Strange sound from back motors

tuxevil · May 8, 2015

tweaker said:
Yes there are 4x 2mm bolts 2 on each side of motor.Remove and set aside.
Lift motor off but only enough to get underneath motor to remove small c clip and washer located underneath motor then set aside small c clip and washer.
Now pull off top of motor body it will be hard due to magnetic force.
Once removed check inside and around edges to make sure all magnets are still fixed in place.
If so its not your magnets!!
The motor is still attached to wiring etc and cannot be fully removed further without more technical knowledge but you can now hopefully blast compressed air not only at the top of the motor but underneath which should have a better chance of getting any foreign bodies out.
To reassemble just replace top of motor body carefully it will have a strong magnetic force pulling it shut.
Then replace washer,c clip and 4x 2mm bolts either side.
Quite easy when you see it done and it will save you lengthy delays sending your a/c back to DJI especially if it is only foreign bodies/debris.
Hopefully I have described it well enough to give you confidence in doing this little strip down
This limited strip will give you confidence if its safe to fly or it is indeed a RMA.
HTH

thanks a lot, perfectly explained, and seems pretty easy

tweaker · May 8, 2015

tuxevil said:
thanks a lot, perfectly explained, and seems pretty easy

No problem

Just dont rush it.

Hopefully there will be no loose magnets and it is some field debris

tuxevil · May 9, 2015

tweaker said:
No problem

Just dont rush it.

Hopefully there will be no loose magnets and it is some field debris

ok, i disassemble rear motors today, and i couldnt find anything strange, it seems that on first time i turned them on, after the video showing the problem, debris disapeared

here are the pics.

after that i re assemble it, and turn them on, and everything seems normal

tweaker · May 9, 2015

Glad things worked out for you and you have confirmed there is no loose magnets/damaged wire inside motor.
Also glad your a/c is not of action and you managed to strip down the motor okay.
Pretty study inside and in my view it would take a major collision to loosen those magnets.
AS pilots we are always thinking worse case scenario but thinking through logically before jumping to conclusions will hopefully help getting to root cause of the problem.
This strip down is good in understanding if the a/c is fit to fly or a potential RMA.
Glad things worked okay for you.

m00se · May 10, 2015

this is from photo 1588, looks like the bell housing may be cracked.

also in 1589 there is some blue compound on one of the stator poles, maybe it collided with the bell housing? perhaps the motor was assembled with the compound still wet?

did nothing fall out when you took it apart?

The Editor · May 10, 2015

m00se said:
View attachment 1603

this is from photo 1588, looks like the bell housing may be cracked.

also in 1589 there is some blue compound on one of the stator poles, maybe it collided with the bell housing? perhaps the motor was assembled with the compound still wet?

did nothing fall out when you took it apart?

Good spot.
Ground that bird immediately!

m00se · May 10, 2015

Hahah , thanks, I've been changing motor bearings all day, I guess my mind was in the right place when I saw the pics.

The Editor · May 10, 2015

m00se said:
Hahah , thanks, I've been changing motor bearings all day, I guess my mind was in the right place when I saw the pics.

Yup, that's why it is SO important to find the cause of any abnormal behaviour or sound before you fly again.
@tuxevil - there is no fix for that which will be safe. Your only option is a motor swap. As you appear to have the same symptoms from two of your motors, if it was my Inspire, I would tear down all four motors and inspect/replace as necessary.

m00se · May 10, 2015

The Editor said:
Yup, that's why it is SO important to find the cause of any abnormal behaviour or sound before you fly again.

yep, it is clear from the video that something is wrong, if it isnt a crack in the bell then it is something else.
I just put a motor back together, spin it up and heard a rough noise. Opened it back up again and found a very small piece of chipped magnet.

tweaker · May 10, 2015

Yep good spot.

As Editor says thats why its important to get to the bottom of any unusual noise.

Glad I could help you id the issue.Sorry it resulted in grounding of a/c. But at least you now know!

Maybe something for us all to be aware of especially if you have not had any hard landings/prangs?

Manufacturing weakness in bell housing?

m00se · May 10, 2015

take a close up photo of the outside of the motor bells if you would, maybe we can see a crack there too, there appears to be a visible spot of damage in your video, but the quality is a bit too low to see for sure

tuxevil · May 10, 2015

m00se said:
View attachment 1603

this is from photo 1588, looks like the bell housing may be cracked.

also in 1589 there is some blue compound on one of the stator poles, maybe it collided with the bell housing? perhaps the motor was assembled with the compound still wet?

did nothing fall out when you took it apart?

i just disassmble that motor again, and it seems that "crack" is just a "line", a "scratch" on the paint with the flash effect
i took more pics of it, from several angles, even from outside from the exact point where it must be.

tuxevil · May 10, 2015

if I buy a motor 3510, i can swap the bell housing right?

m00se · May 10, 2015

well, i cant tell if its a scratch or crack, so i'll leave that up to you, but there are scratches on the magnets visible in these new photos. indicating where something has been between the stator and the magnets........

tuxevil · May 10, 2015

m00se said:
well, i cant tell if its a scratch or crack, so i'll leave that up to you, but there are scratches on the magnets visible in these new photos. indicating where something has been between the stator and the magnets........

I agree that there was something inside, i think its unavoidable (that word exist?) couse the motor need ventilation, and we cant flight only in clean enviroment

That scratches on magnets would affect it performance? Or put in risk the A/C?