remember hearing Bre Pettis say that one of his thoughts, after having used a laser cutter for so long now, was that he had wished they had found a larger one).

Using these rough guidelines and inspired by Bart's design, I worked on designing and constructing my own laser cutter. Bart's design is really great, and he's put some wonderful work into it. Not only that, his v-rail design looks to make creating even large machines relatively easy. Unfortunately, with such a large demand for his parts, I decided that I might have to try an alternate design, and went with a more traditional bearings-on-linear-shafts design. The buildlog folks have amazing solidworks skills, but being new to building laser cutters, I decided to just sketch something out on a piece of paper, order a bunch of t-slot parts, and figure it out as I went.

The general design keeps very much with what other folks have been up to -- a t-slot frame, where the laser sits at the back, and a 2-axis CNC system sits in the front. Most of the difference is that I've added some room at the back under the laser to hide the electronics. Keeping SLS in mind, I'm also trying to keep a bit of height in the build chamber itself for future tinkering.

The "top" axis consists of two shaft mounts at either end (that mount atop the pillow blocks), one containing a NEMA17 motor mount, and the other an idler pulley mount.

The carriage for the Z mirror and focusing lens mounts on several smaller pillow blocks as well. Like the buildlog design, I'm using the inexpensive mirrors, lens, and the respective holders from lightobject. The idler and carriage have mounts for these parts, but still need some work. I also still have to add the tension mounts for the "bottom" axis belts to the shaft holders.

The "bottom" axis is driven at each end by a NEMA17 stepper. I thought this might be easier than using a single dual-shaft stepper in the middle, and designing my own drive system. It does require a bit more electronics (namely a second stepper controller on that axis), but otherwise should simplify things mechanically quite a bit.

The steppers are the standard, torquey steppers that Adafruit sells. I think the dual-shafted steppers used on the Buildlog 2X laser have nearly twice the torque, but there is very little friction in this design -- so these should be more than okay.

I'm on iteration 2 or 3 on most of the parts so far (since this is a learning experience for me, too). The second iteration of the NEMA17 holder is pictured above -- it has mounts to fit in standard 20mm t-slot, and is reversible, so you can flip it around (for the other side).

The idler design is very simple and low-cost, but I'm not sure it will end up working in the end. Here, instead of a bearing, the idler cog simply slides upon an M5 machine screw, while two jam nuts ensure that the screw holds in place and doesn't move. This seemed to work great before I started tensioning the belts, but now there appears to be quite a bit of friction, so I'll likely have another look at this design, and try to find some small (inexpensive) bearings.

---

That's my quick update! While the design is still a work-in-progress and I'm refining and printing out the custom bits, the rest of the parts are all sitting on the workbench waiting to be added in as soon as the axis design works pretty well. It's kind of been my hope that using these 3D prints I could get the system to work well enough to then design and cut out a more precision set of axis parts using the cutter. That being said, as I learn how to design for strength and resolution limits the quality of parts is getting better, and the latest set of parts is remarkably rigid -- so much so, that I'm hopeful they might not need to be replaced, and could serve as a long-term set of functioning axis parts for the machine.

I'm very much planning to make the source files available on thingiverse when I have a working design, in the hopes that folks with a reprap, cupcake, or thingomatic who are also interested in using their 3D printer to bootstrap their own laser cutter might find them helpful.

thanks for reading!
~peter

RepRap @ HacDC

2011-05-25T13:10:00.000-07:00

HacDC, Washington DC's hackerspace, is building a Prusa Mendel. You can track our progress at the HacDC website (linked above) or if you're really interested, see what's going on behind the scenes on our wiki page.

The Ultimaker available for pre-order now!

2011-03-28T01:59:00.000-07:00

The last few months have been very busy ones for us, we done quite some testing with the Ultimaker, started a company, searched for the right material suppliers, worked on our webshop, and so on. We initially planned to start in December but the combination of starting a new company and developing an all new 3D printer design took more time than we counted on.

As of NOW the Ultimaker is available for pre-order from our shop, yay! We will ship it in four to six weeks.

In addition to the many people who have contributed to the Ultimaker (RepRap community, thank you!!), we would especially like to thank the participants of first and second Ultimaker workshop at the Utrecht Fablab Protospace for providing such a lot of feedback to us, it has been really helpful in making the Ultimaker a great product.

Why the shameless plug? Because we couldn't have built this product without our participation in the RepRap project, which has always been a great experience. We hope to keep cross-fertilizing each other and have overlapping communities. Also, sooner or later someone is going to print an entire Ultimaker. Also, the shop sells plastics (many colours available) and at some point we want to sell many separate parts that are useful for all you DIY 3D printer builders. I thought it was appropriate to post this here too. If not, I apologize.

Adrian Heads North

2011-03-22T03:16:00.000-07:00

Dig out your Pocket Tech (or Diary) and make a note of the 28th of March.

Adrian Bowyer The man, maker and reprap visionary is coming to Sheffield to visit the Sheffield Reprap Users Group.

Everyone is welcome, if you would like to drop in and meet Adrian, see some Reprap machines, hear Adrians presentation or get in touch with the User Group, sign up for a ticket (currently free) and come visit us.

eTickets are available online here: http://reprap1103.eventbrite.com/

Please do take the time to register for a ticket as this will help us towards making sure we have enough space to get everyone in.

Sheffield RepRap Group Builds a Prusja

2011-03-07T12:23:00.000-08:00

The Sheffield Reprap Group building a Prusja Mendel abely assisted by Jean-Marc who brought along the RP'd parts and some other kits to make up the build.

To read about the evening and the next planned build day follow this link:

Warez for the Min1284p Controller Board

2011-01-18T10:43:00.000-08:00

Having set off to build and use the awesome FiveD on Arduino firmware for my minimalist DIY micro-controller board I found we were short a boot-loader. Unfortunately the ATMega1284P whilst being a drop in replacement for the Sanguino's 644P doesn't have a boot-loader ready to go and is arguably a little way off the beaten Arduino Path. I modified the Arduino IDE 22 source for the stk500v2 boot-loader and have managed to persuade this to load and work.

You can get the modified source and a pre-compiled hex file (20Mhz crystal) here.

I guess this is also a do-able upgrade path for owners of through hole Sanguino boards.

Make a Rugged Stepper Driver

2010-12-19T07:37:00.000-08:00

First part of my two part project to create a decent rugged stepper driver board is complete.

The project is written up as far as it goes here.

This is a simple, manually configured driver board that can do micro-stepping and can be made by a kitchen table constructor. It is not meant to be small and there are no surface mount components used in it's design.

Based on the Toshiba TB6560AHQ stepper driver IC it features 2.5A continuous and 3A peak drive with advanced current control features. Plenty for any model of RepRap.

The second part of this project is to convert the design to a SPI based programmable controller with step and direction signals that allows full 5D driving from a micro-controller with a limited pin count. (28Pin Arduino)

But first to build a few of the manual boards and evaluate them on my Huxley build.

Mechanical Build Done

2010-11-26T04:18:00.000-08:00

The mechanical part of my Extended Huxley build is done. Excepting of course the parts I want to print with it and replace. But that comes later.

Detail shots to help other builders, together with commentary and some notes on what I discovered could perhaps (perhaps not ?) be improved can be found on my Blog.

The Palace of Glitering Technological Delights

Building Huxley

2010-10-14T05:48:00.001-07:00

Here's the Huxley I have been building. The plastic parts were kindly printed out for me by Nophead and the print quality is really excellent. It was almost a shame to use them. But I got over that.

I have blogged the build so far on my blog and docs site.

As you can see from the piccy the mechanics are almost done except for the Y axis. I am struggling to locate a suitable 2d drawing of the squashed frog that I can put hole centres on and extract dimensions from. Adrian and Erik have been helping with this so hopefully we will have a solution soon.

The Huxley is slightly oversize as it has been scaled up to take standard lengths of Silver Steel (Drill Rod in the US) as guide rails. The dimensions I used for the threaded rods have been added to the the wiki Huxley pages.

Quick Arduino or Netduino Shields

2010-10-09T11:42:00.000-07:00

Ok what’s a Sanguino guy doing messing around with little Arduino’s?

Actually I happened across the Netduino product offering which like the RepRap project supports open source as an operating principle.

http://www.netduino.com/

The strength of Netduino is that you can program it in C# easily with break points, variable modifications, basically everything you could ask develop/debug environment, except modify
the code on the fly.

How is C# open source?

Microsoft has released the entire .NET micro framework and porting kit under the Apache license, while continuing to support with a small team on the Codeplex website. In support of open source the netduino people are busily extending the support where it can interact easily Mac's and Linux as development platforms.

From a RepRap standpoint I am experimenting with this and specifically looking at creating a virtual com port driver so that we can leverage the micro framework for USB, network and SD card connectivity in front of the Arduino type processors.

The netduino family currently has two members. The base Netduino and the Netduino Plus that has a micro SD card and Ethernet interface on board.

From netduino

Since the netduino is open source we could use the same processor chip with a few components to provide USB interface on steroids for the RepRap project.

Ok back to shields, I ordered a shield kit along with the netduino to experiment with.

From netduino

In working on USB drivers I needed to switch the Netduino from USB debugging to serial debugging and I was able to reuse the USB serial cable from my Sanguino project as the serial interface.

This involved hooking up four wires, which tended to come out so I needed an adapter shield for something a bit more robust.

Not wanting to use up the one shield I had on hand for this simple task I went for the quick, dirty (more on dirty later) and cheap (especially cheap!) solution.

Running down to the local consumer electronics store I was able to procure a perforation prototyping circuit board with equally spaced holes 0.1 inches apart.

Perfect quick cheap solution? Ah not so fast; there is a fly in the ointment when come the Arduino form factor! It turns out that the Arduino is only partially laid out on the 0.1 standard grid!

From netduino

The ones that are, are the power pins and analog pins on the bottom of the board and digital pins 0-7 on the top side of the board. Everything else seems to be offset 0.05 inch off of the standard grid, as you can see from the close up picture with the two jumper wires.

From netduino

Since my project serial cable interface project did not involve the upper range digital I was still free to proceed. So using the one proto board as an outline, I took a marker pen and drew around the basic outline and used a band saw to cut the board. If you do not have such a tool a hack saw could still make short work of it.

So in short order I had created my serial cable interface shield with a couple of big mistakes as my first effort.

From netduino

Ok what were the mistakes? First off I made a cut out for the power plug as I had noticed that the circuit board wasn’t flat when I did trial fittings on top of the Netduino with pieces of wire to test alignment, not realizing that connector pin strips would offset the board just enough to clear the power connector.

The second is that I put the serial interface on the centerline of the board which seemed logical at the time.

From netduino

However in doing so, I covered up access to the USB port!

Ok back to the drawing board, here’s how I would make a second attempt.

From netduino

I then got extremely busy at the day job and wasn’t able to return to this for a bit. In the meantime I decided that I didn’t care about it being nice and neat and here’s the next iteration.

From netduino

So another quick trip to the band saw to flip the connector up on top and some quick hot gluing and problem solved!

As to the upper digital pins not being in the 0.1 registration layout you can do like I did and simply make a cutout for them; then use a pin strip with wires to come back to the main area of the perf board.

As a side note the Netduino has a 3.3 volt processor that is 5V tolerant on the digital pins, most people suggest using a 3.3v USB cable, my suggestion is to stick with the 5V cable as you can take power from it and inject it on the 5V pin and have full functionality and power via the serial cable.

Plus you can reuse the cable with the Sanguino and other Arduino’s clones out there!

mass produced boards

2010-09-14T15:36:00.000-07:00

Hi,

I've got a team of people building RepRaps in the San Diego area. We are building Arduino Mega shield boards similar to the Pololu Electronics specified here:

http://www.reprap.org/wiki/Pololu_Electronics#Even_more_simplified_version_by_Peer

We are building in an extra stepper axis for people who want to experiment with dual extruder print heads or motorized belts. We want to fund a large run of boards. We would like to have the design professionally manufactured. This would mean very high quality boards at a low price. I plan on restricting the minimum component size to 0805. These are easily reworkable by human hands.

We want to fund the effort through the Open Hardware Bank.

http://www.wired.com/gadgetlab/2009/03/open-source-har/

The more parties interested in these boards the easier it will be to finance them. If you would be interested in purchasing one of these boards, please email me at brian dot korsedal at gmail dot com. I'll keep you in the loop on our progress.

If you would like to contribute or review the design before it is manufactured, please keep scanning blog posts. As the design matures, I'll post design files and ask for feedback from the community.

Making a lid for a potentiometer mounting box

2010-08-28T00:07:00.000-07:00

In which your narrator shows you a few tricks of the trade with thin-walled prints.

Do you want to read more?

Designing with a Reprap machine in the loop

2010-08-25T23:19:00.000-07:00

In which your narrator celebrates a return to craftsmanship made possible with the addition of a Reprap printer into the design process.

Do you want to read more?

Darwin makes a Child Mendel Video

2010-08-24T23:18:00.000-07:00

Hello All,

I've learned so much from the RepRap journey and I've been looking for a way to give back to the community for all that it has given me. I felt the best way to give back was to start videoing my progress from a Darwin RepStrap to a Mendel. Four months after I started filming I can finally share. I hope this video can be a tool for increasing the size of the community, and ultimately increase our momentum. We really are on the ground floor of a world changing technology!

Thanks for all the tinkering!

- Gavilan

onshoulders.org

This video can also be found here.

selective laser sintering part 8: reciprocating laser cutter

2010-08-24T18:49:00.000-07:00

Hi folks,

On Saturday afternoons, like any good grad student, I visit my parents place to do my laundry. While it's spinning around, my dad and I usually get up to some neat projects, and this is what we worked on this week.

I've had an idea for a while that one might be able to build an inexpensive laser cutter using a 1 Watt IR laser diode, as opposed to the larger 20-100 Watt CO2 tubes traditionally in something like an Epilog laser cutter, using a bit of a trick. Traditionally laser cutters have a lot of power, and (to my knowledge) are generally fixed focus, meaning that the focal point -- the hottest portion of the cutting beam -- stays at a fixed depth relative to the material that you're cutting.

Because commercial laser cutters have so much raw power, it doesn't so much matter that they're slightly out of focus at the top and bottom of the material -- even diverged, the beam still has enough power to cut. This gave me the idea that if one could dynamically adjust the focus of the beam, starting at the top of the material and moving it progressively deeper for a given x/y point along the cut path, one might be able to steadily "bore" through the depth of the material by having the most powerful part of the beam moving through the depth of the material. The advantage to this would be that one would be able to potentially use a much less powerful laser diode, and it would be much less expensive than a traditional laser cutter -- but the cuts would take much longer to create. Given that even inexpensive laser cutters are traditionally out of reach of most hobbiests or folks in the reprap community, this seemed like a potentially handy enabling technology. Working on the Open SLS 3D printer project, I also had the idea that since you have the laser there anyway for creating 3D SLS prints, you might be able to use the exact same device without the powder chamber create 2D laser cut objects -- essentially having a hybrid printer capable of 3D prints, 2D cuts, and 2.5D laser cut 3D objects (and any combination thereof). That seemed like an extremely fruitful thing to pursue, so away we went.

The test rig is beautifully simple. Borrowing from an idea my friend Trevyn at the local hackerspace had about using CD/DVD drive head mechanisms as very small CNC axes, my dad and I took apart a bunch of old drives from our junk pile and found the three nicest axes of the bunch. We stripped them down, attached two together perpendicularly to create a 2 axis table, and attached a third axis orthogonal to the table as the Z (depth) axis. Overall, the travel on each axis is very short -- on the order of about 1.5 inches (3-4cm) each, but this is more than enough for experimentation. The entire 3-axis device is very small, and fits in the footprint of a DVD drive -- infact, many of the structural components from the drives were used in the construction of the structural parts of the mini CNC system.

The laser from the SLS project was attached to the vertical axis, and the steppers (which seem to be 5V) were attached to the dsPIC and stepper controller I built for the SLS powder test rig. I wrote some simple code to move the table in a square pattern around 1cm on a side, and reciprocate the laser up and down at each point on the square-shaped path.

I loaded some flat black plastic into the device (I only had the back of a CD case -- about 1mm thick, and I'm not sure what the material is), and gave it a shot. To my surprise, it worked! The process was a little slow (it was probably cutting at around one inch per minute), but it worked -- all without any adjustments or calibration, on the first try.

I need to find some thicker material to test, as well as different material. I'd like to try black acrylic sheets, as well as black ABS sheets, if I can find them. For fun I taped a few sheets of the CD-case together, and it seemed to cut through most of two of them, but I have a feeling that the speed and depth will have to be adjusted for each material type and thickness. Pragmatically, I think my "reciprocating laser cutter" technique will have some limitations, and perform better when the focal length of the laser is large, producing a narrow, sharp focus, and reducing the amount of material around the perimeter of the hole that the beam has to melt to get to the "sweet" spot of the new focus, although this effect may be somewhat mediated at least in part by moving more slowly and in smaller steps down through the material. Through experimentation, I would be happy if I could successfully cut through 3mm material, and very happy with 4.5mm material -- thicknesses that start to become structurally useful in terms of creating 2.5D objects (like my entirely laser-cut linear axis ).

As a side effect of the boring process, one appears to be able to control the depth of the material that's taken off -- such that you will likely be able to mill to a specific depth in addition to cutting or etching, by simply adjusting the depth that the reciprocation process stops at.

Thanks for reading! :)

[part 1] [part 2] [part 3] [part 4] [part 5] [part 6] [part 6 video] [part 7] [part 8] [cogsci.mcmaster.ca/~peter]

Make a minimalist Atmega 644p/1284p Based Micro-Controller

2010-08-24T08:46:00.000-07:00

If you want a fun way to start with Amforth, a DIY Sanguino, a DIY RepRap Controller or just an Arduino compatible with more welly this one is for you.

This project was inspired by the Arduino and the Sanguino but was primarily for use as a RepRap Controller and general purpose Amforth development board.

http://aka47.adsl24.co.uk/serendipity/index.php?/pages/min644p.html

SuperSkein Update

2010-08-18T23:52:00.000-07:00

Okay thanks to a ton of great dev work from Revar and Clothbot, SuperSkein is now in a form I could recommend at least for test-driving in the community. The lack of infill is going to be trouble on some (okay many) builds, but with a config.txt file for settings and useful stuff like .dxf export and the MeshMRI, I feel like it's maybe worth it to show off so people can throw rocks at it.

Multiplatform downloads:
http://github.com/MaskedRetriever/SuperSkein/downloads

Right now the code's definitely not at it's prettiest but it'll slice pretty much any* .stl file, and the MeshMRI will give you a good idea as to why things are going screwy if you're not able to slice a file.

*as long as it's binary and not ASCII

RepRap @ FAB6 International Conference, Amsterdam

2010-08-13T00:35:00.001-07:00

Next week, the Sixth International FabLab conference will be held. The theme is "Industrial (R)evolution":

This year’s theme is Industrial [r]Evolution through which we will explore the implications and consequences of personal digital fabrication for art, business, industry, culture and education. We are poised on the threshold of a new era, like that of the Industrial Revolution, emerging from access to low- cost, high-precision fabrication tools and powerful Internet-based communication capabilities which are changing the ways we think about and approach innovation, invention, intellectual property, creative processes, computation, manufacturing and distribution, business models, and social and cultural networks. In a world where anyone can access the tools to make or create almost anything, the possibilities are limitless. This is the Industrial [r]Evolution, a socioeconomic and technical [r]evolution from mechanical means of production to digital means of production and communication.

Obviously RepRap will be represented there. By Adrian (per video conference), Rhys and myself. Adrian will talk about the legal implications of affordable, widespread 3D printing capabilities, Rhys will talk about multi-material printing and other recent and future developments and my part will be about the enormous adoption rate and other interesting statistics derived from the RepRap Survey. This will include previously unreleased information, but I will publish it around the time of the talk. Given your enormous collective effort, you guys deserve to be among the first to get this data!

I must say that I'm also looking forward to the other talks in our Thursday session:
Ron Weiss (video): BioFAB
Adam Arkin (video): Programmed Assembly of Cellular Networks
Josepn Jackson (video): DIY Biology

Larry Sass: Instant Fab Lab
Vicente Guallart: FabLab House
Matthias Kohler: Digital Materiality
Dale Dougherty (video): Makers

Hod Lipson: Rapid Assemblers
Jonathan Ward: Additive Assembly of Functional Digital Materials
Bre Pettis (video): The Robot that Sharing Built
Etc.
The full schedule can be found here. I will try to blogs about the other talks.

SuperSkein

2010-08-07T18:14:00.000-07:00

For the past two weeks or so I've been fairly obsessed with my latest distraction, SuperSkein:

http://github.com/MaskedRetriever/SuperSkein

It's certainly no SkeinForge killer at this phase, but I like to think that, written in Processing (which is crossplatform and basically Java), and starting from a pretty aggressively Object-oriented stance, it'll be much easier to maintain, branch, and improve upon than SkeinForge and perhaps in the end, even better.

As it stands there are two cases where I think it already beats SkeinForge:
* Meshes which are very large (SuperSkein is fairly fast even at 500k+ triangles)
* Meshes which are flagrantly non-manifold (such as just about any character design with an armature)

It can't do multiple shells yet, but some of the math groundwork is already put in. If anyone wants dev permissions just message me on GitHub and I'll add you.

Official Google Blog: Update on Google Wave

2010-08-04T14:38:00.000-07:00

Official Google Blog: Update on Google Wave: "Urs Hölzle"

Google's staged introduction of Google Wave killed it. It's useless as a communication tool unless you can involve the entire group of people you want to communicate with. But because (as usual) they were stingy with their invites, it wasn't possible to create a wave among your entire handbell choir, or boyscout troop, or 4-H club, or whatever. So nobody used it, and as the invites became more free, nobody was using Wave because Wave seemed useless.

Nothing wrong with Wave; everything wrong with people's perception of it.

Wave also needed to be integrated with other Google products, so that as your waves got updated, everything you visited in the Google universe should have had a link to Wave.

No more melting extruders: Removing PTFE from the hot end

2010-08-02T23:17:00.001-07:00

Hi folks,

Just a quick and very sleepy post before bed.

I have a confession. My extruder works far less often than it's in a melty state of not-workingness. And this makes me sad. And causes me to spend unneccessarily on PTFE barriers, which invariably melt due to being in contact with a 240°C heater barrel, causing the extruder to irreparably jam. This is just silly, and I decided that I needed a new hot-end extruder design if I was going to go more than a few weeks without a catastrophic extruder failure.

At first I had a look at the new design for the MK5 extruder, but it still uses PTFE (though I'm told not as a structural component), and it looks to contain far more custom machined parts and thus will likely be far more expensive. Being a graduate student, I decided to think cheap, and see what I could do with the parts I had. Recently, an all-steel hot end was put up on Thingiverse ( http://www.thingiverse.com/thing:3452 ) that looked very promising, but I didn't have much luck trying to drill a very accurate 3.2mm hole down the middle of an M6 steel bolt.

In the end, after some tinkering and chatting with my Dad, we settled on an all-metal hot end based on the parts that we had available. We used the existing MK4 hot end parts, and similar to lampmaker's all-steel hot end, we 1) reduced the nozzle to half height to reduce the length of the hot zone, and 2) added a thermal break in the brass heater barrel. We constructed some heat sink plates out of aluminum, and tapped these plates to M6 to encourage a good thermal contact between the barrel and the fins. A couple of small fans were also added, as in lampmaker's all-steel hot end design, to cool the fins.

Because the force of the fans was so great, and because this is new extruder was to be used on the simple and inexpensive acrylic makerbot-clone with a heated build table and chamber, we added in a small baffle to prevent the fans from cooling the print itself, and instead direct the air flow upwards.

We completed the design Saturday night, and so far after about 5 hours of printing, the hot end has performed virtually flawlessly. Because this design uses parts that people with already-clogged MK4 extruders will likely have on hand (except for the aluminum), and because you could conceivably make this with very simple tools, this design might be a great solution to either fix your currently broken hot end, or to experiment with an inexpensive, alternative hot-end design that you should be able to increase the temperature on to encourage a pretty good flow.

(click to enlarge)

happy tinkering! :) i hope this helps!

Anyone Got a Good Slice Organizer?

2010-08-02T10:39:00.001-07:00

I'm trying to get some momentum built up on an open source (and cleanly written) slice application here:
http://github.com/MaskedRetriever/SuperSkein

The code is (more or less) cleanly written but I've got a bug I'm having trouble tracking down, and I know for a fact Forrest Higgs has a slicer that solves this, but as far as I can tell he hasn't posted his code.

Basically, my sorting algorithm is orphaning edges, resulting in ugly jaggs around the perimeter near the end of each layer as the sorter picks up those last edges. Anyone have a better algorithm than the one I'm using?

Radiant heat?

2010-07-17T12:15:00.001-07:00

Hello everyone:

Thinking today about rep-rapping, I had the idea of trying to use radiant heat as a way to anneal the build object. this would be instead of a heated build chamber ( which presumably relies on convective heat transfer ), and probably in addition to a heated bed.

The idea is: could heat lamps with infrared output optimized for ABS's spectral properties, combined with the use of black ABS, cause the object to stay hot enough? Some quick reading seems to indicate that the ideal heater would emit 3500nm light to match best with the best aborbtion of plastics [http://en.wikipedia.org/wiki/Infrared_heater]

Maybe like These

I'm also thinking that the sides of containing envelope could be light colored or metal, so that they re-reflect as much light as possible onto the object. A black-colored bed might absorb enough light to cause it to heat without a separate light source.

This of course violates the reprap 12V goal; but it seems possible that a reprap placed in bright sunlight to utilize solar radiation to elevate temperatures somewhat, if the build envelope is designed to optimize solar gain. Solar ovens can easily get to 100C with very basic aluminum foil and a single reflector.

Has anyone tried this kind of approach?

changing the game, and using kapton tape as a slide

2010-07-15T17:51:00.001-07:00

Hi folks,

I've been working on redesigning the design for an entirely laser-cuttable x/y stage, and have some neat progress.

This design also uses a rack and pinion system, with a bunch of changes:
1) the linear gear is mounted horizontally, rather than vertically -- the weight of the entire axis is no longer suppored by the gear itself, but rather by a structural outcrop.

2) the axis is driven at four points (two from each side), rather than only a single point. this removes a lot of the shearing/binding issues. this is accomplished using a captive system of gears sandwiched inside the axis itself to transfer power from the stepper to four points along the edges of the axis.

3) a long piece of kapton tape is used as something like a linear slide, significantly reducing the friction between the axis and the linear gears that it rests upon. the axis slides *really* well with the kapton tape.

The result is a working linear axis that can be entirely constructed with a laser cutter, using only a handfull of screws, a $5 stepper, and a few pieces of kapton tape as vitamins. That's fantastic! :)

Thoughts:

So far it works pretty okay! There are a couple refinements to make:

4) Right now the gear on the stepper is just press fit -- I really need to key the gears and motor shaft, as the press fit wears quickly with the hardboard.

5) The gearbox is mostly just eyeballed, and there's probably an ideal solution when solving simultaneously for (a) a rack, with (b) two gears of radius R1, being driven by (c) another larger gear of radius R2; all for a given tooth size. Myself and a bunch of other physicist/math nerds at school have each had our hands at the problem, but haven't come up with a fantastic method of solving it yet (start with C, then find all the angles that B can attach to C, then determine if the distance between the centres of the two gears B modulo the gear pitch is an integer for each angle?).

Other thoughts:

6) This design seems great for the cross-axis. I have a similar design for the supporting axis with a MUCH larger captive gear system in it -- I'm not sure if the friction would be too much in that situation, or if it'd work out okay. (I stick a tiny washer under the gear, to reduce the friction a great deal -- maybe a nylon washer, or some kapton tape might also work out well?).

The alternative might be using a combination of two of these tiny "captive gear" axes, one at each end, for a supporting axis. This adds an extra stepper to the design (which is a negitive, although these ones are only $5!), but it also keeps the whole system fairly low, which would be kind of nice!

If anyone is curious to tinker, I've put the design files up on Thingiverse ( http://www.thingiverse.com/thing:3554 ). Happy tinkering, and thanks for reading! :)

[part 1] [part 2] [part 3] [part 4] [part 5] [part 6] [part 6 video] [part 7] [cogsci.mcmaster.ca/~peter]

Sheffield RepRap Users Group (UK)

2010-07-14T06:28:00.000-07:00

When: 26 July 2010, 19:00 till 21:00
Venue: The GIST Lab
Address: First Floor, The Workstation, 1 Grinders Hill / Brown Street, Sheffield, United Kingdom, S1 2BX

This month is the inaugural meet-up to help the group find its feet and shape the way it goes forward. It's a loose agenda, and an informal set-up.

Everyone Welcome
No experience necessary. Let's face it, this is the future we're building!

Interested in experimentation and building machinery that can self replicate?

In a nut shell RepRap is an open research project to make Rapid Prototyping Machinery that can Replicate it self ultimately completely but working towards is acceptable, hence RepRap. This event is a meet-up for folks who want to find out more or get involved, and to work on projects that push forward the boundaries of this technology research.

It's not dry research though .... we build stuff too. And that stuff will eventually be able to build itself ... welcome to the self-replicating machine odyssey!

Fore details and a map see :-

http://s1reprap1.eventbrite.com/

The Sheffield RepRap Users Group shares community space with the Sheffield Arduino Users Group (Shacknet)

http://thegisthub.net/groups/shacknet/

Amongst others at the GistHub

http://thegisthub.net/groups/

selective laser sintering part 7: x-y axis

2010-07-07T15:08:00.001-07:00

Hi folks,

Just a quick post -- I've been tinkering with the idea of making an entirely laser-cuttable x-y axis using nothing that isn't laser cut except bolts, nuts, and steppers (essentially things that wouldn't be immediately available at the simplest of hardware stores, plus the steppers).

I thought I'd post my progress so far, even though the latest iteration isn't going so well. Basically driving a long axis from one side introduces a shear force, so you typically would drive it from the center (like with a belt, or lead screw), drive it from both ends (either with two motors, or a long shaft that transfers the drive from both ends), or try and come up with some very precise linear rails and bearings that prevent all the shearing and torquing from happening. I chose to try that last bit, since all the other options involve extra parts (like shafts, belts, or screws), or extra motors. This isn't working out so well, but I still thought I'd post some pictures and my progress for informative purposes (sometimes design iterations that don't work out so well are just as informative as ones that do).

Happy to accept design thoughts from folks who have attempted this before?

thanks for reading!
Peter

[part 1] [part 2] [part 3] [part 4] [part 5] [part 6] [part 6 video] [cogsci.mcmaster.ca/~peter]

RepRap.org DNS change

2010-07-01T14:56:00.000-07:00

Just a short notice. We've switched DNS servers for RepRap.org. This should've gone completely unnoticed because we thought we knew about all subdomains (like forums.reprap.org). It appears we had an incomplete list and forgotten some of the lesser used ones, but it's not clear if we're missing more. So, a question to all of you:
If you notice a broken RepRap.org related service, please post a comment and Jonathan, Adrian or myself will get on it a.s.a.p.

whoah, it works! (inexpensive dual z-stages for SLS)

2010-06-28T21:02:00.000-07:00

Hi all,

As a quick follow-up to my last post, I thought I'd do a quick test of the dual z-stages without aligning anything just to see if the whole rig was in the ballpark of working.

It works! almost every nut in the thing unscrewed itself, but it works! :) and it's about 300 steps/mm with all the gearing and the screw pitch, so it's super precise!

Dismantling the Extruder

2010-06-24T12:55:00.001-07:00

Last night I took apart Kurzweil's extruder in order to replace the insulator.

First I liberated the whole hot end from the extruder in order to pull the insulator out. I ended up with this (apologies for my crappy cellphone photography):

Now I know when building this extruder James and I pushed the insulator all the way into the nozzle, but check out the plug of ABS that formed between the insulator and the smaller nozzle canal. My hypothesis is that at some point the nozzle got clogged and a little bit of ABS was able to squeeze between the insulator and the nozzle. Then it cooled, and the next time I operated the extruder, that little plug-seed got melted again, and some of the pressure that should have been sending the filament out of the front of the nozzle got put towards increasing that plug with new melted filament. All this is exacerbated by the fact that the insulator just above the nozzle was able to buckle and bulge out.

I was curious what that crazy bulge looked like inside, so we cut it open.

What my badly-focused cellphone picture doesn't show is that there is clear evidence of back-flow up the insulator around the filament, or in the vernacular, extruder FAIL.

The replacement we'll be using for the insulator is a thinner PFTE tube surrounded on the nozzle-side by a PEEK tube and on the other end by a similar tube of what I'm pretty sure is aluminum.

After getting the insulator out, I took the nozzle apart so I could redo it, (1)to ensure proper thermistor placement and (2) so I could use Kapton tape, which is easier to maintain than fire cement, as the rest of this post will reveal. I started by cracking off the fire cement layer by layer with some pliers. The Ni-chrome heating element survived, but the thermistor was too tightly sealed into the hole on the side of the nozzle tip, and I ended up having to just tear the leads off and dig out what was left with a pointy implement. Then I put the nozzle in a cup of acetone for a while to soften the ABS still stick in the very tip, which worked like a charm.

So now we are in the market for a thermistor. I looked all over, but nowhere seems to have all of these qualities at once:

200k ohm
shaped like this =O instead of this -[]-
operating temperature range high enough for ABS (235-240C°)
a response curve compatible with the preexisitng software on Kurzweil
being sold in reasonable quantities (no, digikey, I do not want to buy 2500 thermistors!)

Hopefully the fellas at BfB will be able to help out, but in lieu of that, any tips would be greatly appreciated.

Selective Laser Sintering Part 6

2010-06-21T14:20:00.000-07:00

Hi folks,

I thought I'd take a second to make a quick post about some of the interesting bits of the new open selective laser sintering printer that I've been designing in between finishing up my dissertation. (I'm also looking for an interesting postdoc (or maybe the right industry job, if it's research oriented and challenging) -- if you're interested in learning more, please have a look at my graphical portfolio / academic CV. My background is pretty diverse, and I'm quite interested in branching into cognitive robotics, rapid prototyping, and potentially making these technologies a little "smarter", more accessible, inexpensive, or otherwise more capable. )

One of the overarching design goals of the project is accessibility -- it's very important to me that the design be easy to create, and very affordable. Infact, I keep a $200 high-mark in my head, with the goal of designing something that doesn't exceed that mark in terms of the parts cost. With these goal in mind, I've been designing a proof-of-concept that gets creative in order to keep things inexpensive while making them easy to create.

The typical components of an SLS system are a build chamber with a Z table, a powder feeding mechanism (that often takes the form of another Z-chamber, indexing up to feed powder in concert with the build chamber indexing down to receive the powder), and a x-y pivotable mirror or other system able to accurately aim the focus of the laser in two dimensions along the surface of the build chamber. With X-Y systems being relatively common (using anything from a few slides and lead screws or belts, like on the darwin or mendel, or using a pivotable mirror like on the first SLS powder test rig), I figured the tricky part would be in designing the feed and build chambers, and keeping this inexpensive. This could then be paired with an X-Y stage with the laser attached, and one would be set.

The design I've come up with is something that I'm really happy with. The whole idea is that, if you have access to a laser cutter, making complex custom parts can essentially be done for the price of the material. The more parts that can be cut, the fewer vitamins one would need -- and the lower the cost.

The following dual z-stage (feed and build chambers) that I've designed uses almost entirely laser cut parts -- ideally acrylic, but the engineering model I've build is made with hardboard (and even this might work out okay). The only vitamins currently are machine screws, as well as two large carrige bolts and two nuts that are used as the lead screws. (There are of course motors and electronics that also count as vitamins, but these are likely to be with any reprap system for a generation or two yet).

Two motors are used -- one for each Z-axis (build and feed). Here is one of the sample steppers for this engineering model, plus its mounting plate.

These two motor mount plates attach to a base plate. On top of this base plate is a system of laser-cut gears, where the nut for the lead screw is held captive in a large gear. The ratio of these gears is 4:1, so the motor can apply a good amount of torque to the nut and screw.

The nuts are also held in place with the top plate -- it acts as a bit of a keeper, to make sure the large central gears don't shift and can rotate in place, while also allowing access near the sides for manual turning just incase.

Here's one of the tables, turned upside down. It has a little system in it to hold the top of the carrige bold steady.

The chambers have two parts: the squeegee system, that sits on top, and the actual chambers themselves. The above is the piece that sits on top of the chambers.

The top piece has a system of groves similar to the first SLS powder test rig, except that this one is raised up a bit -- I had some concerns that since the plastic-on-plastic slide mechanism was also at the interface between powder and squeegee, that this might potentially clog fairly easily. With this new design, the slide is raised up one level of plastic, and a tiny little squeegee is glued under the slide itself -- so there's very little contact with the powder level, and much less potential for clogging.

The slide, with a little squeegee underneith.

The chamber system has two chambers, feed and build, that slot together and fit together with teeth. The intention is for these to be a close fit and glued together -- here things look a bit loose, but that's because I cut this model with 3mm material (for ease), rather than the 4.5mm material that the slots are designed for.

The top piece with the squeegee slide mechanism fits on top of the chambers.

And then the tables and dual z-stages slip right inside the chambers. There's still a bit of work to be done with alignment (in particular, the mounting plates that attach the dual z-stage to the chambers is out a little bit), but you can manually index the gears with your fingers and the tables slide up and down quite well -- and with quite a resolution! There is a little see-sawing back and forth from the size of the nut compared to the material that the gear is made out of, and also the give in the material, but I think this will likely be sorted out fairly naturally as those issues are addressed.

---

And so, there's the working prototype design for a dual z-stage mechanism with build chambers, for $2 in carrige bolts and nuts, $2.50 in hardboard, and $2 in machine screws! :) There will likely be some other materials required, such as a seal, but I'm thinking of using a dense foam similar to the seal material used on the first powder test rig (think pool noodle foam), that should be very very inexpensive as well.

While the design is very inexpensive, there are a few tradeoffs: There's likely to be quite a bit of backlash in the gear system. The trick is that, for this application, the tables should only (ideally) ever move in one direction throughout operation -- either up, or down -- and as such, the backlash shouldn't be much of an issue.

For the X-Y stage, I've decided not to use the pivotable mirror again, and instead make a simple one (mostly laser cut, again) using belts, that will fit over top of this system. I also harvested the stepper mechanism from a CD drive head, which I'd like to mount the laser to, in order to be able to easily adjust the focus online. During my tests just holding things in my hand, it seemed like the laser did particularly well when it was a little out of focus, and it would greatly aid testing if this didn't have to be adjusted manually! Also, it seems like a neat idea to be able to adjust focus online -- perhaps dynamic resolution at build time (heating large versus small areas), or even cutting (having a perfect focus), although I'm not yet sure where that last one might come in handy. (As an aside, I keep having ideas of building a larger x-y stage and trying to use the whole system as a dual SLS sytem and low-power laser cutter by placing a dark plastic sheet over top of the build chambers, and making a "reciprocating laser cutter" using the CD-head mechanism to 'bore' the focus into the material, but that's just unverified brainstorming right now. :) ).

I hope you've enjoyed this post! back to thesising!

Keeping with being open-source, I've placed the design files for the first powder test rig, as well as this current full design project, up on thingiverse:

Powder test rig: http://www.thingiverse.com/thing:3389

This project: http://www.thingiverse.com/thing:3390

thanks for reading! :)

Peter

[part 1] [part 2] [part 3] [part 4] [part 5] [cogsci.mcmaster.ca/~peter]

Hackerspace Brisbane gets its first Mendel!

2010-06-14T22:50:00.001-07:00

lots more pics here:
https://sites.google.com/site/davidbuzz/hsbne-mendel-reprap

After a number of days of furious tweaking it prints!

problems included:
* pulling the extruder apart at least 10 times
* a leak
* a hot-zone conection failure
* a missing bearing
* mis-aligned cogs
* PTFE failure ( saved by a hoseclamp)
* two thermistor problems
* inverted end-stops to normal
* stepper driver pinout weirdness and ground loop issues - 5 hours here!
* X & Y axis needing reduced stepper power
* E & Z needing increased stepper power
* cog on X stepper came off
* X stepper mounted 4mm too low
* X belt too loose, then too tight, then too loose!
* a couple of random nuts falling off from someplace
* smooth-rails on X were insufficiently tightened, see belt issue.

first printed object:
after cleanup:
http://picasaweb.google.com/lh/photo/q1qvq6G888HLm9C-5g-s_g?feat=directlink
before cleanup:
http://picasaweb.google.com/lh/photo/D94zNVAgEhVCH13FNk1RCQ?feat=directlink

a bit of video of a bit of the first print:
http://www.youtube.com/watch?v=kD24JKtSIRU
* at 1:40 I show overhead view at 2:00 you see electronics on the back at 2:25 you see host software.

Extruder Problems

2010-06-14T19:50:00.001-07:00

Scott and I had our first RepRap session this evening. First off, we made sure the extruder was connected up correctly. When James and I were building Kurzweil a year ago, we lost the "12 Way Connector" that came with our BfB kit. We fudged a solution to get the extruder connected, but it's fragile, and got messed up during transportation across campus for the end-of-year poster session a month ago. Printing a new 12-way connector is an excellent candidate for a future project.

Once we were sure the extruder was connected properly, we performed the tedious but necessary rituals of bed-leveling and z-axis-setting (thus further fueling my desire for one of those well-constrained Mendels...).

We started noticing problems while printing the test rafts. The extruder was clicking, and I could see the filament jumping back, so I released the pressure bearings a bit. I may have gone too far, because the flow from the extruder became pretty feeble, so I tightened them back up half as much as I loosened them. That seemed to make the extruder run more smoothly but the flow was still pretty weak resulting in this test raft:

I think the problem is either in the tension of the pressure bearings, or some kind of clogging in the nozzle or the insulator, which, if you were wondering, looks like this:

I know that the bulge is a problem others have run into. The Bfb kit called for us to cut off a ring of the nozzle to restrain the insulator, but we didn't have the tools to do that and Ian at BfB assured us we'd be fine without it... I'll look around for solutions but if anyone reading this has a take on the situation I'd really appreciate the input.

...And We're Back

2010-06-14T18:40:00.001-07:00

While today is not the first time I've worked on the RepRap since I last posted 14 months ago, it is the first time since then I've documented my struggles. Let me bring you up to speed (I'll try to keep it short)...

In the Fall semester of 2009 I took a Computer Architecture course taught by Michael Siff at Sarah Lawrence College. For my independent project I attempted to design a system of modular mechanical logic gates. I seriously underestimated the scope of this endeavor. I was trying to simultaneously:

learn Blender
learn Skeinforge
design complex pieces using Blender
maintain and troubleshoot Kurzweil

All while also trying to keep up with an intense Psych class and a very full Music program. Needless to say, I did not succeed, though I learned the hard way that making an idea into reality never goes as smoothly as one first imagines.

Slightly discouraged, and reluctant to set myself up for disappointment again, in Spring 2010 I took a break from RepRap. And then I graduated.

Now, in what may be my last month and a half in the Westchester area, I've set another possibly preposterous goal: wherever I go next, I want to take pieces for a Mendel with me. But this time I have help!

Scott Calvin, an SLC Physics professor, and my excellent Don, wants to learn the RepRap so future SLC students may experience its agony and glory. And what better way to learn how a machine works than fixing one that don't work so well? Hopefully with our powers combined, we will be able to get this puppy running.

selective laser sintering part 5: the laser

2010-05-31T20:25:00.000-07:00

Hi folks,

Just a quick post, since it's been a little bit since I made one. My thesis has been keeping me busy these days, which is good since there's been a lot of waiting for things to come in the mail. I ended up settling on a 1000mw 808nm laser diode for the first tests, and ordered some wide-spectrum glasses (600-1100nm, OD4) just incase I need to try a few different diodes.

I built a current-limited variable voltage supply using a reference design in the LM317 datasheet this past weekend, and added some large capacitors to try and filter out any large bumps. The laser diode didn't come with a datasheet, but the ebay seller listed it as running at approximately 2.2V at 1.2 amps. The supply is limited to 1.2 amps, but so far very slowly adjusting the voltage up (with a 10-turn pot), I'm only at ~1 amp at 2.5 volts, and that is about as far as I dare turn it up just yet.

There hasn't been much tinker time with the laser yet, but I did take it to some failed prints made with black ABS. The laser has no trouble melting the black ABS plastic from makerbot, or even cutting it and boring holes in it, depending on the distance. Using a print that's only a single layer thick, the laser seemed to be able to cut through fairly quickly, but also if the focus was such that a small area about 0.5 - 1mm wide was illuminated (instead of a point), it melted the layer rather quickly -- I think this is going to work just fine.

Now, to find some ABS plastic in powder form. The laser didn't heat or cut white polystyrene, so I think colour is still definitely going to be an issue here -- particularly in finding a black thermoplastic powder. I'll have to try some tests with the powder coatings that I have from earlier as well, although our tests with a 20W CO2 laser weren't encouraging, and the end result was partially fused but very, very brittle. This kind of makes sense, since powder coatings are meant to be very thin coatings, and are also meant to cure over 6-12 minutes at relatively high temperatures. I'm eager to try Vik's suggestion of a dark coloured sugar, just out of curiosity, to see what that might be like.

I have also decided to replace the SLS powder test rig that I described in previous posts with a much more full sized model, and I've been working on building this in my spare time over the past few weeks. More on this soon, hopefully. :)

thanks for reading,
peter

Hydra-MMM v1.4 Finally Released!

2010-05-12T09:23:00.000-07:00

I have gone ahead and released v1.4 of the Hydra-MMM software and firmware (https://sourceforge.net/projects/hydra-mmm/), and let me start off by saying that this release is HUGE! There is a ton of new features and changes from the previous release. I probably should have made 2 or 3 intermediate releases over the past few months, but the end of my undergraduate degree required a lot more time than I anticipated. So onto the major additions in the new firmware

One of the biggest changes to the new firmware is the addition of slave PID temperature control. This allows the main Arduino Mega to focus all its attention on the movement and acceleration computations, while the slave Arduino is busy doing PID calculations to regulate all the temperatures. Using this method, I was getting a 20% performance increase on the master firmware which means less pausing between print commands. This leads to improved print quality and smoother motion. See the readme file in the sourceforge release for details about the slave setup. In addition to the option for slave PID control, the internal PID control on the master firmware has also been updated so that it can control up to 3 different temperatures. This is intended to be used with 2 extruders and a heated build table. I don't think many users will require more than that at this point in time, but it is very easy to add more if required.
Another big change in the v1.4 release that has been very helpful to me is the addition of absolute position logging via an attached EEPROM. This allows the machine to retain its knowledge of position even after the machine is powered off. While the user coordinate system may change from build to build, an additional absolute coordinate system has been added, and this is what is stored on the EEPROM. I have tested this using the 512 byte EEPROM already included with most Arduinos as well as an external AT24C1024 connected via I2C. While I am currently only using this storage for the absolute positioning variables, there is lots of potential here for new features in the future.
There has also been a lot of changes to the multi-headed operations included in the firmware. Now that I have a machine that I can test these functions on, I have been able to improve the routines and fix any minor bugs that were present. I have successfully used these functions in several multi-tool builds that I have done and they are very simple to implement. My next big task in this arena is likely going to be figuring out how to generate multi-funtion Gcodes that can be used for doing both milling and prototyping or something of that nature. At the moment I am just splicing together 2 seperature Gcodes with the appropriate tool switching commands in between. Automating this process would be a nice addition and I believe skeinforge has the ability to calculate both additive and subtractive toolpaths so it should be possible.

If you want more details, the full list of changes from the readme file in the sourceforge release is below

- Added slave temperature control so that the master Arduino can allocate all its resources to handling the machine movement and not dealing with PID temperature control, see the new Hydra_Slave_Temp_Control sketch for the slave firmware and be sure to edit the master firmware to use slave control as well
- Added M301 and M302 commands so you can easily check to make sure your slave Arduino is communicating to the master correctly
- Internal PID control (if you chose to not use slave control) is now updated so that up to 3 temperatures can each be PID controlled by the master (extruder 1, extruder 2, and heated table)
- EEPROM position logging so that absolute positions can be retained even after being powered off, exiting the GUI triggers this to happen (M900 command)
- Added G80 and G81 drill cycle commands for intended use with PCB milling (advanced drill cycle operations not currently supported), this is untested though so use at your own risk!
- Added support for Ncodes at the beginning of each line with the program line as the parameter (ie "N51 G1 X1.00 Y0.00 Z0.00 F30") as programs like MasterCAM like to add this in the gcode file
- Added M120 and M121 codes to run the stepper extruder forward and backward, can use these to pull filament backwards at the end of a move to prevent excess nozzle oozing or to start filament flow at the beginning of a layer
- Added a G5 jog gcode for simple movements without needing to know your current position
- Added ability to jog individual Z-axes using the T18 command without triggering the switch_tool routine
- Added a M6 tool change Gcode, the continue_pin button must be pressed once this is done to continue
- added M500 Gcode command that waits for user confirmation (by pushing the continue_pin button) before proceeding
- Limit switch current position handling updated to give more accurate end positioning
- Extruder federate calculations updated to provide better results with our current setup (0.5mm nozzle)
- sticky federates are now supported
- minor bug fixes to multi-headed tool operations (Tcodes) now that I actually have a machine to test them on
- several updates to the startup and exit routines
- updated steps_to_take variables to be longs instead of integers because users with high microstepping rates were able to overrun the integer data types on long moves (thanks martin!)
- stepper motor driver enable logic can now be swapped for different motor drivers so that HIGH or LOW can be used to enable the driver

As always, the release files can be downloaded from the Hydra-MMM Sourceforge page at https://sourceforge.net/projects/hydra-mmm/. Give it a try and let me know what you think!

Now, onto the second reason for this post; finding some beta testers to help me improve this firmware! The firmware has a lot of different functions, and for that reason there is a lot that needs to be tested. While most users don't have a 4-headed machine, rapid prototypers and homemade CNC machines are both relatively common. If anyone out there is interested in helping out with testing or developing the Hydra-MMM software or firmware, please email me at hydra.mmm.project@gmail.com or shout out in the comments!

Hydra-MMM Prototype Finished!

2010-05-06T10:13:00.000-07:00

The end of the semester is here and after many many hours of hard work the Hydra-MMM prototype has been completed. The design was rigorously tested and accomplished many of the initial goals that we set out to achieve. The machine proved it had the ability to perform many different tasks including CNC milling, rapid prototyping, and even making some basic single-sided SMD circuit boards! With movements speeds of 200 inch/min and a positional accuracy of 0.001 inch, the machine not only attempted these tasks, but performed exceptionally for such a low-budget machine. The software and firmware developed for the project also proved to be a success and was extremely versatile allowing for all of these functions without modification. The firmware has enough G, M, and T codes packed in that it was able to take gcode programs from several different software packages with almost no modification and successfully run them on the machine. The results were simply amazing for a machine at this price level and I look forward to how the Hydra project evolves over the coming years. To wrap things up, here are a few pictures of the final prototype

The final cartesian robot with the accompanying electronics enclosure. Most of the connecting wires were removed from this picture for a little cleaner look, but they are pretty easy to snap back on with the rear panel on the enclosure.

A backside shot of the machine with all the cables attached and my Mac running the show

A close-up of the electronics enclosure showing the estop switch and an optional input button for tool changes and things of that nature. There is one fan missing from the above pictures as it was somehow lost during the last week of the project and we couldn't find 2 other matching fans in town. The box houses the new a4983 stepper drivers and a beefy 30V power supply. It also has a custom breakout board for the Arduino Mega that allows all of the connections to the microcontroller to plugged in with ease.

A rear view of the enclosure showing all of the connections and inputs to the internal electronics. We have 7 stepper motor outputs for a single X motor, 2 Y motors, 2 Z motors, and 2 possible extruder motors. It also has a solid state relay for controlling an attached spindle and a nice panel mount USB connector for interfacing with the Arduino.

The project has been a lot of fun, and I would love to get some input from the community about some future ideas for this technology. There is a host of additional videos and pictures from the last few weeks that I may post sometime in the future, but for now I am out to celebrate the end of the semester and a successful end to my undergraduate career! Cheers!

inexpensive, simple, acrylic makerbot-inspired 3d printer with heated table and build chamber

2010-04-18T13:24:00.000-07:00

Hi folks,

I thought I'd take a second to post some pictures from a design that my father and I have been working on for a while. Our goal, after making a 3d printer with a much larger bed size, was to make a smaller table-top one that I could keep with me in my apartment. Being a grad student (poor) who doesn't like the smell of heated plastic, but who also wants fantastic prints, we set out to design something inexpensive with a contained chamber, with a print size at least the size of a makerbot. In the end, my dad did a fantastic job designing and building the machine, and I think it has some neat features with respect to their simplicity and inexpensiveness that future designs might consider or adapt.

Overall, the design probably cost around $200-$300, all said and done (minus the 5lb spool of ABS plastic). We built 2 sets of makerbot electronics for about ~$225 (so, around $100 for one set), probably spent around $100 on extruder parts like the motor, barrels, and things (these have become pretty expensive as of late from makerbot... I think our first extruder using bits from the RRRF was probably only $20 or so :) ), and finally there's probably about $50 of acrylic for the sides and z-axis. We had some $5 steppers hanging around for the X and Y axes, where the slides were taken from matched sets of old inkjet printers, and the Z-axis stepper is from an old plotter.

Probably the neatest aspect of the design is the Z-axis. It's a "cigar box" design, and is almost entirely made out of acrylic. The essence of the design is that a large rectangular piece of acrylic moves up and down along the Z, sandwiched between several other pieces of acrylic. A single threaded rod is used as a lead screw (compared to four threaded rods with the Makerbot design), and the MK4 extruder mounts to the Z using a right-angle bracket. The advantages of this design compared to the traditional makerbot design are that it's likely far less expensive to produce and requires far less parts (no timing pulleys, belts, and one quarter of the lead screws and nuts), and as such is probably much easier to align, too. If you laser-cut the parts, you could probably have a simple design that would cut out on a single sheet, and end up with a complete Z-axis that you could bolt together fairly easily, as well. The disadvantages are that the design needs to be able twice as tall as your maximum build height, but that's not too bad at all if you only have 6-7 inches of Z travel -- infact, its probably about the same height as a makerbot right now).

Other bits of interest include the build chamber and the magnetic heated build platform. The build chamber currently isn't actively heated, but from the heated table and a fan on the variable voltage regulator, it gets up to around 40°C while building. The nichrome wire for the heater barrel is 8 ohms rather than 6 ohms, to give a bit larger heat zone, and we run it a bit higher than 12v. The table has four 2 ohm (25 watt, I think -- from memory) power resistors, and it's fed with about 18v, and heats up to 100°C in a couple of minutes (it's very fast).

I've included bunches of pictures below. As always we're happy to hear comments or questions.

The build was the 'tin-tin' rocket from thingiverse, which I figured would be a particularly challenging raftless build given that the only contact points between the table and the model are three ~2mm points. (I paused and added a little tape to the build at one point, and held it in place near the very top scared that it would fall off, but I really shouldn't have done this because it was doing fine and now the top is a bit funny... :) ).

(click on the thumbnails for larger pictures)

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thanks for reading! :)

peter
[peter's website]

Hydra's First Print!

2010-04-15T04:06:00.000-07:00

So after working ~30 hours on this project over the last 3 days we finally printed a part on the Hydra platform! Some details on the print:

Printing speed: 40 IPM

Stepper driver movement method: Half-stepping

Resulting resolution: 0.00125"

Printing medium: ABS plastic

Nozzle temperature: 240C

Print bed material: plexiglass

Firmware: Hydra-MMM v1.4 (to be released to the public soon)

Host Software: Hydra-MMM v1.3 GUI

Gcode generation software: Skeinforge

Total time for print: 9 minutes

And without further ado, here is a picture of the test print in progress

A YouTube video of the print is here: http://www.youtube.com/watch?v=V-_Qu8GxbtI

We were actually able to extrude the top layer of the dodecahedron just fine which was surprising from past experience. I think our extruder speed is a bit on the slow side so we are actually stretching the filament a bit as the machine moves from point A to point B. This stretching effect puts it in tension and allowed to to span the void across the top of the object without drooping down into the interior of the part. I suspect that voids up to ~1 inch would be possible to span at the moment with further gains possible using active cooling or from further tweaking of the print speeds. You can also see from the video that we have a heated platform setup, but it was not used for this print as we are still waiting for our 1" wide roll of Kapton tape to arrive.

First impressions of the part were very impressive. The machine has incredible accuracy and rigidity compared to my first repstrap I built using a belt drive mechanism with a threaded rod frame. We still need to figure out how to get Skeinforge to vary the start point of each layer. For this print, each layer started in the exact same spot so we have a relatively prominent seam on the side of the part. I know the setting exists, but Skeinforge is a little cryptic and every time we think we found it, we export the gcode and the problem still persists. We got it to vary the start point on the base layers, but the walls all started at the same location. We will keep investigating, but if anyone knows a solution feel free to shout out in the comments! Even with this problem, the surface accuracy was astounding, but should probably be expected with a machine as accurate as Hydra. I can't wait to add some microstepping drivers and see if we can improve the already impressive 1.25 mil accuracy that we have with half-stepping.

As far as the software and firmware, this was the first real test of the Hydra-MMM firmware and it's handling of the stepper-driven extruder. Up until this point, most of the testing centered around X, Y, and Z moves. For prototyping, the extruder stepper motor is added and needs to be controlled by the firmware. The Hydra v1.4 firmware has the ability to independently move the extruder motor, which is useful at the start of a layer when you want to get the filament flowing before moving and at the end of the layer when you want to pull the filament back and stop the ooze. Before starting each layer we moved the extruder stepper forward a few steps to get the filament to start coming out of the nozzle before beginning the XY moves of that layer. This helped ensure that we didn't have any gaps in the part where the plastic wasn't being deposited. Currently, the extruder motor speed is defined by a variable E_STEPS_PER_INCH, which was first found theoretically and then slightly tweaked to match the real work results. We simply varied the number until 1" of movement resulted in 1" of filament being printed. This number could be decreased to stretch the filament (smaller filament) or increased if you wanted a thicker extrusion. Changing the feedrate of the XY moves will change the speed of the extruder motor to match this velocity, but the relation between these two remains constant. Later versions of the firmware may allow for variable speeds of the extruder motor, but at the moment the results are good enough that I am not sure this is required.

We will hopefully be getting the heated bed up and going tomorrow so we may have some better prints to show off, but in closing, we also printed a traditional test object on the machine before shutting it down for the night. Cheers!

Starting a new online store for Reprap electronics rep-up.com

2010-04-08T11:41:00.001-07:00

I am posting about a online store my son and I are starting called rep-up.com Our goal is to sell Reprap and Makerbot electronics and parts. In order to try and fund this startup we have started a kickstarter project which you can get to at www.rep-up.com for now. Any body looking to bid this is for the US only because of shipping.

Our goal is to focus on boards and kits right now.

Mini-Mendel is built and working!

2010-04-08T00:01:00.000-07:00

I built another child machine, this time a Mini-Mendel:

For some more details and pictures, see my blog post here.

Hydra Takes Its First Steps!

2010-04-05T19:46:00.000-07:00

So I have been way behind on the blog posts over the past week, but we just hit a pretty major milestone with the Hydra multi-headed manufacturing machine project. The mechanical construction for the cartesian positioning system was finished at the end of last week and all of the major parts we were waiting on had also arrived by the weekend. Many many hours were spent over the weekend to get all the motors, couplers, electronics, and software working as desired. I'll go into more detail below, but for the impatient ones, here are some pictures of our progress

Close-up of the Bosch Colt router mounted on our Z-axis assembly. The router fits very snuggly in it's custom mount and appears to have some very impressive runout figures. You can also see that a second support was added to the Z-axis to help prevent it from wobbling. The additional of 2 more sleeve bearings definitely made the assembly more rigid.

Overview of the whole machine with all the motors mounted and electronics wired up. Taking a piece of advice from Tony Stark, we decided to run before we could walk and attempted some simple milling. A small piece of low-density wood was mounted to the table and cut using a general purpose dremel cutter. The Gcode was written by hand and tested using the Hydra-MMM host software file previewer before being sent to the machine. The cutting path was very simple, but it proved that the machine worked and that the spindle was more than capable of cutting these low strength materials. We then moved on to bigger fish...

Attempting some PCB milling using PCB-Gcode and some Eagle board layouts. A piece of cheap double sided copper clad from radio shack was mounted on the table and the Drewtronics 45 degree bit was used for the cutting.

If you want to see a video of Hydra doing PCB milling, I posted our first attempt on YouTube so you can see how this thing performs: http://www.youtube.com/watch?v=1v6gg4_JAmI

The final result of the PCB milling. The PCB drill bits from Drill Bit City have not arrived yet so no holes were drilled, but the accuracy of the traces was very promising! By the way, in case anyone was wondering, the board is a PIC stepper motor driver that I designed similar to the ones I posted about a week ago.

So now to the details...

There were a couple big setbacks that kept the project from doing any cutting earlier in the weekend. The first, and most dangerous was the fact that the couplers we had made to connect the motors to the ACME screws were slipping. The set screws we had used weren't holding well enough and the screws were simply tearing up the surface of the ACME screw shafts. To fix this we made the couplers have double set screws (one on each side) and also filed a D-face into the ACME screw shafts so that one of the set screws could grip that instead of the round surface. This seemed to solve the problem, however, we have also added some loctite to our shopping list as I have a feeling the vibrations from the motors are the culprits here.

The second hurdle was figuring out how to mount different materials to the work table. The intention had always been to use some type of clamp set with a wide array of tapped 1/4-20 holes, but we hadn't really thought much about how long this would take. We ended up drilling and tapping 49 holes (7x7 with 2" spacing) in the 0.25" thick aluminum table. This was no small task and took a pretty long time especially for the tapping. The end result looks very professional and has more than enough strength to hold the parts we intend to machine.

Finally, there were some minor issues with the electronics as well that will need to be addressed before further testing is performed. The stepper motors we are using have a 2.5 Ohm resistance per phase. If they are being run in a unipolar configuration, this means there is only 1.25 Ohm resistance from the coil end to the center tap. We are running the motors from a 5V supply which means we are pushing about 4 Amps per motor. The motors are only rated for 3 Amps so extended operation at these conditions may very well damage the motors. However, the larger concern is the fact that we have 5 motors that are each drawing 4 Amps. That is 20 Amps just for the motors! This is causing some serious heat issues within the electronics. The plan is to add some TO220 power resistors to decrease the current draw to around 2 Amps and add some heatsinks to boot. This will have to work for the time being as I am still having trouble getting my a3982 motor drivers working. I actually got one to work for about 30 seconds, but then I started to increase the current and am pretty sure I ended up blowing the chip again. No idea how I am doing this as I am using the exact values the reprap stepper driver v2.3 circuit is using and I have checked them against the a3982 datasheet and it shouldn't be possible to exceed 2 Amps current output. Not sure how it's happening, but the chips keep dying so I may have to look at some other alternatives. The Pololu a4983 stepper drivers with microstepping seem very nice at inexpensive as well. If I can't get my own circuit working, I will likely end up buying a few of those.

It's been a long day, so that is all for now, but we are hoping to have the extruder working by the middle of the week so keep an eye out for some more updates!

Hydra: Cartesian Robot Assembly Completed

2010-03-31T05:00:00.001-07:00

So after about 7 hours straight working in the shop on Monday, the assembly for the cartesian, 3-axis robot is completed. We ended up working through lunch so you might see some tired people in the pictures. It was pretty exciting to see the machine start to take shape after all the hard work we had put in making the aluminum parts. Here are some pictures from the build

Most of the parts laid out at the beginning of the morning

Y-axis assembly completed with the X-axis carriage in place. The X-carriage has mounting holes for 4 different Z-axis assemblies. 2 on front and 2 on back.

X, Y, and Z axes completed and assembled. We have a 2nd Z-axis assembly that wasn't in this picture too

Another angle showing the Z-axis and X-axis details. The screws at the bottom of the Z-axis weren't tightened because we have a slight alignment problem we need to fix first. Also, the writing on the side of the Y-axis uprights and several of the other pieces will be faced off before our final presentation to make everything look a little cleaner.

We were able to test out the "feel" of the movement along each axis and it was surprisingly smooth. I was pretty impressed considering we used some pretty cheap plastic sleeve bearings. That said, I am sure using skate bearings or something of that nature would have been much smoother, but our initial calculations said we might have problems with the radial forces during heavy machining. We still have 1 or 2 holes that need to be fixed to make everything fit perfectly, but for the most part, the assembly of the 3-axis robot is completed and we can move on to the subassemblies such as the extruder, heated build table, and spindle mount. Pretty exciting day!

selective laser sintering printer: part 4 (putting it all together)

2010-03-30T20:55:00.000-07:00

hi folks,

a couple rainy days and the dorky need i have to make this thing work mean, another SLS post! :)

(click on the thumbnails for larger pictures)

i designed a new enclosure for the SLS printer that would let the build chamber, z-axis table (inside the chamber), pivotable mirror, laser, powder feed system, and electronics all fit together. i've been designing the system with the hopes that it would be both easily created by others and inexpensive, and so currently the whole system is essentially just a whole bunch of laser cut acrylic parts, a bunch of inexpensive steppers, and a trip to the hardware store for some bolts and ABS pipe. (i have some thoughts to design a laser-cuttable gimble system for the pivotable mirror, but that's a bit in the future).

the pivotable mirror just rests on top of the sides, which are set at 45° and directly above the build chamber.

one of the things i've been really trying to be creative with is the powder feed mechanism. traditionally, a commercial SLS printer will have two chambers with indexing z-axis tables, and a roller. one chamber will start with a thin layer of powder (the build chamber), and the other will start with a large amount of powder (the material supply chamber). after each layer, the build chamber will index down a little, the supply chamber will index up a little, and a roller will roll new material from the supply chamber to the build chamber.

the key elements here are supplying the build chamber with a thin, repeatable layer of powder, and having a lot of supply powder. i wanted to try and avoid having *two* chambers with indexing tables, as well as a roller (it seems like a lot of extra space and mechanism, if you can design something functionally equivalent). the system i came up with is as follows: a thin piece of acrylic rests on the platform above the build chamber, and it can slide back and forth overtop of the build chamber using a rack and pinion system. the sliding sheet is sandwiched in so that it can only ever move back and forth over the build chamber (not side to side, or up or down), such that if a layer of powder were put ontop of the build chamber, it would wipe off any that exceeded the height of the chamber itself. (this whole sliding thing is essentially the roller, but more of a squeegee)

in that sliding piece is also a long, thin slot. ontop of this slot one would put a little hopper full of powder. when the table indexes down, the slide will slowly slide over the chamber, the powder will fall down into the chamber, and ideally the slide will wipe away any that exceeds the height of the chamber. that's the idea, anyway. :)

the electronics are mounted under everything, with easy access. i had a few spare boards left over from a batch sent to goldphoenix that used a dsPIC33FJ256MC710 on them, so I repurposed them (since they have a breakout header for about 30 pins!), and plugged it into the little 4-axis stepper controller board from the previous post.

the sides were designed with lots of slots and holes, so that little extra bits could easily be added or removed or modified later without drilling anything. it's really handy! :)

here is the (almost) whole system, with a red laser pointer being used as a test.

(the stuff in the build chamber is actually the foam top of the table -- there isn't any powder yet. i hope the foam table will act as a bit of a seal, too, and prevent much powder from escaping below).

the powder hopper -- it's not very big, but the total chamber build volume isn't too big, either. i just glued this together tonight, but it's not glued onto the slide just yet.

after over-voltaging a bunch of DVD laser diodes, and taking apart a bunch of laser pointers for their collimating lenses, i've decided that it would just be a lot easier and more precise to find a pre-made laser module (and, so, i've been looking around ebay for one for the last week or so). i'm thinking 250mw minimum (like the DVD laser burner), but there are bunches of inexpensive 808nm 1000mw diodes on ebay. since these are near infrared, there's a much better chance that they'd be able to work on materials other than pure black plastic, and the additional power means a bunch of good things, including that each layer could be sintered quicker. (unfortunately it also means that one's eye could be damaged even that much quicker -- and the infrared lasers border on what is visible to the eye, so it's a bit more dangerous than a visible diode).

any thoughts for a complete (inexpensive) laser module with a collimating (or focusing, or both) lens would be fantastic, and as always i'm happy to hear comments/questions, or thoughts on where to find very fine ABS, nylon, or other thermoplastic powder.

thanks for reading!
peter

[part 1] [part 2] [part 3] [cogsci.mcmaster.ca/~peter]

New Arduino Mega Shield for CNC interface!

2010-03-22T11:03:00.001-07:00

So I have been working in Eagle for about 2 months now and have made a few designs here and there to support the Hydra-MMM project. I just made one in the past week that I thought might be useful to the community. The design is a snap on shield for the Arduino Mega that allows the Arduino to interface with diy CNC machines that are built upon a parallel port (DB25) interface. These machines use a printer parallel port along with computer software (Mach 3, EMC, etc) to control the movement of the axes. The processing is done on the computer CPU instead of being done on an Arduino or something of that nature. Here is a few pictures of the actual eagle PCB

2 sided PCB board layout with the big 25 pin parallel port interface in the middle

Schematic of the parallel port shield

The reason I wanted to make a parallel port interface is because we are hoping to use our machine for both CNC work and rapid prototyping. By using a common parallel port interface we can have a single electronics control box (ECB) that has all the stepper motor drivers, extruder controllers, spindle speed controllers, and everything of that nature inside. I'll have more information on our ECB over the next few weeks, but for now a screenshot of the setup is below. Note that most of the electronics have not been modeled in the CAD program yet, so they are not shown, but their placement should be obvious.

Electronics Control Box (ECB) with power supply, Arduino Mega, stepper motor outputs and endstop/encoder inputs

The ECB can than be connected by a parallel port cable to either a computer with a 25 pin printer port or to the Arduino Mega with the new parallel port shield. The Arduino Mega will be running the Hydra-MMM firmware, but any reprap firmware variation would work. The main concept is that once connected via the parallel port to the ECB, the Arduino would have access to all the stepper motor drivers and endstop sensors that it needs to print! The parallel port pinout is as follow:

1 Estop

2 Xstep

3 Xdir

4 Ystep

5 Ydir

6 Zstep

7 Zdir

8 Astep

9 Adir

10 Xlimit

11 Ylimit

12 Zlimit

13 Alimit

14 Spindle/extruder on

15 Aux Input

16 Spindle/extruder speed control (pwm)

17 Coolant/Fan on

18-25 Ground

Some readers out there may notice the fact that there are no temperature sensors on the parallel port pinout. There are 2 AD595 thermocouple IC circuits built into the shield for measuring the temperature of the nozzle heater and also an optional heated build table. The main reason I did this is that I noticed that the analog wires for temperature measurements pickup a lot of noise if you run them over long distances. By having them mounted directly on the shield that attaches to the Arduino, that noise is minimized. I have tested a prototype pcb using this technique and the improvement in noise suppression over the same breadboarded circuit is amazing! The shield also has an onboard LM7805 5V regulator so that it can be run off the same power supply you are using to power the stepper motors (in our case 30V). This may also help reduce noise as the regulated 5V output is filtered and likely suppresses some noise in the process.

Another reason people may want this shield is that diy CNC machines have been around for much longer than the Reprap project. Many people already have the electronics for a cnc machine that is based around a parallel port interface, however, they are now wanting to try out rapid prototyping using the Reprap Arduino firmware. This shield would let them do that pretty easily.

The eagle files for the shield can be downloaded here: https://sourceforge.net/projects/hydra-mmm/files/Electronics/Arduino-Mega-Parallel-Port-Shield/

As I said, I have only been using Eagle for about 2 months so I would love some feedback on the design. Let me know what you think!

extruders...ugh

2010-03-21T22:58:00.001-07:00

i really need to find a better way of extruding plastic.

our first extruder worked fantastically for a long while, until the heater element got a little too hot and broke. we must have built 5 or 6 different extruder heads in the past month or two with parts from makerbot, and it just hasn't gone well. this is the latest, and i thought we really had it -- until i looked over, and noticed a two inch long blob of plastic steadily coming out from between a swollen barrier, and the heater barrel. a first for me. and, on only the second print.

please, someone, come up with a better method... maybe a ceramic barrier, or something? these PTFE barriers, brass barrels, and wait times for shipping are starting to get expensive after the n_th iteration. o.O;;

Open Source Circuit Boards using RepRap Tech

2010-03-21T17:58:00.000-07:00

We are constantly pushing to increase the number of parts the RepRap can make for itself. Why not its own circuit boards? Back in April I blogged on my experiences milling circuit boards on a Darwin. Just because the Darwin couldn't do it out of the box [so to speak] doesn't mean that this won't once be realized.

...I couldn't wait. For the last six months I have been building a larger, tougher, cnc / mill for milling circuit boards. The printed part count is low. I was only able to print the bearings and motor couplings. However, it is still a RepRap in spirit... if I can be so bold. The electronics are Gen 2, with an Arduino at the heart, and the firmware and host are variants of the RepRap firm and host.

After finding most of the ways not to do it I am finally getting high resolution, repeatable, double sided, drilled and scored, boards. Here is an opto endstop 2.1 board that recently came off my "tough" cnc.

I'm still documenting my experiences and getting some bugs out of my updated firmware and host. In the mean time I prepared a video of the board being made. Seeing is better than reading, anyways.

It is my hope that the lessons I've learned through making my own circuit boards will eventually lead to a true RepRap solution. Either Mendel will show itself to be tough enough, it can print something tough enough, or this work will lead to a new species all together that mills itself instead of printing itself. :)

Thanks RepRappers for all the help along the way!

Final call to do the RepRapSurvey.org

2010-03-18T03:08:00.001-07:00

Hi, first of all I'd like to thank everybody who took the time to click through all the boxes! Your input is very important to our research, my graduation and to help the RepRap community flourish!

We're closing the survey today, to start data analysis. So if you haven't done the survey yet, you're still in time! :)

It takes 15 minutes on average.

http://www.reprapsurvey.org

Thanks!

Erik de Bruijn

Wiki Goodness!

2010-03-17T06:36:00.001-07:00

For those of you who have been keeping up, there has been some talk of major wiki maintenaince being done "soon".....

It's here! The time is finally come! We have migrated the main http://www.reprap.org website over to the same platform/wiki and database as the "objects.reprap.org".

Oh, and we've upgraded it all to the latest version of mediawiki while we were at it!.

These sites are now essentially equivalent, so a page that used to be at:
http://www.reprap.org/bin/view/Main/XXXXXXX
can now be found at either of these:
http://www.reprap.org/wiki/XXXXX
http://objects.reprap.org/wiki/XXXXX

OK , so all the lovely content from the old "TWiki" is still there, and all the content from the 'objects' wiki is still there so the world is a great place. Almost.

Please do bear with us as a now take time to shuff the deck-chairs a little. we'll be reworking the navigation a little, and trying our best to please everyone, so it's sure to work. :-)

If you want to see what content got migrated from the old retired "TWiki" - we conveniently labled them all with a "Category:Twiki" tag. so you can see a full list here: http://www.reprap.org/mediawiki/index.php?title=Category:Twiki&action=edit&redlink=1

I hope that's enough info for now!

David Buzz.
Reprap Wiki Hacker.

P.S. Long live the wikifiddlers!

Hydra Joins the Acceleration Party... with multiple heads

2010-03-14T10:01:00.000-07:00

So after about a week and a half of work I uploaded a new release of the Hydra-MMM software and firmware to the sourceforge page this afternoon (https://sourceforge.net/projects/hydra-mmm/). Most of the work was done on the firmware because I got the crazy idea in my head that I wanted to be able to do accelerated movements in 3 dimensions. While this seems somewhat simple at first, I had a hell of a time getting it all to work out. Here are the main problems I ran into

If you have a constant acceleration with a non-zero initial velocity, the time interval for stepping cannot be directly determined. A quadratic equation needed to be used to solve for the time interval. This is due to the fact that the motor speed is dependent on the stepping interval (delay between steps), and the distance the machine travels is also dependent on this velocity as well as the constant specified acceleration.
(Solved) For some reason, every time I derive the kinematic equation to relate distance, velocity, and acceleration together I get a different result than that which is in the physics textbooks I have used in school. If V = delta x / delta t, and a = (V-Vo)/delta t, if you combine these you get a*deltat + Vo = V = deltax/deltat. Multiplying both sides by deltat, you get a*(deltat^2) + Vo*deltat - deltax = 0. The equation in my textbooks is1/2*a*(deltat^2) + Vo*deltat - deltax = 0. I was forgetting that the V term is actually Vavg which would equal (V-Vo)/2 which answers the factor of 2 difference. Thanks for pointing this out guys!
Solving quadratic equations while moving is not a good idea. It was too slow and it was actually limiting my maximum speed (the delay from solving the equation was greater than the interval I was using for stepping). The whole idea of doing this is to allow for faster and smoother stepping so a change was needed. I decided the best way was to compute the acceleration scalers (% of desired speed) for each step and to store those in an array. See the next point.
Storing large arrays (200+ items) of floating point numbers eats up SRAM real fast. A 200 item float array requires 200*4 Bytes = 800 Bytes! That is almost all of the available memory on the ATmega168! To fix this I scaled the acceleration scalers up to integer values. The scalers only range from 0.0 to 1.0 so this was not hard to do and it cut the memory usage in half (integers only require 2 Bytes instead of 4 Bytes for floating point numbers).
I originally intended to have separate acceleration and deceleration calculations, but it proved to be must faster to just calculate the acceleration values and then duplicate those in reverse for deceleration. I also has a problem when solving the quadratic equation for negative acceleration. The radical is negative if Vo^2 < -2*a*deltax which can happen for deceleration. See the 2 figures below.

Figure 1 - Acceleration from 0 to 80 inch/min

Acceleration is smooth from 0 to 80 inch/min with no errors in the calculations.

Figure 2 - Deceleration from 0 to 80 inch/min

Note the circled section where there should be 2 or 3 more steps before getting to zero velocity, however, this is the area where the value inside the square root was negative and thus, it could not be calculated.

So again, it was must easier to just use the acceleration calculations where acceleration is positive and the value inside the square root can never be negative. To help with this problem, I also added a startup speed variable so the motors can start from a specified velocity. For example, if they have no problem jumping to 0 to 30 inch/min, start them at 30 and then ramp up to 80. While this change, as well as only calculating the positive acceleration values got around this problem, I am still intrigued why this was happening.

Eventually, I got everything working, however, it took much longer than I expected. The end result is pretty awesome and allows for a much smoother initial startup as the motors can start from a lower speed and slowly ramp up to the higher speed. Before this, they were just instantly trying to run at the desired feedrate and that made things pretty shaky. I can't wait to test this out of the machine once we get the X and Z axes fully operational (hopefully in the next 2 weeks). I now also have a great deal of respect for Adrian who also got this working on the Reprap front. I wonder if he had as many problems as I did??

Anyways, in addition to adding acceleration to the mix, I also added support for multiple toolheads (the end goal of the Hydra-MMM project). This includes functions for switching heads and tracking the location of each head while building. I still have more work to do with this, but the basic functionality is there. See the release notes below for all of the other new features added in the 1.3 release!

- Acceleration is now supported and computed using kinematics (no linear approximations here!). The computations are performed before each move and have been optimized to reduce CPU and SRAM usage.

- Added support for several T (toolhead) commands for managing up to 4 independent toolheads. See firmware for list of new commands. Also note that there are new parameters that must be declared if multiple toolheads are to be used. See the top of the firmware.

- Added support for physical max and min endstops on each axis

- Maximum software endstops added in case physical max endstops are not available

- PID temperature library and cpwStepper library are now options and can be excluded from the firmware if it is not desired

- GUI now supports M105 command to receive temperature from the firmware and print to screen

- Fixed bug with time to move calculation being dependent on the x axis

- Lots of optimization to get the firmware small enough to fit on the ATmega328 (reduced total firmware size more than 6KB!)

- Serial baud rate changed to 19200 for compatibility with Reprap and Makerbot hardware

As always, you can download the release files at the sourceforge project page:https://sourceforge.net/projects/hydra-mmm/

Let me know what you think!

first tests building a selective laser sintering printer: part 3

2010-03-12T19:35:00.000-08:00

Hi folks,

This is just a quick post, but I thought I'd post some progress:

The ball-joint system that I'd thought up for the pan-tilt mirror in [part2] was a bit haphazard and didn't work very well, so I decided to rethink the whole thing. A gimble would be idea, but placing the steppers right on the gimble axes wouldn't yield a workable resolution, and would need some gearing to make it work. To keep things simple, I wanted to figure out a way to use lead screws (to get that extra precision), without having to worry about printing some gears out.

I was trying to think of a simple system that would allow you to use a lead screw with a gimble, but there are tricky issues where the motor itself would need to pivot. I left the idea with my dad for a week (especially so I wouldn't be tempted to work on it instead of my thesis), and I'm pretty impressed with what he made. There's still some backlash in the nuts, and ideally you could use even smaller steppers (or, servos, if you could find some really tiny, really high resolution ones), but I think it'll work just great for testing!

Right now I'm tinkering with ideas for how fresh material will be delivered over the build chamber. I'm thinking simple, inexpensive, and easy to make... make your mistakes cheaply, after all...

alt=""id="BLOGGER_PHOTO_ID_5447959549545405538" />

this last one is a 2 second exposure, where the simple square that i coded into the dsPIC controller can be seen (though it's a little blurry). The test square is about 100 steps on a side, and that translates to about 1cm of travel from about 10-15cm high -- so if the mirror assembly is around 5-10cm up, there should (hopefully) be plenty of resolution for the ~1 inch diameter build chamber.

(ps -- still no luck on finding inexpensive thermoplastic powder, the consistancy of flour. happy to hear thoughts on this that haven't already been covered in the past couple posts).

thanks for reading :)
~peter

reprap/makerbot gcode visualization tool (3b) code posted

2010-03-07T21:25:00.000-08:00

Hi folks,

just a quick note: i've (finally) posted the code to the gcode visualization tool (version 3b) for toolpaths exported from skeinforge. the code is in an attachment on the discussion thread on the forums: http://dev.forums.reprap.org/read.php?12,27884

sorry about the lateness of posting the code -- it had completely skipped my mind! happy tinkering! :)

~peter

--
previous posts:
version 3b ( http://builders.reprap.org/2010/01/added-streaming-to-gcode-visualization.html )
version 2a ( http://builders.reprap.org/2009/09/reprapmakerbot-gcode-visualzation-from.html )

Don't tap stepper motors

2010-03-07T18:34:00.000-08:00

I was ready to mount a stepper motor on a mcwire-ish x axis and decided to tap the holes of some nema 17's I bought for reprap a while back. Never did I imagine that the small metal filings would sneak through the cracks, and because of the powerful magnets inside, wedge between the magnets and the heads causing the motor to cease its steppity rotation... aurghhhh. Well at least I didn't spend a lot for the two I messed up. Next time I just use the right screws, even if it takes another trip to the hardware store. Just thought I would mention this to anyone else thinking to do the same

Repola Computations

2010-02-28T18:30:00.000-08:00

[Updated: Attached new images to show more accurately the curve scales. Previous images lacked an accurate 'zero' frame. Also added a 'zoom' image to show spline error up close]

I have made some progress working thru the conversion of linear segments into an N dimensional spline path.

I've created a simulated environment for the RepolaRap XY platform to test some of my ideas out. I created an algorithm curve consisting of line segments of various lengths, and fractally segment it so I get a few quiet areas with long straight segments, as well as some noisy areas with lots of tiny segments.

My goal will be to produce an complete description of every control that must change at each precise moment, and approximate this with spline segments to within as much accuracy as is needed to get an accurate build.

This first image shows the general shape that I've been testing with. The blue segments are simple euclidean line segments, and would represent the output of a G-Code interpreter of all three axes, as well as extruder rate (integrated to get an extruder 'position'), temperature control, fans, and any other special devices that would need to be controlled. Although I assume these are straight linear segments for my simulation, the conversion to splines does not actually require they be linear, only that some function be described that can give its position at some time t.

The red segments in this image represent the spline approximation for the X and Y axis converted into two angles for a two link arm. The simulation allows for distinct pivot arm lengths, but I have assumed they are the same in this image, E.G, that the extruder will be able to reach the exact center point of the build platform.

Mapping the angle positions across time results in the following chart. I have chopped it into the modular domain, rather than extend it beyond the 360 degree motion that actually defines model space. I point out those cases where the apparent branch cuts actually do not exist in the simulated revolutions. As I have mentioned previously, only one axis actually needs 360 degree freedom (the build platform); the radial arm only requires 180 degrees, so no it does not require welding, and no special logic for handling the branch cut is needed.

My next goal is to figure out a way to dilate or compress the time component such that one axis will always move at maximal jerk, acceleration, or velocity. I think this will happen by cutting each spline segment into as many as six segments as different limits are hit. I've included the stock graphs for the equations that will need to be dilated, consisting simply of the first, second, and third derivatives of the angular motions.

I fully expect during extrusion that the extruder will actually arbitrate the majority of time, with the exception of very noisy, very short segments. As I've not yet gotten this logic in yet, it's hard for me to judge yet.

One last image here shows what the spline error tends to look like. This image was generated by finding a region with some error, and zooming into it 100x. This is the first angle area on the right near the top of the path.

Hydra-MMM Software/Firmware updated to v1.1

2010-02-26T09:20:00.000-08:00

First off, I am thrilled to see how many people were willing to try out my software and firmware. Thanks for all the feedback from the community! I pushed out an update this afternoon that added several of the features that were most requested. A summary is below:

v1.1

- Extruder support added that automatically determines correct extruder speed based on XYZ specified federate

- Support for external motor drivers added, the option is now at the top of the firmware to choose to use dir/step method (for external driver) or defining each coil and using MOSFET transistors or something of that nature (see below)

- Wiring diagram added by request to show how to hook up a stepper motor without an external motor driver

- Made preview window larger and added ability to change the size easily in the Processing sketch (variables pw_width and pw_height)

- Sample gcode file added by request

The biggest things here are that external motor drivers are now supported. This means that the firmware can now seamlessly be used with a Reprap or Makerbot machine. There is still one limitation that the current firmware assumes you have a stepper motor driver. If you happen to be using a custom extruder board with RS232 comms or something of that nature, you will have to either throw together another external motor driver or just grab 4 FETs and wire the motor up as shown in the schematic below.

If you do choose to go with the above method, the advantage is that you get a microstepping driver for only a few bucks! I hope to add RS232 or RS485 comms soon, but being that I won't be using that method for Hydra, it is a low priority at the moment (unless I get a lot of feedback saying this would be useful!). So as always head over to the sourceforge page for the latest and greatest: https://sourceforge.net/projects/hydra-mmm/

first tests building a powder-based stereolithography printer: part 2

2010-02-25T22:24:00.000-08:00

hi folks,

i thought i'd take a break from applying to postdocs and things, and tinker a bit more tinkering with progressively building the powder-based stereolithography printer rig:

(click on the thumbnails for larger pictures)

i decided that rather than go pickup a spare gen3 electronics set, i'd just build a stepper controller board and plug it into a dsPIC breakout board (thinking that the printer will need at least 3 steppers -- two on the pivotable mirror, and one to index the table, plus however many other motors for laying down new layers of powder).

i picked up some L293D H-bridges, and after a good afternoon had a 4-channel stepper controller (or, alternatively, one stepper channel could be used to control two DC motors). around this time i also remembered how very long it takes to build things on perfboards with through-hole components, and how much time surface mount components and the folks over at gold pheonix have saved me in the past couple of years :).

the stepper controller can take separate voltages for the two left and two right channels, although one channel has to be between 4.5-7v to supply logic voltages to the L293D H-bridges. it also supports both unipolar and bipolar steppers -- i just added two pins to the 4 stepper header that supply the motor voltage, incase it ever needs to be used for unipolar steppers.

after some tests plugged into the dsPIC33FJ256MC710 board, i decided to start working on the pivotable mirror mechanism. the pivotable mirror has to reflect the laser beam through variable angles such that the entire print space of the chamber is accessable, and at a sufficiently high resolution to be able to print things (not that we know what that resolution has to be just yet, so higher is better, while still maintaining some speed. in the event its too slow, the laser diode could always be pulsed, too).

i've never made a pivotable mirror before, and there seemed to be lots of different ways to go at it. you could have two spinning mirrors slightly out of phase, and rasterize a pattern, you could attach some mirrors to a galvanometer, or a bunch of other ways. my goals for the project are, as much as possible, to keep things fairly simple and off-the-shelf. i decided that the spinning mirrors probably weren't a great idea, since you'd likely want to be able to have a sustained beam present at a given location for some time, and to be able to move that beam progressively (or, at least, this seems like a good way to start -- maybe the spinning mirror idea would work out pretty well, heating up an entire layer gradually and simultaneously).

the idea i went with was to have a single mirror mounted to a small sheet of acrylic. this acrylic sheet would pivot about its center, and have two ball joints on both the X and Y axis that would move back and forth on tiny lead screws connected to steppers, allowing the mirror to be aimed.

finding some small ball joints wasn't very easy, and so i ended up using some pretty big ones from tiny tripod camera mounts i found at the dollar store. i used some epoxy to hold a long screw coupling to the center of the ball joint (to act as the nut), and found some long machine screws to use as the actual screw. couplings are a big problem, so i whipped up some compression based ones out of a few layers of acrylic and aligned them *by eye* before supergluing them. they actually worked not horribly, but a much better solution has to be thought up that doesn't require precision machining equipment.

here is a whole single-axis mechanism: stepper (bottom), stepper-screw coupling, screw, nut (but really it's a large screw-screw coupling), and the ball joint (top).

the steppers were mounted to a sheet of acrylic

and here's the little table, with the ball joint on the pivot point (center), as well as the mounting holes for the other ball joints for both the X and Y axis. the mirror would be mounted to the center point.

and here's the whole mechanism together, with stepper control. i tested it out, and there are a bunch of issues that need to be resolved, and so i think it will require some redesign (though it was a good test -- i've never designed anything like this before):

1) the stepper-screw couplings need to be VERY precise, so i'll have to figure out a better way of mounting the stepper to the screw.

2) the ball joints are huge, and i don't think they're the ideal solution as the ball-holder section of the joint can spin if there's any friction between the nut and the screw, leading to reduced motion of the mirror, and importantly, an inaccurate idea of where the mirror is actually pointing.

3) ideally the ball itself (or whatever pivot joint is used) should be mounted as close to the surface of the mirror as possible -- the more distance between the pivot and the mirror, the more skew things will have (although, this can be compensated for in software as long as you know the distance).

4) generally the whole mechanism is pretty big, and I think could be reduced quite a bit.

i have some thoughts on redesigning things, but i'm curious to hear others thoughts?

---

laser update:

i've accidentally overvoltaged more DVD burner diodes than i'm willing to admit -- without part numbers or datasheets on the diodes, this is *very* easy to do. i'm keeping an eye out on ebay for an inexpensive module that includes both a 250+mw diode with a collimating lense that reduces the beam width to somewhere on the order of 0.5mm to 1.0mm. there are plenty of ~808nm infrared diodes on ebay that can be had inexpensively and that are on the order of 1000mw, but that just seems both dangerous (the beam is invisible), and difficult to work with / align / etc.

---

plastic powder update:

i've decided to try and make some ABS plastic powder, since it seems really difficult to find ABS in powder form (it's most commonly granules, filament, or sheets). i'm thinking of a belt sander or some of the options mentioned in the comments on the last post -- the trick is that the whole SLS printer has the best chance of working when the powder size is very fine. we took a bunch of our failed prints from the repstrap and put them in a pop can to melt down with a blow torch. not the best option, but it's freezing cold outside, so slow cooking them under a candle or something similar likely wouldn't work. it's almost melted in spots, and i'd like it to be pretty consistent before heading to a belt sander:

---

past posts:
[part 1]

---

so, that's the progress so far. i'm going to rethink the pivotable mirror and try to think of some small pivot joints, and also give some thought on attaching a stepper to index the table up and down (although i'll likely run into some problems with alignment in developing some way to couple the stepper shaft to the screw -- so this will require some thought as well).

thanks for reading! thoughts appreciated :).
~peter

Hydra-MMM Software and Firmware v1.0 Release!

2010-02-25T05:28:00.000-08:00

So I have been working pretty diligently over the past 2 weeks on the software and firmware for the machine. Enough additional features were required that the software and firmware was completely written from scratch. So onto the details...

Firmware: The firmware is written in the Arduino development environment and is currently being tested on an Arduino Mega. The Mega was needed due to the large number of pins required for a multi-headed design. The firmware communicated to the host software via a USB serial connection and has a large collection of standard G and M codes that it accepts as input. A custom stepper motor library was created (cpwStepper) that allows for multiple stepping modes to be used on the machine. The stepping mode can be changed mid-build via a custom M code. The modes available include wave drive, half-stepping, full torque drive, microstepping 4x, 8x, 16x, 32x, and 64x. For our purposes, anything past 8x microstepping will likely be too slow as we are already gearing the machine down significantly through the use of a leadscrew. The firmware also features a PID temperature controller through the PID Library available from the Arduino Playground. There are many additional G and M codes added as the machine will need to be able to accept standard machine codes for milling as well. Some of these include a set/return to reference position, enable/disable software endstops, set/disable maximum speed setting, set current position as home, and many more. The readme file in the release linked below has more details about the complete code list.

Software: The software is written in Java via the Processing development environment and thus can be run on Windows, Mac OS, and Linux. I have tested the software on all 3 platforms and it works flawlessly assuming you have Java and USB serial drivers installed. The software is what is used to send individual commands or complete gcode files to the machine. Sending files to the machine is extremely easy and robust. The file sender also includes a preview window to show exactly what each command that is sent to the machine should be doing. For example if the last command sent to the machine specifies that the extruder lay down plastic from X0.0 Y0.0 Z0.0 to X3.0 Y2.0 Z0.0, you will see a thick line appear on the virtual build table corresponding to where the extrusion should take place. Movements without extrusion or cutting are represented with a thin line. This file preview ability is also available without actually sending the file to the machine. If the independent file preview is used, there will be a timeline skimming bar along with a play button to move through the build and preview what is supposed to happen. This is extremely useful for checking a gcode file for incorrect commands before actually sending it to the machine. The software is also able to pause sending a file mid-build and perform any number of other operations while being paused. This includes sending individual movement commands, setting a new temperature, setting/returning to a reference point, and lots more. All in all, it is a very robust alternative to what is currently out there.

Here is a screenshot of the GUI:

The software and firmware has been packaged and is available to download at: https://sourceforge.net/projects/hydra-mmm/

I would love any feedback on the project so please feel free to try it out and let me know about any suggestions for improvement!

first tests building a powder-based stereolithography printer: part 1

2010-02-15T00:21:00.000-08:00

hi folks,

i'm a bit sleepy, but i thought i'd post this while it's fresh:

after seeing really interesting powder-based printer designs like this one, that place down a layer of powder then "print" a binding material onto it, i began to wonder (as others have) if we could build a similar setup using ABS powder and a laser diode to fuse the material together. designs like this have a bunch of benefits, including the potential to use the powder as it's own support material. (and, after a few weeks of tinkering with building an extruder for a second printer that *constantly* clogs, i think i needed a break to think about better days when we won't need to rebuild extruders, or hope we build working ones in the first place... ). my goals for this tinkering are to build things with common off-the-shelf materials wherever possible, and so I went searching for some form of ABS powder, as well as a laser diode.

After some searching, it looks like ABS powder really isn't easy to come by, and it's most often found in pellet form. Zach had a similar idea a while back ( link ), and so I asked him if he'd had any luck. He said he never got past the materials research stage, but that polyester-based powders used as powder coatings sounded promising since ABS powder was so hard to come by.

I figured that if I was going to use a DVD burner laser, I'd need some black powder to absorb the radiation (since a 250mw red laser is relatively low power to melt plastic that isn't black). I sent an email to our local hackerspace in hamilton, thinkhaus, and folks were really encouraged by the idea. One of the folks there, jason, ended up finding a local place that manufactures powder coatings. I called up a fellow there and told him about the idea, and he was extremely kind and prepared up some samples of black powder coatings, one a polyester, and the other a polyester-epoxy hybrid. jason and i did some tinkering with both these as well as some laser printer toner (since it's carbon mixed with a polymer). jason tried both with the hackerspace's laser cutter, as well as just heating a bunch of the stuff up in a popcan. in both cases each powder (polyester-based, polyester-epoxy hybrid, as well as laser toner) fused, but the product was VERY brittle. the pop-can tests that melted material to be a few millimeters thick showed that the problem seems to be with the material itself -- unfornately, even relatively thick pieces would snap pretty easily. (though powder coatings do contain quite a few different materials in them for curing, flow, and pigment, so it's quite possible that some particular combination might work).

so, not much luck on that front. i would really like to get my hands on a good couple of cups of black ABS powder, or make some. (random thought: i think the size of the powder will be fairly critical -- ideally one would want to maximize the ratio of surface area to volume of each little ABS grain, such that the laser diode could more easily heat up relatively little volume).

---

so, i decided to work some on a little test rig to try out different powder materials (and, conceivably, with some better seals, you might even be able to use it for liquid stereolithography). i figure that you don't need a great deal of print volume to test if the material is viable or not, so i decided to make a "mini stereolithography" system -- infact, it's almost pocket sized, save some of the larger mounting bits.

here's my progress so far (in picture form):
(click on the thumbnails for much larger versions)

first i went out and picked up this DVD burner. it's a 24x (the fastest i could find), so the diode in it should be around the 200-250mw range if memory serves. (clearly here i should add in the usual warnings -- LASERS CAN BLIND YOU AND THE FOLKS AROUND YOU INSTANTLY, unless you know exactly what you're doing and take appropriate saftey precautions, you shouldn't attempt this!).

off came the cover

and here's the diode -- it's even labeled (the pins are DVD, GND, and CD). The CD one is likely infrared, and even with lightscribe likely only within the ~40mw range -- so not too useful. But still plenty powerful enough to blind me instantly, and invisible so I'd never know. So I left that pin alone! :)

i soldered some leads on the diode, and tested it out to make sure the pins were correct, and to get an idea of the voltage.

even though the diode was still in the focusing housing, i thought i'd give it a try to see what sort of heat it could produce on some black plastic. the focus of these lenses is on the order of about 1mm from their surface, so the material has to be up pretty close.

having the diode on for a couple seconds heated it up pretty well, and i tried moving the head back and forth a bit and it produced a really faint line. so, it works, but i decided to take the diode out and not deal with all the optics in the DVD burner that weren't really required for this.

there are lots of interesting beamsplitters and lenses and such in modern CD/DVD combination readers/writers, and i often save these bits for tinkering. the diode was epoxied in, so it took a little bit to get it out.

i put some wire wrap leads on the diode

and tested it out. for some reason i remember reading the current should be around 200-250ma, but i'm not sure where. this turned out to be about 2.5V for this diode.

a quick test with the diode right against the surface --

this worked *much* better than when the diode was within the DVD burner optics, and even quickly turning the power on and off yielded distinct melting.

being a laser, the beam should be coherent and come out in a straight line with some width -- so i decided to see if i could get the same results from a bit of a distance -- a few centimeters above the plastic. unfortunately the laser beam divered quite a bit, and this didn't yield any melting, even for quite a few seconds of exposure.

(as can be seen here -- no melting under the raised laser diode configuration)

---

i had wandered around home depot for half an hour or so for ideas to make the indexing build chamber for the powder. i figured that a simple idea would be to just make it round, and find two pieces of pipe that fit snugly within each other -- the outer one would be the chamber, and the inner one would have a little piece put over the top to act as a "table", and index down within the larger outer pipe by a small lead screw or some other mechanism. here are the various pieces of pipe that i found. i think the outer pipe (the black one) is around 1.25 inches in diameter.

here are the critical bits. there's the black outer pipe for the "chamber" (left), a smaller white pipe that fits right into it that's threaded on the inside to be the "indexing table" (right), and a third pipe that screws into the "indexing table", that acts as the lead screw (center). you could attach a stepper to this, or just index it down manually.

here's the "indexing table" piece (top) fitting right into the "lead screw" (bottom).

and here's the whole idea, where the "table" and "lead screw" fit with the "chamber".

they fit together something like this, where the "table" ends up mostly inside the "chamber", starting mostly near the top but being able to be pulled down quite a bit. the "lead screw" piece is always outside of the chamber, and doesn't move up or down. (the "table" would index up or down, while the "chamber" and "lead screw" parts would be vertically stationary).

i foraged around looking for something to build the actual "table" out of, and was thinking plastic or even cardboard, so that you'd get a bit of a very rudimentary seal around the edges (although it's probably not critical if a little bit of the material leaks out). one of the folks at the hackerspace offered me some dense foam, and it seems like an even better idea than the cardboard -- it's pretty stiff but also a bit flexible, and expands to form a seal while still making it easy to move the table up and down! i cut out a circular piece to fit the "chamber", about 5 to 10mm thick.

checking the fit, it was nice and snug, but easy to slide the table up and down. i epoxied it to the "indexing table", making sure not to get any onto the "chamber".

it was around this time i had a crazy idea, and noticed that the "chamber" happened to be around the same size as the hole for the spindle cap in the DVD drive! i was thinking about how to mount the table, and decided to give it a try, so i cut out the spindle cap cover.

and removed it, revealing a nice perfectly sized hole!

AND it looks like everything fits! the chamber fits right ontop of the hole without falling in, while the table slides right through it with a bit of space to spare.

look at that!

the indexing table needs some guide rails to make sure it only goes up and down, rather than spinning in place, when the lead screw is rotated. i found the rails used in the DVD burner, and made up some slides and holders out of acrylic.

from top to bottom, here's the foam table proper, epoxied to the "indexing table" piece. the indexing table has a plastic guide (two holes, drilled in a piece of scrap acrylic) superglued to it. the "lead screw" screws into the indexing table, and beside the lead screw at the base is a keeper for the rails, also made out of some scrap acrylic. everything is resting on a piece of scrap acrylic that's being used as a base.

and here it is with the chamber on top, too.

the bottom of the "lead screw" should be resting flat against the base, and after measuring everything when the table was indexed all the way up, i determined that the setup would need a bit more height than just the DVD drive cover would have, so I brought it up a bit with some L-brackets. (it actually needs to come up a bit more, but I didn't have any larger brackets, so I made up some little acrylic spacers for screws, too).

and, here it is all together. too cool! :) i drilled some holes in the metal DVD case beside the spindle holder aperture to act as upper keepers for the guide rails.

---

so, that's my progress so far, and now i'll have to forage for some tiny steppers to both index the table, as well as move the laser on the x and y axis. the travel is extremely small -- the build area will be about an inch in diameter, with a height of about 1cm. that's pretty tiny, but should be more than enough to test different powder materials to see if they can successfully build very small parts with sufficient structural integrity. the neat thing is that the whole thing can come apart pretty easily, so it can be washed out to prepare for a new material. hopefully once the steppers and axis are on there, it'll still be just as easy.

hope you've enjoyed my little story! (and i hope my supervisors don't read it -- i'm supposed to be working on my dissertation).
~peter

My approach for motor control - spline segments

2010-02-12T08:44:00.000-08:00

On the message boards, I talk about using spline segments instead of linear segments on RepRap. While I am still working out the firmware, I wanted to document the technique as I have had a few requests for how I might do 'complicated' spline curves in firmware without using too many cpu cycles or multiplications or what have you.

It basically boils down to an iterative, stepwise approach. I allow the host to perform all of the expensive calculations beforehand, and then pass off and buffer a set of integral value 'stepwise splines' onto the firmware. As you iterate the computation, the values follow a particular cubic spline at each step.

On the host side, you have some curve through 5D space that you want to approximate:

x(t) = some function that describes the position of the X axis at time t.

y(t) = some function that describes the position of the Y axis at time t.

z(t) = some function that describes the position of the Z axis at time t.

e(t) = some function that describes the 'position' of the extrusion motor at time t.

c(t) = some function that describes the 'position' or tempurature of the extruder at time t.

The 'position' for e(t) and c(t) are abstract position; Taking the derivative of e(t) describes feed rate, and the curve for c(t) will most likely be a constant temperature, so in these cases, a spline curve may not quite fit the problem domain; however, as you will see, the computations do not add a lot of overhead, and it may yield flexibility later, if, for example, you wanted to vary the extrusion rate, or ramp up or down tempurature as you slowly moved the extruder head along some path.

For stepwise spline approximation to work, the 't' time variable must be segmented to the point where you only need the specific positions at t=0, t=1, t=2, t=3, ...; this involves choosing a particular spline step rate per second that will set your maximum spline accuracy. Too high of a value, and the precision required to prevent too great of error becomes a bottleneck. Too low of a value, and you may end up with steps that must be passed into a linear interpolation phase (For example, if x(3) = 10, x(4) = 30, y(3) = 15, y(4) = -3, you need to add bresenham on top of step spline. Not a big deal, but it does increase risk for bugs and code complexity.)

My computations indicate that 48 bit is fine for up to about 2000-3000 steps per spline segment. A few bits can be saved because accelleration and jerk will never be very high, relatively speaking, and can be simple 32 bit values, sign extending to the 48 bit value where needed. My computations also indicate I should be able to attain more or less 5000 spline steps per second.

Before I go into how we compute the step splines, I want to briefly reinforce the simplicity of the algorithm on the firmware side. I outline the primary firmware loop here:


LOOP FOREVER

  Perform comms time slice

  start_new_spline = false
  if t > number_spline_steps
  then
    t = 0
    number_spline_steps = next number_spline_steps
    start_new_spline = true
  else
    t = t + 1
    start_new_spline = false
  end if

  for axis = 0 to 5
  begin
    if start_new_spline
      axis_vel[axis] = next axis_vel[axis]
      axis_acc[axis] = next axis_acc[axis]
      axis_jer[axis] = next axis_jer[axis]
    end if
    axis_pos[axis] += axis_vel[axis]
    axis_vel[axis] += axis_acc[axis]
    axis_acc[axis] += axis_jer[axis]

    target = Get top MSB portion of axis_pos[axis]

    if axis is stepper,
    then
      Step motor in direction defined by sign of target - current; possibly no step if sign is 0.
      increment or decrement current defined by the same sign.  possibly unchanged if sign is 0.
    else if axis is PID control
      Set pid target = target computed above.
      Execute pid cycle on pid controller.
    end if

  end loop

END LOOP FOREVER

The comms logic feeds in and buffers values associated with 'next' variables, possibly buffering multiple segements to allow a few short segments to exceed the communication rate, assuming that they are preceeded and followed by a few longer segments. At most, you must perform multi-word additions and a few bit shift operations.

On the host side, it will perform some math to compute a standard cubic spline. For the example I'll give below, the curve is one that accelerates across X,Y starting from a standing stop and accelerating to 90cm/minute in a 1mm diagonal span, where one linear step on X or Y should cause the extruder to advance one step for feed rates.. (I do make some assumptions about extruder,motor capability that may be a bit optimistic, everything assumes a motor step yields .1mm motion.)


x(0) = 0, x(1000) = 10, dx(0) = 0, dx(1000) = 0.03
y(0) = 0, y(1000) = 10, dy(0) = 0, dy(1000) = 0.03
z(t) = 10, dz(t) = 0
e(0) = 0, e(1000) = 14.14, de(0) = 0, de(1000) = 0.0424
c(t) = 210, dc(t) = 0

For each axis, I follow the general outline described in my blog post on stepwise splines, and arrive at:


xaxis_pos = 0, xaxis_vel = 43, xaxis_acc = 258, xaxis_jer = 258
yaxis_pos = 0, yaxis_vel = 43, yaxis_acc = 258, yaxis_jer = 258
zaxis_pos = 42,949,672,960 (=10.00 fixed point), zaxis_vel = 0, zaxis_acc = 0, zaxis_jer = 0
eaxis_pos = 0, eaxis_vel = 61, eaxis_acc = 364, eaxis_jer=364
caxis_pos = 901,943,132,160 (=210.00 fixed point), caxis_vel = 0, caxis_acc = 0, caxis_jer = 0

If you run the algorithm above with these initial values, you should find that after 1000 iterations, x and y have moved 10 units each, the extruder has 'moved' 14.14 units. You'll find that the error for the fixed point iterations is about 10 microns.

At the assumed rates of 5000 iterations per second, this spline and motor accelleration occurs in about .2 seconds.

the anti-heated-bed?

2010-02-11T21:42:00.000-08:00

I've been following this "heated bed" technology recently, as it seems to do a reasonable job of reducing warping... but its not "perfect", so I was thinking of alternatives.

In the commercial machines, they enclose the entire unit, and make a "hot box", which aparently works well. Everyone says "repraps can't do that because the printer parts will soften/melt", so instead we have:
"headed beds" :- http://hydraraptor.blogspot.com/2010/01/hot-metal-and-serendipity.html
"heated bags" :- http://blog.reprap.org/2008/12/roast-in-bag-duck.html
"heated blower fans" :- http://www.neufeld.newton.ks.us/electronics/?p=761
etc.

So I thought: "there has to be a way to just put the whole thing in a simple heated box".

So I Ask myself, and you all.....
What temperature should a "heated box" run at?
Is it less than the critical melting/softening temperature of ABS ( or PLA )?
If it is OK, then why haven't we tried this?
If the box temperature is "too high" for the normal parts, then what change/s need to be made to a mendel to make it more "temperature resistant"?
The wooden/aluminium mendel/s would be an instant winner here, but is there something we can do to ABS to make it heat-resistant? ( eg: perhaps build an entire from pewter using lost-ABS casting? like: http://blog.reprap.org/2009/12/metal-bits-from-reprap.html )

I don't have all the answers, I just pose these questions for group input. Comments please!

"Ola" with two arms..

2010-01-31T17:45:00.000-08:00

I spent some time saturday working on the prototype encoder electronics. I originally created a simple test board with two photo-transistors and a single LED to see if pursuing it further would have likely success.

This effort resulted in this simple board; one LED, two photo-transistors.

Today, I went further, since the test board could detect a white/black edge printed on my inkjet. I made a 6 photo-transistor device using ordinary stripboard; still one LED, as these things produce a LOT of light. The reason for so many photo-transistors : the tranistors create pairs of voltages that a comparator will use to decide which one is looking at blackness, and which looking at white. Using two in this way reduces the effects of ambient lighting, ink reflectivity variations. Two pairs will provide Quadruture encoding, and the third pair will decode digitally printed absolute position markers.

Here's a more wide-angle shot to give an idea on the size of these components. The 6 transistor board is a bit longer than I wanted, but I still think it will work, and doing it this way allows a larger margin of error when I print the encoder wheels.

On the mechanics front, I finally got the 1.2 motherboard to drive the stepper motors. I found programming it much less intuitive compared to the Mega; you have to manually reset the board and get the timing just right in order to upload new firmware; it does appear there is an 'auto-reset' jumper, but the pre-assembled electronics does not include the jumper pins. I may eventually add a switch here to ease programming. Oh, and it took me an hour to figure out why the firmware did not download to the board. After I got a successful firmware download, I went searching for pin numbers so I could create a simple motor test, and eventually (after 3 hours) cobbled something together that worked. When I looked at the firmware source, I originally missed the #if guards, and mistakenly copied in the pin numbers for the 1.0 motherboard; needless to say, this worked for the X-Axis, but Y gave me a silent treatment, whereas and Z screamed painfully in a high pitch voice. There went another 2 hours testing cables and boards and trying this and than thinking I did something wrong when setting the signals in firmware.

I've uploaded a video of both axis turning; one continuously in one direction, and the radial arm reversing back and forth. Note that I turned the speed way down on this test; I had done this as part of diagnosing the problems I experienced when using the wrong pin numbers; I left it slower under the false impression that they would skip less -- unfortunately, they still skip a little at this slower speed when reversing. I intend on getting cubic splines up as quickly as possible, since these will integrate accelleration directly into the stepper logic.

Ola learning to dance

2010-01-23T12:35:00.000-08:00

I made a little progress this morning. It took a while to convince the RepRap stepper control that it should listen to my Mega Arduino, but eventually, it gave in. Turns out I had the pin numbers reversed. Oopsie.

Anyway, I took a short video clip showing the somewhat boring radial motion of the build platform. The motion appears very smooth. It is not exceedingly strong, I can stop and cause the stepper to begin stepping skips by grabbing the platform, but I don't think that will create any issues for RepRap printing.

My next step will be to get radial motion on the radial arm platform too, and then create some tests to see if I can calibrate and draw 2D shapes accurately with a mounted pencil.

I apologize for the audio quality; it's my first attempt to upload video/audio.

Update: I got the second motor mounted and working, sort of; Ran into a few issues: 1) The radial circle was quite a bit off, more than 1/2 cm; so I had my son spin it while I held a pencil steady to get a new better circle, and cut it out on the scroll saw (My friend says I should use a router and a jig; probably if I need to make another repolarepstrap, I may try that out), 2) so, now the belt for the radial arm platform is too long; ideally, it would be 2 inches (5 cm) shorter; as it is, I sanded out part of the side support to prevent the pulley from rubbing. That brings up 3) the pulleys are slipping around the stepper axle. I either need to add a flat so the screw pins can hold onto the axle better, or use epoxy or something and just permenantly fasten the pulleys -- which I want to wait on because 4) I may need to get another pulley as I sort of stripped one of them trying to drill it out to fit the axle; it is very rough and skips belt teeth.

Geared Nema 17 Extruder

2010-01-22T09:34:00.001-08:00

I didn't have a lot of luck with the standard Mendel direct drive pinch wheel extruders, most likely because the steppers I had were not strong enough. I ordered in some 5 kg*cm Nema 17's, but unlike the datasheet, they had substantial flats on the shafts, which made building a direct drive extruder problematic. So, I thought I'd try building a geared extruder, using printed gears.

Surprisingly, the gears didn't fall apart right away, and I was able to generate 5.5 kg of pull on a PLA filament before my pinchwheel started slipping. It needs a bit more work, but it looks promising!

More details on the RepRap Wiki -

http://objects.reprap.org/wiki/Development:Geared_Nema17_Extruder

Wade

RepolaRap Motor Mounted

2010-01-17T08:44:00.000-08:00

I got around to going to the hardware store to find screws to mount my motor down. The specs that came with the motor indicated M3 0.5P screws, but they lied. I ended up getting some imperial (Can't remember the exact size now). In any case, it worked.

The side pieces made out of poplar or birch -- I had it laying around in the garage. The two pieces are mounted to the upper radial platform using 3 cross dowel nuts. The motor plate is attached to it using 2 cross dowel nuts; my original vision was to use three but I didn't quite line it up right, and besides, with the bolts tightened, I think it will be okay. Even if it is not, a simple screw in the corner should secure it.

I'm going to try to wire up a single stepper driver, and see how effective it is at turning the table before I work on the other mount.

RepolaRap Calibration thoughts

2010-01-14T19:59:00.000-08:00

I've received a few ideas from others now, for how I might calibrate a RepolaRap XY axis. I may need to leverage some of these ideas eventually, but I wanted to describe my thoughts for how I might do this. The RepolaRap XY has intrinsically soft, round curves, and normally, we want it to do hard angles or straight lines. I'm still working out the math itself, but I think all the variables can be accounted for using the following procedure:

Assumptions:

Backlash can be ignored, or measured using the encoder wheels and compensated adequately when reversing motor directions.

My 13cm radius encoder wheel can achieve minimum 2500 steps per revolution at 75 LPI (30 lines per cm) Sebastian pointed out a reflective encoder that appears to be able to get 3x this resolution, so I'll start off with worst case on the lowest resolution model.

I can get my ink jet computer to print out the encoder wheel with good accuracy on a material that works with the LED/photo-transistors.

The encoders should let me accurately measure platform angle from an arbitrary home position on both platforms. The build platform angle is truely arbitrary. It's only affect is to build a rotated model, and who cares, since we can just rotate it around and viola! The radial arm home angle, however, is very important. Get it wrong, and straight lines turn into weird curves, and extrusion material volumn doesn't match print speed.

There are also two slight unknowns that should also be measured: the planer radius between the base / radial arm pivot and the extruder tip, and the limit circle diameter of the model space (I.E, the maximum radius of the largest circle you could print.)

My approach would be to manually rotate the table so the extruder was relatively near the center. This allows me to pretty accurately model the extrusion rates relative to platform rotations. Then, execute the following program to create a calibration thread that can be measured directly:

Rotate Radial Arm 180 degrees

Rotate Build Platform -90 degrees

Rotate Radial Arm 60 degrees

Rotate Build Platform -90 degrees

Rotate Radial Arm -120 degrees

Rotate Build Platform 60 degrees

Completed

This diagram shows where the measurements need to be made:

Hopefully, I'll be able to test this out within a week or two.

added streaming to gcode visualization tool

2010-01-14T09:59:00.000-08:00

hi folks,

i was tinkering with the gcode visualization tool, and it now streams the transparency by gcode index instead of layer. this gives a neat effect, and looks like you're watching the part build on an actual machine. i hope you like it!

Meet Ola, the RepolaRap (At least, her first parts)

2010-01-12T17:50:00.001-08:00

Having acquired all the non RP parts to build a Mendal, I started down the path of building the RP parts out of MDF and angle aluminum. The STL model files are not very suitable to be built directly out of wood, at least, with my own woodworking skills; I decided to alter things around a little, and after 3 versions of the X-Axis chassis and bearings, I was still unhappy with the state of things and the progress.

I figured there must be an easier way to DIY, and decided to try an idea I posted on this blog about 3 years ago. I discarded other ideas because, well, frankly, I think a polar bot would look really cool, and has some intriguing possibilities -- being able to print an 28cm / 11" diameter timing belt gear pulley to replace the MDF, for example, assuming I can avoid warp, so I can give friends mostly non-MDF Repolarap parts of their very own, maybe even more quickly than I could print out the parts for a mendel for them (maybe? Okay, maybe not.. that would be a really big part and very liable to have accidents partway thru; and thats not even thinking about the 42cm / 16" gear needed by the radial arm.)

So, I created a design in blender, tweaked it a bit (Okay, a lot), and posted in the forums to see if anyone had tried anything similar or had any suggestions or comments. After becoming more confident that something like this might work after creating a bearingless "mockup" in MDF (the wheels two wheels and an unusable upper radial arm that I did not take a picture of), I decided to take it further and ordered some 5mm steel balls to use in the bearing races, timing belts, and pulleys for the steppers sitting idly in the "here are my Mendel parts" bin. Unfortunately, I separated the orders by a few days -- I bought the steel balls thinking I wouldn't be ready to attach motors for another few weeks. Looks like I underestimated my woodworking skills, or overestimated the difficulty in building the XY stage prototype, or both. Anyway, the steel balls arrived today.

The build platform (medium circle), bearing races (the two smallel dark circles, steel balls already inserted), upper radial arm platform (the funny shape one with one of the bearing races on it), lower radial arm (BIG circle), and the base (the square with a bearing race on it). You probably don't need to, but can refer to the draft WIKI page on this design for a render I put up while working thru the design in blender.

I anchored the build platform to the upper radial arm platform, with intervening bearings to make it turn easily and smoothly. I'll still need to figure out how to put something on top of this to get plastic to adhere. The 4 machine screws visible are just there because I was too lazy to take them out when I disassembled the structure to take pictures.

Then, I anchored the lower radial arm anchored to the base, with intervening bearings to make it turn easily and smoothly. You have to proceed in this order because the nut (or bolt head) to lock down the pivot points become entirely inaccessible between the upper and lower platform. The hole you see here provides access for the bottom bit on the build platform pivot. Theoretically, I could drill out windows to get access to these, and still might because I may like to adjust platform bearing compression without having to take everything apart.

Finally, I screwed down the 4 machine screws into captured nuts I had already installed on the lower radial arm platform to firmly attach the radial arm parts together.

If I were to do it over again, I'd change the machine screws with inverted bolts up, glued or epoxied to prevent them from rotating, and ensuring enough recess space to allow the lower platform to rotate.

It'll be a few more days before I can actually see if the motors are going to move this. The wheels spin freely, have very little play in any except their intended degrees of freedom, but are a bit heavy. It might take a while to visuallize the motions. Think sort of like "Spirograph (tm) on steroids" and you get a feeling for how it works -- Radial motion on the build platform makes concentric circles around the build platform pivot. Radial motion on the radial arm makes circles half the size and touching the rim of the build platform. If you move each axis at a constant angular velocity, it draws big Rose Curves. Oh, the extruder stays stationary relative to the two platforms -- it will move only up or down relative to someone watching the machine.

Anyway, I plan to build motor mounts with a simple box in the corner on the upper bearing arm platform, and on the base. A 10 tooth pulley will drive a belt that wraps entirely around the appropriate circular platform. At 200 steps or 400 half-steps per rev, that should give near about .1mm accuracy everywhere the toolhead can reach. The belt doesn't seem to move up and down vertically when interfaced to the rim on the MDF, but I may need to put some guides nearby to keep it on the straight and narrow.

The wheels are a little wobbly (1-3mm wobble or so). I made the mistake of cutting out the circles prior to drilling out the center. Oops. If I were to do it over, I'd trace the template on a square with the hole drilled in, and be a bit more careful when cutting that out. I can always remake these, in any case; with a scroll saw, it takes about 10 minutes.

Hacking on the code...?

2010-01-02T18:32:00.000-08:00

I've been hacking on variations of the reprap code now for around 5 years.

Anyway, I've never really been able to publish anything worthwhile as it's either specific to my junk-strap, or it's so small it's pointless setting up a site, repository, whatever, and as a result I've not been able to "prove myself" worthy of the blessing that would be SVN access. ( wouldn't that be handy, hint, hint).

I constantly see requests in the forums for people saying "it'd be nice if..." or "can the firmware do X" and thinking to myself "I've written that, but how do properly *share* that: Sending a tarball of my firmware is bound to end in tears, as it's based the main firmware, but hacked up for my non-standard setup ( mega, gen2 electronics, DC extruder, graycode stepper drivers, etc )

So anyway, As my firmware has been getting further and further from the one-true-way, and it didn't support 5D ( a killer feature AFAIAC ) , I'm integrating the two, and sharing it all!

here it is, my integrated, feature-ful, experimental, probably-busted firmware code:
http://github.com/davidbuzz/reprap-firmware-fork/commits/master
( a work-in-progress)

My added features:

DC motor and encoder wheel support in the 5D firmware
quadrature/graycode stepper control ( in addition to the step/direction controls)
open-loop DC motor control of the Z axis ( well any axis really, but it's only slightly useful on a Z)
support optional firmware "features" with #defs define which "features" apply to which motherboard/reprap types. include reasonable defaults for 4 different reprap types.
mega support. ( not entirely by me )
auto-shutdown on idle ( not by me )
useful comments in the DDA code to un-confuse users. ( this code is unintuitive and complicated for the new user )
I merged in recent mendel work too..
removed assumptions about RS485 always being wanted, it's an optional "feature" now.
and the added bugs of course!

Once "stable" (ie bugs removed) this firmware is aiming to be as close to a "universal" firmware as I've seen. ( ie it should support darwin,mendel,makerbot, custom, etc with a little extra effort).

Buzz.

happy hacking 2010.
( patches encouraged/welcome)

Job for a reprapper?

2009-12-21T13:38:00.000-08:00

Got a PhD? Working on RepRap? Here's a possible job just brought to my attention:

http://jobs.phds.org/job/17366/clemson-university/post-doctoral-fellow-in-rapid-prototyping-and

Get paid to spread the word...

Success!

2009-12-08T06:13:00.000-08:00

A victim of our own, that is...

Blogger only allows 100 blog authors, and the RepRap Builders' Blog has just hit that limit.

However, as you may have seen below, Buzz has set up the RepRap Blog of Blogs here:

http://pipes.yahoo.com/davidbuzz/reprap_aggregation_pipe

that unifies all RepRap Blogs (including this one) into a single stream.

So now you new RepRap Bloggers create your very own personal blog using blogger or anything else that will generate an RSS feed:

https://www.blogger.com/start

Then go to the Blog of Blogs and follow the instructions at the top to add your feed to it.

We'll keep this Builders' Blog running too, of course, for the convenience of the existing users. Likewise we'll keep the Core-Team blog running and feeding in too.

Printed Mendel

2009-12-06T21:29:00.000-08:00

So, not complete yet - it still needs electronics, the extruder nozzle, the lasered thick sheets, and a few more belts, but all the printed parts are there.

I'm very impressed with Ed's design - it's very sturdy, compact, and easy to put together. The threaded rod frame is a lot easier to get right, and a lot sturdier than the old set-screw smooth rod deal on Darwin. The bearings seem super smooth, and I have high hopes for the printing speed of this machine.

It's also very portable - you can easily pick it up with one hand and toss it around.

Can't wait to get it running!

Wade

Yahoo pipes reprap aggregation

2009-12-01T22:49:00.000-08:00

Can't keep up with all the different RSS feeds for reprap related goodness? Didn't realise there are (at least) 25 different reprap blogs? Just want to see it all in one place?

here's the link for you. this agregates all the reprap related blogs I could find into one convenient meta-blog using the yahoo pipes drag-n-drop technology. neat!

http://pipes.yahoo.com/davidbuzz/reprap_aggregation_pipe

( contains buttons for adding to your rss reader of choice, like google, yahoo, aol, newsgator, JSON, whatever )

If you find more blogs, just let me know, and i'll add them.
All posts ( irrespective of the source ) are sorted by the post date.

The Arrdvark is here

2009-11-26T03:59:00.000-08:00

Wondering around t'internet I fell over this.

http://antipastohw.blogspot.com/2009/11/aardvark-0836-released.html

In and of itself I guess we need to ask the question what relevance does it have to this project.

In a nut shell it is the Arduino IDE and libraries etc ported over for development on a currently limited bunch of ARM based microcontrolers.

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1250709267

How cool is that board.

In essence this means that there is an easier (Arduino friendly) option for those interested in ARM based RepRap controllers to develop in a way that is compatible to a degree with the code base etc from the project to date. 32bit Rep Rap, ooooooh.

I don't know how good this is yet, as I don't have an ARM equipment, maybe someone really in the know would like to comment.

3D Scanner

2009-11-25T12:25:00.000-08:00

Hi,

I saw an awesome article on wired. I was wondering if anyone has considered mounting a webcam next to the print head and using it as a 3D scanner. Maybe enabling adding features to premade objects. Scan in the object, manipulate it in our design software, add a feature and then print this feature onto the object.

http://www.wired.com/gadgetlab/2009/11/amazing-software-turns-cheap-webcam-into-instant-3d-scanner/

Building an ABS build base

2009-11-24T01:56:00.000-08:00

During my early attempts to get my Bits from Bytes machine printing, I ended up burning a rather nasty hole into my build base when I accidentally left the machine alone with the extruder still hot. So i decided to build another cover over that one in order to protect it that would stop any more damage to the base. Simon Kirkby found a source of ABS and built a platform for his makerbot and I decided to take it full size, so it also provides a very strong ABS-ABS bond for my rafts. After 3 months of using that one it ended up too warped and damaged to use. But then that was the point, because it didn't damage the acrylic.

So with the help of Trent Lloyd I made a new one and filmed the process(Trent did a great job with the camera as well as editing the whole thing together, removing most of my pointless rambling and mistakes when we made this, though obviously plenty still remains). If you look carefully in the background you'll see some guys assembling the extruder for a makerbot in the background.

Apologies if it gets a little confusing. I realized while we made it that due to all the glue being used, it wasn't really viable to do multiple takes if we glued it down properly, so we never ended up glueing the ABS sheet down. If you can keep track of when it's supposed to be on and off then it should all makes sense. Also, you may wish to glue down your sheet before you drill the holes, we made this in a hurry and I possibly explained that part out of order. Either way, hopefully this will help people with making their build platforms from ABS and wood. Expect a new one one how to do this with the mendel within a month or two.

Shameless plugs: This was filmed at the Perth Artifactory's (www.theartifactory.org) reprap night which occurs every second monday, next night is on December 7th. Our Mendel is flying out of my machine as fast as I can orient the stl's and print them, slowed only by the need for sleep, machine malfunctions and the demands from my boss to work.

The perth local reprap site is found at http://www.reprap-wa.org . We run a somewhat quiet mailing list currently at http://groups.google.com.au/group/reprap-wa. And I update occasionally on my reprap blog at www.freeasinsteins.com (get the joke?)

Teaser: The artifactory has decided to assemble our mendel in a single day, something we will do with a webcam running the whole time. If our internet gets running we'll webcast this, but at the very least we'll have a time-lapse of it being made for you all to see. If we web-cast we'll announce here first.

-Peter "letsburn00" Hillier

Another 3D Capture Technique

2009-11-19T23:12:00.000-08:00

A quick heads up for another webcam based 3D Capture Technique that claims rapid capture.

http://mi.eng.cam.ac.uk/~qp202/

Ponoko Darwin Progress

2009-11-14T17:29:00.000-08:00

I started building my Ponoko Darwin about a year ago. Got everything put together in about two months. Needed to upgrade the PC connected to the reprap, took on a job working for a start-up, and had no free time whatsoever. I still need to have a reprap, so I got started working on it again. Found several problems:
1) I have a Reprap Mother Board v 1.0, which isn't documented. Had to buzz out the pins.
2) I'd failed to solder the motherboard's stepper connectors; just diagonal pins.
3) In spite of what the website says, the Reprap's opto end sensors are inverting. When empty, they emit +5v. When interrupted, they emit 0.45v. Had to invert the sense. Perhaps the Sanguino test firmware should say "ran into endstop" when that happens?
The tests are running now. The X and Y operate fairly smoothly. Z is a bodge. WAY too much friction, even though I used a dry teflon libricant. Fails to move even when I have the stepper driver cranked all the way up. Will only move if I help it along. I suspect the problem is in the ball chain's mating with the gears. Advice cheerfully accepted for alternatives.

One More Machine

2009-11-09T11:46:00.001-08:00

Mo stopped by today to pick up the set of Darwin parts I printed out for his team of engineering physics students at UBC. They've got some interesting plans for their Darwin, but I'll let them explain what they're up to.

Instead of a case of beer, Mo, Jacob and Bing paid for this set with a box of MXL pulleys suitable for Mendels and Darwins that Bing imported from China, plus a hardcover copy of Cory Doctorow's novel Little Brother. I've been a fan of Cory's novels ever since I read Printcrime, which I was introduced to by the RepRap forums, and his latest novel features an interesting take on 3d printers. Sooner or later I'm going to have to send Cory a set of parts!

So, next up, Mendels!

Wade

Rapman 3.0 commissioned

2009-11-08T21:22:00.001-08:00

We printed the traditional minimug after a morning tuning the system. This was my first try at printing the minimug. I was running the extruder 5 degrees too hot for the batch of ABS that I was using and the y-axis drive shaft was loose. You can see how the top melted from the extruder running too hot.

Here you see the taping of the first successful minimug print with a tripod-mounted Flip.

The completed minimug on its print raft.

The completed minimug peeled off of the printing platform

A closeup of the completed minimug. There are a few print hairs on the inside which were easily removed.

Thanks are due to the many fellow Rapman builders at the BitsFromBytes Forums and especially to Bogdan Kecman who has been an constant source of useful advice on getting past the little problems one encounters in getting the excellent Rapman Reprap printer going successfully.

Okay, I think I'm getting the hang of Skeinforge.

There was a little displacement for the first 10 layers because of a loose y-axis belt. I paused the print and tightened the belt. After that the print went smooth as silk.

Forty percent fill, 50 mm 15 toothed involute profile gear. Printed at 16 mm/sec in about 45 minutes.

Another Child Darwin

2009-10-29T13:46:00.000-07:00

In the hopes of increasing my printing speed, and to confirm that it is actually possible to make a RepRap with RepRapped parts, I've printed out and assembled a child Darwin. It's mechanically complete, and the axis all run quite nicely - at least 3000 mm/min so far on the X and Y. I have yet to get a firmware that will run the stepper based pinchwheel extruder, so no minimug yet, but I thought I'd post my results so far. I'd love to hear from anyone who has a stepper driven extruder running with any of the Arduino/Sanguino/Extruder controller firmwares. Also, a big thank you to Barry, who soldered up and donated the stepper drivers and opto endstops!

Also, while I've been assembling the 2nd Darwin, I continued printing out parts, and am now just a few parts away from completing a third set of printed Darwin parts. They're going to some students from UBC, more about that later. Interestingly, the parts fit on the bed when you dump them out of a bucket onto the bed, but unfortunately, the Darwin isn't able to utilize the entire bed space for printing. :)

Here's the parent machine:

A little worn down, but still printing!

Wade

Lazy Susans and filament

2009-10-28T07:53:00.000-07:00

Three millimeter filament generally comes packed in two formats, first as ...

coils as seen with the four 5 lb lots of PLA at the seen on top of a standard shipping spool of ABS seen carrying 20 lbs and capable of carrying 40 lbs which is the second format.

While several solutions have been confected to deal with coiled filament, I wanted to use ABS directly off the spool. Having lived and worked in Guangdong in China for several years I became happily acquainted with the lazy susan tables which enabled hungry Cantonese dinner parties to load their rice bowls at dim sum restaurants with a minimum of fuss.

The ball bearing race mechanisms for such tables are readily available in larger US hardware stores for about $10.

I also bought a pair of precut plywood rounds at the same store. Once I locked the race down, I lubricated with a light oil spray.

What you wind up with is a mounting table for quite a heavy spool of ABS which uncoils with about an ounce of force.

I suspect that one could knock together a much smaller spool for coiled filament and use the lazy susan arrangement for those as well. Given that most extruders exert kilograms of force to push filament into the extruder barrel this arrangement shouldn't cause feed problems. I'll keep you posted on how it works out.

Colour Printing - the next step

2009-10-28T06:18:00.001-07:00

To follow on from the basic twin extruder test in the last blog, here we have the results of my first test using support material

The machine is loaded with two colours of ABS, mainly for convenience at this stage, Black for the object and Yellow for the support material.

The file chosen is a bearing cap, printed from the bearing axis up, this has a semi-circular void that runs front to rear of the part. Actually this file prints very well without support material but it is a small part suitable for testing the head change.

Small it may be, but it still contains a fair number of layers and therefore lots of head swapping!

The first test was done with a hand edited file, I added several new lines of G_Code to manage an orderly change over from one head to the other. On more complex parts, it would not be practical, the new codes need to be added by Skienforge.

Skienforge already deals with support material by issuing a temperature change to flag the start and end, I need several other codes inserting at this point. To do this I have made a simple modification to Skienforge to pick out the support material, then insert my new codes as required.

The image shows the first complete part made by running the file from Skienforge.
Finish on the part is crude as the G_Code has been generated with 0.4mm layer thickness, this ensures a relatively quick build and gives a manageable file size.

The print is far from perfect, but I have to say I am encouraged by the results.

Cutting Spur Gears with Meccano

2009-10-20T08:07:00.000-07:00

An item of interest I found when worrying the web about gears.

Meccano Gear Cutting Machine

It is a machine made from meccano that can cut more meccano compatible gears using a Threading Tap. It uses an existing Meccano spur gear as a template for the one to be cut.

A novel way to make gears without a lathe.

Interestingly enough it should be only a small set of modifications to make the machine able to cut worm gears by hand also without the need for a lathe.

I don't have any Meccano but thought this would be useful enough to cover here for those who might.

Just about done

2009-10-18T20:24:00.001-07:00

I finally sorted out the last parts of the extruder on my Rapman and should be able to start printing after I get acquainted with the operations manual.

I need to put that spool of ABS on some sort of bearing loaded rack so that the ABS will feed into the printer smoothly.

Colour Printing

2009-10-18T09:55:00.000-07:00

First attempt at two colour printing, not the most astonishing object but you can see the potential.
The print has been done on a BfB V3 machine fitted with twin extruders. The two single colour objects were printed together from one file, the two colour object by swapping heads through the build, changes triggered by G_Code.
You can see the potential for running support material along with the main print, swapping seamlessly back and fourth between the two.

The wall is single filament thickness so alignment has to be reasonably good between the heads. The object is far from perfect as its only the third print of a new machine fitted out with the twin head.
More to follow on this.

Open-Source to the rescue!

2009-10-13T13:36:00.001-07:00

To build anything in a RepRap, you need to have a 3-D design, save it as a STL or triangle mesh file, and load it into the RepRap host software (or skeinforge).

To create these designs, RepRappers use different programs - Either an adapted 3-d modelling programs, originally used for animation (like Blender and Art of Illusion), or freeware versions of CAD software (like CoCreate). These solutions work, and work well, but each program has seperate advantages. I've been looking out for a 'better fit' - a CAD-style program, that supports building meshes and solids.

Make magazine today furnished me with a link to FreeCAD.

It's pretty slick - either I'm quite lucky, or it works quite well. Within a few minutes I was able to load it up, get started, create a small cube model, export it to an STL file and import it successfully into the RepRap Host software (not always an easy thing!).

OK, lets give it a real test...

Let's load up some data from a complex file: a human head.
To really test it, I created a large sphere, stuck it on top, and did a 'union' (Join).
This is not nice: most complex geometries cause all sorts of bent and broken and backwards triangles. Lucky there is an analysis tool to point all this out:

From FreeCAD

Pressing some of the 'repair' buttons sorted all this out.

From FreeCAD

This exported easily to an STL file: and then loaded straight into the host software.

From FreeCAD

It started to slice and print to gcode : it got to 55 layers through before I got bored and turned it off.

FreeCAD is currently alpha software so far, but certainly one to watch!

Sorry for the off topic post

2009-10-11T16:27:00.000-07:00

Hi,

I'm building a reprap, but I'm way over the alloted schedule I made for myself (big surprise, when is anything done on time... :( ). So I've had to make a choice between continuing to work on my reprap or to do other things that I scheduled for this time.

I put my reprap on hold for now. I'm working on a designed based on a robotic arm and using FPGA's. If you want to know anything about it or would like to continue working on something similar, I'll email you what I got.

I'm taking a trip around the globe. I'm riding my bike from San Diego to San Francisco for three weeks in November. Then spending December with my family in Michigan and South Carolina. Then I'll spend six months circumnavigating the globe. The current travel plan is Hawaii, New Zealand, Australia, Japan, Philippines, Indonesia, China, Malaysia, India, Russia, most of the countries in Europe, Iceland, Greenland, Canada, then home. If you live along my route and wouldn't mind letting me sleep on your floor or couch for a day or two, drop me a line. :)

You can also follow my progress on:

http://thebikepacker.wordpress.com/

Again, sorry for the spam, but technically I am a reprap builder and this is a blog for builders.

Cheers!

-Brian

One step forwards

2009-10-10T12:49:00.001-07:00

G'day all.

I've been quiet recently - I had packed everything away into the garage as we were planning to move. Plans change, we're now not moving so I unpacked the RepRap and fired it up.

From ResistorHeater

First problem : blocked nozzle, due to a broken thermistor - overheated - and set the ABS solid.
Cleared down and drilled it out.

I replaced the thermistor with a spare 100k makerbot one - my last spare.

Interestingly enough, I soldered in a 100k thermistor from Maplins into a spare circuit, connected it up, and the temp read about 20C at room temp, and 34C while holding it - pretty good without any change in configuration. It might be a suitable replacement for the 'official' ones.

Replacement thermistor in, I warmed up the heater and 'let rip'

From ResistorHeater

It works! Extrusion is pretty slow (232mm/minute) and wide (nearly 1mm diameter through a 0.8mm nozzle) but it comes out reliably and pretty consistently. Temp was about 225C and power (screw thread/servo) at 180/255.

Now I have something working, I can refine the nozzle size ( I should be able to get some 0.6mm B&Q nozzles) and the original BfB 0.4mm nozzle, plus I have some small drills.

I now need to get my settings and speeds right in the host software - my current version is months old, maybe I should update. I've been thinking about upgrading to version 3 electronics, too, but with the excellent Mendel design out with a much smaller footprint, I quite fancy that. It might be time to build a Mendel using my Darwin....
:-)

Working with Cotronics 907

2009-10-07T22:59:00.000-07:00

I let the first application of Cotronics 907 on the Rapman extruder barrel air dry overnight. The material was quite hard. The next morning I used some fine grit sandpaper to smooth it down so that the mounting flange could slide over it. It took some time to smooth it out sufficiently, but you can see that it dressed dowquite nicely.

I was also able to dress the PEEK thermal break so that it fit into the extruder barrel socket firmly without jamming.

Unfortunately, I read the oven curing instructions incorrectly and encountered a problem that the Cotronics people were very open about with this product. If you don't cure it properly and heat it too hot and too fast, it tends to form blisters which separate the ceramic slip from what you are putting it on. Thus my careful sanding and dressing of the flange joint was for naught. It is worth noting that once I saw the bubbles I was able to remove the 907 with the wire wheel on my bench grinder relatively easily while it was still warm.

From there I applied a second coat, this time with the flange in place so that I wouldn't have to do any sanding. Doing it that way I was able to put the basic underlayer for the nichrome heating coil, the flange fillet joint and the flange pad all on at one go.

After four hours of air drying, two hours curing in my fan oven at 90 C, another hour of post curing at 120 C and a final post curing hour at 200 C, I was able to secure the nichrome heating coil as per BitsFromBytes instructions on yet again.

On that I put a slip coat of 907 and after it had air dried was able to put a coat 907 to secure the leads for the heater as per BitsFromBytes instructions. I was also able to place the thermistor in its socket as you can see from the following picture.

Using the "helping hands" electronics jig, I was able to secure the thermistor leads and the extruder assembly. This was very handy because it let me monitor the assembly for shorts in both the heater coil and the thermistor while I was applying the 907 ceramic adhesive.

I will be letting it air dry till morning after which I will do the 8 hour curing and post-curing in the fan oven. Hopefully, I didn't overdo the ceramic application and the curing will be successful.

Getting away from fire cement...

2009-10-06T23:38:00.000-07:00

I'm currently finishing building a Rapman variation on Darwin. The construction has gone remarkably smoothly until recently when I began to build up the extruder's heater barrel. I had the whole thing finished with the nichrome and thermistor properly embedded in fire cement which encased the aluminum barrel.

When I tried to insert the PEEK thermal break, however, things went wrong. The PEEK cylinder jammed in the extruder barrel's sleeve and in trying to get it back out again I managed to apply a bit of torque to the barrel. This shattered the fire cement.

I was able to recover both the thermistor and the nichrome heater wire, largely because the fire cement, even oven cured, has the consistency and tensile strength of dry silt mud. I cleaned the barrel with a small screwdriver and electrical pliers with zero trouble. You can see the results here.

I had used ceramic coatings before with nichrome and called Danny at Cotronics in Brooklyn. He recommended their 907 formulation which is, if I've read the data sheet correctly, a mica-based ceramic adhesive formulation with considerable compressive and tensile strength. Better still, I was able to order it through a retailer, McMaster-Carr, here in California in Long Beach. I was able to get it ordered, shipped and delivered overnight using a local courier service for about $5.

You apply 907 with a brush. The adhesive in liquid form is a bit like very wet clay mud getting an even coat on the aluminum barrel was quite difficult. Once dried, however, it developed a very hard, glassy surface as you can see here.

Right now I am trying to decide whether I should sand it down before or after I heat cure it. If I'd been smart I would have painted it on after I installed the heater barrel flange, then having to slide the flange over the ceramic adhesive wouldn't have been an issue.

It adheres very tightly to the aluminum.

PLA vs ABS - warping

2009-09-27T17:13:00.001-07:00

Warping was a major issue for me when I was building larger objects out of ABS plastic. The lack of warping with PLA is quite striking; I thought I'd post a comparison photo here for the rest of you to enjoy. The x carriage on the left was made with ABS, and the x carriage on the right is PLA, as well as the idler bracket in front. That ABS x carriage isn't the best part I made out of ABS, but it isn't the worst either; most of my larger parts exhibited worse warping than that.

Scaleable encoders

2009-09-20T12:46:00.000-07:00

I've heard a lot of people talk about high resolution optical encoders being quite expensive. I've decided to use cheap optical sensors from optical mice to make optical encoders for little optical elves who live in optical cities making optical cookies with their little optical ... whoa ... shrooms are kicking in ... Anyway, Avago Technologies makes some pretty good ones. They optically measure the mouse sliding over a surface and convert this to a 16-bit delta X and 16-bit delta Y. The $2 encoders get 1600 dpi and the more expensive ~$6 encoders get 5000 dpi (claimed on the data sheet, not experimentally verified).

They perform multiple useful things.

First, they constantly measure the change in X and Y. This can be used to make a linear optical sensor or a rotary optical sensor (you measure the tangent). I think the rotary sensor might need a look up table to translate from delta Tangent to delta Angle, but this can be determined in the future. The linear sensor can measure travel in two dimensions. If it was possible to mount it under the table of the maker bot, it could record the XY motion at the same time.

Secondly, most can capture a 32x32 image. Some update this image over 1000 frames per second. This can be used to read a printed strip to update the absolute angle. In my design I have a strip of binary hamming encoded numbers that my sensor will periodically read to update the angle.

Third, the resolution scales linearly with the distance of travel. I use this to record angle. If I need a more accurate angle measurement, I increase the diameter of the strip it reads. I'm planning on printing my strips on CD labels (not how it looks in the picture). I'm using a half circle strip. The CD labels are about 118 mm in diameter. Therefore my strip is 118mm * PI / 2 (half circle) / 25.4 (mm to inches). About 7.29 inches long. My optical mouse sensor has a claimed resolution of 5000 dpi. Therefor my sensor has a theoretical resolution of 36468 ticks. I'm a bit skeptical of manufactures claims, but I should be able to get between 14 and 16 bits of resolution.

Fourth, as the machines scale up I want to maintain the same level of accuracy at the tip of the machine as the smaller machines have. This means that I will need much higher accuracy of the encoders. I accomplish this by making the encoder bigger.

Fifth, it might be possible to operate some of these devices as a camera to image objects far away. Some have a laser built into the device. These emit coherent light. Great thing about coherent light is that if your optics are focused to infinity then everything looks in focus. It doesn't depend on the distance. It might be possible to mount one of these next to the print head and use it to image the surface we are printing on or the object we are printing. This is a bit of a stretch, but it might work.

Sixth, one could be mounted on the print head to calibrate it's motion. A calibration algorithm would move the head down till the sensor is just above the surface of the table and then move the head in the XY plane. Using data from the sensor the motion of the print head can be characterized and corrected.