Got the prototype of the arm fully running this last week on an Arduino using the Adafruit motor shield. Everything went together pretty smoothly and the steppers are certainly strong enough to move the arm around. however, I did find a few problems:
- There are some design issues with the 3D printed parts. I should have these resolved by the time our meetup happens this weekend.
- The stepper motion is really jerky, to the point where it would be tough to make a straight line. I was surprised to see this given my experience with other stepper systems. I suspect that there are two issues… one is that I am using full steps instead of microsteps (this will change shortly) and that I am using a motor shield that uses a pair of DC motor H-bridges rather than a true stepper driver. I know true stepper drivers sense load and send a sinusiod to the motor rather than a square wave, thus moving more smoothly
- Bearing seating is the last one. On the forum David H mentioned that this would be a problem and, I dismissed it (whoops). there is a radial load on the bearings from the belts that twists the arms. I think this can be managed by putting oversized washers in place of the standard M8 washers.
I look forward to our discussion this weekend, we are on the cusp of moving our attention to software rather than hardware.