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Mavic Air 2 got crazy and crushed

Kotsos5

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Hello everybody yesterday I tried to fly my MA2 around 21.30, it told me compass error re-calibrate so I did and I got the success message, later when I lifted it I saw it didn't follow my commands and when I tried to call it down, it got a crazy turned right, started to speed up and lower and hit a tree. Here is the log file, can you see it and determine what might got wrong?
 
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Hello everybody yesterday I tried to fly my MA2 around 21.30, it told me compass error re-calibrate so I did and I got the success message, later when I lifted it I saw it didn't follow my commands and when I tried to call it down, it got a crazy turned right, started to speed up and lower and hit a tree. Here is the log file, can you see it and determine what might got wrong?

When you got the Compass error did you Turn Off the Drone and Move it to another Position and take off or did you just do the Calibration ?

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Kotsos5

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When you got the Compass error did you Turn Off the Drone and Move it to another Position and take off or did you just do the Calibration ?

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I don't remember if I close it but I think that I did the calibration the exact moment I got the error, and then I got the ok from the app.
 

sar104

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Okay - as expected that reveals what happened. At takeoff the aircraft's IMU heading was approximately west (285°), so it was nearly 90° off. That leads to the curved (a.k.a. toilet bowl) flight path as the FC's attempts to correct for positional drift lead it to apply those corrections orthogonally to the required direction.

heading.png

The problem was indicated before takeoff by the compass error message, but DJI doesn't explain that well. The problem was almost certainly not a bad compass calibration, but actually the compass reading incorrectly due to a local external magnetic field - probably metal under the takeoff surface. Rebar in concrete is a common source of that issue.

Calibrating the compass didn't change anything. Moving the aircraft to a different location (the extent of the magnetic interference is often just a few cm) might have fixed it, but in any case, the essential test before takeoff is to ensure that the indicated heading in the app agrees with the actual heading on the ground. Had you done that then you would have noticed that it was wrong.

For a more detailed discussion, if you are interested:

 

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I don't remember if I close it but I think that I did the calibration the exact moment I got the error, and then I got the ok from the app.
So this for me is the Human Error of the crash,

Whenever you get a Magnetic / Compass error it is imperative that you shut down the Drone and find another take off point to fix it.

The problem is once the Compass has been Hammered , nothing you can do to fix that until it Restarts the drone. and this happens to many pilots.

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slup

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...The problem is once the Compass has been Hammered , nothing you can do to fix that until it Restarts the drone.
Perhaps I'm not following your expression "Hammered" correctly ... but just to be clear, a compass deflected by magnetic disturbance will be corrected once away from the disturbance.

The IMU on the other hand, will not immediately correct itself if it have been initialized by a disturbed compass (if the AC isn't a M2 that haven't been moved since power on) ... in order to re-initialize the IMU a power cycling is needed.

... it's the wrongly initialized IMU that cause incidents like this.
 
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Kotsos5

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Perhaps I'm not following your expression "Hammered" correctly ... but just to be clear, a compass deflected by magnetic disturbance will be corrected once away from the disturbance.

The IMU on the other hand, will not immediately correct itself if it have been initialized by a disturbed compass (if the AC isn't a M2 that haven't been moved since power on) ... in order to re-initialize the IMU a power cycling is needed.

... it's the wrongly initialized IMU that cause incidents like this.
Ok some thoughts here, so you mean after a faulty compass indication and calibration I have to also re-calibrate IMU? Also do you also believe that If I have moved to another point I could fly the drone without recalibrating the compass but just by turning off and on the drone?
 

Thomas B

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Ok some thoughts here, so you mean after a faulty compass indication and calibration I have to also re-calibrate IMU? Also do you also believe that If I have moved to another point I could fly the drone without recalibrating the compass but just by turning off and on the drone?
1. No
2. Most likely if the magnetic interning substance was the out of proximity to your drone.
 

Kotsos5

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the essential test before takeoff is to ensure that the indicated heading in the app agrees with the actual heading on the ground
Can you please explain it more clearly? You mean that if I wanted to confirm that everything's ok then If I turned the drone right for example by holding it, will also show the indicator in the app turning right? So in my occasion with the interferenced compass If I turned it right while holding the app showed it is turning left for example?
 

sar104

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Can you please explain it more clearly? You mean that if I wanted to confirm that everything's ok then If I turned the drone right for example by holding it, will also show the indicator in the app turning right? So in my occasion with the interferenced compass If I turned it right while holding the app showed it is turning left for example?
You don't have to touch the aircraft to verify that the aircraft heading arrow shown on the app agrees with the direction that it is actually pointing (north, in this particular case). That's all that is needed - if that is correct then the IMU heading has been correctly initialized.

Ok some thoughts here, so you mean after a faulty compass indication and calibration I have to also re-calibrate IMU? Also do you also believe that If I have moved to another point I could fly the drone without recalibrating the compass but just by turning off and on the drone?
You have misunderstood @slup's post, and I'm guessing that you didn't bother to read the discussion that I linked to above either. When the aircraft is powered up the IMU heading is initialized by the compass. If the compass is wrong due to an interfering external magnetic field then the IMU is incorrectly initialized. That's fixed by restarting the aircraft away from the external magnetic field, not by calibrating the IMU.
 

slup

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...you mean after a faulty compass indication and calibration I have to also re-calibrate IMU?

No calibration of the IMU is needed ... I said IMU initialization.

It's the IMU that tells the flight controller in which direction the AC points during flight ... for this to work the IMU needs to be initialized to the correct & true direction ... that info is delivered by the compass in the power on moment. So if the compass is deflected due to magnetic disturbance during power on the IMU will be wrongly initialized ... in other words, the AC will not have the correct info about which direction it points.

To be sure that the IMU initialization have been done correctly ...

After powering on your drone, connected to your RC/app & placed it in the take-off spot ... but before lift-off, ALWAYS check that the drone icon on the map in your app is pointing equal in relation to other objects in the map as the drone does in reality ... if not, abort launch attempt, POWER DOWN & move away, power up again and repeat.

Below was your situation at take-off ... if the AC was pointed to North in reality, below is a clear indication that the IMU was initialized wrongly ...

1620598472180.png


Also do you also believe that If I have moved to another point I could fly the drone without recalibrating the compass but just by turning off and on the drone?

All a compass calibration does is to let the compass know the amount of magnetic disturbance that the AC internals generate ... so it can be deducted & let the compass measure the earth mag field correctly. So ... if you haven't added or taken off any equipment from the AC a compass calibration is rarely needed (some firmware's request a calibration each 30 days or depending on distance from the last power on location though ... but actually not needed due to those reasons).

So ... always distrust a compass calibration prompt in the app, always power down & move away do another take-off location & try again.
 
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Mike Mas

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Just not following all the "Cross Exam" to the pilot on which way the drone was pointing. It means absolutely nothing in this case regardless of which way the drone was pointing when it lifted off and has zero to do with the problem!

In decades of flying drones, I never once looked at its true direction and never lost a drone!

Be Nice!

Mike
 

DavidT_ NZ

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No calibration of the IMU is needed ... I said IMU initialization.

It's the IMU that tells the flight controller in which direction the AC points during flight ... for this to work the IMU needs to be initialized to the correct & true direction ... that info is delivered by the compass in the power on moment. So if the compass is deflected due to magnetic disturbance during power on the IMU will be wrongly initialized ... in other words, the AC will not have the correct info about which direction it points.

To be sure that the IMU initialization have been done correctly ...

After powering on your drone, connected to your RC/app & placed it in the take-off spot ... but before lift-off, ALWAYS check that the drone icon on the map in your app is pointing equal in relation to other objects in the map as the drone does in reality ... if not, abort launch attempt, POWER DOWN & move away, power up again and repeat.

Below was your situation at take-off ... if the AC was pointed to North in reality, below is a clear indication that the IMU was initialized wrongly ...

View attachment 128910




All a compass calibration does is to let the compass know the amount of magnetic disturbance that the AC internals generate ... so it can be deducted & let the compass measure the earth mag field correctly. So ... if you haven't added or taken off any equipment from the AC a compass calibration is rarely needed (some firmware's request a calibration each 30 days or depending on distance from the last power on location though ... but actually not needed due to those reasons).

So ... always distrust a compass calibration prompt in the app, always power down & move away do another take-off location & try again.
A very thorough reply. I have never experienced one of these problems with my Air 2. Do you have any recommendations (if time and reactions permit it) on an emergency stop sequence to avoid the flyaway or hitting the tree, if there is an issue with the IMU and/or compass - even if it means stopping the rotors completely (i.e. stalling the drone)?
 

sar104

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Just not following all the "Cross Exam" to the pilot on which way the drone was pointing. It means absolutely nothing in this case regardless of which way the drone was pointing when it lifted off and has zero to do with the problem!
Actually it has everything to do with the problem, because it confirms the incorrectly initialized IMU heading, which was the direct cause of the crash.
In decades of flying drones, I never once looked at its true direction and never lost a drone!
Provided that your luck holds, you may be happier being lucky than knowledgeable.
 

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Just not following all the "Cross Exam" to the pilot on which way the drone was pointing. It means absolutely nothing in this case regardless of which way the drone was pointing when it lifted off and has zero to do with the problem!
It appears that you don't know anything about a yaw error.
It's not the direction the drone was facing that's the problem.
He was asking to compare with the direction that was recordeded in the data.
If they are different, that indicates the cause of the problem.

Lots of drones have been lost because of this.
It's always better to learn from the misfortune of others than find out the hard way.
 
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Meta4

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A very thorough reply. I have never experienced one of these problems with my Air 2. Do you have any recommendations (if time and reactions permit it) on an emergency stop sequence to avoid the flyaway or hitting the tree, if there is an issue with the IMU and/or compass - even if it means stopping the rotors completely (i.e. stalling the drone)?
If you are ever unfortunate enough to suffer a bad yaw error, you probably wouldn't have any time to respond anyway and any attempted control imputs won't have much effect.
The speed is always a big shock.
It's best (and easy enough) to avoid getting into that situation.
 

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