Compass error when launching from ship

Gringorio · Oct 17, 2021

Just wanted to show the compass error I get when launching from the ship. This has happened many dozens of times in many locations and conditions with no issues during the flights. The error occurs with hand launches too and returns upon hand catch on the ship. This is with the Mavic 2 Pro. Sharing for discussion purposes since is it an error I ignore as it corrects itself once away from the ship. I'm not looking for solutions as there are none. I just find it interesting.

eEridani · Oct 17, 2021

Do some Googling for compass errors on board ships - it's been a problem since the invention of the magnetic compass hundreds of years ago. Today's ships, way too much metal. Probably a good idea you aren't calibrating before launch.

sar104 · Oct 17, 2021

Gringorio said:
Just wanted to show the compass error I get when launching from the ship. This has happened many dozens of times in many locations and conditions with no issues during the flights. The error occurs with hand launches too and returns upon hand catch on the ship. This is with the Mavic 2 Pro. Sharing for discussion purposes since is it an error I ignore as it corrects itself once away from the ship. I'm not looking for solutions as there are none. I just find it interesting.

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The M2P has firmware that detects and corrects for magnetic errors provided certain conditions are met. Specifically, it must be powered up and not moved before launch. When it takes off and the magnetic heading changes as it leaves the region of magnetic interference while the rate gyros detect no rotation, it resets the heading to match the new magnetic heading. This post and thread illustrates the process:

Compass error demonstration

Ok my apologies, I don’t own a Mavic but I know how my phantom standard and i1 reacted in these exact same locations, pix below. With a compass error. I was totally wrong for flying in these areas but I clearly remember how my drones reacted after take off. I had to walk out of the block to keep...

mavicpilots.com

But that's not what your video appears to show, since the initialized heading before takeoff seems to be correct. The magnetic error is likely due to the magnetic modulus being out of range. That functionality is explained in this post:

A short explanation of compass function, calibration and errors.

BACKGROUND The aircraft compass is often misunderstood, both in terms of function and purpose, but it is important to understand what the compass measures, why, and what happens to that information. At the most basic level the purpose of the compass is to measure the earth’s magnetic field in...

mavicpilots.com

Sparky76 · Oct 18, 2021

I tried to launch my Mini2 from the roof of my car, same issue, too much metal and get the "need to calibrate compass" message. Get 10 feet away and it's fine.

Capt KO · Oct 18, 2021

If the compass is calibrated and correct before getting on board, it will correct itself after it leaves the ship. Same as on land if you're in a magnetic interference area. It also happens with my truck.

sar104 · Oct 18, 2021

Capt KO said:
If the compass is calibrated and correct before getting on board, it will correct itself after it leaves the ship. Same as on land if you're in a magnetic interference area. It also happens with my truck.

Not necessarily. It depends on the model and how it is powered up. The real problem arises if the aircraft is powered up and the IMU heading is incorrectly initialized by the compass due to magnetic interference. When the aircraft leaves the ship the compass will become correct, but only certain DJI models and firmware versions have the ability to recognize the situation and correct the IMU heading when that happens.

MAvic_South_Oz · Oct 18, 2021

sar104 said:
When the aircraft leaves the ship the compass will become correct, but only certain DJI models and firmware versions have the ability to recognize the situation and correct the IMU heading when that happens

Could you list models that do this ?
It wouldn’t be easy to find elsewhere, and could be helpful to know for very rare flight situations.

sar104 · Oct 18, 2021

MAvic_South_Oz said:
Could you list models that do this ?
It wouldn’t be easy to find elsewhere, and could be helpful to know for very rare flight situations.

The only one that I can confirm is the Mavic 2 series. The Mavic Pro did not have this capability. And while I'd have expected the more recent models to have included it, that is not obvious, at least based on numerous reported flight problems caused by compass errors.

MAvic_South_Oz · Oct 18, 2021

sar104 said:
The only one that I can confirm is the Mavic 2 series. The Mavic Pro did not have this capability. And while I'd have expected the more recent models to have included it, that is not obvious, at least based on numerous reported flight problems caused by compass errors.

That certainly is a brilliant feature, and you'd think it would be included in more recent models.
Hopefully something for analytics people to keep an eye out for when looking at those particular crash (fly off) threads.

Gringorio · Oct 18, 2021

sar104 said:
The M2P has firmware that detects and corrects for magnetic errors provided certain conditions are met. Specifically, it must be powered up and not moved before launch. When it takes off and the magnetic heading changes as it leaves the region of magnetic interference while the rate gyros detect no rotation, it resets the heading to match the new magnetic heading. This post and thread illustrates the process:

Compass error demonstration

Ok my apologies, I don’t own a Mavic but I know how my phantom standard and i1 reacted in these exact same locations, pix below. With a compass error. I was totally wrong for flying in these areas but I clearly remember how my drones reacted after take off. I had to walk out of the block to keep...

mavicpilots.com

But that's not what your video appears to show, since the initialized heading before takeoff seems to be correct. The magnetic error is likely due to the magnetic modulus being out of range. That functionality is explained in this post:

A short explanation of compass function, calibration and errors.

BACKGROUND The aircraft compass is often misunderstood, both in terms of function and purpose, but it is important to understand what the compass measures, why, and what happens to that information. At the most basic level the purpose of the compass is to measure the earth’s magnetic field in...

mavicpilots.com

Thanks for the explanation and links!