ESC and PWM frequency or Motor Cause High Pitch Whine?

[jeff22]

I just finished up a Gelande II cruiser build using an Axial AE5 ESC and a RC4wd 35T Motor.

I have a pretty loud high pitched motor whine that takes away from some of the enjoyment of driving such a scale truck.

I was going to try a different motor but after doing some reading it seems the PWM frequency of the ESC can also cause the whine.

The AE5 has a PWM frequency of 1kHz. My SCX10 has an AE2 with a PWM frequency of 6kHz with an Axial 27T motor and is much quieter.

Does anyone have any experience in how to reduce the amount of low throttle motor whine? Should I change the motor or ESC or make the biggest difference?

[Olle P]

It IS the PWM that cause the whining. Its frequency determines the pitch of the whining, which in turn has some influence on how loud it seems (and is).
An easy fix to reduce the loudness from brushed motors is to add a capacitor between the motor leads. The bigger capacitance the better.
The capacitor will smoothen the signal to make it more low amplitude saw-tooth than high amplitude square.
Two potential problems arise:
1. High capacity capacitors are electrolytic and thus directional. Can cause problems when you feed a signal in reverse (to brake or back up).
2. With a smooth signal the motor will need more throttle to start.

The low PWM frequency of the AE5 is advantageous for good motor behaviour at low throttle in all aspects but sound (noise).