Place to buy & Gear questions

I can't help you on the first question, but on the second:

1. A 7.5 deg/step motor is very coarse (24 full steps per rev). The most common quality steppers here in the USA are 0.9 deg/step (200 full steps per rev).

2. To increase the effective steps per revolution, you put the small gear on the stepper and the large one on the driven element. The effective number of steps is simply the original # of steps X the gear ratio. eg. a 10-1 ratio would give you effectively 240 steps per rev. Remember that ordinary spur gears are going to introduce at least a bit of backlash; spring loading the motor gear against the driven gear can almost eliminate it.

3. Most modern stepper driver boards can 'microstep' (increase the strength of one set of magnets while decreasing the strength of the other set in small steps) . The effect is the same as having a motor with smaller steps. these drivers commonly have switch-selectable full-step, 1/2, 1/4, 1/8, 1/16, 1/32, and 1/64. A 1/64 step board driving your existing motor would give you effectively 24x64=1536 steps per revolution with no gears and no backlash. Microstepping also has the advantage of making the motors quieter. Note that this kind of board will require at least a 12V supply to drive a 5V motor.

Dick