For two days ago, I carried out a waypoint flight at night to check if it worked to use a previous planned WP mission at night and also to see if I could use Night mode when using WP.  Both were successful, but I encountered several warnings about compass needing calibration.  I thought this might have to do with the recent update, so I carried out the calibration and did my flight.
It is also important to say that this exact takeoff point is one that I frequently use a lot as it is on a manhole cover (which makes it level) in the middle of a park lawn.


Yesterday, I did a flight during daytime from the same spot and got no warning, but I also tried the same later yesterday from the same spot to do another night session.  I then got the same warning to calibrate, but when I moved away from the manhole the warning disappeared.  Trying to start from the manhole again, the message reappeared, but I also got a new message about avoiding metal or magnetic objects.


For both messages, see enclosed pictures.

What I find strange is that I have been taking off from the same spot a lot of times (during daytime), but get this problem during night (very dark as yo may see from one of the pictures - that even is in night mode).

My question is if the drone is more prone for such problems when taking off in the dark, or if this may be related to something else.

With regards to the low light warning, touch the "unable to take off" title and see if that opens a drop down menu. If so, make any required aknowledgements and acceptances and see if that 'problem' disappears.

BUT BE WARNED, DO NOT take off until the GPS icon is white.
If you launch the drone in poor light, with insufficient GPS, the drone is likley to switch to ATTI mode.
Also be aware that GPS ONLY position holding is NOWHERE near as good as that provided when VPS works, so DO NOT fly near objects etc. and remember you may not have OA.


I get the low light warning and that block nearly every indoor flight but once the drone is airborne the drone 'realises' that the lighting is sufficient for the VPS to work.
Outdoors, in true darkness, may be a different matter.

Almost certainly the compass problems are caused by the manhole cover. The geomagnetic filed is distorted in the vicinity of the cover.

You answered your own question when you mentioned taking off from a manhole cover.  A huge chunk of ferrous steel is a terrible location from which to launch.

BudWalker Posted at 9-8 06:46
Almost certainly the compass problems are caused by the manhole cover. The geomagnetic filed is distorted in the vicinity of the cover.

If I hadn't experienced the same thing several times in a variety of environments, none of which had any magnetic interference, I would have agreed.
But this has happened to me in different spots and no amount of compass calibration made any difference.
Neither did moving the drone to other places.
The drone's orientation was always displayed correctly.

It wasn't until I clicked on the warning and saw the specific mention of being unable to take off in low light environments that I was able to launch by illuminating the area around the drone.
I don't know why it only happens sometimes, but I know it has nothing at all to do with the compass or magnetic interference.

There is no reason that the drone shouldn't be able to launch in the dark (and it usually will).
There is no reason for DJI to bring up a compass warning because of low light, but they sometimes do.
DJI has really fouled up with this one.

As I explained in the post above and as your description confirms, this particular issue wasn't related to the manhole cover.

But despite that, launching from on or close to iron or steel objects is very risky and should be avoided.
It can cause serious incidents that often involve uncontrollable high speed flight that ends in a violent crash.
In most of those cases you wouldn't get any compass warning, but the cause of the incident that confirms it was a result of magnetic interference at startup could be seen in the recorded data for the flight.

Don't launch from iron or steel, including reinforced concrete which is full of invisible steel reinforcing and is the most common source of the issue.

BudWalker Posted at 9-8 06:46
Almost certainly the compass problems are caused by the manhole cover. The geomagnetic filed is distorted in the vicinity of the cover.

If that is the case, why did this just happen when it was dark and not the other 20 times I have taken off from the same place in daylight?

Dirty Bird Posted at 9-8 09:29
You answered your own question when you mentioned taking off from a manhole cover.  A huge chunk of ferrous steel is a terrible location from which to launch.

The only time I had a problem was when it was dark, not the 20 other times taking off from the exactly same spot.

Labroides Posted at 9-8 15:35
As I explained in the post above and as your description confirms, this particular issue wasn't related to the manhole cover.

But despite that, launching from on or close to iron or steel objects is very risky and should be avoided.

This has only been a problem when it was dark, not otherwise, and I have never experienced any strange behaviour (and the first time i experienced it, I calibrated the compass and took off from the manhole).

Sean-bumble-bee Posted at 9-8 06:23
With regards to the low light warning, touch the "unable to take off" title and see if that opens a drop down menu. If so, make any required aknowledgements and acceptances and see if that 'problem' disappears.

BUT BE WARNED, DO NOT take off until the GPS icon is white.

I have only done this related to an earlier planned Waypoint mission, and it definitely is without obstacles.  It also flew the mission perfectly (and using Night Mode).
I will definitely check next time to see what indformation I get pressing the warning symbols, and I will never take off unless I have a required numer of satelites, because I assume this is the way way to loose (or crash) your drone.

fgange57 Posted at 9-9 00:34
I have only done this related to an earlier planned Waypoint mission, and it definitely is without obstacles.  It also flew the mission perfectly (and using Night Mode).
I will definitely check next time to see what indformation I get pressing the warning symbols, and I will never take off unless I have a required numer of satelites, because I assume this is the way way to loose (or crash) your drone.

I will never take off unless I have a required numer of satelites, because I assume this is the way way to loose (or crash) your drone.
What is the "required number"?
Trick question .... because there's no required number.
You just need the drone to let you know that it has full GPS reception  (the GPS icon has turned white).
But there's no single number at which that happens.

Also ..  waiting for GPS won't ensure that you don't lose or crash your drone.
For instance, if you'd powered up somewhere that magnetic interference caused a yaw error, your drone could still zoom away uncontrollably and crash, even if you waited for full GPS reception.

fgange57 Posted at 9-9 00:27
If that is the case, why did this just happen when it was dark and not the other 20 times I have taken off from the same place in daylight?

I think the way it works is the Flight Controller tries to use the "visual compass" if it decides it doesn't trust the magnetic compass. A "visual compass" has been around since, I think, the Mavic 2. The magnetic compass is preferred. So if neither is available the FC asks you to fix the problem with the magnitic compass.

Labroides Posted at 9-8 15:26
If I hadn't experienced the same thing several times in a variety of environments, none of which had any magnetic interference, I would have agreed.
But this has happened to me in different spots and no amount of compass calibration made any difference.
Neither did moving the drone to other places.

Although the orientation may be correct the FC can decide it can't trust the magnetic compass. The geomagnetic distortion caused by ferrous material (e.g. manhole cover) is characterized by both errors in direction and errors in field intensity. For any given point in the distortion just one, both or none of these errors can exist. (Overall, these errors have to sum to 0.0).

  

The FC can't know if a direction error exists. This can only be detected by the pilot seeing that the heading indicator shown on the map is incorrect.

  

However, the FC can determine if a field intensity error exists. If so, the FC tries to switch to the "visual compass". If it can't do that it asks the pilot to fix the magnetic compass.

Dirty Bird Posted at 9-8 09:29
You answered your own question when you mentioned taking off from a manhole cover.  A huge chunk of ferrous steel is a terrible location from which to launch.

I'm glad the OP mentioned that...

but Yeah, OP-find somewhere else to launch. It needn't be a perfectly level spot...or take a bit of a mat- apiece of carpet turned upside down on the grass-etc... or just launch from your hand.

otherwise, if the problem goes away, and you're positive it wasn't the manhole cover, consider it was caused by the aurora (space weather being at high fluxes this year)  or even the Russians testing a new drone interference...

BudWalker Posted at 9-9 06:07
Although the orientation may be correct the FC can decide it can't trust the magnetic compass. The geomagnetic distortion caused by ferrous material (e.g. manhole cover) is characterized by both errors in direction and errors in field intensity. For any given point in the distortion just one, both or none of these errors can exist. (Overall, these errors have to sum to 0.0).  The FC can't know if a direction error exists. This can only be detected by the pilot seeing that the heading indicator shown on the map is incorrect.   However, the FC can determine if a field intensity error exists. If so, the FC tries to switch to the "visual compass". If it can't do that it asks the pilot to fix the magnetic compass.

I understand the OP was launching from a manhole cover but the instances where this has happened to me (5 or 6 times in the last year in different locations hundreds of miles apart), there was absolutely no magnetic interference in the vicinity and the compass warning was completely false.

No amount of recalibration and moving the drone to other locations made any difference.
Once I worked out the low light aspect and illuminated the area around the drone, I was able to launch.

BudWalker Posted at 9-9 05:47
I think the way it works is the Flight Controller tries to use the "visual compass" if it decides it doesn't trust the magnetic compass. A "visual compass" has been around since, I think, the Mavic 2. The magnetic compass is preferred. So if neither is available the FC asks you to fix the problem with the magnitic compass.

This makes a lot of sense.  Thank you for your input.

Labroides Posted at 9-9 04:41
I will never take off unless I have a required numer of satelites, because I assume this is the way way to loose (or crash) your drone.
What is the "required number"?
Trick question .... because there's no required number.

To me, a "required number" is easy.  Just as you said, when the GPS icon has turned white (and I happily wait a little longer to gather even some extra satellites).

Do you have any experience where magnetic interference where the drone got uncontrollable?

In any case, what I will do next time I am at my training ground, I will use a magnetometer I have on my phone to compare the magnetic signal on the manhole and compare it with what I find some meters away (in fact, I just have to move one meter aside for this message to disappear.

BudWalker Posted at 9-9 05:47
I think the way it works is the Flight Controller tries to use the "visual compass" if it decides it doesn't trust the magnetic compass. A "visual compass" has been around since, I think, the Mavic 2. The magnetic compass is preferred. So if neither is available the FC asks you to fix the problem with the magnitic compass.

I will check the "problem spot" with a magnetometer app I have on my phone and compare it with reading a few meters around (and will update this thread with my findings)

Hi there, we apologize for the inconvenience. Please proceed to restart the device and could you check your firmware if they are showing the latest version as of below.

Date: 2024.09.05
Aircraft Firmware: v01.00.0700
Remote Controller Firmware: v02.07.0000 (DJI RC 2)
                                                     v01.01.0300 (DJI RC-N2)
DJI Fly App iOS: v1.14.0
DJI Fly App Android: v1.14.0

Looking forward to your reply.

fgange57 Posted at 9-9 00:34
I have only done this related to an earlier planned Waypoint mission, and it definitely is without obstacles.  It also flew the mission perfectly (and using Night Mode).
I will definitely check next time to see what indformation I get pressing the warning symbols, and I will never take off unless I have a required numer of satelites, because I assume this is the way way to loose (or crash) your drone.

"and I will never take off unless I have a required numer of satelites, because I assume this is the way way to loose (or crash) your drone."

In a night flight that would be true..... or be prepared to handle ATTI mode.
But in daylight I often launch with insufficient GPS, the ground being in a GPS shadow and a little height gets the drone into good GPS reception. With such flights IT MUST be remembered that the homepoint will often not be set to the take off point, it will be set to where ever the drone first gets sufficient GPS.
I then bring the drone overhead abd reset the homepoint to the drone's location.

"To me, a "required number" is easy.  Just as you said, when the GPS icon has turned white " great answer.

fgange57 Posted at 9-10 00:00
To me, a "required number" is easy.  Just as you said, when the GPS icon has turned white (and I happily wait a little longer to gather even some extra satellites).

Do you have any experience where magnetic interference where the drone got uncontrollable?

Do you have any experience where magnetic interference where the drone got uncontrollable?
I have analysed the flight data for many yaw error flights and know well how they happen and what the results are.

I have never had one myself because I know to avoid the circumstances that create that problem.


In any case, what I will do next time I am at my training ground, I will use a magnetometer I have on my phone to compare the magnetic signal on the manhole and compare it with what I find some meters away (in fact, I just have to move one meter aside for this message to disappear.
There's no need for that at all and it probably wouldn't be helpful.
Your drone has a magnetic sensor already ... the compass sensor.WHat you need to do is:
1.  Avoid launching from iran or steel, including reinforced concrete surfaces.
2.  Ensure that the drone icon in your map window is pointing the same direction as the real drone ie.  Both pointing east or both pointing south etc.

DJI Natalia Posted at 9-10 01:40
Hi there, we apologize for the inconvenience. Please proceed to restart the device and could you check your firmware if they are showing the latest version as of below.

Date: 2024.09.05

I can confirm that I have the same date and versions you describe.

Labroides Posted at 9-10 04:55
Do you have any experience where magnetic interference where the drone got uncontrollable?
I have analysed the flight data for many yaw error flights and know well how they happen and what the results are.

Checking the drone icon is a very good suggestion. Thank you.

Today I have carried out a few tests of different magnet fields and also what they to to an ordinary compass.  Since the readings I got from the manhole not really give a lot of distortion on an ordinary compass, I guess the explanation about visual sensors being in use by day not can be used by night probably is the best explanation to the cause, but I still have not tested the magnetic field at the manhole at night.  I want to do this as well, as there are several street light near by, and if those cables run through the manhole, the magnet field potentially may get a lot higher when current runs through them.

You can see my tests here:

I have now done a final test.
I brought my compass to the manhole during daytime, and I can confirm that the manhole messes up the compass.
I also checked to see if there were differences in magnetic distortion at night, but the reading seemed to be more or less the same.

I can then conclude two things:
1. At night, do not take off from metal objects.
2. It seems like the drone uses a different kind of compass or navigation system at day, because I never got this problem during daytime, and I have taken off from this sport a LOT of times.

MY video:


PS. I was at a mountain/hill today (approx. 560m above sea level) and planned to take off from a flat stony area, but noticed that two different maps showed I was at a completely different spot.  I measured the magnet field and got as much as 60microTesla.  Moving 15 meters away, and all was good.  Just saying this to make you aware that other things than visual objects may cause problems.

fgange57 Posted at 9-10 10:20
Today I have carried out a few tests of different magnet fields and also what they to to an ordinary compass.  Since the readings I got from the manhole not really give a lot of distortion on an ordinary compass, I guess the explanation about visual sensors being in use by day not can be used by night probably is the best explanation to the cause, but I still have not tested the magnetic field at the manhole at night.  I want to do this as well, as there are several street light near by, and if those cables run through the manhole, the magnet field potentially may get a lot higher when current runs through them.

You can see my tests here:

Today I have carried out a few tests of different magnet fields and also what they to to an ordinary compass.  Since the readings I got from the manhole not really give a lot of distortion on an ordinary compass,
So launching from steel manholes is asking for trouble - don't do it.

I guess the explanation about visual sensors being in use by day not can be used by night probably is the best explanation to the cause,
No, it's a terrible explanation.
Your drone uses a magnetic compass in every flight to give the gyro sensor it's initial directional values.
Bad crashes due to yaw errors usually happen in daylight when most drone flying is done.
But they can also happen at night becuase the laws of physics don't switch off at night.

but I still have not tested the magnetic field at the manhole at night.
Really ???

I can then conclude two things:
1. At night, do not take off from metal objects.
No, no, no.
If it's an unsafe practice at night, it's just as unsafe in daylight.

2. It seems like the drone uses a different kind of compass or navigation system at day, because I never got this problem during daytime, and I have taken off from this sport a LOT of times.
Your drone works exactly the same in dark as it does in daylight.
I have had to deal with this a few times and tested to find the explanation.
I've explained that the night issue is due to a DJI screw up that sometimes gives you an incorrect warning message, but only at night.