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I have been testing a new brushless motor for an RC plane. It is a 2200KV motor controlled by a 30A BLDC ESC. I heard a grinding noise coming from my motor, as demonstrated in the following video: Video Here

I have not been able to find a video where someone's motor produced a similar sound. I feel like I have checked many of the usual troubleshooting issues.

  • This is a new product and has never been crashed. I checked for damage from manufacturing and there aren't any dents or deformations.
  • Magnets on rotor seem to be level and secure
  • Unsure about state of bearings. I thought one seemed to be spinning strangely (as if misaligned) but when I reevaluated it seemed fine.
  • Shaft is straight
  • A few coils are every so slightly loose... doesn't seem like it would be enough to cause problems
  • Screws for mounting clear both the stator and rotor. Seem to be magnetically attracted to rotor, but when I removed the screws then the same sound was produced.

I would like to believe it's just the cause of a bad bearing, but there were a couple times where the motor spun just fine after I had reassembled it, which leads me to believe something else is awry. I'm just a rookie at RC, so I'd like to get the opinion of some more experienced ears.

Is it possibly an issue with the ESC? I did solder the ends of the power wires. I was careful not to overheat, but possibly not careful enough?

  • Hi! Are you able to try swapping out the ESC to confirm that the issue is with the motor? – ifconfig May 28 at 20:26
  • Also, do you notice any odd noises when you rotate the bell by hand? – ifconfig May 28 at 20:27
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It looks like a bad phase to me. Check the resistance of each phase, wire 1 to wire 2, wire 2 to wire 3, and wire 1 to wire 3. If one of those is much higher resistance or shows no continuity, then you've got a bad phase. I suspect this is the issue.

Also try swapping the motor to a different arm. This will eliminate the ESC as the issue. If the problem follows the motor to the new arm, then the the issue is the motor, if it stays put then it's the ESC. A bad FET or gate driver in one phase on the ESC can cause the same symptoms as a damaged phase in the motor.

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  • Thanks, I will try that. I tested the motor with a different ESC and this fixed the issue. I'm betting your answer still applies -- if some connection is loose in the ESC wiring then that might explain it. – frc_contributor May 28 at 23:39
  • Yep, a bad phase could happen either in the motor or the ESC. Could be a blown fet on one of the phases of the ESC. I'm glad that fixed it! – QuadMcFly May 28 at 23:57
  • Huh, interesting to hear; I never thought about the drivers for a specific phase going out in the ESC. You say that the ESC was the problem, @frc_contributor? – ifconfig May 29 at 5:18

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