How to test if a brushless motor is good or bad
 

I just read this on rc-tech and thought I'd share. I searched here first and didn't find anything definitive, so I thought this would be a welcome addition to archive. What I read-

I'm not sure how much you know about these little beasties....but they are built in theory similar to a motorcycle alternator....in fact.....nearly exactly. If you're running cars....you are probably using an in-runner type. Most of the aircraft guys use out-runners....where the moving piece of the motor is a bunch of strong magnets glued to the inside of a bell housing surrounding the field. The whole system is a lot like a three-phase alternator. Without pulses from the ESC in the correct sequence....the motor won't run. I haven't had a motor go defective yet....but I have had an ESC lose a phase. The motor just sits there & gets hot....grunts....but doesn't turn.
Now the test.... Remove your motor and chuck the shaft in a drill....or better....a drill press. Secure the non-moving part of the motor so that it won't turn. Spin it up to make sure all is secure....you certainly don't want to see your motor go flying across your shop. With the motor shaft spinning at as high a speed you can muster from your drill...get out your volt meter....set it to AC vots and measure the voltage between all leads. They should all be about the same. If not..... one of your windings has shorted or maybe open. If your motor gets warm during this test.....it's defective.
Flash

good find Harold. Interesting way to test. For me, when it stops turning altogether I know it's toast.:whistle:

Sounds like a good way to test to me.

Its like using a brushed motor as a generator. By spinning the output shaft, the windings then generate electricity and put it out through the power leads.

There's a guy floating around the web that took a RC boat hull. He used a Nitro motor, connected its output shaft with a collar to the output shaft of a brushed motor. He then tied the leads of the brushed motor to the power leads of a BL esc, which inturn powered a BL motor that turned the prop. So it was a nitro motor turning a DC motor making power to send through a BL esc which powered a BL motor that turned the prop....

wow, that sounds like removing an engine from a car starting at the headlights and removing the car from the engine? It would be cool to see though!

I think he was going for a diesel-electric type layout. Except nobody makes hobby-sized diesel engines...

Yeah, back in the day of crimped endbell brushed stock racing cans we used to use another motor connected with a shaft coupling to make our own "dyno". Read the output of the other motor which was turned into a "generator". Just spin 'er up on the power supply and play with the springs/brushes for the max RPM out of them.