Help me figure out why the M2P crashed ?

[Meta4]

Magnetic interference should trigger a pop up similar to a high wind warning. Someone at DJI needs to hear this feedback.

If the magnetic influence is significantly stronger than the earth's normal magnetic field you do get a popup warning.
The trouble is that the a low strength magnetic field that can upset the initialisation is not necessarily much stronger than the earth's magnetic field but its orientation can be different from the earth's field.

 

[Simmo]

When you here those final 6 words......
'Please check it on the map'....
Dont just check that the H is around about where you are standing...
Check that the AC is pointing the same way physically on the ground, as it is indicated on the map.....

 

[Deleted member 95801]

As @Meta4 concluded, this was almost certainly due to a distorted magnetic field at the takeoff point. As it climbed out of the distorted field the IMU and magnetic yaw values diverged, and that's reflected in the disagreement between the IMU velocity and position.

View attachment 72452


It's the result of an unstable positive feedback loop in position control. Consider the situation where, as a result of a yaw error, the aircraft is facing north but the FC thinks it is facing south. Now imagine that a slight breeze from the south starts to push the aircraft to the north. The FC detects that motion to the north and knows that it needs to exert thrust to hold position. But, because it thinks it is facing south, it applies forward thrust (negative pitch). It's actually facing north so that exacerbates the drift to the north, and so it applies more forward thrust to compensate. Now you have uncontrolled linear flight to the north.

This and the video you posted below explains exactly what happened with my Mavic Pro last evening. It rose from the ground to about 20 feet, then started circling right into the Toilet Bowl Effect. I had no idea what was going on at the time. It responded well to my commands and I went for a 10+ minute flight. No warnings flashed on my screen and it landed fine when I brought it back. The ground I took off from was part of a parking lot.

Thank you so much for such a clear understanding of what is going on.

 

[Thomas B]

Magnetic interference should trigger a pop up similar to a high wind warning. Someone at DJI needs to hear this feedback.

But it needs to stay on the screen until fixed unlike the popup wind, etc warnings.

 

[Dakrisht]

But it needs to stay on the screen until fixed unlike the popup wind, etc warnings.

100%

 

[Billyboy72]

Your whole flight was done with GPS health of 0-1 (out of 5)
The data you posted doesn't show the crash.
It's a 24 second flight and the data just stops with the drone 47 feet up and flying at 18 mph.

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It looks like you lost connection before the interesting part started.


Fixed??
Your compass was warning you of a local magnetic field problem.
Re calibrating your compass couldn't possible "fix" the problem the compass warned you about.

The symptoms you describe are classic Yaw Error symptoms.
many similar stories have been reported from launching from reinforced concrete surfaces.
Launching from reinforced concrete surfaces is just asking for trouble.
It had nothing to do with the buildings and everything to do with initialising your mavic in a magnetic field, probably caused by steel reinforcing in the concrete sidewalk.

Yup side walks are a killer for GPS in most cases. Way too much steel rebar criss crossing like a tic tac toe boards on steroids.

 

[Billyboy72]

Sidewalks and concrete slabs have miles of steel rebar below them. Either hand launch or walk to the grass with a cheap landing pad is honestly the best way to avoid this. Or attempt to avoid depending on the area. My profile shot is a prime example of an

 

[Billyboy72]

Ugh!! My profile pic is an overhead shot of some of the worst with rebar and other interference issues. From steel rebar literally all over then the added saturation of wifi thru and thru I either have to leave to launch or take off from the middle of the parking lot if no cars happen to be in an open area.

 

[DanMan32]

I agree when stationary, GPS does not have a heading. But once you move a few feet, you now have a heading by comparing position A to position B. That can then be used to verify compass and apply appropriate compensation. I once had a phone that had GPS but no compass. Only way to get heading was to move, but I did get an accurate heading at that point on maps. Go app wants an accurate compass on the mobile if you want the map/radar to be heading up rather than north up.
Which leads me to another point. Checking if AC heading shown on map/radar agrees with actual heading may be difficult if you're not sure which way north actually is, and your mobile compass is out of calibration. They are notorious for losing calibration. But then they are usually around all sorts of magnetic interference.

As for my P3, I suspect either loose compass wiring, or needing degaussing.

 

[sar104]

I agree when stationary, GPS does not have a heading. But once you move a few feet, you now have a heading by comparing position A to position B. That can then be used to verify compass and apply appropriate compensation.

No - that's not correct - those are fully independent variables. The position difference gives velocity (speed and direction). It doesn't say anything about the direction that the aircraft is facing, because the FC has no way to know whether it is moving forwards, backwards or sideways.

I once had a phone that had GPS but no compass. Only way to get heading was to move, but I did get an accurate heading at that point on maps.

That's because you could visually determine your orientation relative to your direction of motion. The FC has no way to do that.