This paper presents a novel design by integrating a planetary gear train (PGT) within a brushless dc (BLDC) motor to be a compact structure assembly. It provides functional and structural integrations to overcome the inherent disadvantages of the traditional designs. The effects of the gear teeth on the magnetostatic field of the BLDC motor associated with the kinematics of the PGT are investigated. By designing the number of gear teeth integrated on the stator and magnet poles on the rotor, the cogging torque of the proposed motor configuration is effectively reduced. The magnetic field distribution and the output torque of the novel design with different standard gear modules are numerically calculated by two-dimensional finite-element analysis. Through the kinematic analysis that utilizes the fundamental circuits, feasible solutions for the number of gear teeth of the PGT are determined to meet the desired speed ratio.
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