I will have external torques acting upon an axle to which a motor is connected. I want my motor control system to fairly precisely compensate for most of the torque that the motor imposes on the axle itself due to things like motor frictional losses, induced eddy currents, etc.
In other words I'd like it to appear from outside as if the motor doesn't exist. If one were to spin the axle with their hand the axle should continue spinning at that rate until externally stopped, and you should have to do no more work to stop it than you would if the motor weren't present (ideally).
My motor will need to operate around 10W and -200 to 200RPM. Ultimately this system will be used to modify the stiffness of a mechanical torsional spring without adding damping.
What considerations do I have for motor type selection/design if I want to:
- mimimize the needed loss compensation torque
- simplify the control system
I assume brushless non-geared motors are superior from a friction perspective, however I understand permanent magnet motors have significant eddy current losses and also suffer from "cogging" which may complicate control.
- What methods exist for predicting/estimating the magnitude of these torques from commonly available motor specs?
- Which motor losses are typically constant and which vary with temperature / velocity / other factors?