Design and Control of a Permanent Magnet Spherical Wheel Motor With a Radially Segmented Belt and a Virtual Shaft

A novel design for a permanent magnet spherical wheel motor (SWM) is proposed to enable controlled rotation direction while ensuring stable and precise rotational control. The proposed motor features a belt-shaped stator, which is derived from conventional motor systems but employs a belt-shaped structure, enhancing scalability and modularity. To regulate the rotation direction effectively, a virtual shaft mechanism is introduced, in which additional permanent magnets are placed orthogonally to the primary rotational direction, enabling controlled axis stabilization. A prototype SWM was developed with a single-phase, four-belt configuration and six stators per belt, and its operation was successfully demonstrated using Hall sensors, an FPGA-based controller, and parallel inverters. Under a 12 V dc-link and no-load conditions, the motor speed was controlled from 50 to 500 rpm by adjusting the PWM duty cycle. One of the key challenges in evaluating the motor’s performance was the lack of an established method for accurately measuring rotation direction and speed. To address this, we proposed and implemented two measurement approaches: 1) image processing-based tracking; and 2) tachometer-based speed detection. Using these measurement techniques, we further analyzed the motor’s behavior under a friction load of approximately 10 mN $\cdot$ m. The results demonstrated continuous 360-degree directional switching at 45-degree intervals, while maintaining a speed of 300 rpm. This article introduces a novel method for designing and controlling a permanent magnet SWM with adjustable rotation direction, demonstrating its feasibility for future mobility applications.