Friday, February 29, 2008

I tried printing the Z toothed pulley rim last night. On larger movements my repstrap performs pretty well (like the outer circle), but on smaller movements there tends to be quite a bit of deformation (like the inner circles). Part of this may be the way the pen is suspended giving it slight free motion, I'm also going to try putting some grease on the worm gears so there is less freedom in the axis when the direction changes.

I've updated my CAD plotting library.
I printed this file:

With this result:

Circles, lines and arcs are now supported. Most of the inaccuracies are to to the pen not being well secured.

Thursday, February 28, 2008


RepRap Timelapse Part 1

I bought a Canon SD 750 with built in timelapse mode. Here's my first two timelapse vids of me trying to print a minimug. Better ones and higher quality vids to come.

RepRap Print Timelapse from Zach 'Iowa' Hoeken on Vimeo.

Wednesday, February 27, 2008


Steppers and couplings

It's been quiet for the past few days. My day and night job have really been eating into my Reprap time.

My USB work has pretty much hit a plateau until my Jan Axelson book on USB programming arrives. That will be towards the end of next week. In the mean time I've spent a few hours hammering at the stepper instructions till they're all working right. I'm also getting used to all of the things that can come unstuck on my stepper board and how to diagnose them from how the stepper is behaving.

I slapped my multimeter on in amperage mode and discovered that one phase of the motor consumes a max of 220 milliamps with no load. That drops to about 190-195 as I crank the speed up. When I accidentally leave one of the phases charged it jumps to about 340-350. When that happens both the motor and the SN754410 heat up quite quickly. As a result of that I reprogrammed the firmware to turn off both phases 10 millisecond after the end of a run. That keeps the motor and the SN754410 quite cool. That's good, because the motor tends to skip when it heats up.

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First Builders Post

I've been working on my repstrap for a while now and have posted a few pictures on the forums now and again but this is my first post on the blog. My aim is to build a repstrap almost completely from Lego that will be capable of making the parts for a darwin.

I improved the X axis today then did this constraint bracket print. This is my most successful yet as there is very little deformation of the part. I also added strips of thin smooth cardboard under and at the sides of the X axis to make motion smoother and reduce the 'looseness' or 'play' of the axis.

I've got lots more photos on my Flickr.
Next I need to build a Z axis and get my extruder working properly.

Tuesday, February 26, 2008


McWire Timelapse Vid

NYC Resistor Timelapse from Zach 'Iowa' Hoeken on Vimeo.

Me working on my McWire machine while my friends build a loft in the background. Fun!

Sunday, February 24, 2008


Preliminary measurements on the Sharp IR distance measurement chip

I did a quick lashup for doing some rough measurements with the Shart IR distance measurement instrument I bought.

Here you can see the instrument itself to the left and above the prototype USB controller board. I slapped on a few extra screw terminals to handle the three lines off of the instrument.

I was able to get it to spot a piece of 3 mm HDPE feedstock at 500 mm away. This one has a range of about 1500 mm and a voltage range of 0-2.75v. Given that it costs right at $12.50, that's not bad performance at all. Sharp has another model which is focussed in to 300 mm. That might a nice one to mount on a Reprap to scan an ongoing print job.

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Dyslexia and the MC14069UB chip

I had planned to get a lot done on Tommelise 2.0 today. The good Lord knows that I worked hard enough to have got a long way. I had planned to graft the MC14069UB inverter chip onto the prototype board and see how big a problem it was going to be to save a few pins on the PIC 18F4550. Sadly, a lifelong affliction of mine, dyslexia, made the day a living hell.

Things started nicely enough. I grafted a 14 pin socket onto the prototype board and isolated it from the 18F4550. Then I added another connection to the output pin that is the first of two pins going to the SN754410 quadruple half-H driver chip that controls the first phase of the stepper and connected it to one of the six inputs for the MC14069UB inverter chip.

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Saturday, February 23, 2008


To every thing, there is a season...

Well, I've been putting it off, but with the success of the USB prototype controller board, it is finally time to say goodbye to Tommelise 1.0.

I'm clearing a place under another work table for it. Snake the mascot will be moving to Tommelise 2.0 as soon as there's a place for him to coil around. :-)

And so, we begin again.

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Stepping out with USB

Got it! Eat your hearts out! :-D

Running a stepper motor from the USB prototype board was a little trickier than I'd hoped, but a lot simpler in other ways. The tricky part had to do with the tricky little ways of the 18F PIC chips. I set up the stepper to run on 6 pins of Port D. For the longest time I could write code on the IDE and simulate it and it would do what I wanted. When I programmed the actual chip, however, it wouldn't.

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UV resins, pot-life

Zach asked me recently what the pot-life of these resins was.
That's quite an important issue as nobody wants resins to harden in your gear overnight or even worse, while you are printing.

I have found out that on my standard, high reactivity resins (composed of high amounts of any of the new catalyzers, between 4-5 weight% of new catalyzers along with 4-5w% Benzophenone (BP) and 2w% N-Methyldiethanolamine) they have a pot life of a mere 5 days.
This means, to be safe, that you have to clean out your gear with solvents say, every 2 days. Far from ideal.

I know a couple of additives that will lengthen pot-life. One of them is a stabiliser called Hydroquinone. This is a very effective chemical that will stabilize the final resin-mix. I have done a test batch with around 0.05w% of it and these are the results:

The mix containing Benzoinisobutylbether (aka, the expensive mix) has not improved noticeably in pot-life.
The mix containing Benzil (aka, the cheap mix), after 10 days, the resin has remained very fluid, but the reactivity to UV exposure is quite lower.

Conclusions: the expensive mix still has the same problem, and has lowered reactivity. The cheap mix has at least double pot-life, but the reactivity is reduced as well.

Where to go from here: I have to make tests with less concentrations of Hydroquinone (blow 0.01w%). I have to get myself some EDTA, another chemical that will probably longer pot-life without hopefully reducing reactivity.

Wednesday, February 20, 2008


Extending the USB prototype board

My eyes finally gave out this afternoon with staring at the painfully slow unfolding of optimal variable selection for neural nets while I was doing quality assurance for a new piece of production software. Fortunately, I was able to launch a test run of several hours and got a few minutes to rest my eyes and do something different for a change.

The "different for a change" was actually not all that different. I cobbled an SN754410 quadruple half-H driver chip onto my working prototype USB board.

It's not exactly an elegant design, but it works. I'm really starting to hate these last few spools of solid core wire I bought from Potter's. The plastic insulation on the wire shrinks outrageously when I use it to connect strips. I didn't have nearly that kind of trouble with the wire from Radio Shack. Unfortunately, Radio Shack wire tends to come in two colours, orange and black, which is nice for All Hallow's Eve decorations, but not very useful for many other applications.

Anyway, I just finished a continuity and voltage check under power. I had one missing wire and one dry joint, both of which I fixed. I'll do the check over again in the morning after I've been awake a few hours to double check my work.

I've found that if I do wiring up one day followed by a first board check a few hours later with my multimeter and then a second check the next day before I start plugging in chips I save myself a lot of drama with chips crackling like distant gunfire and overheating voltage regulators. It only took me about 25 years to figure that out. :-s

I should be able to try to crank up one of the new stepper motors either tomorrow or Friday at this rate.

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Parts Arrived To Fix Pillar Drill

The parts arrived today to fix the pillar drill, so we had a session in the workshop and stripped the broken pieces from the drill. Ready to refit the new pieces tomorrow.

They must have had problems with the originals because the replacements have thicker castings and a metal crank instead of the plastic one.


First Print!

I'm slightly embarrassed to post this, seeing as I've been involved with this project for nearly 2 years now. However, yesterday evening, I had my first print ever! It was a very exciting moment for me and there was some shouting, dancing, and jumping around. Personally, I think this is a testament to how powerful the idea of RepRap is. I have been working my butt off with the project for 2 years while having essentially nothing to show for it. I firmly believe that this technology has the potential to change the world for the better.

Of course, the print itself was nothing amazing, but it is definitely a start. I used CAPA as the print material. The electronics used were the Arduino electronics controlling a Darwin machine. There is a bug with the Arduino SNAP based firmware, so I was experimenting with the new GCode interpreter firmware for the Arduino.

I have to say it was a wild success, because with the GCode firmware I was able to very easily make a test shape and have it printed. I spent some time tweaking parameters and such, but its nice to see that the GCode stuff works quite well and has the added benefit of allowing you to easily switch your RepRap machine over to a milling machine if you so desire.

Finally: I have a good lead on fixing the SNAP based code which will all allow the Arduino electronics to be 100% compatible with the RepRap host software. I'll try it out tonight and report back.

Tuesday, February 19, 2008


Good to go!

I threw away about 90% of the features that Jan Axelson was kind enough to include in his very comprehensive VB.NET sample code and kept the bits that I needed to keep a nice, fast data link going between Tommelise 2.0's PIC microcontroller and the PC.

I now have the equivalent of Vladimir's test code, except now it is .NET and it is multi-threaded as well. The next step is to slap an SN754410 onto the prototype board and get a write code on both sides to start doing stepper motor control directly from the PC. This is REALLY nice!

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Bingo! The PC-side Visual Basic 6 problem solved!

As I reported earlier, I got the PIC18F4550 prototype board working and was able to talk to it from my PC using the compiled Visual Basic 6 app that Vladimir Soso of Oshonsoft thoughtfully supplied along with his USB extensions to his PIC 18F family BASIC compiler.

Things clouded up and rained, so to speak, when I tried to translate his Visual Basic 6 code into Visual Basic .NET. I kept hammering at it and talking to friends who had also done a lot more transition of code from Visual Basic 6 to Visual Basic .NET 2003 than I had. I'd, after all, only transferred about 150K lines of my own coding. I shudder to think how many lines poor Tyson transferred about 4 years back. After chatting with Tyson and about 10-12 hours of playing chimpanzees on keyboards in my spare moments while I was doing production runs, I finally came to the conclusion that I was wasting my time trying to run Vladimir's HIDTerm.dll in any of the .NET IDE's.

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Monday, February 18, 2008


3D Scanning for stupid people... me. :-D

I've been mulling over ways to get my little Cyclops 3D scanner project going again with a minimum of effort. I decided to leverage what I already know how to do rather than get into all the drama of patching multiple scans that other open source 3D scanning systems like David do.

David uses a line projecting hand laser and a little PC web cam and a LOT of PC processing power to get you a 3D surface description of an object. It occurred to me that I already know how to make both encoders, gearmotors and steppers to work with PIC's. If I were to buy a little Sharp IR distance sensor like one of these.

I could shortcut much of the software sophistication that the Germans have gone through with David. You point one of these little chips at your object and read off a voltage and then translate the voltage into a distance. Mount one of these to swivel up and down and keep track of where it is at and put your object on a turntable with the same kind of tracking and you've got a very simple IR radar set that can easily develop a surface description of an object.

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USB I/O on the PIC18F4550

This morning I took a few minutes before starting work and finished checking out the sample PC-side I/O programme to make sure that it was behaving as advertised and then cleaned out Oshonsoft's A/D code from the sample firmware so that I would have a clean start for building up a firmware programme for running Tommelise 2.0.

USB sends out and receives groups of 8 bytes of data very, very quickly. The PC-side app is written in Visual Basic 6. It randomly selects values for the 8 bytes of outgoing information. The firmware takes those 8 bytes and adds 1 to each of them. When the PC-side app asks for the information back you can see that 1 has been added to each byte.

You can see the values for the bytes that the PC-side app sent out (red arrow) and that the values sent back have 1 added to each of those bytes (blue arrow).

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Sunday, February 17, 2008


USB up and running

After several run ups I got the USB extensions to my Oshonsoft BASIC compiler working. It turned out that Vladimir had sent me a .reg file that you had to put in the software folder THEN do the install. When you did that it worked. Sneaky!

I took a shot at trying to run my prototype board this evening. I had counted pins wrong and had the power and ground lines running to the wrong pins. That caused my 7805 regulator to overheat, but didn't appear to hurt anything else. After I fixed that...

Bingo, it worked! Windows did its little noise that it makes when it notices that a new USB device has been detected and the whole tootie.

I'm designed my prototype board somewhat differently than Vladimir's and didn't include his pot adjusting voltage to a A/D pin. The software that Vladimir sent along for the PC side comms, however, recognises the board perfectly.

The 10 foot cable I used works properly, so Tommelise 2.0 doesn't have to be particularly close to my PC. I can say goodbye to serial comms and Max232 chips. Life gets a lot nicer with high speed comms. A LOT of the stuff that I was trying to do in the firmware is going to happen in the PC now where I can put Visual Studio to work on it rather than figuring out screwy little ways to make things happen in firmware.

One really, really cool feature of both USB and the prototype board is that if you don't have power on the prototype board the USB provides the 5 v power to run the 18F4550 chip and the darned thing runs properly anyhow.

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Hiccough in compiling USB support

I got the board built and this morning was setting up to compile the sample programme from Oshonsoft to try out on the board when I got "message 17: support for USB implementation not enabled" on my screen. I uninstalled and downloade a fresh copy of the compiler and still got the same message.

I emailed Vladimir at Oshonsoft about the problem. He is usually lightning fast in getting such things sorted out, but I'm a bit worried in that he's been seriously ill in the last 6-8 months and is apparently from our last communication with him only just now beginning to dig out of the financial mess that his illness put him in.

It may be a while before I can go further along this path, so I'm going to work with serial comms on my old 18F4610 chips in the meantime. Fortunately, I have some in stock. I'd hoped not to have to use them further, though. :-(

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Saturday, February 16, 2008


Built PIC USB prototype board

I had all the parts for making my first PIC USB comms board more or less when my son called late Friday afternoon asking if he could come home for the 3 day weekend. Things got a little slowed down for me as a result. :-)

Anyway, my son came for a study weekend. He had a lot of reading to do, so I undertook to try to cobble a prototype board together to get used to USB comms between the PC and the firmware. All I lacked was a 0.47 uF ceramic disk capacitor for the Vusb pin (pin 18) on the 18F4550. I wandered down to Potter's and then Radio Shack looking for such an animal and came home empty handed.

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Friday, February 15, 2008


Starting with USB

Well, I have all the parts now to get away from serial comms and over to USB 2.0. Instead of buying a chipset that attaches to my current PIC (this being the mainstream approach, I understand), I'm simply upgrading to a PIC that can handle USB by itself. My firmware compiler will handle that.

I've started with's basic demo board for USB comms and scraped all of their little twinkly LED's off, which leaves me with this very, very basic board.

It also leaves me with 29 usable pins to control Tommelise 2.0

(Read the whole story)

Thursday, February 14, 2008



Both my Radford Brothers order (nylon threaded rod) and my Digi-Key order pitched up at lunch today. I have basically everything I need to build Tommelise 2.0 except for the #28 nichrome 60 wire which in en route and the extra Jameco motors which I haven't ordered yet.

The USB connectors are the right ones this time. I'll have to either hijack the USB cable off of my printer or buy one down at Potters.

The nylon threaded rod looks good. The #10-24 is a bit too floppy to use without securing both ends while the 1/4-20 looks like it can be used as its steel counterpart. It's feather light.

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Ianus Bearing Mounts

Now I can start on work towards the slides etc for Ianus, here is the assembled bearing mounts ready to mount on trolleys. The idea for these came from clever but simple, the best ideas always are. We are using Skate bearings (608 ABEC 7) here, M8 x 20mm Machine Screws and M8 Nuts. These screw right into drilled and tapped holes on the trolleys.


Ianus Frame Assembly

Ianus frame assembled and screwed down to base board gantry not tightened up to base frame yet as it needs positioning etc.


Ianus Initial Assembly

Ianus initial assembly, Note working lunch on table.


Ianus is born

Ianus is born (well the prototype test bed is at least)

Ianus is a dual head Cartesian with Independent Z axes on a common X and common Y platform.

The Y axis is the worktable which is full width and slides backwards and forwards on the bed frame.

The X axis is mounted to the head of the gantry and slides full width.

The independent Z axes are mounted to the X axis on the gantry one per side initially, though this could be modified to present more independent Z axes ie 4.

The tubes and fittings I wanted have arrived and I have assembled them to trial the ideas. I bought the pipe and clamps from they are located in Normanton, West Yorkshire, UK

Wednesday, February 13, 2008


GM-17 gearmotor mount complete

I finally found time to cobble together a working mount for the extruder's GM-17 gearmotor. Talk about a fiddly piece of work. I made it out of bits of aluminum extrusions as you can see.

Getting all of the pieces to fit together and then getting the GM-17 aligned properly with the 1/4-20 threaded rod that makes up the polymer pump was a major undertaking.

(Read the whole story, such as it is)


Three reviews

Some weeks ago Sebastien recommended a book and two articles to me. They were...

Rapid Protyping - Laser-based and Other Technologies by Venuvinod and Ma (book, 2004)

Conceptual framework for the thermal process modelling of fused deposition by Yardimci and
Güçeri (article, 1996)

Three-dimensional finite element analysis simulations of the fused deposition modelling process by Zhang and Chou

I bought the book and Sebastien was kind enough to provide copies of the articles to me so that I saved several weeks waiting for them to arrive through interlibrary copying services.

(Read the reviews)

Monday, February 11, 2008


Cheap, reliable UV Resins: confirmed!

Continuing tests on the recently discovered photoinitiator mixes:

I made a series of tests I figured to see which of both mixes fares better. The resin in itself here is regular Polyester resin. i bought mine at the Drugstore. Found it for 7€ a kg.
The photoinitiators are as follow: Benzil+Benzophenone is the cheap mix, Isobutybenzoinesther+Benzophenone (BP) is the expensive one. I added N-Methyldiethanolamine (MDEA) as a co-initiator for Benzophenone. The mix proportions are: (roughly for now, I'll investigate into precise mixes later)
Polyester resin: 20g
BP: 1g
Benzil/Isobutybenzoinesther: 1g
MDEA: 2g (will try with 1g later, this stuff yellows the mix and maybe makes it to flexible)

The layer thickness is 1mm in every test. No mentionable shrinkage has occurred in any of the tests below.

Test A) 5 minutes of UVC irradiation, followed by 2 minutes of UVB
results: Benzil+BP harder than IsoBBesther+BP, the first a little, the last one still quite sticky

Test B) 5 minutes of UVB followed by 2 minutes of UVC
results: both deal very similarly. Result more solid than in A)

Test C) 5 minutes of combines UVB+UVC
results: both very similar, somewhat stickyish

Test D) 7 minutes combined UVB+UVC
results: both compounds, curing almost finished

Test E) 10 minutes combined UVB+UVC
results: curing finished in both compounds

The last test I did was an interlayer-adhesion test with and incorporated deep cure test.
What I tried to find out is how well 2 layers of resin glued together after the first one had been subjected to 5 minutes of combined UVC+UVB irradiation, to set it just enough to leave it sticky. After that I poured a similarly thick (1mm) layer of resin on top and irradiated it with 10 more minutes of UVC+UVB to simulate the last curing step of a printout, as well as an accumulated UV exposure to the lower layer.

results: Both mixes react similarly. The first layer after 5 minutes exposure is solid enough not to move or sag anymore, but the top surface remains a little sticky, like a sugar stained surface. I deposit another 1mm layer and start irradiating again for 10 minutes. After this, I try to pry between the 2 layers with a toothpick and cannot create any kind of separation. The lower layer is completely cured. The top layer is, of course, completely cured also. The expensive mix may be a tad harder.

This looks really good! I'm specially happy with the cheap Benzil+Benzophenone mix! The end product is a 1,5x2cm pad of transparent, glass-green, hardened resin. Th ereason why I chose 1mm thick layers is because I wanted this product to be able to work on thick dispensers. Nevertheless, when using such a thick layer, some sort of filler materials (silica powder) will have to be added to ensure that the 1mm thick thread will not sag while it is deposited, creating deposition errors. The resin has the perfect viscosity to be used in <0.6mm threads.
I wonder if this has a low viscosity enough to be used in one of them piezzo-electric ink-jet cartridges, hmmm.... maybe adding some styrene as a solvent/monomer would help?....

Additional data:
UVC source is a germicidal 36W, 256nm fluorescent
UVB source is a actinic or blacklight 40W, 365nm fluorescent
I will in the future purchase a 65W UVC and 4 compact 18W UVB lamps to build a reflector backed irradiating lamp which will cut the times by at least 3 and distribute the rays more evenly.

Sunday, February 10, 2008


Stress cracks and fixes

I noticed that my compression setting the top bushing opened a little stress crack at the top of the seating groove for the threaded rod in the cast plastic polymer pump. Apparently, that casting plastic is a little brittle or I'm a bit brutal. It's a tossup for now till I hear how the other folks using those cast parts are getting on with them.

(Read the whole story)

Saturday, February 09, 2008


More work on the Tommelise AEM Mk 2 extruder

I don't carry a cell phone. The only time that I want to talk to people is when I'm in my home office working. Other times belong to me.

I did a six mile hike around Spanish Bay and out to Bird Rock this morning. It was pretty crowded, parked cars mostly, because of the AT&T Pebble Beach National Pro-Am. Not many people. They were all rubbernecking up on the golf courses.

We had a big storm a few nights ago. Very high surf. The poor boardwalk looked like it had been subjected to shock and awe. Ten and twenty meter lengths of it had been picked up and hurled by the storm surf and were stacked like jackstraws all over the area. There were chained trash cans made from 55 gallon drums that were smashed flat by the waves. Half meter granite boulders dredged up from the bottom of the bay and tossed ashore were scattered all over the place.

On the way back from Bird Rock I saw and heard a Red-Winged Blackbird singing it's heart out while clinging to a cattail stalk. I don't remember their song being that rich and sweet before.

When I got home I discovered the purchases that will let me try to build a USB controller for Tommelise 2.0 had arrived. I hadn't expected them till Monday at the earliest. The book, Rapid Prototyping by Venuvinod and Ma that Sebastien suggested that I get had arrived two. It felt a little like Christmas. :-D

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Easy couplings

The little Jameco #237818 bipolar stepper that I am trying to use in my Tommelise 2.0 design is great, except for one little thing, viz, the drive shaft size.

At 0.8 inches (2 mm) it is deucedly difficult to attach anything firmly to it. Last week, I simply tapped the end of my #10-24 threaded drive rod and epoxied the stepper drive shaft into it. While that works, I'm not all that happy with the result.

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Thursday, February 07, 2008


Shopping for less noise

Back when I was designing Godzilla year before last I discovered that steel threaded rods (3/8-24) tended to get quite loud when you drove them much over 5-10 mm/sec. As the thrust collar moved up and down the rod you'd have a situation rather like a guitarist moving his fingers up and down the frets on the neck of his instrument. The spinning rod would have several resonance points where it would get quite loud as the positioning table moved back and forth.

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Tuesday, February 05, 2008


A new adventure begins

I ordered the parts to make the new USB controller board. The hardest part was finding the USB Type B connector. After getting a look at what they are charging for USB cables I suspect that I'll be making up my own from scratch as well. I'm going to be needing a particularly long one.

I'm trying to get my head around what the firmware for Tommelise 2.0 needs to look like when all the really tough calculations can take place in my PC. The bandwidth on the USB port is going to be several magnitudes larger than the old serial interface, so it looks like the PIC is going to spend most of its time simply shoveling in data in a form more or less ready to use by the SN754410 chips and keeping track of things like the limits detectors. I'm thinking that I might well try to run each of the SN754410 chips with a smaller PIC like the old 16F628A. That would let give me fewer worries about pin counts on the 18F4550. How I put that all on a Euroboard is another issue. I expect that I am going to have to make smaller boards for the individual stepper controllers. Oh well, well see how that works out as I get further into the project.

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Monday, February 04, 2008


USB 2.0 on Tommelise 2.0

Once I bit the bullet and decided to go for USB 2.0 comms for Tommelise 2.0 and tentatively chose the 18F4550 as the target PIC chip things started getting very easy. As usual, the PIC data sheet for the 18F4550 was pretty opaque. On the web, however, it turns out that a lot of people have been exploiting the 18F4550 for USB connectivity. I found this link very useful. Not only does it give you a schematic, but it also gives you a full, working set of PC side and PIC side code that makes things work.

As well, they use a bootloader for chip programming. I wonder if my Oshonsoft BASIC hex will be compatable with that?

This is getting to be fun!

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Sunday, February 03, 2008


It's become pretty obvious

I've been running the stepper all day. It can change direction in a single step and can hit 15+ mm/sec, all while burning less than half an amp/phase.

I never got the gearmotors to hit more than 1.7 mm/sec and I had continual troubles accounting for the momentum that built up in the firmware when I was running them at full tilt. Chris thinks that the problems with encoded gearmotors can be solved and I have no doubt that he is right. The problem that I'm having is that while I have not doubt that they can, it would appear that I'm not the guy who can solve them.

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Acorn nuts

If the inside of your acorn nut nozzle looks anything like this :-

You may want to extend the thread with a bottoming tap, or shape the end of your heater barrel like this :-

More details here: and here:

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Testing the new coupling

I did a quick lashup of what I wanted the threaded rod mounting to look like on Tommelise 2.0 and gave the new coupling a go. I carved a little poplar block to keep the coupling nut aligned and used baby talc to reduce the friction between the block and the base.

Here you can see the ensemble in action.

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Saturday, February 02, 2008


Trying a new coupling idea

The Jameco stepper that I am using has a thin, o.08 inch (2 mm) drive shaft. Attaching such a thing to a threaded rod presents problems. I began by using duct tape for preliminary tests. I needed something a bit more permanent, however, and decided to try something new that leveraged the generally good reports that I've had from other people in the Reprap project about JB Weld epoxy's ability to handle mechanical stress.

I began by tapping one end of the #10-24 drive shaft with a 3/32 in bit in my Dremel hand tool. The 3/32 bit at 0.09375 inches in diameter is just a shade bigger than the 0.08 inch drive shaft diameter. For those of you who are not familiar with drilling metal you should know that you can burn drill bits out very quickly if you don't keep the hole wet with coolant. I make my own in a small squeeze bottle out of a teaspoon of peanut oil (actually any cooking or machine oil will do), a few drops of diswashing liquid and the rest of the small (usually no more than 6-8 oz size) squeeze bottle is filled with water. Shake that up and you have quite a decent drill coolant for effectively free.

You can see here that I've wrapped the threads of the rod in several folds of a paper towel so that the vise doesn't mar the threads. One other advantage with drilling with a coolant besides saving your bit is that the drilling goes a LOT faster. You will also notice that most drill bits tend to be slightly magnetised, so the metal swarf (bits of metal drilled out of the hole) stick to the bit.

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Better measurements

This morning I tapped the #10-24 threaded rod and used a friction fit to secure it to the drive shaft of the stepper motor. I was able to get pretty much the calculated speed of 20.1 mm/sec when I drove the coupling nut back and forth on a closed circuit of 100 mm in each direction.

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Friday, February 01, 2008


First measurements

I bought a foot of 10-24 threaded steel rod and a coupling nut and attached it to the stepper with a makeshift duct tape coupling. I used a coupling nut as a thrust collar.

Initial measurements indicate that with a 5 msec delay I can achieve 7.6 mm/sec translation speed and with a 2 msec delay a 15.1 mm/sec translation speed. The stepper motor seems to be able to apply a respectable amount of force at those speeds.

For purposes of comparison a #10 thread is approximately 3/16th inch in diameter and just a bit over 4.8 mm. The pitch in metric usage is 25.4/24 or about 1.06 mm.

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The 15 degree, bipolar stepper BLASTS!

I took a little time off this morning and reprogrammed the Tommelise 1.0 controller and used the X and Y gearmotor driver outputs to run the new little 15 degree step, bipolar stepper motor. I had remarkably little trouble getting it going.

Here you can see it running with a 50 msec delay between steps which gives it a rotational rate of about 50 rpm. I ran it this slow so that you can see the motion.

I found that if I ran it anywhere near what it was capable of that the little duct tape flag that I attached to the drive shaft simply became a blur.

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