[TheOtherCliff]

Output page Neutrals should be high enough to run motors when testing with Output -> Test Outputs

Important, and you didn't mention it:  Input page Throttle Neutral should be about 40 higher than Throttle Minimum.

[vgwit]

Input page Throttle Neutral is 39 above minimum.

Have tried to look at possibility of ESC firmware upgrade. But BlHeli Configurator can not read my ESCs. I see serial port connected but after a while it disconnects and says to change port or reboot.

My ESCs are DYS BL20A with BlHeli firmware. So today I've tried to change output mode from PWMsync to OneShot125 and motor stattering with lowest motor disappeared! Have made a couple of flights in AltVario  without crashes. Hope it was the only reason of my headache last weeks. Next plan is flights in Rate mode.

[TheOtherCliff]

That really sounds like an ESC firmware issue; there are some ESC firmwares that don't work well with some motors.

So was it always the lowest motor that had a hard time starting?

There is a more called Rate Trainer that sounds good for learning Rate.

[vgwit]

That really sounds like an ESC firmware issue; there are some ESC firmwares that don't work well with some motors.

It is not quite clear for me because I used these ESCs in PWM/490 mode with these motors on CC3D without problems. But Revo+PWM/490 also results in motor statter.

And yes, lowest motor.

I've got already some experience in Rate mode including flips and rolls :-). Got it first from FPV Freerider simulanor.

By the way, trying to find a way to diagnose my problem I've found a way to record signal ESC sends to motor. My quad has additional small board with STM8s chip that governs beeps, LEDs and camera lens tilt. I added a code to measure ESC's pulse duration and send it to PC via bluetooth. The only problem is small distance from PC to quad. Here what I can see, for example for motors 3 and 4.