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Odd crash from in-flight compass error

mouseykins

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My poor Mavic is now in two pieces after experiencing a compass error seconds into flight. The specifics:
  • Mavic was placed on sunroof on top of a Range Rover. No compass errors reported during start-up
  • Mavic took off fine then immediately tilted in a sideways direction and flew out of control in an arc at speed
  • I attempted an emergency landing but only managed to fly smack into a wall, breaking one arm of the Mavic.
  • Flight logs show the compass error occurring and persisting from 2.9 seconds into flight
I understand metal from a vehicle can interfere with a compass but would have expected to see the warning during start-up. Could it be that because I was launching from the glass of the sunroof the compass was fine, then during take-off the metal of the vehicle started causing a problem?
 

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My best guess is the compass was pointing one way for north while you were on top of the car (due to the cars interference), then when you launched and put enough distance between drone and car suddenly the onboard compass snapped to true north confusing the drone?? either way launching the drone from a potential source of compass interference is not the best idea
 
My poor Mavic is now in two pieces after experiencing a compass error seconds into flight. The specifics:
  • Mavic was placed on sunroof on top of a Range Rover. No compass errors reported during start-up
  • Mavic took off fine then immediately tilted in a sideways direction and flew out of control in an arc at speed
  • I attempted an emergency landing but only managed to fly smack into a wall, breaking one arm of the Mavic.
  • Flight logs show the compass error occurring and persisting from 2.9 seconds into flight
I understand metal from a vehicle can interfere with a compass but would have expected to see the warning during start-up. Could it be that because I was launching from the glass of the sunroof the compass was fine, then during take-off the metal of the vehicle started causing a problem?
I don't have time to look at the log right now, but from what you say, it appears that your yaw value was initialized on the wrong heading. Thus even though the AC was facing say North, it thought it as facing say East. When you took off it tried to position hold by making little corrections based on it facing East. Those corrections were the wrong ones as it was actually facing North. It realized something was wrong but when it tried to correct for the deviation and hold position, it continued to correct in the wrong direction, resulting in your crash.
That's just my guess without looking at the logs. -CF
 
Whoa! Seriously? You launched from on top a a vehicle? I kind of figured myself, without actually daring to ever try it, that it might cause a seriously misaligned compass alignment on start-up. Oh wait....It seems it actually did! Sorry you verified my suspicions. Today's lesson for everyone: Stay well away from ferrous metal and magnetic sources during launch.
 
Whoa! Seriously? You launched from on top a a vehicle? I kind of figured myself, without actually daring to ever try it, that it might cause a seriously misaligned compass alignment on start-up. Oh wait....It seems it actually did! Sorry you verified my suspicions. Today's lesson for everyone: Stay well away from ferrous metal and magnetic sources during launch.
I would have suspected the same thing - if it's an issue to see a compass warning on start-up. Not after take-off.
 
I don't have time to look at the log right now, but from what you say, it appears that your yaw value was initialized on the wrong heading. Thus even though the AC was facing say North, it thought it as facing say East. When you took off it tried to position hold by making little corrections based on it facing East. Those corrections were the wrong ones as it was actually facing North. It realized something was wrong but when it tried to correct for the deviation and hold position, it continued to correct in the wrong direction, resulting in your crash.
That's just my guess without looking at the logs. -CF
Thanks. I agree, this does seem the most likely cause. Just a bit surprised I didn't receive a compass warning at start-up, it only occurred immediately after take-off. Lesson learned. Don't launch atop metal objects!
 
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Thanks. I agree, this does seem the most likely cause. Just a bit surprised I didn't receive a compass warning at start-up, it only occurred immediately after take-off. Lesson learned. Don't launch atop metal objects!

You typically won't get a compass error at startup, because the FC has no way to know that the measured magnetic heading is incorrect. It's only once it begins to fly that the problem manifests itself.
 
A quick way to check your compass is to look at the little radar map before launch. The radar icon should correspond to whichever way your drone is pointing in relation to the RC in your hands.
 
2 days ago, I launched my MA from the top of a concrete fire pit with a huge metal lid. DAH! The Compass Error warning came on, but I did not heed the alert. Needless to say as I was returning to Home manually, I hit auto return to Home..... and then it freaked out and crashed into a tree. Even though I tried my best to avert the object. I'd had the same COMPASS ERROR warning when attempting to launch anywhere near my truck. Had to reset the COMPASS. Lesson for beginners. Ground the aircraft if you get any alerts. Don't fly until you fix the alert. Otherwise it'll set you back the cost of the MA. Purchased a TESLA app to test any suspicious, doubtful launching areas. And there is common sense. You don't need to download that.
 
When thing get crazy hit the “pause” button and hover, rather than try to maneuver, then you have time to collect your thoughts and plan your next action rationally rather than reacting instinctively.
 
You typically won't get a compass error at startup, because the FC has no way to know that the measured magnetic heading is incorrect. It's only once it begins to fly that the problem manifests itself.

When hand launching a MP2 from the ship I'd always get a compass error. I'd launch and fly anyway and once the Mavic was away from the ship the error would go away. Never had any flight control issues when launching with the error, not sure why? Over 50 flights on that campaign.
 
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