Just finished my Pi based MoCo system. Just thought that I would post in case anybody else was interested in his sort of system. It's stepper based multi axis. It's intended for time lapse and stop motion photography. The final unit will be a portable keyframing unit. I developed a simple board to sit on top of the pi. The system is sown below on pan and tilt but you can control multi linear and multi rotational axes.
Videos:
https://vimeo.com/55058402
https://vimeo.com/56879272