Multi-physics Analysis and Optimal Design of an Outer Rotor Surface Mounted Permanent Magnet Synchronous Motor for Coaxial Drone

This paper deals with the multi-physics analysis and optimal design of an outer rotor surface mounted permanent magnet synchronous motor for coaxial drones. The propulsion system of a coaxial drone has a structure in which the top propeller, top motor, inverter, bottom motor, and bottom propeller are arranged at short intervals on one vertical axis, which has the advantages of compact size compared to multi-copter drones and high safety in unstable airflow. However, there is a disadvantage that there is almost no airflow between the upper and lower propellers during operation, so the motors and inverter located in that position are not well cooled. This disadvantage can cause demagnetization of permanent magnets and deterioration of windings due to temperature rise inside the motor during operation. Therefore, motors for coaxial drones need to have stable thermal characteristics. They also need to have a high specific power to reduce the Maximum Take-Off Weight (MTOW) of coaxial drones. To achieve these goals, multi-physics analysis of the motor, i.e., electromagnetic, thermal, and mechanical analysis, is essential. Therefore, this paper proposes a multi-physics analysis and optimal design process of an outer rotor surface mounted permanent magnet synchronous motor for coaxial drones, and based on it, performs multi-physics analysis and optimal design of motor. The multi-physics analysis of the motor is performed based on finite element analysis, Computational Fluid Dynamics(CFD), and thermal equivalent circuit method, and the optimal design of the motor is performed using the Response Surface Method(RSM) considering the results of the multi-physics analysis. Finally, the final model resulting from the optimal design is manufactured, and experiments are conducted to verify the validity of the multi-physics analysis and optimal design results.