Experiment to change the back and forth arc motion of a hobby servo into a stepped circular motion.

See the video here:

http://www.flickr.com/photos/spikenzie/3291883934/in/photostream

Get your hands on some supplies:

A. You will need some 1/8" acrylic sheet.
B. Standard size hobby servo.
C. A couple of 2-56 3/4" bolts with nuts.
D. Some acrylic glue.
E. Some plastic rod. (Get this at a hobby shop, Plastruct 1/4" clear acrylic rod PN#90294)
F. An Arduino. The sketch I used to make the video is in the examples that come with the Arduino software as part of the servo library. It is called Sweep. I did modify it a bit so that the sweep (arc) was smaller, so that the thing only clicked one gear at a time.
G. A laser cutter.
H. A paper clip and elastic band.

Build it:

1. Cut acrylic on laser. NOTE:The round holes into the back plate are smaller then the holes in the notched gear. This gives a press fit into the back plate, but a sliding fit into the gear.
2. Cut two short lengths of rod, about 1" each.
3. Put the notched gear over one of the rods.
4. Press the rods and guild into the back plate. Add spacers as needed. (Glue if not tight enough)
5. Install servo with bolts.
6. Attach arm to servo with a paper clip.
7. Add elastic band so that the arm and stopper are pressed against the notched gear. (This does not need to be too tight.)
8. Load your arduino with Sweep sketch, adjust the 0 and 180 up or down so that it clicks nicely.