I am working on a vending machine project and I will be in need of 9 small motors. I want these to be very small, but they will need enough torque to turn a coil that pushes about 8 - 10 “Fun Size” candy bars. I figure I can calibrate the motors so that when I apply a certain voltage for a certain time, I will get one full rotation of the coil, thus dispensing one candy bar. But I can see that over time, the coil will most likely need to be reset, as I will probably NOT be getting exactly 1 rotation, but maybe more like 1.01 rotations each time. So I was wondering if anyone could suggest a solution to this problem. Is there a simple encoder solution I could use to make sure I get one exact rotation each time? Or even just a simple mechanical solution to allow the coil to turn, but then lock it when it reaches the starting point again?
I am also hoping somebody may have a good source for cheap DC mini motors. I need 9 of them, and would like them to have gearing already attached to create torque. Servos are too expensive. I am planning on using a shift register (or 2) to control the motors with minimal output pins. I also need pins to drive an LCD and a 12 or 16 key keypad. So I need to reduce my pin usage. Are there any good old devices I could get for cheap off Craigslist that would have good motors for this? I salvaged some from some old projectors, and I plan on testing with those, but I really want 9 matching motors.