Rotors making a strange noise, very low rumble

Pedro Coelho · Sep 28, 2015

So I replaced one of the motors on my P3 Pro after a crash. Everything seemed fine, but now it seems that one of the motors is making a low rumble when I accelerate. It sounds as if one of the motors is having a hard time catching up to the other motors. Anyone ever deal with this? Should I just replace all 4 motors?

Any comments would be appreciated. Thanks!

Pete Leare · Sep 28, 2015

Does it make the same sound without the props on? Could just be an out of balance prop..

nickyb · Sep 28, 2015

Props balanced okay? Has the motor shaft had a knock? Maybe check to see if it spins 'true'

Pedro Coelho · Sep 28, 2015

No, I dont think it make the noise with out the props. Ive read a few things about balancing props. How do I go about it? Any links? Do I need to buy new props?

N017RW · Sep 28, 2015

Keep in mind if you test without props that the throttle will not appear to respond properly cause it is not in flight.

The MC expects to detect a change in aircraft attitude or motion in response to an output to the motors. Without props that can't happen so it keeps trying and this can fool people into thinking there's a problem when none exists.

Pedro Coelho · Sep 28, 2015

nickyb said:
Props balanced okay? Has the motor shaft had a knock? Maybe check to see if it spins 'true'

What does "Spin True" mean?

I replaced the one motor because I could feel that there was some resistance on it when I would spin it with my hand. The other motors felt fine.

nickyb · Sep 28, 2015

Pedro Coelho said:
What does "Spin True" mean?

I replaced the one motor because I could feel that there was some resistance on it when I would spin it with my hand. The other motors felt fine.

basically the central shaft is not out of alignment and does not 'wobble' while it turns.

Pedro Coelho · Sep 28, 2015

nickyb said:
basically the central shaft is not out of alignment and does not 'wobble' while it turns.

Would I be able to feel that with my bare hands? Everything seems fine to me. Nothing feels loose at all.

Should I just buy new props if its a balancing issue?

N017RW · Sep 28, 2015

Aside form bearings there's no moving or wearing parts in the motors. They are very reliable sans trauma (crash) or foreign material.

If there's no 'play', friction, or lash than all is likely OK.

Pete Leare · Sep 28, 2015

You should only need a new set of props if they look physically damaged, nicked etc otherwise you can balance them and make necessary corrections by sanding or adding tape etc.

Pedro Coelho · Sep 28, 2015

Pete Leare said:
You should only need a new set of props if they look physically damaged, nicked etc otherwise you can balance them and make necessary corrections by sanding or adding tape etc.

Does anyone recommend a new set of props I should buy? Carbon Fiber perhaps?

Pete Leare · Sep 28, 2015

I'm not sure you can buy 100% CF props.. I have a set of CF 'reinforced' props. Whatever you do I would stick with DJI official props for the P3, but you can't beat the stock white ones IMHO

nickyb · Sep 28, 2015

Pedro Coelho said:
Would I be able to feel that with my bare hands? Everything seems fine to me. Nothing feels loose at all.

Should I just buy new props if its a balancing issue?

Better await to someone else posts a bit more about it, I'm only thinking logically and don't want to advise the wrong thing to you.

Someone once told me to make sure the motors are clean, free of debris, especially after each flight as grit etc can cause premature wear to the motors/bearings. He uses a can of compressed air, like you do to clean a keyboard. Just an idea. Good luck.

N017RW · Sep 28, 2015

Good tip, but to ease minds the bearings are sealed so don't lubricate as this just makes a mess, retains and grit, etc., and would make the air blasting less effective.