Motor or ESC board failure? How can I tell?

[Wokka Wokka]

Hi, I did do a search, but couldn't find anything with an absolute answer, happy for someone to point to a thread if one exists.

I have a Mavic Pro that has an ESC error on No 4 (rear right) motor. The rotor doesn't take part in the little start up dance with the other three rotors.

Dos anyone know if there's a way to diagnose if this is a motor failure or an ESC board failure? Would be good to know before I start ordering replacement parts. I couldn't see anything in the assistant software, so it might be that there isn't a way to know.

I know you can't easily check the motors, since brushless motors need an ESC (not like the good old days when you just stuck some DC on it and see if it spins).

If there's no real way to tell, then I guess I'll start with a new arm/motor since that's the cheaper part.

Aircraft history:
Board damage is possible, I bought this second hand (for very cheap) after it had a massive smash, one side of aluminium bottom plate was 2mm lower than other, and had cracked in 2 places. I already ordered a new bottom plate and one of the ribbon cables from the gimbal to the main board, since it had popped off and the clip in part of the connector had broken. (I like fixing stuff, and I know you can buy bits easily enough)
Initially none of the props turned, that seems to have been due to the connector on the right side, coming out, put that back in and no1-3 all seem happy, just not no 4.
The hit was to the fron left of the aircraft, and I think also to the rear right leg (the tab that stops over rotation of the arm was almost completely off), so the motor could be damaged from the hit. I've had the motor out, but can't see anything obvious.

 

[xspwhite]

Can you take the motor apart?

 

[Wokka Wokka]

Not sure what you mean.

I can remove the motor from the arm, though there's not much cable slack.

I can't see any way to take it apart any further, or what inside could be fixable?

It looks OK physically, so anything that is wrong is likely to be too difficult too repair (such as damaged windings). It feels the same as the others when manually rotated.

I might try desoldering the motor, then putting it on one of the other motor connections to test. If the motor is dead, I'll have to desolder it anyway, and if it's the ESC I'll have to desolder all motors, so either way it's coming off.

 

[xspwhite]

Not sure what you mean.

I can remove the motor from the arm, though there's not much cable slack.

I can't see any way to take it apart any further, or what inside could be fixable?

It looks OK physically, so anything that is wrong is likely to be too difficult too repair (such as damaged windings). It feels the same as the others when manually rotated.

I might try desoldering the motor, then putting it on one of the other motor connections to test. If the motor is dead, I'll have to desolder it anyway, and if it's the ESC I'll have to desolder all motors, so either way it's coming off.

The only thing I can think of is a loose or unglued magnet. Other than that, could be a mainboard issue. Which seems to be pretty common in crashes.

 

[Jeffm912]

Brushless motors are pretty resiliant. If the windings are not burnt, you could smell it close to the motor, and the magnets are all there it is likely the esc. Cheaper to test the motor on another esc than buy a new motor and find out yours is fine. Check the esc once the bird is powered up with a multi meter and proceed from there. Could end up being a loose wire or a cold solder joint that popped off during the crash.

Jeff

 

[Wokka Wokka]

Thanks for the replies.

I have a multimeter (and a 20 year old degree in electronics), so allegedly know what I'm doing.
I tried seeing what happens on the working motor during startup, seems to be some brief spikes of DC that show something's happening (pretty low reading between grey and black wire, but aligns with the prop moving).

I have the same voltage pattern on motors 1, 2 & 3, but none on number 4 (between any pairs of wires), so it looks like the ESC. I should have guessed, the ESC is more expensive, but as Jeff pointed out, not as expensive as buying a motor/arm THEN having to buy the ESC.

Thanks again.

 

[xspwhite]

Thanks for the replies.

I have a multimeter (and a 20 year old degree in electronics), so allegedly know what I'm doing.
I tried seeing what happens on the working motor during startup, seems to be some brief spikes of DC that show something's happening (pretty low reading between grey and black wire, but aligns with the prop moving).

I have the same voltage pattern on motors 1, 2 & 3, but none on number 4 (between any pairs of wires), so it looks like the ESC. I should have guessed, the ESC is more expensive, but as Jeff pointed out, not as expensive as buying a motor/arm THEN having to buy the ESC.

Thanks again.

Makes sense. These motors have no brushes, and they completely rely on the ESC to run..

 

[FoxhallGH]

You might get something useful out of the attached doc's - which describe how the DJI ESC works ...

 

[Wokka Wokka]

Just to close the problem out , and for anyone searching with a similar problem, It was the ESC.

I bought and installed a new ESC board, now all 4 mototrs do the happy dance at start up, and I can start them ready for flight.

Not a difficult repair, but you want to be alright at soldering, and have a decent soldering iron. The solder they use seems to have quite a high melt point, an those huge blobs are not easy to get liquid sometimes (especially the ones on the thick gauge wires from the battery board).

I de-soldered the motor and LED wires to the front arms, then removed everything else from the aircraft to make it easier to work on (took out compass board, power board and rear arms).

The really thin wires from the compass board need care, especially when trying to cut the rubber blob covering them away.

Take photos so you know which wire goes where!

 

[Jeffm912]

Glad you're able to fly again. Take care.

Jeff

 

[Texas Mavic]

@Thunderdrones

 

[Former Member]

The solder they use seems to have quite a high melt point, an those huge blobs are not easy to get liquid sometimes (especially the ones on the thick gauge wires from the battery board).

The really thin wires from the compass board need care, especially when trying to cut the rubber blob covering them away.

Job well done. The solder has a high melting point, plus it is covered in conformal coating to insulate it, so breaking the bond the first time is the hardest.

The smaller wires from the front arm LEDs, and the compass wires are tough. You cant really cut and splice the wires together if you make a mistake, because the wires have internal waterproofing as well as external insulation.

Replacing the ESC board is the single toughest repair on a Mavic, but the OP shows that it can be done. Just be careful with all tee ribbon cables, dont damage them, and also dont let solder or flux splatter on to adjoining components. If that happens, you will get a short, and might never be able to identify it.

 

[JCTOTI]

Thank you all for the feedback and information, I have a DJI mini 2 with "ESC Connection Error (Code: 30085).
A motor is bad, I replaced it, but the problem continues.
I will change the ESC board, please cross your fingers.

 

[lyndern]

Thank you all for the feedback and information, I have a DJI mini 2 with "ESC Connection Error (Code: 30085).
A motor is bad, I replaced it, but the problem continues.
I will change the ESC board, please cross your fingers.

we have the same drone and same problem but I can't tell if it's the motor or the ESC board.