Help! Does this sound like a broken motor?

[madjedi22]

After a nosedive onto a sidewalk about a week ago my brushless motor seems to be making a weird rubbing/vibrating sound at low rpm and making less power, (although it’s possible it’s all in my head). As far as I can tell there’s no visible damage to the motor, (no cracks or dents and the shaft looks straight). It’s the FT power pack A motor and in my FT tiny trainer it struggles to maintain altitude at half throttle on a 3s. I understand that this is a hard question but I don’t know what else to do besides buying a new one. Any advice is greatly appreciated!

 

[quorneng]

1. Does it turn freely with you fingers with no rubbing sound, no matter how small?
The outer rotor (bell) is a very close running fit over the inner part. It is possible you have bent the shaft. It is also possible the impact may have dislodged one of the magnets causing it to rub.
2. When you run the motor without its prop does threaded part spin exactly on its axis?
If the motor shaft has bent the threaded end will appear to wobble. Even a tiny wobble is unacceptable.
3. Is the motor getting hotter than it used to?
If something is rubbing the motor will try to maintain the same speed as before and draw more amps. It will get hotter. If this is the case the motor will soon fail completely usually shortly after takeoff!
If there is any doubt about the motor get another. It is not worth the risk of crashing the plane.

 

[madjedi22]

1. Does it turn freely with you fingers with no rubbing sound, no matter how small?
The outer rotor (bell) is a very close running fit over the inner part. It is possible you have bent the shaft. It is also possible the impact may have dislodged one of the magnets causing it to rub.
2. When you run the motor without its prop does threaded part spin exactly on its axis?
If the motor shaft has bent the threaded end will appear to wobble. Even a tiny wobble is unacceptable.
3. Is the motor getting hotter than it used to?
If something is rubbing the motor will try to maintain the same speed as before and draw more amps. It will get hotter. If this is the case the motor will soon fail completely usually shortly after takeoff!
If there is any doubt about the motor get another. It is not worth the risk of crashing the plane.

1If I rotate the motor very quickly using my fingers it sounds like it’s making the sound (I’m not entirely sure how to describe it but it sounds tougher than before the crash)
2 when I run the motor I can’t see any wobble at all in the prop shaft
3 while flying with it it hasn’t been noticeably warmer than before, or really, warm at all.

 

[Merv]

No visible shaft wobble and no visible damage to the bell.
Could there be some kind of grit inside the motor?

You might take the motor apart and scrub it with an old toothbrush to remove any grit.

 

[PsyBorg]

Look at the gap at the bottom of the bell between it and the base. Its hard to see but it looks like the bell may have slipped down slightly. I have had this issue before after hard crashes on several motors over the years. they are just press fit and once they slip they will always be a problem. If it has and that looks like a FT radial I would contact FT support and see about a replacement.

 

[Wildthing]

If you have a air compressor try blowing the motor out, any little grain of dirt can cause the noise. I would even power it up and blow it out while it is spinning.