I have used a Radio Shack rotor for several years, but I finally got sick of never really being sure that the antennas were pointed in the right direction. The problem is worse with AO-40 S-band reception, since the dish antenna beamwidth is much smaller than that of a UHF or VHF Yagi beam. A pointing error of 5 degrees can cause a significant loss of signal strength with a 60cm dish, and more than 10 or so degrees of error pretty much wipes out the signal.
"Real" ham radio antenna rotors have a potentiomenter coupled to the drive train, so that there is continuous, unambiguous feedback of the antenna position. After much thought I devised a simple, cheap, and reliable way to add a feedback potentiometer to the Radio Shack rotor.
Have a look at the pictures. They are worth a thousand words. Note that you have to chop a hole in the top of the case to provide room for the pot. I weatherproofed the case by epoxying a PCV pipe cap over the pot and the hole.
Here is a parts list:
Rotor: I used the Radio Shack one. I suspect that the Radio Shack rotator is actually identical to models sold by other companies.
Gear: From Small Parts, Inc. (www.smallparts.com) It is part #GD-4860, cost about $6. It is a 60-tooth 48-pitch plastic gear with a 1/4" hole. Small Parts has a catalog full of cool stuff. Try to order some other stuff with the gear, to offset the shipping charge.
Potentiometer: A Bourns 3540-series 10-turn pot, resistance 2k ohms. (Any standard 10-turn model whould work). Mouser and Digi-Key carry them. The Bourns model is very accurate and well-made. I got it at a hamfest for three bucks. New, they run $12 or so. The actual resistance value depends on the rest of the control circuitry, but you should probably not make it more than 2K or so, to reduce noise pickup.
Metal plate: A bit of scrap aluminum about 1.5" x 3".
Nuts and Bolt: From Home Depot :-)
Cap over pot: A 1" PVC pipe cap, also from Home Depot.
When the rotor turns 360 degrees, the 10-turn pot turns about 9.3 turns. When putting everything together, make sure that the rotor can travel over its full 360-degree range without jamming the pot at the ends of its rotation.
Let me know if you have any questions, and if it actually works for