Mavic Pro crash - Help appreciated to understand failure

[Sanmer]

Hi all,

Last month I was flying with a friend and we lost control of the aircraft. Fortunately we were able to bring it back close to our position and it crashed against some thin tree branches where it got tangled and luckily we could reach it. The only damage is on the propellers.

The drone has been landed since, and just recently I could get the .DAT file. It can be downloaded from this link:

87.02 MB file on MEGA

mega.nz

Any help in understanding what went wrong is greatly appreciated.

Thanks!

 

[Meta4]

The drone has been landed since, and just recently I could get the .DAT file.

It would be more helpful if you could post the .txt file from the phone or controller you used.

There are a couple of options ...

1. Go to DJI Flight Log Viewer | Phantom Help
Follow the instructions there to upload your flight record from your phone or tablet.
That will give you a detailed report on the flight data.
Come back and post a link to the report it provides and someone might be able to analyse it and give you an understanding of the cause of the incident.
or
2. Just post the .txt file here
or
3. If you use Airdata, you can view the flight data on Airdata and post a link for the Airdata report

 

[slup]

This is a yaw error... but not the typical where the craft have been powered on in a magnetic disturbed location which deflects the compass & initialize the IMU wrongly.

If checking off the compass & IMU at power on we see that they have the same value... that doesn't change major after take off. The main incident start later at 84sec into the flight when the craft already have flown 57sec on a 53m height. All this give clear evidence against a failed IMU initialization at the power on moment due to a disturbed compass.

If looking at the difference between the magyaw (compass) & the IMUyaw we see that initially all looks normal with a slight difference of approx. 7-8 degrees in average which is well within the normal. Then suddenly the deviation goes to over 40 degrees & the Flight controller switch to ATTI mode (green background in the chart)... & after this all goes haywire. The navHealth included in the chart give away what the flight controller thought about the positional reliability... 5 is best, 0 is worst & a HP isn't recorded if the value is below 4.

(Click on all charts below to make them larger)


So what's wrong then... If we try to compare the different sensor values for yaw to figure out which one that differ & likely is the culprit. Available for us is the magyaw (compass), the IMUyaw & the gyro.

We already see the difference between the magyaw & IMUyaw in the chart above... but which one is wrong?

Below I have chosen to depict IMUyaw unwrapped... meaning the graph is built by adding & subtracting degrees endlessly, it's not depicted on a 180 or 360 degree axis, this to be able to compare it with the gyro which is "unwrapped". Value wise the IMUyaw & the gyro will differ... this due to that the gyro always starts at 0 degrees when the drone is powered on while the IMUyaw will get it's value from the compass. But this at least let us compare the 2 graphs shape wise.

As seen here below the 2 graphs follow each other pretty well shape wise... which then should mean that the IMU & the gyro is the 2 correct ones & that the compass is the culprit.



This is also supported if looking into the DAT log event stream...



So the reason for the incident in this flight is most probably a failing compass... if it's temporary or permanent is hard to say just out from the DAT log alone unfortunately.

*ADDING*

Might add that this incident was a yaw-error under development. Since the IMUyaw was correctly initialized at power on & by that, the Flight controller had full knowledge about in which direction the drone was pointing, meaning no control issues had still occurred (over time it would have as the wrong compass values had slowly started to feed in IMU adjustments). What made the flight confusing & out of control was the ATTI mode itself... the OP lost horizontal hold & the drone drifted with outside forces affecting it & didn't provide any braking with stick release.

 

[GFields]

Sorry for your loss but hope that the above infromation helps

 

[samysys]

@Sanmer,

Can you still post the txt flight log here? I think @slup has already find out the cause but I wonder if the cause can be identified by studying the log.

 

[BudWalker]

Hi all,

Last month I was flying with a friend and we lost control of the aircraft. Fortunately we were able to bring it back close to our position and it crashed against some thin tree branches where it got tangled and luckily we could reach it. The only damage is on the propellers.

The drone has been landed since, and just recently I could get the .DAT file. It can be downloaded from this link:

87.02 MB file on MEGA

mega.nz

Any help in understanding what went wrong is greatly appreciated.

Thanks!

First a couple of questions.
1) Have you flown the MP since the incident. If so, were there problems on these flights and can you provide the .DATs for these flights?
2) If it's not been flown can you do a test? Power up but don't start the motors. Hold the MP straight out in front of you then turn (your body, not the MP) through 720°. Try to hold the MP level; i.e. don't let it roll or pitch. Next, lower your arms so that the MP is pitched down (say 30°) then rotate through another 720°. Next, do a compass calibration. Next do the two 720° rotations described above. Finally, please provide the .DAT
3) Have you recently attached an external device to the MP? Particularly to the rear of the MP. An external device can affect a compass.

A failed compass is a possibility but the data can also be due to a compass that needs calibration. Initially, there weren't any problems when the MP was headed North. Problems occurred as the MP turned South. A compass needing a calibration often is incorrect in some directions and not in others.

The MP actually has two compasses; one in the rear and one in the front. In this case the back compass was being used. Not the front compass which appears to be correct. Comparing the correct front compass magYaw(green) against the back compass magYaw error(black) it can be seen that the back compass magYaw error does not occur when the heading is between about -50° then clockwise through north to about 80°. Shown here with the white background.

The grey background are the opposite headings between about 80° then clockwise through south to about -50° where the magYaw errors do occur.
@slup