compass error

[2refi]

During flight with my Mavic pro I got the message "Compass error". It was in a session POI, 30 m AGL, radius 30 m. When I tried to increase the speed a little, the meassage ocurred. This happend twice from the same starting place. I have started from that pace many times witout any problems. It is the first time I get this message using the Mavic. I hope somebody can tell why it happend, and how to get the Mavic safely down again.

 

[Former Member]

It happens due to magnetic interference and can be terrifying when it happens while airborne. If a person is lucky, they can finesse the drone down. If not, it's going in big circles until it hits a tree.

The best way to avoid it is to calibrate your compass before every flight. If it continues to happen in the same place you have flown before many times without a compass error, it's possible that one of your compasses is malfunctioning.

 

[Machineshop]

There might be a high KP index, I use an app called HOVER and it has a measurement for the area you are in.
The Kp-index describes the disturbance of the Earth's magnetic field caused by the solar wind. The faster the solar wind blows, the greater the turbulence. The index ranges from 0, for low activity, to 9, which means that an intense geomagnetic storm is under way.
Low index, ok to fly, high index, probably risky.

 

[Former Member]

Cool.

 

[sar104]

There might be a high KP index, I use an app called HOVER and it has a measurement for the area you are in.
The Kp-index describes the disturbance of the Earth's magnetic field caused by the solar wind. The faster the solar wind blows, the greater the turbulence. The index ranges from 0, for low activity, to 9, which means that an intense geomagnetic storm is under way.
Low index, ok to fly, high index, probably risky.

I have never seen a log file showing magnetic distortion from a geomagnetic storm, and historical data show that significant magnetic field disturbance is incredibly rare. GPS reception is far more likely to be compromised than the earth's magnetic field, and I've never seen that either.

 

[Machineshop]

And here I thought I was smart for a change. Oh well.

 

[Meta4]

There might be a high KP index, I use an app called HOVER and it has a measurement for the area you are in.
...The index ranges from 0, for low activity, to 9, which means that an intense geomagnetic storm is under way.
Low index, ok to fly, high index, probably risky.

Since it's coming from the sun, if it had any effect, it would affect thousands of drone flyers at the same time.
We still haven't seen any evidence of the KP index having had any effect on any drone flight.
And yes, it wouldn't show up in your compass.

 

[Turn11]

If a person is lucky, they can finesse the drone down. If not, it's going in big circles until it hits a tree.

Question, IF ATTI mode were programmed into the MODE SWITCH, could an OP fly out of the situation? If windy I expect it would be pretty interesting to get home safe I expect.

 

[Former Member]

Question, IF ATTI mode were programmed into the MODE SWITCH, could an OP fly out of the situation? If windy I expect it would be pretty interesting to get home safe I expect.

I think the compass is still active in Atti mode, just the GPS is turned off. So, no Im not sure it would help!

 

[sar104]

I think the compass is still active in Atti mode, just the GPS is turned off. So, no Im not sure it would help!

ATTI mode doesn't use the compass, and so the aircraft will fly just fine in ATTI if compass errors occur in P-GPS. That's why the last resort of the FC when compass errors happen is to switch to ATTI.

 

[Former Member]

ATTI mode doesn't use the compass, and so the aircraft will fly just fine in ATTI if compass errors occur in P-GPS. That's why the last resort of the FC when compass errors happen is to switch to ATTI.

So, if a pilot is flying and his drone starts to do the toilet bowl, he should switch into atti?

 

[sar104]

So, if a pilot is flying and his drone starts to do the toilet bowl, he should switch into atti?

Absolutely. Immediately. If they have that modification implemented, of course, since the Mavic doesn't have a stock ATTI mode switch like the Phantoms.

 

[Former Member]

Absolutely. Immediately. If they have that modification implemented, of course, since the Mavic doesn't have a stock ATTI mode switch like the Phantoms.

How would a pilot manually switch into atti mode if the modification is not implemented and the drone is toilet bowling? This would be a good safety lesson for a midair loss of navigational guidance.

 

[sar104]

How would a pilot manually switch into atti mode if the modification is not implemented and the drone is toilet bowling? This would be a good safety lesson for a midair loss of navigational guidance.

Without that modification there is no mechanism on a Mavic to select ATTI mode. That's why I strongly recommend the modification, replacing either sport or tripod (on the M2). I replaced sport mode on my MP and M2P since you can also set the maximum pitch in ATTI mode to sport-mode values - just in case anyone feels they need it for performance in high winds.

 

[Former Member]

Without that modification there is no mechanism on a Mavic to select ATTI mode. That's why I strongly recommend the modification, replacing either sport or tripod (on the M2). I replaced sport mode on my MP and M2P since you can also set the maximum pitch in ATTI mode to sport-mode values - just in case anyone feels they need it for performance in high winds.

Sounds like if your compass goes out of calibration midflight, and you're in any mode without the mod, you're in for a rough ride.

 

[sar104]

Sounds like if your compass goes out of calibration midflight, and you're in any mode without the mod, you're in for a rough ride.

It's not going to go out of calibration in mid-flight - what typically happens is that it reads incorrectly at power up due to local magnetic interference and then incorrectly initializes the IMU yaw. After takeoff the magnetic interference goes away, the compass now reads correctly, but the IMU yaw is still wrong.

 

[Former Member]

It's not going to go out of calibration in mid-flight - what typically happens is that it reads incorrectly at power up due to local magnetic interference and then incorrectly initializes the IMU yaw. After takeoff the magnetic interference goes away, the compass now reads correctly, but the IMU yaw is still wrong.

Is it possible to have no error message when you take off, and then during the flight the drone starts the toilet bowl effect? Would this be an example of what you mention here?

 

[sar104]

Is it possible to have no error message when you take off, and then during the flight the drone starts the toilet bowl effect? Would this be an example of what you mention here?

That's how it generally happens. At takeoff the compass and IMU yaw values agree - as they must since the IMU yaw is initially just given the compass yaw value (+ local declination). Even though the yaw value is wrong the FC cannot know that, and so there is no error.

Unstable flight occurs once the compass starts reading correctly but the IMU yaw is still wrong - IMU yaw is primarily updated by the rate gyros with the compass just correcting for drift and bias, and it cannot reconcile a sudden change in compass reading without the rate gyros having recorded a similar rotation.

Toilet bowl flight, specifically, is a subset of the various types of unstable flight that occurs when the yaw error is around 90°.

 

[Turn11]

Are there any apps that would measure the presence of magnetic interference at a given location.
I am assuming the answer is no since I don't recall any mention in the past.

 

[sar104]

Are there any apps that would measure the presence of magnetic interference at a given location.
I am assuming the answer is no since I don't recall any mention in the past.

There are magnetometer apps, but there is a much simpler method - just ensure that the aircraft orientation arrow on the map screen is pointing in the same direction, relative to north, as the aircraft is actually facing. If it is then the IMU yaw value will be correctly initialized.