Motor noise/vibration help

[jancellor]

Please help me diagnose a potential issue on my 16X. Since new, there has been a quiet growl/purr at low speeds that may be completely normal. Yesterday, I went for a ride and noticed a significant vibration that may have been the same growl/purr but siginficantly worse and enough to make me ride slowly and go home. Today, that vibration has gone.

Firstly, about the growl/purr that has existed since new. Actually I first noticed it after my first/second ride but it may have been there before. It's like tiny pop/tick that happens every ~8mm of forward movement, or ~80 ~160 times per revolution. It's very even so it's not something catching on the tire tread which is not as even. It's also louder when more torque is applied for the same speed (I do this in the house not riding but with my hands applying forces to the pedals and moving the wheel very slowly). It seems that above about 3kph, the noise suddenly disappears (as if maybe a centripetal force prevents whatever is hitting something from doing so). When riding, I hardly notice this, apart from when going slowly up a very steep hill. I speculate that this noise comes from the reversing polarity in the motor coils and something is being moved back and forth. It sounds to me like something that will potentially fatigue and break over time.

Now, there was a signifant vibration on the pedals that actually tickled my feet yesterday. Unless I'm going mad the wheel was definitely behaving differently. Same shoes, same roads, a fairly strong headwind but nothing particularly unusual. When pushing the wheel with the trolley handle I thought I could feel the same extra vibration. It was a high frequency, low amplitude vibration that tickled rather than shaked, if that makes any sense. The pressure was a bit lower than normal but I've tried it this morning both below and above and I cannot reproduce the same issue any more. This is all the information I have unfortunately.

1. Is the growl/purr simply something normal that exists on all wheels?
2. Does anyone know the rotor/stator count on the 16X?
3. What was this weird tickling vibration and have any of you had it?

Thanks for any help!

(King Song 16X, total wheel distance 1000km, wheel age 2 months, 60kg rider, CYT C-1488 tire, 1.6bar, some bumpy off-roading, many bumpy roads)

Edited July 24, 2020 by jancellor

[Chriull]

9 minutes ago, jancellor said:

Does anyone know the rotor/stator count on the 16X?

On https://ecodrift.ru/2019/06/24/kingsong-ks-16x-disassembling/ is a picture showing all the permanent magnets. Of the rotor are only partial image.

The low speed growl/purr, especially under burden comes from position change per magnet and coil.

At higher speed i assume different algorithm can be used for smoother operation.

This growl/pur can be amplified (resonance) by many different issues like loose motherboard, pedal hanger, axle or a broken (instable) shell.

[jancellor]

Thanks for the link. If I'm counting correctly that's 60 poles (30 pairs) and 54 stators. I believe the voltage applied to the three windings would change 180 times under a simple control algorithm for maximum possible torque (ignoring potential complications from the actual PWM algorithm used). Anyway, this corresponds fairly closely to the 160 ticks/pops per revolution I estimated.

But you're also simply stating this is normal motor noise. That's reassuring but I may make a video later. It's notable that Ecodrift say they find the wiring could have been much neater. I would imagine (as a layman) that this allows unnecessary coil movement.

I'll bear in mind other loose parts could amplify this vibration though I believe the wheel is solid currently. I still don't know why it seemed so bad yesterday.

[Chriull]

13 minutes ago, jancellor said:

I still don't know why it seemed so bad yesterday.

Another reason for this behaviour could be some kind of firmware current limiting. This protects the wheel from overburdening the internal components especially at lower speeds which allow higher currents.

Recently with an KS18XL such a rattling sound occured during stronger braking. First suspicion was that this came from the fw update to 2.02. Further inspection showed that it was a crack in one of the inner shells were it is fixed to the pedal hangers.