Today I went out to test how the compass react to ferrous material just for fun and to learn how sensitive it is.
Some common ferrous metals include alloy steel, carbon steel, cast iron and wrought iron.
A ferrous metal is any metal that is primarily composed of iron and has magnetic properties.
A magnet will stick to ferrous material and will not stick to non-ferrous material.

In the pictures below you can see when I tested it against the big Bofors gun.

5 cm from main gun body.                                                         


1m from main gun body.



2m from main gun body.


3 m from main gun body


You should really never have to recalibrate to compass. 9 months ago I got my Mavic 2 Pro and calibratede it. I have since then flown over 100 times on various plases and never had to calibrate it.  Happy flying.

Its amazing how many times Ive gone to fly from the ground and got the recalibrate message only because there is metal thats hidden like rebar in concrete.   Always good to have a reference place that you know is good so you can check before a calibration.  If I think its in the ground I will take off and hover for 30 seconds low to allow the drone to catch up before setting off.

DAFlys Posted at 8-1 07:18
Its amazing how many times Ive gone to fly from the ground and got the recalibrate message only because there is metal thats hidden like rebar in concrete.   Always good to have a reference place that you know is good so you can check before a calibration.  If I think its in the ground I will take off and hover for 30 seconds low to allow the drone to catch up before setting off.

Yes. You can see the compass reading when you start and when you are taking off, so a couple of meters above ground you will see that you are OK. I was one a bit surprised when I took of from a small bridge, that I was sure was made of concrete with rebars in it as well as steel railings on either side, but that did not affect the compass at all. Perhaps the steel railings where to small and one meter away was enough not to effect the compass. To get recalibrate the compass, you would have to be in the red as there is no warning even if the yellow is quite large. It looks like it changes from yellow to re first at compass value of 500. I noticed that the IMU reading disappears when you start the prop's or take off.

very informative! thanks for the test.

Hello there kyalami. Good day and thank you for sharing these information with us here at DJI Forum. Have a safe and a happy flying always.

kyalami Posted at 8-1 08:12
Yes. You can see the compass reading when you start and when you are taking off, so a couple of meters above ground you will see that you are OK. I was one a bit surprised when I took of from a small bridge, that I was sure was made of concrete with rebars in it as well as steel railings on either side, but that did not affect the compass at all. Perhaps the steel railings where to small and one meter away was enough not to effect the compass. To get recalibrate the compass, you would have to be in the red as there is no warning even if the yellow is quite large. It looks like it changes from yellow to re first at compass value of 500. I noticed that the IMU reading disappears when you start the prop's or take off.

Steel reinforcement pops up in the strangest places,   Ive found it in sea walls and gravel paths,  both caught me by surprise.

DAFlys Posted at 8-1 07:18
Its amazing how many times Ive gone to fly from the ground and got the recalibrate message only because there is metal thats hidden like rebar in concrete.   Always good to have a reference place that you know is good so you can check before a calibration.  If I think its in the ground I will take off and hover for 30 seconds low to allow the drone to catch up before setting off.

Its amazing how many times
What's really amazing is how little people )who have been here for ages), understand about how their drone's compass
works.


Always good to have a reference place that you know is good so you can check before a calibration.
That doesn't check your calibration at all.
It just shows that the compass sensor works, but nothing about the calibration.
And if the compass didn't work you'd know without this "test".

If I think its in the ground I will take off and hover for 30 seconds low to allow the drone to catch up before setting off.
And that won't do a thing to prevent a runaway yaw error crashing your drone if you launch from the wrong spot.

FriedChicken_II Posted at 8-1 08:42
very informative! thanks for the test.

You are more than welcome and I also learned something on how the drone reacts and the distances. Of course, if the ferrous material is less that this huge cannon I am sure you can get closer. I will later do another test when I find something different to test on and see how sensitive the compass really is. So far I have not yet come a cross anything that has stopped my flying.

DAFlys Posted at 8-1 23:16
Steel reinforcement pops up in the strangest places,   Ive found it in sea walls and gravel paths,  both caught me by surprise.

Hi Da, yes, it is amassing. Just as a joke, perhaps the Mavic 2 Pro could be used for searching hidden treasures in the ground. Of course, no gold, silver or copper would be found. he he he he........  But then again, you could also use an ordinary hand compass for doing the same.

Did some further test today regarding the compass. One was on the top of metal roof of my car and one was on carpark above a shopping centre.
This was on the roof of my car. Have never see such high value.


This was about 0.5 on the ground away from the car



This was about 1m away from the car on teh ground and very good value.


This was on a roof car park above a shopping centre and away from the rebar on teh ground and between the rebars.


This is on the rebar itself and still quite good. Unfortunately I do not know the size of the rebar and how deep down it was. But I am sure this would not cause any problems.



It looks like putting the drone on the roof of the car when it went to a staggering 999 value caused it to wanted to be recalibrated, which was the frist time I had to do this and it is OK now.
I did this for my self just to learn a bit about what ferous materials can do to your drone and how carefull you should be. Happy and safe flying all.