I don't know if sci.engr.mech is the appropriate newsgroup for this inquiry; if anyone knows a more appropriate group, please let me know.
Someone needs a way to run a small electric motor at variable speeds over a dynamic range of 100 and still produce a smooth motion. That is, once the motor is geared down properly, the shaft must turn anywhere from 5rpm to 0.5rpm without jerking. Torque is not likely to be an issue--I can turn the load to be driven with the fingers of one hand.
Can this be done with a DC motor, with the appropriate type of controller? What type?
Is it possible to run a stepper motor over that much of a range and somehow remove the jerkiness from the motion? (We could run the stepper motor at whatever absolute speed produced the best results, then gear it down appropriately; however, the speed of the motor would still vary by a factor of 100.)
This project must be done on the cheap, using surplus or home built equipment.
If the dynamic range is simply too large, then I suppose one alternative might be to use several interchangable gear reducers. What are the chances of finding gear reducers with dimensions similar enough that they can be swapped out?