Help interpret flight record

[gershee]

Flight record has been uploaded.
I took off and about 30 seconds in the flight the bird took off sideways FAST towards a tree and I couldn't control her. managed to get control of her and bring her down but what happened here?
Please help and thank you.

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[sar104]

It looks, superficially, like a yaw error, even though none were reported and the M2 has a firmware change that makes that less likely:




Can you pull the DAT file from the mobile device (FLY067.DAT)? That will have the necessary magnetometer data.

Mobile device DAT file: How to retrieve a V3.DAT from the tablet

 

[gershee]

It looks, superficially, like a yaw error, even though none were reported and the M2 has a firmware change that makes that less likely:

View attachment 76587


Can you pull the DAT file from the mobile device (FLY067.DAT)? That will have the necessary magnetometer data.

Mobile device DAT file: How to retrieve a V3.DAT from the tablet

Thanks for the quick reply.
Bird seemed to have taken off drastically at a heavy angle and didn't respond to controls. Managed to keep her in the air and land safely but this is NOT the first time this has happened.
Looking forward to the explanation. Thanks.

 

[sar104]

Firstly, it looks like your compass needs to be calibrated. Have you added any equipment recently?

 

[gershee]

Firstly, it looks like your compass needs to be calibrated. Have you added any equipment recently?

View attachment 76592

Added equipment? Nope. Stock.
I calibrate the compass whenever it tells me to. Every third flight or so depending..
How can you tell?
What else can you tell me?
Thanks again.

 

[sar104]

Added equipment? Nope. Stock.
I calibrate the compass whenever it tells me to. Every third flight or so depending..
How can you tell?
What else can you tell me?
Thanks again.

Look at the difference between the IMU yaw and the magnetic yaw, plotted above as a function of yaw. The 2π periodic variation is a dead giveaway that the magnetic field of the aircraft hasn't been subtracted out by calibration. And if it is telling you to calibrate that often then that, itself, suggests a compass issue. What do the interference values look like as you rotate the aircraft in the horizontal plane?

 

[gershee]

Look at the difference between the IMU yaw and the magnetic yaw, plotted above as a function of yaw. The 2π periodic variation is a dead giveaway that the magnetic field of the aircraft hasn't been subtracted out by calibration. And if it is telling you to calibrate that often then that, itself, suggests a compass issue. What to the interference values look like as you rotate the aircraft in the horizontal plane?

I often have the bird on inside of my van. This seems to always result in needing a compass calibration. That is the reason I calibrate so often, I believe.

 

[sar104]

I often have the bird on inside of my van. This seems to always result in needing a compass calibration. That is the reason I calibrate so often, I believe.

If you mean that you power it up inside your van then I would definitely recommend that you stop doing that.

 

[gershee]

If you mean that you power it up inside your van then I would definitely recommend that you stop doing that.

Well I dont power up the drone in the van preflight but there are times post flight I bring the drone into the van while it's still on, engines off though.

 

[BudWalker]

Firstly, it looks like your compass needs to be calibrated. Have you added any equipment recently?

View attachment 76592

If either the data before time = 0.0 or the data after time = 0.0 is ignored there doesn't appear to be a 2π periodic variation. As per usual Yaw-magYaw begins at about 0.0° but then changes to -11.8° to reflect a geoDeclination of 12.45°. The odd thing is that in the 12 secs before motor start the Yaw-magYaw changes to -30°.



Further, the FC didn't then attempt to correct this as you've observed in your experiments. During the 12 sec interval before motor start the M2 was being rotated CCW 100° by the pilot. At the beginning of the rotation Yaw-magYaw immediately reverted to 0.0°. Then, navHealth increased, first to 3 and then to 4 coincident with a large, incorrect, change in Yaw-magYaw.

Got all that? I think the FC got confused and the flight started out with an incorrect Yaw value which contributed to the IMU errors later.

 

[sar104]

If either the data before time = 0.0 or the data after time = 0.0 is ignored there doesn't appear to be a 2π periodic variation. As per usual Yaw-magYaw begins at about 0.0° but then changes to -11.8° to reflect a geoDeclination of 12.45°. The odd thing is that in the 12 secs before motor start the Yaw-magYaw changes to -30°.
View attachment 76658


Further, the FC didn't then attempt to correct this as you've observed in your experiments. During the 12 sec interval before motor start the M2 was being rotated CCW 100° by the pilot. At the beginning of the rotation Yaw-magYaw immediately reverted to 0.0°. Then, navHealth increased, first to 3 and then to 4 coincident with a large, incorrect, change in Yaw-magYaw.
View attachment 76659
Got all that? I think the FC got confused and the flight started out with an incorrect Yaw value which contributed to the IMU errors later.

I'm not convinced. If you remove the t < 0 data then the 2π periodicity is still there in my opinion:



And the change in the yaw error before motor start is due to the aircraft being rotated:



Or viewed in yaw space:




The reason that it doesn't get corrected, I suspect, is that the change doesn't occur on takeoff - when I ran the tests it only reset on takeoff.

 

[BudWalker]

I'm not convinced. If you remove the t < 0 data then the 2π periodicity is still there in my opinion:

View attachment 76664

And the change in the yaw error before motor start is due to the aircraft being rotated:

View attachment 76665

Or viewed in yaw space:

View attachment 76667


The reason that it doesn't get corrected, I suspect, is that the change doesn't occur on takeoff - when I ran the tests it only reset on takeoff.

You're right. I didn't notice the 360° rotation towards the end of the flight.

It's clear that the Yaw-magYaw error is dependent on Yaw.

 

[gershee]

I'm not convinced. If you remove the t < 0 data then the 2π periodicity is still there in my opinion:

View attachment 76664

And the change in the yaw error before motor start is due to the aircraft being rotated:

View attachment 76665

Or viewed in yaw space:

View attachment 76667


The reason that it doesn't get corrected, I suspect, is that the change doesn't occur on takeoff - when I ran the tests it only reset on takeoff.

So how do I avoid this in the future?
Calibrate compass and imu each flight?

 

[sar104]

So how do I avoid this in the future?
Calibrate compass and imu each flight?

I doubt that will help if you are already calibrating regularly. You didn't answer my question in post #6 about the compass interference value as you rotate the aircraft.

 

[jonthecourier]

So for those of use that never had any trouble and have only ever done any calibrations more that once, and the bird has never asked what should we read into this ????

 

[Thomas B]

In abscence of notifications from the drone or unexplained unusual flight activity, ....if it ain’t broke don’t fix it

 

[gershee]

I doubt that will help if you are already calibrating regularly. You didn't answer my question in post #6 about the compass interference value as you rotate the aircraft.

"What do the interference values look like as you rotate the aircraft in the horizontal plane?"

Sorry I'm not even sure what this means?
You want me to fly and rotate on horizontal plane and then upload data?

 

[sar104]

"What do the interference values look like as you rotate the aircraft in the horizontal plane?"

Sorry I'm not even sure what this means?
You want me to fly and rotate on horizontal plane and then upload data?

No - the compass interference display in the DJI GO 4 app. Like this - except the M2 only has one compass:

 

[gershee]

No - the compass interference display in the DJI GO 4 app. Like this - except the M2 only has one compass:

View attachment 76837

They seemed to fluctuate between 1-60 depending.
After a lot of movement the reading would stabilize and the number wouldn't fluctuate as much. The icon was always green and seemed strong and stable.

 

[sar104]

They seemed to fluctuate between 1-60 depending.
After a lot of movement the reading would stabilize and the number wouldn't fluctuate as much. The icon was always green and seemed strong and stable.

Those numbers are good - nothing there to explain the behavior. I need to look at one more thing in the DAT data. Standby