Sputtering Motor on f550

[spyncycle]

After two crashes resulting from sudden erratic behavior from my f550, I started poring through the forums looking for help. I thought maybe my Naza was at fault but after reading this very helpful thread:
http://www.multirotorforums.com/sho...avior-NAZA-gyro-going-out-Please-help!/page2!
I decided to isolate the motors and check them one at a time for abnormalities. Sure enough, the number two motor ran fine for 30 seconds, then started to sputter. Here the #2 motor begins much stronger vibration as I ease the power up (20 seconds into the video) then at about 33 second in, it begins to sputter.

I doubled checked connections, and the bullets were making contact and the solder joints are solid. That said, I'm still not convinced there's not a connection problem somewhere. Next will try to run the motor from a different ESC and Channel of the Naza to see if the problem changes at all. This motor seems to come to full speed more gradually than the others on start up then comes to "normal" power at about 50% throttle. No doubt this caused the crashes, only question is why? Vibration seems to vary a bit from motor to motor which I attribute to needing to balance my props. Is there anything else anyone can recommend to troubleshoot?

I am running the stock DJI 30 amp ESC's, Avroto 2814's and the Naza with GPS

Any thoughts appreciated!

 

[gpforet]

Sounds terrible. Also like a bearing is getting hot and seizing. Notice it happens after there's vertical load from prop thrust. Does it also do it without a prop? Sure sounds like a bearing.

 

[spyncycle]

Thanks for the response – much appreciated. I have not tried it with the prop off but I will definitely do that tonight. If you listen to the video above, you'll notice that around 20 seconds vibration becomes much more pronounced. This is true onto of my other motors as well, Although they do not spire as this one does. The other three run smooth. These motors are less than a month old but I've had a couple of pretty decent crashes so I'm wondering if that could've trashed bearings?

 

[spyncycle]

Forgot to ask – is there an easy way to check the bearing? Even after it sputters, it still spins freely by hand when powered down. Doesn't seem to make any sounds until it's up to full speed.

 

[gpforet]

I guess you can check for play in the vertical axis and compare it to the other motors. Another trick may be to spray it with "circuit freeze" or canned air to cool it and see if it quiets down. If the bearing tool a big hit, it could have wacked it out just enough so as it spins up, it gets hot from friction and starts to bind. This is all just a guess but if it's just one motor doing it, and it was crashed, it's a probability. I'm just recovering from a crash myself with two T-Motors impacting concrete on their side. They run up o.k. but weather hasn't allowed me to fly and I worried I may have taken out 2 $60 motors. I feel your pain.

 

[spyncycle]

Doesn't seem to be any obvious difference in play, but I'll look more closely tonight. And yeah, at $60 a pop, I'm hoping this is electrical (read: easily fixed), but I fear you may be right. I will update my post after I swap motors and ESC's on that position. With two other motors vibrating, I have a bad feeling this may have been a three motor crash.

 

[spyncycle]

UPDATE: Well after swapping motors and Naza output/ESC's, I found that the problem moved from motor to motor. Eventually found a bad solder joint under some shrinktube and resoldered a few suspect areas. Bench tests much better and I hoping the problem is solved. Test flight tomorrow will tell for certain. Still seem to have uneven throttle response accross different motors but searching the forums this seems common on the Naza (pre crash mine always leveled once airborn). Fingers crossed.