Torque model for design and control of a spherical wheel motor

Abstract

This paper presents a method of deriving the torque model for a three degrees of freedom (3-DOF) spherical motor such as a variable-reluctance spherical motor (VRSM) or a spherical wheel motor (SWM). The SWM (much like the VRSM capable of offering three-DOF in a single joint) offers the ability to spin continuously while the rotor shaft can be tilted arbitrarily. We derive a closed-form torque model and demonstrate its use for designing the switching controller based the principle of push-pull operation for the SWM. The closed-form torque model given here greatly reduces the torque computation, and simplifies the design of the switching controller.