I’d appreciate any ideas people have regarding an unusual crash that we experienced with a large 34kg quadcopter. Motors are P80 III 120kv, 30" props, ESCs are T-Motor flame ESCs. 12C batteries x 4 10,000mAh.
The aircraft flew just fine for quite some time before both back motors appeared to cut out and the drone just went down backside first.
I’ve seen quads go down when 1 motor or ESC failed but never both back motors going at the same time. All motors seemed functional when tested on the ground after the crash as well so I feel that it’s more of a software issue perhaps than hardware failing in flight.
The first flight seemed alright - just a bit of tuning needed but nothing major.
The second flight - Motor 2 is commanded to maximum because it’s not producing thrust for some reason (probably an ESC desync).
Motor 1 and 3 drop to minimum output to try and compensate.
Motor 2 maybe recovers near or on the ground but it’s too late.
There is no current spike associated with the Motor2 event, only a drop in current as all the motors cut back output to match Motor2. There is a current spike when the copter meets the ground. This rules out anything electrical.
My guess is the ESC is at fault unless you can find a bad connection or something physical that might have caused it.
It’s hard to tell the altitude because of props wash over the baro.
There is a misconfiguration - you have the copter set as a H quad but there are 8 servo outputs with motors set.
Set SERVO5_FUNCTION,0 through to SERVO8
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Thanks for your input here. It does start to look like it might be an ESC desync issue. I will continue investigating but this really helps.
In addition it looks to be a bit overweight/underpowered.
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Another potential issue is that I may have inputted the sensor and GPS offsets incorrectly. Would incorrectly entering the offsets (by as much as 0.5 meters) cause this kind of behaviour? Thanks.
No, I think those position offsets would just have a more minor affect on stability and position holding. They should be corrected of course.
The original problem is there’s no thrust coming from Motor2, so the flight controller keeps asking it to do more.
Thanks for this confirmation. My feeling was that this setting, if wrong, wouldn’t produce the results seen. The aircraft was flying with no offsets inputted for long enough without seeing this behaviour, but i wasn’t sure.