So during Software Freedom day I began hacking on the BeagleBone Black and a small stepper motor. Are only goal was to gain familiarity with the BeagleBone by controlling the stepper motor with Python code that is FOSS.

For the hardware setup I utilized the 28BYJ-48 Stepper Motor, the L293D Driver Chip, a breadboard, some wires, and of course the BeagleBone Black. I had both the chip and motor from a kit I bought from AdaFruit, so I used her guide to wiring the board as my breadboard setup.

When looking for code to run the stepper motor I came across this blogpost discussing almost exactly what I was trying to do. Utilizing this code, David and I (but 99% David) configured the BeagleBone so we could ssh in, and put the bb_pystepper code on the BeagleBone, as well as the adafruit stepper library which was a dependancy.

Unfortunately, when we attempted to run the code I discovered that motor only vibrated, it didn't actual spin. We went to a lab and started testing outputs with an o-scope and a mulitmeter to no avail. We even tried providing power from another source to see if the BeagleBoard was having difficulty driving enough current. Finally I started software debugging which is when I discovered a little variable in the code called steps_per_rev.

This variable describes the number of steps the motor takes in a spin. Currently, it was set to 2048.0, which was far too high for my motor. Essentially, signals were being sent so quickly that the motor was able to register the pulses. After a little bit of playing around we settled on 512 being a solid value. However, I was displeased that my testing required me to actual change the hardcoded value. Instead, I moved the steps_per_rev as an optional constructor argument, as well as moving the pins that drive the motor. This is a sample of how the code runs now with my updates.

$ cd bb_pystepper

$ python

from bb_pystepper import Stepper

mystepper1 = Stepper() # Creates default stepper motor

mystepper2 = Stepper(512.0) # Creates motor with 512 steps_per_rev

mystepper3 = Stepper(256.0, ['P8_17', 'P8_18', 'P8_19', 'P8_20']) # Motor with 256 steps per rev and different pin mappings

mystepper1.rotate(180, 10) # Rotates stepper 1 180 degrees at 10 RPM

(will also rotate stepper2 because they are mapped to the same pin

mystepper3.rotate(-180, 5) # Rotates stepper 3 back 180 degrees at 5 RPM

I am much happier with this version of the code because it allows for multiple motors to be run independantly with different steps_per_rotation. It also should make the selection of the correct steps_per_rotation a lot easier. I still feel that the code could use some improvements for ease of use and general configuring but I will go to that soon. The code also could use some PEP8 fixes, but I am guessing that someone else in the class may want to tackle that.