The drone was perfectly stable but all of a sudden, it toppled and crashed to the ground. Pixhawk doesn’t seem to loose power during the flights. But I can’t understand the cause. Please guide me to debug.
I looked at log 3.
It was going Ok until Motor2 loses thrust, maybe ESC desync, and is commanded to maximum output - Motor1 is commanded to minimum output to try and keep the copter balanced, but attitude control is lost.
On the way down Motor2 recovers and starts providing thrust again - you can see Motor2 and Motor1 end up with similar outputs.
But Motor4 then Motor3 are also battling with desyncs and attitude control is never recovered.
So most likely 3 of 4 motors lost sync with their ESCs at different stages. I dont think it was slipping props because they wouldnt all do it and recover - slipping props would probably stay slipping. What motors, props and ESCs do you have?
I think those ESCs will be borderline with those motors. You might have to change to a good known-brand 4in1 BLHELI32 ESC, or individual BLHELI32 ESCs, that can handle 40 amps with ease.
Even though ecalc says you combination is quite good, those Navigator series motors seem to be built for long flight time with minimum takeoff weight. I say that because they seem prone to desyncs.
We have no idea about the firmware in the T-Motor Air ESCs and how it really operates - that’s we I recommend a BLHELI32 ECS where we know the firmware and settings, and they seem reliable - plenty of people are using them with a wide variety of motors.
The added advantage will be getting the BLHELI telemetry data such as voltage and RPM, and that can feed the harmonic notch filter more directly. If you go down that path call out if you need help, the BLHELI data is worth it.