Toward an Accurate Physics-Based UAV Thruster Model

Small unmanned aerial vehicles (UAVs) come in many types, the most common being fixed-wing and rotorcraft. Most of these are powered by brushless dc motors driving fixed-pitch propellers. Since the thrusters are typically quite powerful, relative to the weight of the aircraft, the motion of these UAVs is usually dominated by the thruster dynamics. It therefore becomes particularly important to have a good model of the thruster, which can be assembled based on simple measurements of the system properties, rather than from exhaustive testing. This paper presents such a model. The governing equations are assembled by considering, in succession, the motor electrodynamics and the propeller aerodynamics. The results of the model are compared to experimental test results for a particular thruster assembly. Agreement between the two is excellent-with an error of 4.7% in thrust and 7.6% in torque under static conditions-thereby demonstrating the validity of the proposed approach.