Help in crash Analysis - Suspecting compass problem


I´m not able to find the causes of this particular crash. It is a Quadcopter with 25Kg, Cube Black and 2 HERE2 serial GPS. Has a radar for height control (crop sprayer quadcopter). The copter went crazy in the moment when changed from LOITER to AUTO. I´m not sure if he flipped over before hitting the ground. The same copter made may flights before with no problems. We are having issues with Compass in Brazil due our week magnetic field (South Atlantic Anomaly). Boths GPSs are mounted outside the UAV in order to minimize interference.

Below the BIN file of this flight.!Am9EOGWyWxXqhOZJ3WGj0cBhlqaU9Q?e=FmivwE

I appreciate some help in tis case.

Tank you.

It looks like the quad was moving then started tipping over before you hit the motor emergency stop.
I cant see the actual cause, but I dont think weak magnetic field will cause that. You would probably benefit from doing the compass/motor calibration anyway.

Someone with more experience than I (and there are many) will need to check the log and see if the cause can be found.

I would probably set FENCE_ENABLE,1 so that you’re forced to wait for a good 3D fix before take-off.

There’s some motor mount twist, CW motors (3 and 4) are working harder to counteract some physical yaw issue with CCW motors (1 and 2). This wont be the cause of the crash, of course, but something to check.
You should set MOT_BAT_VOLT_MIN, MOT_BAT_VOLT_MAX and MOT_THST_EXPO according to the tuning docs
and use this spreadsheet to help

You will also benefit from setting up the harmonic notch filter.

Do you have T-Motor Flame ESCs? If so you’ll need to set these:

And then probably run autotune again without a load.

EDIT: and you can set these too:

For some reason a large Roll (~40°) was commanded when you switched to Auto. I’m not sure why this occurred:

But the result was the right side motors were commanded to ~max, left side dropped to compensate. I suppose as @xfacta suggested because you have a rather large mechanical Yaw bias it leaves less authority for stabilization:

The question is why the roll command (don’t know) but you should fix the yaw bias in any case.

BTW-What’s up with the Skydrones firmware?

@xfacta and @dkemxr, thank you very much for your time.

This particular crash is puzzling my mind (we have about 30 similar units flying). Could there be a monster coincidence that one of the propellers broke exactly at the AUTO switch time and made this tunneau roll ? It was flying OK in LOITER. I also noticed a GPS 2 set as primary near the AUTO event. What could this matter if GPS 1 and 2 are set to GPS_AUTO_SWITCH,2?

I will have to study to understand the yaw bias problem you pointed out. I was not aware of this possibility. On all copters with similar configuration I just used Autotune with 0.75 Aggressiveness with empty tank (copter about 15kg) and so far is working fine.

I use X8 Propulsion systems ( with 3090 propellers and 12S 16Ah batteries.


We operate in Brazil with crop sprayer UAVs whos firmware was updated to accomplish specific crop spraying tasks and updating Radar drivers. We made our own ground station specific to crop spraying market. This specific problem unit still used Cube Black but the new Pelicano 2021 product line uses Cube Orange and HERE3 GPS.

Some info here:

This is usually a mechanical problem from Motor mount/arm twist or frame distortion. It’s often seen on craft with round arms.

I recall seeing a post a couple months ago about the prop adapters failing on that motor/prop power system. Or maybe it was the fasteners, I don’t recall. It seems to me that @Corrado_Steri reported that.

I still wonder what was driving the large Roll command. What was broken when you recovered the craft? Of course this can be misleading as it could have broken upon impact.

Got, it, thanks for the explanation.

Edit: Here is the link about the prop adapter screw failure:

Thanks again.

Things are getting worse…

Today a brand new 25kg Hexacopter (Cube Black on 4.0.5.) had a very similar behavior. Is there a way to check if a ESC has failed? On time 13.28.2 was a “Potential Thrust Loss” and a very strong Roll left. All propellers and motors were OK after the crash. Nothing was broken… I´ll check tomorrow the hardware.!Am9EOGWyWxXqhOZWM5kT7gaKPtzBbg?e=A85zoH

This crash most probably was caused by a faulty Battery voltage sensor. The Thrust Loss was caused by an empty battery…