Hexa back flipped

hi guys,

got a crash today after tuning the copter with autotune. the autotune procedure went well. the copter was quite aggressive at takeoff (fast motor correction) but flying very sharp as I would expect it.

have been flying around few min until I went for a full speed pass. when I pull back the pitch stick the copter went into a backflip and crashed. props off. not sure when the copter disarmed them (in the air or on the ground). what is for sure is that on pitch in and pitch in APM datalog, we can not see clearly at the end of the file the curves going in different directions!

at the same time I have a second question, why I am not getting GPS data on the same scale as the pitch ones and can not compare them over the time.

Thanks for posting in the APM Forum!
This is almost 100% guaranteed to be a mechanical failure of some sort. Motor, ESC or propeller. The sudden divergence of the Roll & Pitch vs the desired roll & pitch is the classic symptom of this.
Looks like it flips back (+ve pitch) and left (-ve roll) so maybe the back left motor or ESC. It’s really hard to say what the cause is. If we had ESCs that told us their woes (which is something we’d eventually like to make) then we’d have a better idea but for now…not exactly sure. Maybe an ESC overheating?

Could it be a Too agressive pid?

Copter is new with only 4 setup flights… Will check esc for pb… They are 30amps tmotor.

Copter is hexa with 4.5kg takeoff weight, tmotor 30amps esc with mn4014 and 18x6.1 props.



No, too aggressive PIDs isn’t consistent with what we’re seeing here. The roll and pitch are tracking well against the desired roll and pitch until one moment where they suddenly diverge. If it was a tuning problem then we would see instability before that moment. It’s much more likely to be a mechanical failure.

in case we exceed the 30A max ESC current for more or less a second, is it supposed to cut off? or just try to cope with the demands until it burns? will check tomorrow the copter ESC for possible burnt one…

I just checked the copter and actually ESC are 40amps so for sure did not exceeded their rating.

I checked mechanical / electrical.

the two back arms are broken. they are 25mm carbon tubes.

would not expect them to break in the air but rather when they touch ground.

props, ESC, motors are all working fine…

any idea?

attached are the PID before and after autotune.

I hope you don’t mind, if I post a similar issue here in your thread.
At the moment I help a online friend to setup his first APM Quad. He is very experienced with copters and had many copters before with KK, Naze and some other FCs.
Now he tries his first APM Copter with APM2.6.

He had his first little hover and testflight and had some issues. The first was a circling in loiter, but that came from having no declination entered. The real problem was a flip, when he switched from alt hold to stabilize.

He sent me a link to a video of that flight and the log file. I attached the log file and here is the video:


any idea?

I am not sure, if I posted the right log to the video. I think it could be this one.


still in the dark regarding the last crash… can anybody check this out?



I have had the same with my Quad (and Octo)
It only happens after an aggressive flight (or during)
In my case I guess it has been the battery.

The battery should be able to give the power needed for aggressive flight.
The engines use “limited” power when hovering etc.
When flying more aggressive, the power drain might be more than your lipo can handle.
30C / 40C etc…
In my case I have changed the batteries to a type which can handle higher currents and it did not happen again.

So at first check your battery and see if it can handle the consumption of all your engines at full throttle
If not replace the batteries for another type.


oups clicked on solved by mistake…

will check the battery current capacity.

[color=#008000]Set as “unsolved”.[/color]

I’m pretty sure i responded on another forum post or somewhere but just in case, i looked at your logs and it’s also a mechanical failure. the flight controller never asks for anything aggressive from the motors but the frame just flips which is most likely an issue with an ESC or motor failing…it could be some other type of power or mechanical failure, we can’t see that from the flight controller logs.

hey renaudbarbier,
i use 40 A t-motor esc. important, in default mode this esc cut throttle if minimum lipo voltage is reach. currently i have not the exact specs in my head. but it is important that you change this in esc setup. if i perform the compass calibration with motor throttle i noticed that some motors stop suddenly and other not if i pull up full throttle. the props was mounted backwards so the copter cant fly away. but after this experience i reprogrammed my esc to the lowest voltage cutoff level. sins i do that, i never get this effect. you have mounted big props. IMO your current is sometimes so high that lipo voltage drop under 3.3V per cell. than your esc s stop powering motors. not all at once mostly only 1 ore 2 motors. but in real flight this perform a crash as yours.

also you write that this happens after several minutes of flight time. that is one indicator more that your lipos reach the minimum voltage. i fly since 20 years helicopter and since 5 years electric helicopter. mostly it is not a good idea to make speed and full throttle tests if your lipo is at the end. this damage surly the lipo and sometimes the model:(.