Practical Analysis and Design of a 50:1 Cycloidal Magnetic Gear with Balanced Off-Axis Moments and a High Specific Torque for Lunar Robots

Future space missions require new robotic technologies, such as precision gearboxes capable of achieving speed-reduction ratios in excess of 1000:1, specific torques exceeding 50 N*m/kg, operation in environmental temperatures as low as 40 K, and operation in low-atmosphere or hard vacuum, with high reliability and lifetime. The tribological challenges associated with lengthy missions in harsh space environments may be ameliorated with contactless magnetic gearing solutions. This paper employs an extensive parametric 2-D finite element analysis (FEA) study to optimize the high-torque stage of a two-stage surface permanent magnet radial flux cycloidal magnetic gear train, accounting for the impacts of practical fabrication constraints, which degrade the achievable performance and shift the optimal gear ratio. This paper presents a novel discussion of the internal stress distribution and the reaction forces acting on the structure of the cycloidal magnetic gear. This paper also proposes a rotor with three sections to simultaneously balance the center of mass, radial magnetic forces, and off-axis torques. A proof-of-concept prototype was developed, and the experimental slip torque and specific torque are presented. The specific torque of the prototype discussed in this paper is competitive with commercial mechanical cycloidal-type drives with a similar torque rating.