New M2P Owner: Understanding IMU, Compass, and Magnetic Interference

[pchaps]

Givens: M2P, folding controller, Go4, MavMount, iPad Air 2 with 2x 80mm 5vdc cooling fans on back. I am reading the forums voraciously for info,
Solve: Mag Interference before 1st flight, flight postoned.
I am a new Mavic 2 Pro owner. After being present for a successful test flight by the seller (a police officer who flies 300RTK at work), I methodicaly went through a checklist before my first solo with the used M2P, I have flown other recereational drones for years but not used to this system. I immediately got a "Mag Intereference" warning and prudently postoned my test flight to learn more, and postpone the flight.

I see that the IMU and the compass (or two) are on-board the aircraft. I am now aware that my test flight LZ was on a concrete driveway, likely laced with rebar. Now I know thats problematic.
While I get ready to go to a grassy field for calibration, I have to wonder about my iPad has external cooling fans, I had to think that the 80mm 5vdc fan have motors may contribute to a magnetic intereference problem (which I did see when I powered up first time).

Seeing that magnetic interference warning message sent me down a rabbit hole of jaw-dropping learning about fly-aways! Did I say Im glad that I didnt take off? Golly.

Given the DJI folding controller / Go4 and MavMount with iPadAir2 tablet and a dual-fan 5v cooler on the back of the iPad, how can I best handle compass calibration?
1. I am going to a grassy field 5 miles away for the compass calibration.
2. Is the iPad itself introducing magnetic problems, even without the cooling fans? Is there a preferred way - perhaps with volume buttons up as that edge has the motherboard inside?
3. Is it realistic to keep the controller away from the aircraft when I calibrate the compass? ( I am working alone). How far away from the aircraft would I need to keep the iPad with the turned-off cooling fans to avoid mag intereference?
EDIT: At this point, I have installed Go4 but due to mag interference error, the controller cant seem to make initial connection to aircraft. Please advise.

Bonus points: is there an advantage to calibrating IMU indoors on a very hot day, to get into the airconditioning and onto a flat tabletop? Its about 100 F temp here today.

 

[Yorkshire_Pud]

Why are you thinking of an IMU calibration?
With an M2P/Z I have done that only once as far as I remember, though it may have taken two attempts for me to do it correctly.
I do not know if, in relation to IMU calibration, there is a temperature thing with the M2P, there is/was with the Phantom 3, but I imagine cooling the drone will not do any harm.

With regards to any magnetic field stemming from a fan motor that was cooling the iPad,I think that is highly unlikely to upset the drone. It might upset the compass in the iPad (if there is one) but you could probably test that independently of the controller by looking at the iPad's compass and you bring the fan closer to the iPad.

With regards to 1) etc. I would switch the drone on now and check if you still get a compass warning.
The range of interference is usually only a few ft.
To calibrate the drone's compass merely setting the controller down is probably sufficient to remove any influence that it has (if any) on the drone's compass, I may have even calibrated the done's compass with the controller hanging from a lanyard around my neck.

I haven't done it yet myself but I may start doing it/the-following. I have gathered, from some recent reading, that it may be wise to look (in the App's map/attitude-indicator) at the direction that the drone thinks it is pointing i.e. N, S, E, W and check that against a compass.

 

[Starz]

Calibration issues can be determined by looking in the app settings.
IMU not only needs a flat surface, but should be level also.

 

[KB9Radio]

I have had an M2Z for several years. I have never had to calibrate the IMU at all in that time. I originally had to calibrate the compass, and it ask almost every time I launched until I figured out it was the concrete I was attempting to takeoff from. I moved onto the lawn and never had the problem again. I later picked up a collapsible hoop style launch pad which is about 4 feet in diameter, and now use it all the time and it works great to keep the props from cutting the lawn. I know the natural thing to do is put it on the concrete, vehicle, deck of some sort, but most of those surfaces seem to have steel of some sort in them. I find dirt of some sort is best to takeoff from. As for compass calibration, all you have to be able to do is glance at the screen. Set it down where you can see it, and proceed. However I have never had a problem holding it, and then keeping the drone at arms length seems to work fine.

 

[Meta4]

how can I best handle compass calibration?
1. I am going to a grassy field 5 miles away for the compass calibration.
2. Is the iPad itself introducing magnetic problems,

You don't need to recalibrate the drone's compass or IMU, it's almost never necessary.
The warning you received after placing the drone on reinforced concrete, was a warning from the compass that the launch site was unsuitable.
It's not a warning of a problem in the drone and recalibrating it won't fix anything.
It's already working perfectly.
Forget about recalibrating things, it's not needed .

 

[pchaps]

Why are you thinking of an IMU calibration?
With an M2P/Z I have done that only once as far as I remember, though it may have taken two attempts for me to do it correctly.
I do not know if, in relation to IMU calibration, there is a temperature thing with the M2P, there is/was with the Phantom 3, but I imagine cooling the drone will not do any harm.

With regards to any magnetic field stemming from a fan motor that was cooling the iPad,I think that is highly unlikely to upset the drone. It might upset the compass in the iPad (if there is one) but you could probably test that independently of the controller by looking at the iPad's compass and you bring the fan closer to the iPad.

With regards to 1) etc. I would switch the drone on now and check if you still get a compass warning.
The range of interference is usually only a few ft.
To calibrate the drone's compass merely setting the controller down is probably sufficient to remove any influence that it has (if any) on the drone's compass, I may have even calibrated the done's compass with the controller hanging from a lanyard around my neck.

I haven't done it yet myself but I may start doing it/the-following. I have gathered, from some recent reading, that it may be wise to look (in the App's map/attitude-indicator) at the direction that the drone thinks it is pointing i.e. N, S, E, W and check that against a compass

Sure, I thought it would be prudent to do IMU and compass calibration as both M2P and Zoom are used and I don’t fully know their history. Is there a great risk to calibrating the IMU and compass of these two new aircraft in my fleet before I do commercial work with them?

Thanks for taking the time to write this very helpful response with some great info! I will go to a field and see if the magnetic interference issue is solved by location. I have to consider how this will affect my work. I travel hundreds of miles on assignment. I’m thinking that I would calibrate in empty fields near my work sites (after 50+ miles travel) rather than on-site where metal structures abound in and above ground. Perhaps you see that as unneeded but if there is little risk in calibration, and the possibility of averting a control issue and incident in an industrial site, then it seems reasonable.

I have flown a Phantom and Naza M v2 based quad from the same spot many times for years and never has an issue. Calibrated with a controller around my neck for 8 yrs. in fact I’ve calibrated compasses there and flown there perfectly. That being said, the M2’s are different systems and this line of learning has already prevented significant problems.

Drone U has a great Q&A about a flyaway at a construction site. Now I’m learning Go4 menus and understand not only magnetic interfence and RFI. Cheers!

 

[Meta4]

Sure, I thought it would be prudent to do IMU and compass calibration as both M2P and Zoom are used and I don’t fully know their history.

If the drones fly normally, recalibrating things won't make any improvement.
If they were poorly calibrated, you'd know as they wouldn't hover properly or fly straight.
Just leave them alone.

 

[Yorkshire_Pud]

I know of no risks in calibrating the IMU and Compass but could be wrong .......but if it's not needed why do it?

 

[KB9Radio]

Usually the compass calibration warning is to let you know that something weird seems to be messing with the compass reading. I've noticed that if you get out into the dirt/grass it always straightens out and is happy. A landing pad is used to keep things clean and the grass away. Mavic 2's have very short legs (none on the rear) and seem to pickup interference very easily. Once I started using a pad and taking off from the dirt/grass, it never asked to calibrate again.

 

[Starz]

no risks in calibrating the IMU

Depends on where the calibration is done. Flat and level surface is best.
I once saw some silly YouTube video where someone was doing an IMU calibration on a wooden picnic table in a park. Doubtful that DJI uses that type of platform in their factory.
The app will tell you if a problem exists.

 

[pchaps]

For those who follow: if you are ready to takeoff in a location where you get a “Magnetic Interference” warning in the controller, but then prompts/allows you to “calibrate compass” do NOT do it in that location. Consider that latter message as really saying: “don’t take off here”. If you choose to recalibrate, move to a nearby open field where there is less interference. Thanks to all who commented. I put the M2P on a wooden fern stand and at least it let me get into the app so that I can explore menus. Now I will work through the manual and menu pages. Cheers!