Torque transfer characteristics of a concentric magnetic gear with varying inner and outer air gaps

This study presents the design, simulation, and physical validation of a Coaxial Magnetic Gear (CMG) prototype optimized for torque density and torque transfer efficiency. Utilizing JMAG-Designer, five parameter sets were evaluated to analyze the influence of air gap thickness from 0.50 mm to 1.50 mm on magnetic flux modulation. Simulation results indicated a peak output torque of 58.04 Nm at a 0.50 mm gap with a numerical efficiency of approximately 99%. To validate these findings under real-world manufacturing constraints, a physical prototype was fabricated via fused deposition modeling (FDM) using High Temperature PLA (HTPLA), Neodymium Iron Boron (NdFeB) magnets, and cost-effective mild-steel screw flux modulators. The outer radius was downscaled from 100 mm to 60 mm, and an air gap of 1.0 mm was selected to accommodate additive manufacturing tolerances and mechanical yield limits. Static experimental testing using a calibrated torque-arm assembly yielded a maximum static output torque of 13.0 Nm with a torque transfer efficiency of 70%. The variance between simulated and experimental results is primarily attributed to r2 radius scaling laws, lower magnetic permeability of the steel modulators, and mechanical bearing friction. The prototype successfully demonstrates synchronized, contactless torque transfer, providing a low-cost proof-of-concept framework for rapidly prototyped magnetic gear topologies.