Why do stepper motors lose steps rather more at high and lower speeds?
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The resonance behavior is still very strongly pronounced at lower frequencies or speeds whereas the EMF increases proportionally to the speed and, as a result, the current always decreases (I = (UV – UEMF)/R) and thus the torque greatly decreases.
The lack of torque reserve in both cases then actually leads to the fact that even a short increase in load or small torque peaks causes the motor to lose steps so it can get out of synchronization and actually come to a standstill. This can be remedied by a higher supply voltage or, on the other hand, a motor with lower winding resistance or lower inductance at the same torque.
How to avoid resonance can be found here
