Effect of rotor slip on the gear ratio of harmonic side-drive micromotors

Stephen M. Phillips, Mehran Mehregany

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


This paper presents a preliminary model of the gear ratio of center-pin bearing harmonic (or wobble) side-drive micromotors, accounting for finite friction in the bearing and at the bushing contacts. The gear ratio of a wobble micromotor is affected by rotor slip, which is a function of motive torque, excitation angle, and friction torque. 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 ideal or nominal gear ratio and is equal to the bearing radius divided by the bearing clearance. The rotor-slip term is shown to be directly proportional to the bushing friction torque and inversely proportional to the square of the excitation voltage. The derived model is used to study the operation of wobble micromotors in nitrogen through gear-ratio measurements. The model fit of the experimental results is within 10%.

Original languageEnglish (US)
Pages (from-to)249-254
Number of pages6
JournalSensors and Actuators: A. Physical
Issue number3
StatePublished - May 1993
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Instrumentation
  • Condensed Matter Physics
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Electrical and Electronic Engineering


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