Noisy geared hub motor

[rocketman58]

I have two trikes, both with Bafang 500w geared hub motors. One has a model G060, and the other has a older CST motor that I purchased used. The 060 is very quiet, and I have no problems with it. The CST motor is noticeably louder. It makes an audible whine when running. This whine gets worse at a certain RPM. The motor seems to work fine, but the noise is annoying. Since it is a used motor, I don't know the history behind it. What would cause a motor to become noisy, and what can you do to fix this?

 

[neptronix]

The Bafang CST has straight cut gears like the mac and is naturally a bit noisy.

If this is a used motor then you should inspect the internals to see if the original gear grease has gone bad. This may be contributing to noise. Mobilegrease 28 would be a very good replacement for the original grease.

 

[amberwolf]

Additionally, if the motor is in a smaller wheel, while that's good for torque it means the motor has to spin faster for the same ground speed, which makes the gears noisier.

And if the controller is sinewave or FOC on the quiet one, but trapezoidal on the loud one, that can increase the noise in the windings themselves.

Different motor casings are resonant to different frequencies, too, so a peak in noise at a certain speed is typical of hitting that point.

 

[rocketman58]

Thanks for the comments, all very informative.

Both of my controllers are square wave KT controllers. A sign wave KT controller is more difficult to find and quite a bit more expensive. Would a sign wave controller be that much quieter? Also would the square wave and sign wave controllers be interchangeable?