Tight/stiff motor (P2) -- what does this mean?

Apr 27, 2015
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Hi all,
I've got a new Phantom 2, and one of the motors is much harder to rotate by hand than others. I have noticed this when I was attaching props. All rotors rotate with a jerking motion (because they bond to magnets), but this one requires considerably more force to "jerk" it from one magnet to another. It feels like it bonds to magnets much stronger than other rotors. It doesn't feel that bearings are tight, but it feels like the rotor bonds much stronger to magnets during each "jerk".
I have not noticed this motor having different performance than other motors when it is powered. I have not noticed that it heats up or has other abnormality when it is powered (although I have taken very short flights so far).
I am afraid that this motor might fail during a flight. Has anyone experienced same symptoms?
Thank you.
The beauty of BLDC motors is that aside from bearings, not much can go wrong. They're the only moving/wearing parts.

Therefore they don't really fail. ESC issues can cause damage to the coils I suppose but most motors not involved in a crash have been damaged by the longer screws needed to use the prop guards being reinstalled after removing the guards.

The increased notching or 'cogging' is as you say a difference in magnets. With no unusual heating or noise from the motor it would seem you'll be fine.
You can check if it's "binding" - install props.. start the quad using CSC - DO NOT TAKE OFF... then shutdown using CSC... and watch if the suspect motor stops first.
Mine stop at nearly the same time.
With no unusual heating or noise from the motor it would seem you'll be fine.

Emphasis on this. Bearing failure doesn't appear to be common but good idea to feel the bell housing of each motor after you land to make sure the temps are consistent. Warm but not hot is fine.
Long shot. You havent left any of the end arm screws off have you. You know thise small philips ones which round really easily. I did this once on one arm and the motor touched the top shell slighly causing some friction.
Thanks to all for valuable responses.
First of all, I now know what this condition is called - cogging. I've googled "DJI Phantom cogging" and found a number of discussions on this topic, as well as general discussions on brushless motors cogging.
Second, I did the "binding" test to see if the motor in question stops before other motors do. Here is the video of my test:
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The extra cogging motor is the top right in the video. It did stop first on every try, but the difference looks negligible to me. Is this difference in fact negligible?

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