PWM frequency

Hi.

I think, I've read that the ARDUINO's PWM frequency was about 490-500Hz.

Somebody told me this was a quite low frequency for DC motor and should be like 20kHz instead.

What do you think ?

For a regular DC brush motor there's no need for faster PWM frequency. I know of several production automotive applications that drive motors at 50 or 100 Hz.

I’m using Arduino PWM here:

So far, so good.
I believe the “tone” heard at slower speeds is the 500Hz.

The main reason to use 20KHz is because at lower frequencies, the PWM may be audible. Only relevant for high powered motors used in a quite environment.