Getting compass error every time I try to take off from new location

[BudWalker]

The calibration will from my knowledge compensate for magnetic disturbances from the drone itself and local deviations. Most likely the World Magnetic Model is implemented to account for declination from true north. It is a complicated process that tries to make a sphere out of a twisted measured field.
A good link here that describes the process.

Magnetometer Calibration - MATLAB & Simulink

Magnetometers detect magnetic field strength along a sensor's X,Y and Z axes.

www.mathworks.com

Hakon

That's a nice reference. Another reference is
Compensating for Tilt, Hard-Iron, and Soft-Iron Effects

The calibration doesn't compensate for local deviations. It can only compensate for magnetic effects that are on the AC itself. The hard and soft iron effects mentioned in the reference are due to magnetic effects on the AC.

You might find this interesting. The MagData player in CsvView presents the magnetic field strength as a colored surface of a sphere. The effects of an uncalibrated compass are easily seen. It was a science fair project that never really proved to be useful. But, it's great eye candy.

MagData Player

 

[Thomas B]

Thanks for clarifying. That makes sense.
What is the best way to reset the mobile device compass on a 9.7” iPad Pro on iOS 10.3.3 ?
Does mounting the iPad on a metal ball used as the tablet holder contribute to this problem?
I use the Skyreat mount in the link below.

Amazon.com: Skyreat Mavic Mini Air Pro Foldable Aluminum Metal 4-12" Ipad Tablet Mount Holder for Dji Mavic 2 Pro, Mavic 2 Zoom/Mavic Pro/Mavic Air,Spark Accessories Remote Controller: Electronics

Buy Skyreat Mavic Mini Air Pro Foldable Aluminum Metal 4-12" Ipad Tablet Mount Holder for Dji Mavic 2 Pro, Mavic 2 Zoom/Mavic Pro/Mavic Air, Spark Accessories Remote Controller: Quadcopter Camera Mounts - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

Open the compass app that came oem with your device, open the compass pas app, follow the directions to calibrate it using the provided directions.

 

[HawkEye76]

So what do you guys do?

IF the map in the bottom right corner shows a proper orientation of the drone and IF the sensors do not show a high number for the compass or IMU, do you calibrate the compass?

I admit that I am sometime lazy, and if both mentioned above looks good, I've launched without doing a compass recalibration...

I do not fly before I have green ready to go. Even if it from a technical standpoint is not strictly needed I do calibrate. It is a bit annoying since you could possibly throw away a good calibration. I do check the heading afterwards.

 

[HawkEye76]

That's a nice reference. Another reference is
Compensating for Tilt, Hard-Iron, and Soft-Iron Effects

The calibration doesn't compensate for local deviations. It can only compensate for magnetic effects that are on the AC itself. The hard and soft iron effects mentioned in the reference are due to magnetic effects on the AC.

You might find this interesting. The MagData player in CsvView presents the magnetic field strength as a colored surface of a sphere. The effects of an uncalibrated compass are easily seen. It was a science fair project that never really proved to be useful. But, it's great eye candy.

MagData Player

View attachment 80974

You are quite right. A bit early in the morning for me. Local deviations are not accounted for.

 

[Brewbud]

Interesting. I have never been asked for a calibration (M2P). I am coming up on a year of ownership next month. The farthest away I have flown from is 38 miles away as the crow flies. I wonder if the required calibration distance makes a difference depending on what area of the world you are in.

 

[120CCPM]

Hi, sorry to review an old thread, but we were discussing this topic (in a very animated way) on the DJI Mavic Mini forum. The topic was whether location-based compass recalibration (enforced by the app, on the MM, as it seems it's also for the M2) has some scientific basis, or if it's just DJI being ultra-cautious, and covering up the mess of conflicting info on their manuals.
I have seen articles where, basically, they were saying that the calibration process would yield different results, depending on the strength and orientation of the Earth's magnetic field, which varies from place to place. I think elevation was also mentioned as a factor that influences the strength of the field itself. Have you heard/read anything in this respect?
I personally don't see why DJI would add this 30-mile (and 30-day) rule and force recalibration (which is a process that could go wrong, if done in the wrong place) unless they had a reason for it.

 

[gnirtS]

What is reason for electronic compass calibration? if anyone is interested enough. Discussion on types of sensor, calibration reasons and so on.

Older DJI devices did not require 30 mile/day recalibration *but* the Mavic 1 had dual compass setup whereas the M2 (no idea about mini) went down to a 1 compass setup. That might have something to do with it - unable to cross check etc.

Some of my other devices with electronic compasses vary wildly in how they handle it. My dive computer only wants calibration when you change the battery, an old Garmin GPS unit i have says the same.

However, my mobile phones and tablets (pretty much all i've ever owned) get inaccurate sometimes in minutes or hours and often need recalibrating daily or even more frequently to maintain any sense of accuracy.

Obviously phones and tablets tend to be moved a lot and come into contact with lots of magnetic materials (wires, loudspeakers, metal desks, cars, magnetic cases etc etc etc).

 

[sar104]

Hi, sorry to review an old thread, but we were discussing this topic (in a very animated way) on the DJI Mavic Mini forum. The topic was whether location-based compass recalibration (enforced by the app, on the MM, as it seems it's also for the M2) has some scientific basis, or if it's just DJI being ultra-cautious, and covering up the mess of conflicting info on their manuals.
I have seen articles where, basically, they were saying that the calibration process would yield different results, depending on the strength and orientation of the Earth's magnetic field, which varies from place to place. I think elevation was also mentioned as a factor that influences the strength of the field itself. Have you heard/read anything in this respect?
I personally don't see why DJI would add this 30-mile (and 30-day) rule and force recalibration (which is a process that could go wrong, if done in the wrong place) unless they had a reason for it.

The FC doesn't care about field strength as long as it's within a band of values, and the field strength isn't used to determine magnetic north - just the azimuth of the horizontal component. The only other thing it needs, to get true north (which it uses for navigation) from magnetic north, is the local field declination. But it cannot measure that from calibration - it has to compute it from its location and a global magnetic field model in the firmware.

So there isn't a credible reason to require calibration just because location changes, and DJI hasn't even uniformly recommended this across the different models. I peripheral reason might be the concern that the compass is more likely to get magnetized during transport. Similarly there may be concerns with drift over time when not used. I've never seen a satisfactory answer to the question.

 

[120CCPM]

The FC doesn't care about field strength as long as it's within a band of values, and the field strength isn't used to determine magnetic north - just the azimuth of the horizontal component. The only other thing it needs, to get true north (which it uses for navigation) from magnetic north, is the local field declination. But it cannot measure that from calibration - it has to compute it from its location and a global magnetic field model in the firmware.

So there isn't a credible reason to require calibration just because location changes, and DJI hasn't even uniformly recommended this across the different models. I peripheral reason might be the concern that the compass is more likely to get magnetized during transport. Similarly there may be concerns with drift over time when not used. I've never seen a satisfactory answer to the question.

Understood. The point was more about the calibration process itself being affected by strength and direction of the Earth magnetic field. As if the parameters used for compensation would vary based on where calibration was performed. You calibrate where the field is strong, you get certain compensation values. Or you compensate at sea level and you get different values from the top of a mountain. Clearly this must be a minor thing (if anything), as many never calibrate the compass and it works just fine. But it puzzles me that DJI went as far as enforcing it on some drones and not others, also considering that this would push people to calibrate in non-ideal conditions.

 

[sar104]

Understood. The point was more about the calibration process itself being affected by strength and direction of the Earth magnetic field. As if the parameters used for compensation would vary based on where calibration was performed. You calibrate where the field is strong, you get certain compensation values. Or you compensate at sea level and you get different values from the top of a mountain. Clearly this must be a minor thing (if anything), as many never calibrate the compass and it works just fine. But it puzzles me that DJI went as far as enforcing it on some drones and not others, also considering that this would push people to calibrate in non-ideal conditions.

The calibration is actually to determine the magnetic field of the aircraft itself - it's not about the external (earth) magnetic field. And so the earth's field, in terms of strength and direction, has no effect at all on the calibration process.

 

[120CCPM]

The calibration is actually to determine the magnetic field of the aircraft itself - it's not about the external (earth) magnetic field. And so the earth's field, in terms of strength and direction, has no effect at all on the calibration process.

Ok, thank you. I'll report that back to the MM DJI Forum.