Help me figure out why the M2P crashed ?

[sar104]

The name Compass Error confuses people into thinking they have to "fix" their compass.
A compass error would more correctly be called a compass warning.

The confusion continues with very few flyers understanding what calibrating the compass actually does.

Exactly right - in these cases it's not the compass that's the problem - it's the local magnetic field.

 

[Dakrisht]

Exactly right - in these cases it's not the compass that's the problem - it's the local magnetic field.

This is such a critical and important aspect of the compass error alert. From reading other threads, many pilots including myself have confused this for simply re-calibrating the compass which is the wrong thing to do.

Costly mistakes but you learn your lesson.

Maybe some more education or awareness / alert on the DJI GO app would go a long way for magnetic interference alerts vs. the small red alert top-left...

 

[Dakrisht]

Here's an X-ray view of a sidewalk:

Steel reinforcing is standard for sidewalk construction in most places.
If it's constructed without reinforcing, it's going to crack horribly when subjected to any load or settling.

No .. the drone would have to be very close (maybe only a few feet) to the structural steel in the buildings.
But if the compass is just an inch or two away from a small steel item, that can do the damage.
Note in the image above, you might put the drone down in the centre of a square, or with the compass right above a crossing point, or where the mess panels are overlapped.
You don't know how much steel is within an inch or two of your compass.
Do you want to buy a ticket in that lucky dip?

Right on. Inches matter in these cases. Also, don’t launch off of sidewalks!

Seems that if I did a hand take off, we wouldn’t be here today!

 

[Starz]

Steel fabric isn’t used in sidewalk construction in Arizona. Must be different in other areas of the country. I’m guessing colder climate may be part of this.

 

[Meta4]

Steel fabric isn’t used in sidewalk construction in Arizona. Must be different in other areas of the country. I’m guessing colder climate may be part of this.

Steel reinforcing is very commonly used in sidewalks all over the world - at least where they want them to be durable and not crack up.
The climate has nothing to do with loading and strength.
In some areas they cut costs and put up with the cracking and heaving where only light loads are expected.
It's always a good assumption that any concrete surfaces will be reinforced since most are.

 

[Texbow]

Interesting post. So If I understand correctly the consenses is that if you receive a notice of magnetic interference, calibration of the compass is totally unrelated to that magnetic issue? The answer is to simply move your location until the magnetic interference notice on your controller clears?

 

[m0j0]

1) Take off was from a sidewalk, M2P initialized, initial compass error. Fixed after calibrating.

Here is my guess before i read the thread. Compass calibration after initial compass error is the problem. There was some mag interference. You calibrated in that interference then flew away from it. Crash... Now I will read what really happened and see just how wrong I am.

 

[sar104]

Interesting post. So If I understand correctly the consenses is that if you receive a notice of magnetic interference, calibration of the compass is totally unrelated to that magnetic issue? The answer is to simply move your location until the magnetic interference notice on your controller clears?

The message is often confusing, because it says calibrate or move. It could result from a change in the magnetic posture of the aircraft itself, which would require recalibration, it could be due to external magnetic interference, which is only fixed by moving the aircraft, or it could be the Mavic 2 simply demanding recalibration based on time and distance.

First step - check the aircraft orientation arrow to see if it is correct relative to north.

If it's wrong then move the aircraft to a location without interference, even that just amounts to holding it in the air - that should fix the direction arrow.

If it's correct then it's not interference, so check the interference levels shown in the GO 4 app. If those are in the green then it's probably just a Mavic 2 looking for recalibration. If they are high then recalibration is needed, which hopefully will fix it. If it doesn't, then something on the aircraft may have acquired enough magnetization to require demagnetizing before calibration will work.

 

[Meta4]

Here is my guess before i read the thread. Compass calibration after initial compass error is the problem. There was some mag interference. You calibrated in that interference then flew away from it. Crash... Now I will read what really happened and see just how wrong I am.

Read post #15

 

[m0j0]

The calibration was probably fine to begin with and fine after recalibration.

That's actually something I never considered.

 

[m0j0]

Read post #15

Wow! So I was wrong. The calibration likely did not cause the problem. Never thought of it like that. Learn something every day.

 

[Dakrisht]

Here is my guess before i read the thread. Compass calibration after initial compass error is the problem. There was some mag interference. You calibrated in that interference then flew away from it. Crash... Now I will read what really happened and see just how wrong I am.

That’s the ticket. I calibrated in a magnetic interference zone and after take off, even though there was no longer any mag interference, drone thought there was and went haywire.

DJI def needs to a bit more in terms of notification on mag interference - lots of pilots think that a simple calibration fixes this but it couldn’t be further from the truth.

 

[m0j0]

That’s the ticket. I calibrated in a magnetic interference zone and after take off, even though there was no longer any mag interference, drone thought there was and went haywire.

DJI def needs to a bit more in terms of notification on mag interference - lots of pilots think that a simple calibration fixes this but it couldn’t be further from the truth.

Well not really. The problem was the takeoff location. Lifting the Mavic off the ground probably took it out of the bad spot and made that calibration correct. Did you take off from the ground/surface? Would be interested to see what happens when you put a compass on the take off spot.

 

[Dakrisht]

Well not really. The problem was the takeoff location. Lifting the Mavic off the ground probably took it out of the bad spot and made that calibration correct. Did you take off from the ground/surface? Would be interested to see what happens when you put a compass on the take off spot.

Took off from the ground. Have taken off from plenty of sidewalks before. And as mentioned, did not notice the mag interference alert, rather the compass calibration error.

Given the severity of magnetic interference, it’s often difficult to identify at first glance especially when you have GPS trying to sync, compass calibration and add mag interference to the mix. A pop up like a high wind warning, etc. would be ideal.

 

[Texbow]

So the answer is if you receive a magnetic interference notification move your location until that is cleared then calibrate your compass if it's suggested to do so.

 

[m0j0]

So the answer is if you receive a magnetic interference notification move your location until that is cleared then calibrate your compass if it's suggested to do so.

No... if you receive an error move your bird and fly.

 

[Meta4]

Took off from the ground. Have taken off from plenty of sidewalks before.

Post #19 shows how you may have done this before without a problem but you can't see how close your compass is to reinforcing steel.
Every time you launch from reinforced concrete there is a risk.

did not notice the mag interference alert, rather the compass calibration error.

You mentioned .. initial compass error. Fixed after calibrating.
That was a warning of magnetic interference.
It says Magnetic field interference Move aircraft or calibrate compass.
But most people only notice the calibrate compass part which is unfortunate since calibrating the compass is not going to solve the problem.

Given the severity of magnetic interference, it’s often difficult to identify at first glance especially when you have GPS trying to sync, compass calibration and add mag interference to the mix. A pop up like a high wind warning, etc. would be ideal.

The first time you tried to launch and got the warning, there was so much steel close to the compass that it brought up the warning.
But after unnecessarily calibrating the compass (which made no difference to the compass or the magnetic problem), you put it down in a slightly different spot where there wasn't enough steel close enough to bring up a warning.
But there was enough steel close enough to your drone that when it initialised and determined where north is, it got a false north because of the magnetic field it was sitting in.
In those situations, you won't see a warning message because there isn't a strong enough magnetic influence to set it off.
But it's enough to do the damage to your initialisation.

That’s the ticket. I calibrated in a magnetic interference zone and after take off, even though there was no longer any mag interference, drone thought there was and went haywire.

DJI def needs to a bit more in terms of notification on mag interference - lots of pilots think that a simple calibration fixes this but it couldn’t be further from the truth.

Compass calibration is one of the most misunderstood things in drone flying.
This hasn't been helped by DJI telling people to recalibrate when moving to a new location when there is no physical need to.
It hasn't been helped by DJI now forcing some Mavic 2 users to recalibrate because they have moved or it's 30 days since they last calibrated.
There's no real reason for those at all. Why DJI have done that is a mystery.

This kind of thing makes some flyers mistakenly believe that calibrating the compass somehow fixes or makes the compass better.
That is completely wrong.

The compass needs to be able to read the earth's normal magnetic field where you are flying.
But the drone has it's own magnetic fields associated with steel components and electric currents and these could interfere with the compass and prevent it from properly doing its job.
Calibrating the compass just identifies and measures those magnetic fields that are part of the drone so they can be subtracted from the total magnetic field the compass reads.
That is so the compass reading is accurate.
If you don't modify your drone, the compass calibration should last a long time without needing to be done again.
My main drone has never had any calibration and is flying perfectly after more than 2.5 years.
If you think your drone is telling you to recalibrate, think again and read the warning carefully.
Unless it's one of the M2s that DJI have forced to ask for calibration, you probably only need to move the drone away from the magnetic interference it's warning you about.

 

[AnzacJack]

Steel fabric isn’t used in sidewalk construction in Arizona. Must be different in other areas of the country. I’m guessing colder climate may be part of this.

plenty warm down here and we certainly use steel in most concrete pouring, including sidewalks. Your local government may be skimping ;-)

 

[Dakrisht]

The first time you tried to launch and got the warning, there was so much steel close to the compass that it brought up the warning.

Ok makes sense and I agree.

Mag interference > warning > move away (correct procedure)

But after unnecessarily calibrating the compass (which made no difference to the compass or the magnetic problem), you put it down in a slightly different spot where there wasn't enough steel close enough to bring up a warning.
But there was enough steel close enough to your drone that when it initialised and determined where north is, it got a false north because of the magnetic field it was sitting in.

So even though the bird was placed in a slightly different spot which didn’t trigger a second mag interference warning it still went haywire because:

A) It was calibrated incorrectly / unnecessarily in / near a mag interference area?

Or

B) Magnetic interference was still present in the second spot, even though no warning?

In those situations, you won't see a warning message because there isn't a strong enough magnetic influence to set it off.
But it's enough to do the damage to your initialisation..

This is the tricky party. Determining with certainty that you are not in a mag interference zone before taking off. Before this thread, I wasn’t even aware of steel under concrete sidewalks, was under the impression that things such as cell towers, steel buildings, construction sites would be the cause of metal-based magnetic interference.

Guess I’m trying to figure out:

Even if the bird is calibrated and the compass is reading magnetic north correctly, how do we ensure that during flight or landing, low to the ground hover, etc. it doesn’t go insane and crash / lose magnetic position...

 

[Meta4]

So even though the bird was placed in a slightly different spot which didn’t trigger a second mag interference warning it still went haywire because:
A) It was calibrated incorrectly / unnecessarily in / near a mag interference area?
Or
B) Magnetic interference was still present in the second spot, even though no warning?

Your first location triggered the mag interference warning because there was a larger a amount of steel close to the compass.
The second was close enough to some steel to ruin the initialisation but not enough to trigger the mag interference warning

Your drone doesn't need normally calibration.
When you picked it up, you removed it from the magnetic field and calibrated it which made no change to the calibration it already had.
Then you put it back inside the magnetic field of the steel mesh which screwed up the initialisation and caused the incident

This is the tricky part. Determining with certainty that you are not in a mag interference zone before taking off.
Before this thread, I wasn’t even aware of steel under concrete sidewalks,

Being aware and avoiding reinforced concrete surfaces or anywhere that could be close to other steelwork, pipes, electric cables, nails or bolts in decking etc will keep you clear of almost all possible magnetic incidents.

was under the impression that things such as cell towers, steel buildings, construction sites would be the cause of metal-based magnetic interference.

Those big things won't have any effect off in the distance.
You have to get close before they upset your compass.
For a steel screw that might be an inch.
For a steel roof or a pile of steel on a construction site, it's something less than 10 feet.

Even if the bird is calibrated and the compass is reading magnetic north correctly, how do we ensure that during flight or landing, low to the ground hover, etc. it doesn’t go insane and crash / lose magnetic position...

If your launch point is magnetically clean, you'll have no magnetic worries in flight - steel on the ground or off in the distance has no effect.
And don't land on steel or reinforced concrete surfaces and your landings should be uneventful.