A customer has asked:
I want to slow down a small hobby sized DC motor to a user variable range that runs from slow to zero RPM. I would simply use a wall wart for a power supply and a potentiometer to set the speed but the load on the motor might change slightly. Although the drag on the motor will be very low, if that drag does change, I would like the speed of the motor to stay fairly steady in spite of this.
A couple of people told me to use a PWM controller for this purpose because a PWM has a range of 0 to 100%. Of course this in not in RPM. One other person said that the motor might not slow down properly because the hertz rating on the PWM could be to high to allow this or because the pulses might not have an adequate amount of strength to excite motor enough to move it at all when the motor speed is set near zero.
I thought about using a steper motor so I looked a an Adafruit Motor/Stepper/Servo Shield for Arduino kit - v1.0 but I know almost nothing about this stuff so I don't know if this would be just the right thing either.
I want to turn a knob to vary the speed of a motor form a few parts of an RPM up to a "slow" speed ...say 60 RPM? ...maybe?
Oh ...comparatively inexpensive and simple to set up would be great as well !