Clicking noise

[jha07]

I've noticed that my hub motor will make a clicking noise if I roll the bike backwards with the controller turned on. No noise when it's turned off. Does anyone know what that noise is? It doesn't sound like it's good for the motor. I'm wondering if rolling backwards will do damage to it.

 

[flecc]

On geared hubs which normally have a freewheel, turning the wheel backwards has the freewheel engaged and the motor turning. The magnet pulls can be felt then, and it is a generating mode, so it's possible that's causing some small back emf causing the noise. Odd, but I can't imagine wheeling it backwards doing any harm, as doing this is common on e-bikes.
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[jha07]

My hub motor is a Crystalyte, so it doesn't have a freewheel.
I sented an email to ebikes about this, and this is what they said...

> When you roll the bike backwards with the controller on, there are
> large currents that flow through the body diodes of the low side
> mosfets effectively shorting the windings together and leading to
> significant drag forces, which can produce among other things clicking
> noises. This is normal, and is not a problem, and rolling the bike
> backwards is generally fine but if you did it at high speeds for a
> long time then you would heat up the controller quite a bit.

I guess I don't need to worry about it.

 

[flecc]

Thanks, I'd forgotten you had a Crystalyte. Direct drive motors do have a high generation capability at low rotations, hence BionX using one for their regenerating motor, so that makes sense from that point of view alone.
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