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Choice of Pole Number of Two-Rotor Axial-Flux PM Motor for Control Moment Gyroscope

Modern low earth orbit satellites use control moment gyroscopes (CMG) for maneuvering. GMC's generally use a brushless DC motor to run an inertial wheel at about 10000 rpm. In this paper axial-flux BLDC motor is considered for this task with a view to design a low volume, low weight CMC. Various axial-flux (AF) motor topologies are possible. However, two-rotor AF topology is found to be more advantageous. The specifications of an existing CMG design, based on a commercial BLDC motor are taken as reference. The approach adopted for the design of the AF motor, to meet this specification is described, while minimizing the motor volume and maximizing the motor inertia. This approach is used for designing two axial flux motors one with 2-poles the other with 6-poles. The resulting CMG designs, based on AF motor are compared with the existing CMC. It is found that the new design promises to reduce the volume of the CMC by nearly 60%.