Tuesday, October 30, 2007
Wanted: Powdered ABS Plastic
Sunday, October 28, 2007
New Stepper Driver... video
Can ya step to this? from Zach 'Iowa' Hoeken on Vimeo.
my camera died at the end, but i was basically done.
Friday, October 26, 2007
Stepper Driver v1.0: Success
1. it doesn't have an onboard microcontroller. instead, it receieves stepping signals from a separate microcontroller such as an Arduino, or even from a parallel port. this adds another layer of abstraction and modularity, which means that if we want to move to a different microcontroller system, then it is much easier.
2. it uses the L297 to generate stepping signals. the l297 is the complimentary chip to the L298 (which both use to actually drive the stepper) there are a couple major benefits of the L297. first, it has current sensing technology that allows it to 'chop' the current going through the coils so that only the desired amount of current goes through. this means the L298 wont heat up when it is holding torque, and your steppers will be driven *very* smoothly, no matter what they are. the amount of current is also easily adjusted by simply turning a trimpot located on the board. secondly, it provides a simplified step/direction interface to the motor. instead of 4 wires and a phase table, you simply set the direction you'd like to rotate with one pin, and then send a pulse on the other pin whenever you want it to take a step.
I actually built and tested it, and it worked GREAT! Seriously, this thing drives stepper motors so smoothly, you can hardly tell its stepping them. I've had problems with the current stepper controllers being 'choppy' and jerky, but they rotate smoothly, and with lots of torque. I took some video of it, but unfortunately my batteries died as it was importing the video. I did manage to get the pictures, but the video will have to wait until I get back home to get a fresh battery.
Talk about a step in the right direction (omg, sorry... i couldn't help it!)
View Flickr Photos
Wednesday, October 17, 2007
The long and the short and the tall
Hopefully you should be able to see a general improvement from left to right. My conclusion is that HDPE is not really suitable for extruded layered manufacture because of its high melting point and mold shrinkage.
More details in my blog: scaling-new-heights
Monday, October 15, 2007
Stepper Motor Driver v1.0
This board is a stepper motor controller. It is designed to be driven externally by a microprocessor, like an Arduino, or it might even work with a parallel port. Its based on the L297 + L298 combo which means that the interface is super easy. There is one pin that specifies the direction of rotation, and one pin that you send a pulse to everytime you want it to take a step. No dealing with funky things like energizing the proper coils, its all taken care of by the L297. Since it uses the L298 as the driver, it can power steppers at up to 2A per coil at 48v.
One of the other neat features is the 'current chopping' of the L297. This chip has sensor lines running from the L298, so it can sense the current through the coils, and will regulate the power to ensure that the desired current is flowing through them. This really comes into play when you drive it with high voltage power, although it does mean that you can basically throw any stepper motor at it knowing that you'll be able to adjust it so that it will run smoothly.
Did I mention smooth running? Holy cow it drove my stepper motors smoothly. A few of the stepper driver circuits I've tried made my stepper motor all jerky and not rotate smoothly at all. This guy made it rotate very smoothly. I gotta say I'm excited to get the manufactured PCB's back and start driving some stepper motors hardcore.
PU Parts by the Kilo!
The Extruder moulding comprise 6 items the drive coupling is supplied for both variants of the Pololu gear motor
The finish is not as good as i had hoped but you have to stop somewhere! and it's certainly perfect for development work and all fits together OK. Some parts may require a small amount of sanding to give a snug fit especially the base of the extruder barrel as it's slightly domed from the moulding process (better to put to much resin than not enough!)
These parts assembled nicely with all holes lining up. I've not done a build with the internals as I've not made them yet but should be OK as dimensionally the same as the RP parts I moulded off. The top half bearing mount will need a small amount of cleaning out as the mould was not perfect in this area, this is easily done with a small knife.
I have also moulded a set of corner blocks and diagonal tie brackets this was a very slow process as i only had 1 mould! but if there was interest i would be happy to make up a new mould so i can make a set at a time i.e. 8 corner blocks and 20 diagonal tie brackets , these have M5 nuts moulded into the resin . Note the two designs of corner block four base blocks with diagonal holes and four top blocks to take the Y axis bearing blocks. The 8Ø holes are moulded using 8Ø bright bar and as such are a very tight fit onto the frame bars and would probably benefit from drilling out to 8.2 or 8.5Ø . I'll let you know how assembly goes!In my earlier post i had done a first set using pressure moulding I found this to time consuming as it needed a slower setting resin due to the pour time to fill the mould so all these parts are made with a single part mould which gives a much faster pour time, critical when the stuff has a 3 minute pot life!
Saturday, October 13, 2007
Go Team Go!
Anyway, the past couple weekends, I invited people out to my workspace to help out with building my McWire Cartesian Bot. Today, 3 people came out! It was a fun day, and I think we all enjoyed ourselves quite a bit. It was so nice to have other people helping me out with this project, as well as just being there to bounce ideas off of. With their help, I got a TON of stuff done that otherwise would've taken me a lot longer. It was a very productive day.
First off, I breadboarded the new stepper motor driver circuit I've been working on. At first it didnt work, but I tracked down the problem to a couple miswirings in my breadboard circuit. After that, I wired it up and it worked great! I wrote a little test program for the Arduino, then lo and behold, the stepper motor started to turn!!! It was really awesome to see a design that I worked on come to life like that. I don't have video, but this stepper motor was turning so smoothly! It was really awesome. It's a L297 + L298 based stepper motor driver, which made interfacing with it super easy. It has a step pin, and a direction pin. Set the direction to tell it which direction to go, and then send a pulse on the step pin to have it take a step. Bingo! Instant stepper control.
While I was messing with that, the rest of the guys worked on the McWire bot. We got all of the rails assembled with lots of bearings and such, which means that in a couple weeks when we get the new stepper boards from china, we'll be ready to rock.
I came to the decision that I'm going to code the Arduino firmware to accept the SNAP protocol from the reprap software. I've been debating the best way to go about interfacing the machine with the computer, and I really want to build on the reprap software that we already have. There are definitely some things that really bug me about it, but having looked through it, I also see some really solid coding that Adrian and crew have put together. It definitely needs a better frontend, and the slice/dice algorithms could use some work, but once I have a reliable machine at my disposal, I aim to transform that piece of software into a lean, mean printing machine.
Anywho, I just wanted to share some progress and let you guys know how awesome it is to work on RepRap with some friends. It can be a bit intimidating when its just you working on it alone, but if you throw some other people into the mix, then it can be very rewarding as well as just a generally fun time.
Monday, October 08, 2007
These are test shapes to get the layer stacking working. More details and a video at: laying-it-on-the-line.
Wednesday, October 03, 2007
Newbie & PU Parts
I'm very fortunate to live very close to the original RepRap in Bath so have taken the opportunity to scrounge some parts from Adrian/Ed. Over this last weekend I cast a complete set of extruder parts in PU (see Adrian's Main Blog entry for method). The first set is yellow as this was all the pigment I had but today some water clear PU arrived so will try for Clear cast later tonight.
The mould halves with the original plugs removed
A small amount of Vodoo to ensure the correct results!
The completed first cast of parts.
I use vacuum degassing of the mould silicone and pressure moulding of the actual parts this gives fantastic detail and allows greater part density per mould.
These parts will be available either via RRRF (sorting details with Zach) or direct from myself as I'm UK and Zach US it will probably be bit of both.
I'm about to start on the Cartesian Robot RP frame parts i.e. corner blocks and angle rod tie brackets, with the intention of completing moulds for all RP parts very soon!
Tuesday, October 02, 2007
PWM Driver Board v1.0 Render
the cool thing about eagle, is that it can be run from the command line. i haven't had time to experiment with it, but it would be very excellent if i could write a script to automate the whole process:
* generate Gerber and Drill files
* generate PDF files of schematic and board
* generate 3D rendering of board
* zip it all up into a file for release on the internet.
having a nice, rendered image of the board will give an excellent guide to assembling the board (that is basically automatic) . it even shows the correct resistor colors! not to mention it looks absolutely stunning!!