Design and analysis of a hybrid stepper motor for actuating the gimbal of control moment gyroscope

This paper presents the design, analysis and development of a 400-step hybrid stepper motor for actuating the gimbal of a Control Moment Gyroscope (CMG). The design of the hybrid stepper motor for achieving a specific performance requires the choice of appropriate tooth geometry. In this paper, a detailed account of the results of two-dimensional finite-element (FE) analysis conducted with different tooth width/tooth pitch ratios (t/λ) and also with different tooth/slot shapes such as square and trapezoidal, is presented. The use of equal t/λ ratio on stator and rotor provides nearly 10% more torque than the case with unequal t/λ ratio, but with corresponding increase in detent torque and distorted static torque profile. The hybrid stepper motor for actuating the gimbal of a CMG requires maximum torque density, less-detent torque or cogging torque, better positional accuracy and smooth static torque profile. For the said requirements different pitch slotting with equal tooth width has to be provided. The magnitude of the cogging torque has almost been reduced to 50% from what it was while employing equal t/λ configuration. From the various FE models subjected to analysis, trapezoidal teeth configuration with unequal tooth pitch on the stator and rotor is found to be the best configuration and is selected for fabrication. The designed motor is fabricated and the experimental results are compared with the FE results.