Motor Screech

[Samson]

My Pro 902 hub motor emits a screeching sound midway through and for most of the acceleration phase or when traveling at around 50% of full speed. As it approaches full speed it becomes quiet. I have read others have noted this with this motor but no ones seems to know the cause. I have the current limited in the controller at 10 amps maximum, I run 44 volts. The sound seems to be emitted by the side of the motor vibrating as far as I can tell. I have opened up the motor hub and the gears and bearings seem normal. This occurred shortly after I started using it but was not present for the first few rides. There is no obvious signs of mechanical wear, I have 1200 Kms on the bike and it is not getting worse or better. Current draw with the wheel off the ground is  only .58 amps suggesting there is no binding. The screeching noise is quite loud, to the point I will be changing to another motor if it persists. Any ideas?

[skylinenitro]

Could the front fork be bent or warped?

[truly_bent]

Just a guess, but it might be a hall effect sensor problem.

That type of screeching sounds similar to to what happens when the RC ESC controllers lose sync. RC controllers don't use hall effect sensors at all, but instead rely on back EMF from the motor to sense position (that's why electric bikes powered by RC motors have to have a running start). If, for some reason, the controller loses sync with the back EMF pulses, the result is a loud screeching, and loss of power, until the controller locks back in.

If your controller board is losing one or more of your hall effect sensors, which let the controller know the position of the windings relative to the magnets, then it might cause that kind of screeching.

Check the fine sensor wires coming back from the motor, and right into the controller board. anything pinched or loose might be giving intermittent feedback.

Intermittent problems are always a bitc.. er, pain.

[Samson]

Just a guess, but it might be a hall effect sensor problem.

That type of screeching sounds similar to to what happens when the RC ESC controllers lose sync. RC controllers don't use hall effect sensors at all, but instead rely on back EMF from the motor to sense position (that's why electric bikes powered by RC motors have to have a running start). If, for some reason, the controller loses sync with the back EMF pulses, the result is a loud screeching, and loss of power, until the controller locks back in.

If your controller board is losing one or more of your hall effect sensors, which let the controller know the position of the windings relative to the magnets, then it might cause that kind of screeching.

Check the fine sensor wires coming back from the motor, and right into the controller board. anything pinched or loose might be giving intermittent feedback.

Intermittent problems are always a bitc.. er, pain.

You may have a point. I looked at the sync signals from the Halls with respect to one of the phase power output signals and there is a significant timing difference, probably several degrees. No easy way to fix this though. I may try another controller at some point. Perhaps the Halls were not positioned correctly. I will have to try running without Halls, the controller is supposed to support this mode.

[Bikemad]

I will have to try running without Halls, the controller is supposed to support this mode.

Although the controller supports sensorless operation, the geared motors do not usually start on their own in sensorless mode.
With a direct drive hubmotor, you normally have to start the wheel turning by pedalling before sensorless operation can occur. Unfortunately, the unidirectional clutch (internal freewheel device) in the geared hubs prevents the motor from being turned, which it must do in order to produce the necessary pulses on the phase wires which the GM controllers seem to require before they are able to start working in sensorless mode.

Alan