Development of a spherical reaction wheel actuator using electromagnetic induction

A spherical reaction wheel is a novel three-axis induction motor consisting of a spherical rotor and electromagnets. The electromagnets allow the rotor to levitate and to rotate about any desired axis without mechanical contact. A benefit of the actuator is to control the satellite for three-axis attitude using the single spherical reaction wheel. In this study, a prototype model of the spherical reaction wheel with a single rotating axis is developed, and a feasibility study on the actuator is conducted. The actuator system is designed through electromagnetic field analyses of the spherical rotor in order to evaluate the levitation force and torque. Dynamic performance tests are carried out under electromagnetic rotation and levitation conditions, and torque-speed characteristics are investigated. Using the test data, torque modeling and velocity control simulations are also performed. Finally, closed loop speed control tests are conducted on the experimental model. The model shows that the maximum torque and speed are 0.7 N m and 13,500 rpm, respectively, and the speed control error is less than 4%.