Finally, some progress on the etch a sketch machine. After releasing the magical blue smoke from many poor transistors, i broke down and bought a motor control shield over the holidays. Two roughly matched steppers salvaged from old printers attached to gears on the etch a sketch.
Straightforward at first, but mechanically tricky. Theres a surprising amount of mechanical backlash, meaning that if you draw say 10mm in one direction, and then 10mm back, you dont quite end up where you started. I tightened up the gearing by epoxying it to the etch a sketch shaft, and i'm doing some backlash correction in software. Still not perfect, but getting there.
Eesh - the video compression makes it look horrid. Heres a pic of the last frame so you can see the drawing.