We’ve got a few flaky NEOs; mostly bad soldering on encoder extensions…
BUT, I’ve got a tough one that has me stumped! When I run a good NEO on my Spark-in-a-box (PWM controlled), it runs forward and backward smoothly. When I plug this motor in, it rotates a TINY big and vibrates. Commanding the other way makes it turn a similar tiny about the other way and more vibration. The vibration speed is proportional to how far I turn the PWM knob. In this state the shaft is extremely hard to turn shading to impossible. It doesn’t matter what position the shaft is in when I start; same behaviour.
I already fixed the obvious one: the black wire was broken off at the JST. Yes, the motor does turn by hand.
Troubleshooting:
- On both good and bad motors, I ran 1 amp phase to phase (three setups per motor). All of them read 0.2 Volts. That seems to rule out a shorted or open phase.
- I fed 5 Volts to pin 6 (red) and ground to pin 1 (black). I get a small current (10-ish milliAmps) on both motors. On the encoder A, B, and C pins I either get +5 or zero, and this changes state as I click the motor between its magnetically cogged positions, with some uncertainty as I bias it clockwise or counterclockwise; as expected. Both motors behave the same. I did not set up to verify three phase quadrature, so that’s still out there.
- Both motors read about 11 kOhms from pin 5 (white) to ground. This is motor temperature, and I’m guessing its a thermistor. I did not heat the motor up to be sure.
- Both motors spin happily when I run them on my brushless drill tester: this is feeding the motor in parallel with the internal brushless motor, so its 3 phase square wave AC.
Any thoughts? Sacrifice a resistor by letting its magic smoke out? Respectful burial? Exorcism? I can set up a scope or a power analyzer if that’s what I need to do next, or crack open the can.
