Saturday, everything was working great.  Flying through the pattern with acceptable power and lap time, battery consumption right on the money where I want it, flight time just right, adequate power.  The whole nine yards.  HAPPINESS!!!

Suddenly, my motor would rev up, and do the delay as normal, but then when it is supposed to come up to speed for flying it will start to rev then cut out, and repeat endlessly.  I have switched batteries and tried a different timer.  Occasionally, it will rev up normally and run until I care to shut it down.  Then the next time it goes wierd on me.  Any clues?  My suspicion is that the speed control has gone bonkers, but then again it could be the motor.          

Tomorrow, I will try it with a different speed controller, and if that isn't the cure, experiment with both speed controllers but with a new motor.  There are only 4 components in the system, it shouldn't be that hard to find out which one has gone nuts (unless it is an interface problem, and I then I am thoroughly hosed!)

Thanks, but none of the above problems are involved.  I think, at this point, I have a bad wire in the motor or the ESC has gone over the hill.  Tomorrow's testing should tell the tale!

Cold solder joint in bullet connector (once had a motor with TWO bad ones)

Exposed brass, bullet connectors shorting out against each other intermittently.  (You'll change motors or ESC's think you got it but the real thing was fising the metal to metal)

Also sounds like what happens when you are up against the cut-off current in the ESC - it shuts down to protect itself...

Sounds like a bad speed control. I had a turnigy that I was testing out do exactly that. I switched to a Castle and problem was solved. Of course it could be any of the above suggestions too. They are all logical. Posting your whole setup would be helpful to all.

One flight it was fine, the next one a problem.  The motor pulls 20 amps, the ESC is a 55 watt Hacker.  Two different timers,  the wiring is well protected (I'll look at it again to see if somehow the insulation got messed up someplace hidden.  More testing today with Andy Borgogna looking over my shoulder to see that I am not missing something.   

OK, check one more thing: trace the motor wires into the case, look for the motor wires shorting out against each other OR against the motor case due to wearing or shifting of the insulators (it happens).

You should be able to do that check with a voltmeter that has an AC range and a drill -- no o-scope required.

(But o-scopes are more fun).

I did the test with the drill and voltmeter.  I got .707, .717 and .737 for my results.  What does that mean?

Hi Larry,
Plug into the wall drill or battery powered?
If you used a plug in the wall job then this difference seems too large. That's more than 4% and it's on the order of a missed turn in one winding. That would be bad.

On the other hand, if you used a battery powered drill, and you got the readings in reverse order (high first then dropping each time) it's because your drivin drill discharged and slowed down.
Then, I don't know what it means.

In general relative balance phase to phase out to be much, much better than one divided by the number of turns on the stator. Much, much as in 1/10 or 1/20 times the 1/# of turns.
For example if the motor was a 12-turn job, and you saw an 8% difference, you'd know that one winding was mis-wired by one turn.
That motor would run, but it would run hot and make grindy noises and pull tons of current because it would be fighting itself every commutation cycle.
The ESC would probably quit if you loaded it hard due to current overload.

Hope that helps,
Dean

Because the problem didnt happen initially, and the voltages are not zero or vastly different, I believe an internal winding is intermittently shorting against the iron or another winding. I have had a similar problem with a cheap motor.

But I still use cheap motors, they are more FUN!    How else could I afford a series of 5 identical motors except for Kv and then see which is most efficient and does what I want.

It was a wall power drillpress.  Gutsy big motor, not likely to vary a bit with the loads imposed, nor degrade as the voltage dropped.  I guess this verifies that the motor is toast.

I've seen pictures of brushless motors opened up -- if you've built a motor out of nails and bell wire as a kid, you should be able to rewind one.  Or if you're going to trash it anyway, give it to me  .