After my last crash the shaft on my rear tricopter motor was tweaked. 

https://www.youtube.com/watch?v=8pLH2GwmsfM

Fortunately I gave each motor a spin manually before powering things on and noticed so I had opportunity to fix it. The motor was clearly rubbing and I imagine would have promptly self destructed had I turned it on.

The motor is a NTM Prop Drive Series 28-30A 750kv / 140w though I would suspect this approach would apply to other motors including those used on quadcopters y6’s octocopters and other miscellaneous multicopters.

In essence, I removed a snap ring from the base of the motor which allowed me to separate the housing from the interior. I then mounted the housing with shaft in my lathe and using a dial indicator centered it up roughly (via nocking) in the chuck.

Once reasonably centered I ran the dial indiactor on the far end of the motor shaft. It was out by nearly 10 thousandths of an inch. I located the high spot and pushed on the shaft to nock it back to 5 thousandths. The process of measuring total outage, finding high point, halving, was repeated a couple times till it was under a quarter thou out.

Remounting and replacing the snap ring I found the motor now sounded healthy. Powering it up verified all was well; disaster averted!

As an aside; the earlier part of the flight actually went quite well. Trying it in a fairly open field made flying the tricopter a bit easier and I actually managed a pretty neat steeply angled circle around 1:36 into the video.

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