Performance Evaluation of Brushless PM Motor with Less-Rare-Earth Mixed Grade Segmented Poles for UAV Applications

Brushless Permanent Magnet (PM) motors have been the obvious choice for Unmanned Aerial Vehicles (UAVs) owing to their high torque and power density. The motors employed for this application generally use radially magnetized arc shaped rare earth PMs in the outer rotor configuration. This paper presents a outer rotor brushless PM motor using less-rare-earth mixed grade segmented poles. The proposed motor, employing a mix of expensive rare earth and inexpensive ferrite PM segments on each pole, is compared against the conventional brushless PM motor. This pole arrangement produces more torque per rare earth magnet volume thus leading to a reduction in magnet usage. Additionally, the proposed motor demonstrates an improved torque quality with a satisfactory overall efficiency.