Help! Geared Hub Motor with abnormal noise at certain speeds

[tmho]

Below is a link showing my geared hub motor is running with abnormal noise at certain speeds. (Please turn the sound volume to maximum in order to hear the noise clearly.) Since I do not have equipment to check the rpm of the motor, I only can use the ammeter of the power supply (at the lower left corner) to show the change in speed/rpm of the motor.

https://youtu.be/oTjsSqiQX9A

The abnormal noise starts at around 0.8A, but it disappear after around 1.6A. The set up in the video is just the rear wheel with hub motor installed onto the bike frame by tightening the axle nut to the rear drop out of the bike frame. The freewheel and the rotor of the rear disc brake have not been installed. The motor is not rubbing on anything which may be the cause of the noise.

I have problems with this motor for quite a while. https://endless-sphere.com/forums/viewtopic.php?f=3&t=78459 is my previous post on it. Now I find that the problem is just running with abnormal noise at certain speeds, so I would like create this new post to get help.

I suspect that this problem is similar to the problem in a car with unbalanced wheel, which the driver will feel vibration at certain speed. When I opened the motor the first time, I used a puller to pull the rotor of the motor out. I deformed it a little bit during the process. The center of gravity of the rotor is then not at the center, which will cause vibration when it rotates. At certain speed, the vibration resonates with the frame which makes the abnormal noise. Am I correct?

If my guess is right, then fixing the warped rotor of the motor is the way to fix the problem. I have tried fixing the rotor with a C-clamp as mentioned in my last post. But I could not get it back to shape, just a little better. Is there any suggestion on how to fix the warped rotor?


I have not tried the motor under load. Will it be possible that the noise go away when the motor is under load? It will take me quite a lot of time to hook up everything so as to test it under load. If it is not that possible, I do not want to waste time on trying that. However, I will still try it finally if there is no way to solve the problem.

Any other suggestion on how to fix this problem is highly appreciated.

 

[tmho]

This morning, I tried test running the motor again. I found that it was running in reverse (yesterday it was also running in reverse when I found the abnormal noise at certain speed). So I followed accountant's chart from https://endless-sphere.com/forums/viewtopic.php?f=2&t=66517&start=25 to get the right wires combination. After that, the motor then runs smoothly and no more abnormal noise at certain speed. Below is a video of it running smoothly.

https://youtu.be/VcAW0W9w7q0

Actually, I have done nothing other than switching the wires. Would the previous problem be the result of a wrong wires combination or a bad connection? Anyway, I am happy now and thanks for all your comments or suggestions.

 

[John in CR]

Would the previous problem be the result of a wrong wires combination or a bad connection?

Yes, that was most likely your problem all along. NEVER try 36 hall/phase combos. Not only is it totally unnecessary, but it frequently leads to erroneous results, because people aren't systematic. There are 6 valid wiring combos for the motor, 3 reverse and 3 forward. All you need is one forward, and it's so simple I could literally find the correct wiring blindfolded. The most common mistakes are:
- swapping more than just 2 wires at a time
- not keeping the phases or hall sets static while trying the 6 possible combinations of the other, which is guaranteed to net you a valid combo, since every combination of phase wires has one valid hall combo, and every combination of hall wires has one valid phase combo. If the valid combo is reverse, simply swap an 2 wires of the set you were keeping static and go back to the others and find the right combo of the remaining 5.