Operation of harmonic side-drive micromotors studied through gear ratio measurements

Abstract

The detailed operation of variable capacitance harmonic (or wobble) side-drive micromotors was studied through gear ratio measurements. The gear ratio of the wobble micromotor is affected by wear in the bearing and by rotor slip. Rotor slip is a function of motive torque magnitude, excitation angle, and friction torques. The gear ratio of a wobble micromotor can be expressed as a constant term plus a term that accounts for rotor slip. The constant term is the nominal gear ratio which is equal to the bearing radius divided by the bearing clearance. The rotor slip term is directly proportional to the bushing friction torque and inversely proportional to the square of the excitation voltage. Micromotor operation in air as opposed to nitrogen demonstrates a significantly larger bushing friction torque.<>