Motor jitter and smoke on Turnigy Plush 30A

[Metori]

Power up, arm. throttle max.
And after this I decrease throttle to zero and in the moment when motor almost stop (ALMOST) I rapidly increase throttle to max again. Result: motor twitching instead of rotation, heats up and smoke.

Can you explain why this situation occurs?

And why all 4 my motors sounds a little cracking noise while running on low speed?

[sskaug]

When increasing throttle rapidly from low running at a low rpm, the motor current can become very very high. And on some motors the current of a coil takes long to decay after a commutation event. This current prevents detecting motor position from the BEMF, and if this decaying time becomes too long, the motor can lose sync. Normally a loss of sync shall not cause smoke, but in some cases the sync loss can look like the motor is actually still running, and if power is high, motor or ESC can smoke.

Demag compensation has been implemented to fight the long coil current decay after commutation.
Also, the throttle change rate parameter can be used to reduce the maximum instantaneous throttle increase.

I believe the cracking noise at low rpm is because the interrupt activity (from input signal etc) moves the motor output pwm pulses a bit, so that sometimes they are longer than normal. Nothing problematic either to motor performance or reliability. But a nuisance.

[Metori]

Thanks for you reply. I have commutation timing set to low and demag compensation to 1. At first I will change demag compensation parameter and check for results today at evening, if it will not help then I try to increase commutation timing.

[Metori]

Little question. Why my throttle is not linear at the end? There is a one step at the end of throttle (about max position). Below this step motor accelerates linearly, but after this step it changes power to max at one moment.
Can I fix this? Thanks, Steffen.

[sskaug]

The step in throttle when going to max is caused by MCU timing. It takes some instructions (and time) to turn motor pwm on and off, which sets a limit on how much power you can deliver while still pwm'ing. At full throttle motor power is always on. The step will be smaller if you run at low pwm frequency.