Semi-Empirical Model for the Prediction of Surface Vibration Amplitudes of kW Class Electric Motors

The ongoing integration of outrunner brushless electric motors into drones and Urban Air Mobility aircraft presents a need for electric motor acoustic predictions suitable for system-level studies. A motor-noise prediction model allows motor acoustics to be incorporated into early vehicle design trade studies. An ongoing effort to develop a motor-noise prediction model, for integration into other system-level tools, is underway. The model is comprised of three main elements which predict the electromagnetic forcing, the induced structural vibrations, and the resulting acoustic propagation. This work discusses the structural vibration element and describes a method to predict surface vibration amplitudes of the motor rotor. The surface displacement amplitude is a requirement for the acoustic propagation element. To accurately predict the rotor displacement, accurate damping values for the rotor structure are required. An experimental investigation of damping values for 1-5kW class motors are presented. A parametric sweep and least-squares-curve fit to a finite element analysis yields a simple curve that can predict vibration amplitude based on a particular driving frequency and mode shape.