Coulomb friction

Coulomb friction is that component of the frictional load of the motor or load which is unrelated to speed. The coulomb friction of the motor itself can be measured by a cogging torque meter. Thus, the torque exerted by a stepping motor is measured when it slowly turns the tested motor first in a clockwise direction, then in a counter clockwise direction. The two waveforms will be found to have shifted by a finite value. One half of this difference is the coulomb friction.