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Magnetic interference
202 16 7-19 21:49
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nullx8
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Thailand
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does anyone have some more "technical" idea about interference errors and what they can cause ?

as example, when taking off from a metal-based surface (eg. a car, or a parking building, traintracks whatever) the compass error is pretty normal.

so assuming the calibration was done before the error, once the Mavic is away from the object that does create the error, can i just assume "everything back to normal" ?

yes, i have read the manual!
7-19 21:49
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Geebax
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Australia
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No, you cannot assume everything will be normal once you move away, on the contrary, you could end up losing control of the aircraft.

Simply put, do not start up the drone anywhere near a source of magnetic influence, because that's when the damage is done. Taking off from a car roof, metal furniture or a concrete surface (containing reinforcing rod) will screw up the compass and probably cause loss of control of the aircraft.

However, if you started the drone from a 'clean' surface, then magnetic disturbance is very much less likely to affect your aircraft.

And compass calibration has absolutely nothing to do with the area or the surface you take off from, and calibrating it again will not solve the problem. The calibration function is provided so the processor in the aircaft can identify the metal components in the construction of the aircraft, and subtract them from the compass reading.
7-19 22:34
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Labroides
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does anyone have some more "technical" idea about interference errors

It's your compass warning you of a problem with your launch spot.
Switch off the drone, move away from the problem it's warning you about and start again.
7-19 22:42
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nullx8
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Labroides Posted at 7-19 22:42
does anyone have some more "technical" idea about interference errors

It's your compass warning you of a problem with your launch spot.

can't really do that mid-air ;)
7-20 04:29
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nullx8
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Geebax Posted at 7-19 22:34
No, you cannot assume everything will be normal once you move away, on the contrary, you could end up losing control of the aircraft.

Simply put, do not start up the drone anywhere near a source of magnetic influence, because that's when the damage is done. Taking off from a car roof, metal furniture or a concrete surface (containing reinforcing rod) will screw up the compass and probably cause loss of control of the aircraft.

well that's exactly the reason for my question .../ how would a "losing control" actually occur ?
since the compass has little to do with flight control, as ATTI mode is pretty much the same.

in fact, if you in-flight and you get a compass error .. this is exactly what happens .. the drone switches to ATTI .. but it doesn't when on the ground, well maybne it does but not exactly pointing it out as the Notification bar is busy telling me about the actual error.


the reason for this question is not me asking for a excuse to fly in a area where it's unsafe.

to give you a practical example, i use to take off from roofs of parking structures, and they almost always re-enforceds with steel in the concrete.

so i have to tip-toe around until i find a spot with no steel in the concrete.
however in like 99.9% of all times .. the second the Mavic takes off and is off the steel enforced concrete .. everything works perfectly .. (green bar)

all the text above assumes they the compass actually is properly calibrated before the drone encounters the surface of course.

like i said, i not looking for excuse to skip steps, knowing the technicals behind however can ease the mind.

like with the parking structure, i know there is no real compass error, it's just a beam of steel under me, 20cm altitude fixes it.

7-20 04:36
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Labroides
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nullx8 Posted at 7-20 04:36
well that's exactly the reason for my question .../ how would a "losing control" actually occur ?
since the compass has little to do with flight control, as ATTI mode is pretty much the same.

Now the details come out.
You aren't talking about simple magnetic interference warnings.
You are describing yaw errors which can be quite serious.

Your problem is launching from close to steel which can causes the compass to be deflected by the magnetic field of the steel.
The strength of the magnetic field is similar to the earth's magnetic field but the direction is different.
Because the strength is similar, it doesn't set off a compass error to warn you.

The gyros in the IMU are initialised based on the incorrectly reading compass.
After you launch and exit the magnetic field if you turn, the gryos disagree with the compass and you get your compass error.
That's followed by the drone dropping GPS and falling into atti mode and depending on the difference between the false compass reading and actual, the drone may zip away in an uncontrollable curved flight at high speed in the worst cases.

Don't launch from steel or reinforced concrete surfaces.
It's asking for trouble.


7-20 04:56
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JJB*
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nullx8 Posted at 7-20 04:36
well that's exactly the reason for my question .../ how would a "losing control" actually occur ?
since the compass has little to do with flight control, as ATTI mode is pretty much the same.

1/  RC/device ON
2/  Switch the drone ON holding it in your raised hand
3/  Auto take off
4/  Hover and check if compass heading is correct
5/ if compass heading is not correct ; don`t fly

PS  do not calibrate in such 'metal' area!

cheers
JJB
7-20 04:57
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HedgeTrimmer
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United States
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Duplicated
7-20 06:34
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HedgeTrimmer
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nullx8 Posted at 7-20 04:36
well that's exactly the reason for my question .../ how would a "losing control" actually occur ?
since the compass has little to do with flight control, as ATTI mode is pretty much the same.

"so i have to tip-toe around until i find a spot with no steel in the concrete."
"however in like 99.9% of all times .. the second the Mavic takes off and is off the steel enforced concrete .. everything works perfectly .. (green bar)"

Hand launch.  


Or launch from a non-ferrious object that is couple feet high.
Example: Once I was forced to launch from concrete driveway.  To avoid issues of magnetic interference, flipped a plastic tub upside down, and launched from it.

7-20 06:36
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DJI Stephen
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Hello there nullx8. Thank you for reaching out and for sharing these information with us. Please be mindful of the location where steel structures and concrete slabs are located when flying. These structures can caused signal interference when flying your DJI drone.  In addition, the said DJI drone can also pick up magnetic interference from the ground, and where you took off from close to a buildings with rebar concrete metal objects on it. Thank you.
7-20 22:06
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hallmark007
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The best way I can explain this is. If you put your Aircraft on the ground in normal circumstances, start it up, then lift it up and turn it 90 degrees to the right both your compass heading and IMU will both move together 90 degrees and no problems.
If you put your Aircraft on the ground and there is magnetic interference only the heading of your compass will change, your aircraft will still take off. But when it clears magnetic interference compass will then move to correct heading which you would think was great. But No, what happens is IMU is then conflicted and confused because of this sudden movement by compass.
7-21 02:11
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AG0N-Gary
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If you go back and read previous "fly away" threads, you'll frequently find in the end that they took off and had a compass error.  There have been plenty of "start it up, take off, and it takes off out of control" reports.  Insist on flying with compass errors will, more than likely, eventually lead to loss of your drone.
7-21 10:42
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nullx8
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Yes hand launch is usually what i do anyway, but with the googles on the head it's rather annoying to do
and parking structure roof's are just the perfect place for some quiet drone flying with googles .. especially in the morning when everyone is still asleep.
no one parks on the roof then anyway ;')
7-23 03:43
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nullx8
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AG0N-Gary Posted at 7-21 10:42
If you go back and read previous "fly away" threads, you'll frequently find in the end that they took off and had a compass error.  There have been plenty of "start it up, take off, and it takes off out of control" reports.  Insist on flying with compass errors will, more than likely, eventually lead to loss of your drone.

well, I would never fly away when the compass error would stay or the direction of the drone displayed on the controller not aligns with its actual direction. that's always the first thing to check.
7-23 03:49
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AG0N-Gary
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nullx8 Posted at 7-23 03:49
well, I would never fly away when the compass error would stay or the direction of the drone displayed on the controller not aligns with its actual direction. that's always the first thing to check.

But there have been several reports in the past of the pilot having no control after taking off with a compass error.  It just flies off into oblivion (or the garden wall).
7-23 22:01
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Peterx
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Germany
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Was that EM or FM error? The EM error is mostly on WIFI driven missions but on Occusync i dont know yet. Next week i´ll own a Mp1 and i´ll test it out on open field and on WIFI pleagued area.
7-24 03:19
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Labroides
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Australia
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AG0N-Gary Posted at 7-23 22:01
But there have been several reports in the past of the pilot having no control after taking off with a compass error.  It just flies off into oblivion (or the garden wall).

there have been several reports in the past of the pilot having no control after taking off with a compass error.
The whole problem is that they don't have a compass error when they take off.
The explanation is in post #6.
7-24 04:16
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