Noise of a drone propeller motors

Summary of e-NVH sound sample
ApplicationDrone (Marvin® quadcopter)
Electrical machineBLDC outrunner (12 stator slots and 7 pole pairs)
Supply conditionRun-up at no-load under non sinusoidal supply
Noise sourcesElectromagnetic (no blades)
See also 

Measurement set-up

Noise is measured 40 cm from the quadcopter on the floor. Blades are removed from the 4 propeller motors to only record electromagnetically-excited noise. The motors are accelerated up to maximum speed. Torque level is very small due to missing aerodynamic load (only friction load).

Sound file and spectrograms

Sound of UAV propeller motors (quadcopter without blades)

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E-NVH interpretations

This sound file illustrates electromagnetically-excited noise of a BLDC high speed motor nearly in open circuit conditions (armature current close to 0). High pitch whining noise is due to resonances between pole/slot electromagnetic excitations and the outer rotor structural modes. This experiments shows that a significant part of the sound of UAVs (Unmanned Aerial Vehicles) is due to electromagnetic noise.

Application to MANATEE

MANATEE software can be used to quickly calculate NVH due to electromagnetic forces both in early design and detailed design phase, including PWM and slotting effects.