Design of a low-mass high-torque brushless motor for application in quadruped robotics

Abstract

The Biomimetic Robotics Group is attempting to build the fastest quadruped robot powered by electromagnetic means. The limitations in achieving this goal are the torque produced from motors used to power the robot, as well as the mass and power dissipation of these motors. These limitations formulate the need for a lowmass high-torque low-loss motor. This thesis outlines the process of designing a permanent-magnet synchronous motor that meet the goals of the robot while minimizing the total mass. The motor designed from this thesis is compared to motors currently used by the Group when quantifying improvements made. In the process of achieving the goal, a design was formulated using fundamental electromagnetic principles. This design was then tested using finite element analysis. The final design was fabricated in house and wired by hand. The fabricated motor was tested to quantify key performance parameters such as peak cogging torque, peak motor torque, and thermal time constant under robot conditions. The motor designed by this thesis was able to produce more torque than the current motor being used by the Biomimetic Robotics Group, by a factor of 1.6, while decreasing the mass by 23%. A lower than desired packing factor was achieved since the motor was wired by hand resulting in a higher power dissipation and lower than expected motor torque. This design will be used in the quadroped robot after improvements are made to the cogging torque and packing factor.