Accurate modeling of motor magnetic moments

Determine an accurate and representative model of the equivalent magnetic moment of the Unitree GO-M8018-6 motor assemblies for predicting magnetic wrenches in high-field environments.

Background

The magnetic-wrench simulation requires effective material parameters for the robot’s motor assemblies, including relative permeability, demagnetizing factors, and volume. Because the exact effective relative permeability of composite motor assemblies is difficult to measure, the paper assumes a conservative worst-case model in which each motor cylinder consists entirely of pure iron with relative permeability μr = 1000. This assumption maximizes the predicted magnetic wrench for a given field strength, but it does not provide an accurate representation of the motors’ actual equivalent magnetic moments. Establishing such a model would improve the fidelity of magnetic-force and magnetic-torque predictions used by the MuJoCo plugin and the Magnet-Aware MPC/WBC controller.