Finite element torque modeling for the design of a spherical motor

This paper presents the method of modeling the torque generated by a variable reluctance spherical motor (VRSM) that presents some attractive possibilities by combining pitch, roll, and yaw motion in a single joint. Unlike prior works on the torque formulation of a VRSM, which were based on a lumped-parameter approach using equivalent magnetic circuits (widely used in developing force/torque models for electromechanical devices), this paper presents a distributed-parameter approach to predict the motor´s magnetic field distribution for formulating the torque of a VRSM. A detailed three-dimensional finite-element (FE) analysis has been performed on a VRSM configuration that consists of both permanent magnet (PM) poles and air-cored electromagnets. The model obtained using FE methods offers more insight and an accurate representation of torque generated by a spherical motor.