Smoking Motors (HELP!!!)

[NHS77]

So I am onto my third build, this time a Dart 400 with integrated PDB from Hobbyking. I opted for a NAZA Lite FC and Multistar 2212 920KV Motors. Everything running on 3S. I finished the build and configured the NAZA Lite with the DJI software. During that time I had the whole rig on 3S power for quite while - without anything happening out of the ordinary.

THEN I armed the NAZA to check the direction of the motors. One motor started turning while 3 only wiggled back and forth a bit. ESC's not calibrated, I thought and raised the throttle. This made the one motor which spun before stopp, while the other three kept wiggling back and forth. Then I noticed smoke coming out of one of the wiggling motors and I detached the LiPo immediately. Upon closer inspection the coils inside that motor are partially black now.

Question 1: Is that motor dead now?
Question 2 (more important): What could cause this?

I checked my soldering connections and everything checks out (+ to + and - to - etc.). I also figure that if I had short somewhere this would have manifested itself way before, since I had the LiPo connected for long while before arming the FC.

I don't dare to give power to the rig anymore before I figure this out, but where to start? (The ESC for that motor looks fine...)

Any pointers would be greatly appreciated!

 

[Craftydan]

If the enamel is scorched, I wouldn't trust the motor. Too much risk of a shorted motor coil, which can take the ESC out with it.

As for what would cause it, I'd first check the motor leads between the ESC and motor -- the ESC clearly has power, but your description sounds like a bad phase -- one of the three wires to the motor is disconnected/broken . . . but three of the four misbehaving and the forth borderline makes me lean more toward the ESCs being to blame. What ESCs are you using? From the sounds of it, they might have a borderline timing issue (which would explain why 3 refuse to work and one almost-sorta-doesn't-quite work).

For future reference (it's not like anyone told you this) when the motors stutter like that, CUT YOUR THROTTLE!!!! It may not seem like it but even at low throttle your current is exceptionally high when the motor isn't spinning, creating back EMF to impede the current draw. As you've seen, it won't take long before the heat builds up and the motor dies. I've had motors stutter a click or two before catching and running -- not preferred but OK -- but if it hasn't started spinning within a second or two, assume it won't and STOP! Find out why and fix it before leaving the throttle open.

 

[NHS77]

Thanx CraftyDan

The ESC's are Afro 20A (SimonK) from HK.
In the meantime, I hooked up a spare 20A ESC from RTFQ to test each motor without going through the PDB. They ALL stutter and the ESC gets warm pretty fast.... Possibly I've broken them all... The motors don't get warm though and no smoke anymore.

 

[joshuabardwell]

The motors don't get warm though and no smoke anymore.

This may simply mean that you have already let all the magic smoke out of them.

 

[ZoomNBoom]

A guess: you used too long screws or bolts to mount the motors, and you damaged the wires that way.

 

[BanditJacksRC]

I actually had a similar issue.

When building my ZMR250 I soldered up all my escs and when arming/ throttle up I notice 2 of the motors were doing that strange twitch thing. I was having trouble soldering those 2 escs becuase I trimmed the motor wires and didn't know about the enamel coating on the wires at the time. I spet too much time with the soldering iron on those escs and am pretty sure i just got them too hot and trashed them.

I could pump the throttle a bit and get them all to spin up properly, but after 1 or 2 flights the quad fell from the sky and I noticed the same blackened area on a portion of the coils, and my esc was also fried.

When replacing those 2 escs i was much better with the soldering and was quickly in and out. I have not had a problem with them as of yet.

 

[NHS77]

I actually had a similar issue.

When building my ZMR250 I soldered up all my escs and when arming/ throttle up I notice 2 of the motors were doing that strange twitch thing. I was having trouble soldering those 2 escs becuase I trimmed the motor wires and didn't know about the enamel coating on the wires at the time. I spet too much time with the soldering iron on those escs and am pretty sure i just got them too hot and trashed them.

I soldered the wires already attached to the ESC to the PDB. Not that I'm a great solderer but they went on fairly quick and since there were a good 2 inches of wire in between I doubt that I fried the ESC's that way. Plus, testing with a new ESC of a different brand I get the same sputtering of the motors. Then again they might be blasted already...

Still not sure how to go about this except exchanging all ESC's and Motors... which would suck.

 

[NHS77]

Additional Info:

Just thought of this as it may be a clue to you guys:

I heard in several setup tutorials on the NAZE FC that power should only be supplied through the included PMU unit and that ESC's should only be connected by their signal wire. So I removed the power and ground leads from the BEC wiring of the Afros. I insulated all removed leads with electrical tape. I don't see how this would affect the ESCs providing power to the motors but perhaps I'm missing something here, so I thought I'd mentioned this.

 

[ZoomNBoom]

again, check the screw length you used to mount your motors. Id bet a beer they damaged the motor wiring.

 

[RAM]

Might be a production problem. I have 4 burnt Afro ESC's sitting here to be used as spare parts. My son bought them brand new for a new build and they all failed instantly on startup.

 

[NHS77]

Alright ZoomNBoom you earned yourself a beer!

I wouldn't have thought it's possible but the screws that came with the Multistars (8mm) are way too long. The wiring for the motors is directly under 2 of the holes, so 2-3mm in the screws start pressing on the wires!!! On closer inspection I cant see bare wires / scratched off insulation.

Having removed the motors I tested the "smoker" with a spare ESC again and spins beautifully: https://www.youtube.com/watch?v=8s2FXMoeAeA

I'm actually surprised it still works but makes me wonder whether to use it now...

 

[ZoomNBoom]

Alright ZoomNBoom you earned yourself a beer!

Awesome. Can I have a Westvleteren 12 please ?

I'm actually surprised it still works but makes me wonder whether to use it now...

I dont think I would. The only way the motor could have shorted out is if the enamel was pierced. Its not going to repair itself. Removing the screw may remove the direct short, but its still an accident waiting to happen IMO. Maybe you could re-apply some insulator or something, I have no idea, and of course, you could rewire the motor if you think thats worth the trouble...

 

[Tannerman04]

I'm having a very similar problem but worse. My ESC has never smoked or anything yet the motor will stutter for around 7 seconds then will beep and stop. I have taking screws out of motor but still have the same problem. I also attached the same motor to a different esc on my quad and it worked fine. Lastly, I tried to calibrate the esc's on my quad (without the screws in the motor), and the motor started smoking. Is it a bad esc?