In-depth learning of cogging/detenting torque through experiments and simulations

The necessity of in-depth learning of cogging/detent torque for mainly undergraduates is discussed with particular attention to its method and tools. The experimental tools developed include a cogging-torque tester, variable-skew rotors for a DC motor and a three-phase hybrid stepping motor having a special rotor construction to eliminate certain harmonic components of cogging torque. Two pieces of software are presented for use in the class and laboratory to supplement the experiment set-ups: one is a motion simulator for a watch stepping motor to demonstrate the notion of detent torque; and the other is for quick computation of the cogging torque primarily to investigate pole-and-slot number combinations for various pole-arc to pole-pitch ratios. The latter can be used to see the effects of construction asymmetry on the cogging-torque's amplitude and frequency. The usage of these tools and software is discussed from the viewpoint of engineering education. The major conclusion is that the variable skew rotor is very suited to in-depth learning of cogging torque but the supplemental use of the computation software is invaluable for gaining deeper insight into this subject.