I am experiencing an unusual behavior of my VTOL during a mission (which I have flown repeatedly with the similar result).
During a mission, while loitering around a point, the aircraft suddenly cuts power of the propulsion motor, looses speed and goes into transition after having reached the minimum speed limit. As such, the failsafe is working properly, however, I can not identify the reason for the throttle cut, as the mission plan does not indicate anything like that.
To be precise, the issue occurs during WP20, which is 3 turns of loiter, after about 2.5 turns, before continuing to WP21 and WP22 (landing). I re-flew the same mission multiple times and experienced the same behavior each time at practically the same point, so one might think that it should be related to the mission plan, but I can’t find any problem with.
Might it be a parameter value that results in this?
It is incorrect to say that thrust is lost as a result of throttle cut.
Transition occurs because the speed cannot be maintained even with maximum throttle and drops below the minimum speed, and then the throttle is cut.
As you can see that VoltR (estimated resting voltage) dropped to 23.3V, it appears that the transition occurred simply because the battery for the thrust motor was empty.
I agree with these statements. It appears there was a loss of thrust despite the vehicle commanding high throttle output.
You can see the current consumption drops steeply before the transition due to low airspeed. This indicates a large electric load (ie. the thrust motor) stopped drawing current.
I disagree with this statement. The battery is likely a 6 cell pack of Liion or Lipo chemistry. The battery voltage range in the log is 21.7 V to 24.7 V, which is per cell 3.6 V to 4.1 V. Mean voltage was 23.3 V which is above nominal voltage for either chemistry.
Note: the 21.7 V measurement occurred during a high throttle maneuver at 8:49 log time; this is before the transition at 11:09 log time. This makes the explanation of ESC entering a low voltage protection less likely.
That said, other causes to the thrust motor stopping could be:
disconnected or loose power or signal cable
ESC went into protection mode (overheated or low voltage)
If the cables look well connected, I would increase airflow to the ESC.
Battery voltage should be evaluated using BAT.VoltR (voltage estimation without sag), not BAT.Volt. VoltR shows the lowest value at 11:09
Since @PascalF says the throttle power cut off is reproducible, it is unlikely to be an accidental hardware trouble. VoltR is just an estimated value, so we should not rule out the possibility that the ESC was on low voltage protection.
I agree with your comment about the possibility of ESC protection due to overheating.
Anyway, thank you very much for your valuable comments.
These are mixed messages.
I believe it’s better to look at the raw value in this case, since the processor knows only generic characteristics of the power source. .
Thanks to all for your suggestions. As said, a hardware trouble is rather unlikely, as I repeatedly flew with the aircraft. Same for the battery issue.
In the meantime, I redefined the mission plan and had flights without the mentioned problem, BUT soon thereafter I got again a problem with power loss in a flight, HOWEVER with a beeping noise coming from the ESC. As I heard the loss of prop noise and the beeping, I immediately went into a dive and sailed the aircraft close to the landing site, where I transitioned to VTOL and landed safely.
It seemed that during that flight the ESC overheated and cut power, resulting in the beeping noise. As such, the probability of overheating in the previous flights is real and I might investigate that idea further.
So far, thank you for the helpful comments.
