Motor making that loose magnet sound but no magnets are loose

So at a certain rpm the motor is extremely loud and after the motor leaves that rpm range its quiet again

The scratches on the magnets are only on one side of the magnets and on all of the magnets

I checked the bearings and all spin like new so its really weird

Im thinking of sanding a bit of the stator down on that part, maybe take of .5mm with sandpaper

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Check the windings. Might be a bit a lose winding which is the reason of this sound.

No loose winding’s anywhere

I sanded down the stator a little and its quieter now but the noise is still here

First thing magnets are magnets they attracted to the case so u will not see them loose but if epoxy is broken u can try push it to the side and it will move and at higher speed it lift ups from “motor can” because of enertion


Can’t blame everything on Jason


I knew someone will say this :smiley:


I can see there is broken epoxy, so yes, your magnets are getting loose. I would remove them and do the process again, it happened to one of my Maytech motors during the 5 kms of use, same issue, but broken magnets every were…I heavily epoxy the magnets to the motor can…No more issues…And also epoxy the retainer ring…

Since it’s only at one speed, you may actually be experiencing some form of resonance rather than loose magnets. The cans of most outrunners are only supported on one end where they attach to the shaft. This means there’s the chance for wobble/flutter or other weird effects that can become prominent at a certain RPM. This is also indicated by the fact that all the contact marks are on the unsupported end of the can.

Hobbyking SK3 6374s have a skirt bearing that supports the can at the other end, specifically to prevent this kind of issue.

If that’s the case, I don’t know how to fix it easily unfortunately. I’d check that your can is at least properly static balanced, but dynamic balancing is kind of out of the scope of most builders, and dynamic balance may be your problem.

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this wouldn’t come out of the blu though. If that was the case, the motor would make that sound from the start at a certain rpm.
My bet is on loose magnets. Try to move/lift magnets with some force with a screwdriver. If it moves it moves, if it doesn’t magnets are probably good.

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Another issue that could be the cause, or even just aggravating an underlying other issue, is maybe the setscrews that hold the shaft into the can are loose. That could happen over time and cause increasing looseness and make the can more prone to resonate.

@Acido, can we get video of the issue please?

I was thinking more of a harmonic speed whine.

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This actually is happening to me too, it sounds like a turbo doesn’t it.

Ive looked at everything on my motor and cant find what is wrong. I battle harden the magnets too.

The only thing I can think of is that its the bearings?

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Video please

I cant get a video as it only happens while riding.

Do you not have a phone that takes video? Video while you ride. I just want sound of it

I do, kinda hard to ride on a beach lol.

… then don’t ride on the beach?


this just started happening to me about a week ago and its getting worse im just going to replace the motor

There are more and more cracks every time i open up the motor in epoxy, 2 motors gone in 3 days…

These motors have bearings on both ends of the stator, I think that maytech started cheaping out on their motors…

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