Friday, October 26, 2007


Stepper Driver v1.0: Success

Another critical milestone in my quest to build the next generation RepRap boards. Last night, I built and tested the new Stepper Driver board. This board is different from the current Universal Controllers in 2 major ways:

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

Looks great, keep up the good work!

I like the modular, Arduino based architecture. I'm waiting for a final integration test, then I'll start ordering the parts. :)
Hi Zach,
Looks good, but I don't understand why it should be "less jerky". If anything I would expect a chopper to have faster rise times so more jerky. Is is simply that you are half stepping rather than full stepping?

thanks! i appreciate the encouragement.


i dont think that rise times have much to do with it. its way smoother in both full stepping and half stepping. my guess is that its simply because the L297 is designed as a stepper controller, whereas our universal controller boards are simply bit-bashing the L298 with no feedback at all.
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