I want to see this design move forward. Before I can work on the mechanical engineering aspects of the motors: I want to work on my position control system.
(Cheap geared DC motors like those from solarbotics/chinese drill motors seem ideal if I can convert them in to servos somehow.
I'm also considering DIY worm wheels drawing from the astronomy or http://en.wikipedia.org/wiki/Magnetorheological_fluid
between clutch plates to manage the holding torque issue with DC, but that's getting ahead of myself.)
Rather than going with the potentiometer/optical encoder positioning that seems popular on many systems/servos: for ultra-low budget reasons: I'm inclided to go with a CCD active motion capture setup wiimote style.
Now: If I put and IR filter on several of these cameras and affix them to the arm on each axis of movement: I imagine I can keep the robotic arm in a room with line of sight to multiple reference IR LEDs, and I can use this code:
to translate the video feed in to positional feedback on the arm.
I guess is what I'm looking for is suggestions/constructive criticism. Trouble you anticipate I might run in to from your experience in such things. Not being a CS/Mechatronics expert, I have no experience to draw from on the: "in over my head" scale.