Magnetic Mountain

[Trackerputnam]

Yesterday I was shooting a property for a client! 40 acres on the side of a gentle slope! There was a nice convient flat boulder to fly from by my truck so I did d! I expected some compass interference and there was some! Calibrate compass or move it said! Well it got gps lock easy enough so I took off and after a bit the compass problem cleared! But throughout the shoot I would get the compass error, even at several hundred feet in the air! Looking at the pictures last night it was plain to see that the hill was a solid chunk of granite! Must be like a giant magnet!

 

[Phantomrain.org]

Yesterday I was shooting a property for a client! 40 acres on the side of a gentle slope! There was a nice convient flat boulder to fly from by my truck so I did d! I expected some compass interference and there was some! Calibrate compass or move it said! Well it got gps lock easy enough so I took off and after a bit the compass problem cleared! But throughout the shoot I would get the compass error, even at several hundred feet in the air! Looking at the pictures last night it was plain to see that the hill was a solid chunk of granite! Must be like a giant magnet!

A fundamental mistake made my many is that because the compass error has cleared you assume the Compass is oK, but it is not.
I made a video showing how this works.

Just know when ever you get a magnetic Interference or compass error you drone is compromised until you restart from scratch .
Let me know if you need me to post the video as I can show it best with the Phantom 4 as example but its the same with Mavics.

Phantomrain.org
Gear to fly your Mavic in the rain
Coal

 

[slup]

Yesterday I was shooting a property for a client! 40 acres on the side of a gentle slope! There was a nice convient flat boulder to fly from by my truck so I did d! I expected some compass interference and there was some! Calibrate compass or move it said! Well it got gps lock easy enough so I took off and after a bit the compass problem cleared! But throughout the shoot I would get the compass error, even at several hundred feet in the air! Looking at the pictures last night it was plain to see that the hill was a solid chunk of granite! Must be like a giant magnet!

The sensitive moment is when the AC is powered on ... then the IMUYaw initializes to the compass value. If the compass is thrown off due to a magnetic compromised take off spot when this happens the IMUYaw will be wrong & that will be disastrous up higher when the AC tries to hold position due to wind for instance. The AC will try to hold position by giving counter thrust to come back to the correct position. If the AC isn't turned in the way the FC thinks it will apply thrust with the wrong motors ... leading to that the position error just becomes larger ... & the FC tries again & again and fail each time. All this happens in lightning speed ... and the AC "flies away" in a very uncontrollable & distinct "bathtub or toilet bowl curved" flight path.

It's one easy check to discover issues like this before you take off & need to experience a "fly away" due to a yaw error.

Always power on the AC well away from magnetic interference. Once on, check that the drone icon on the map in the app so it's pointing equal to reality in relation to objects on the map ... roads, houses for instance. If the icon on map & the drone in reality isn't pointing equal ... power down move away to another spot & power up again & repeat ...

 

[Trackerputnam]

Everything was good except the compass error. It did drift a bit at first till it cleared the compass error. The whole area was giving off problems. In one spot perhaps 250’ up and a hundred yards away from me it would get the error again. It did there all three flights in that same spot! I flew three batteries and had the error on two of the three take offs. Other than the first take off, the drifting Did not occur. I kept it close for the first battery. Just a neat thing to find really.

 

[Meta4]

it was plain to see that the hill was a solid chunk of granite! Must be like a giant magnet!

Granite is composed of quartz, feldspar and a little mica.
None of them are at all magnetic.
Your compass detected a magnetic influence close to the launch point and warned you to move away from it.

 

[LazerMan]

Right but first shut everything down, phone tablet and rc then move 10 or 15 feet and restart everything

 

[Trackerputnam]

Granite is composed of quartz, feldspar and a little mica.
None of them are at all magnetic.
Your compass detected a magnetic influence close to the launch point and warned you to move away from it.

If nothing magnetic in granite, what could be causing the interference?

 

[Meta4]

If nothing magnetic in granite, what could be causing the interference?

Something steel and much closer to your drone.
When you got the warning before launching, how close was the car?
Did you switch off the drone and move away to launch it?move away

 

[sar104]

If nothing magnetic in granite, what could be causing the interference?

Which model of Mavic?

 

[Trackerputnam]

It’s a mavic 2 pro! We were a long way from the truck. Open rock face is where I launched it! No metal anywhere close! I am sure there was something in the area, and the only thing was the rock!

 

[Trackerputnam]

Remember it also was picking up the same interference 300’ up! I have been flying for a long time! I had hiked to the rock because it was right on the property line! Tall grass everywhere else! It’s a pretty remote area and the nearest house/dwelling is a mile away. No fence. Only explanation is something in the environment.

 

[Meta4]

Remember it also was picking up the same interference 300’ up!
Only explanation is something in the environment.

Nothing on the ground will have any effect on your compass 300 feet up in the air.

 

[Trackerputnam]

I am just describing the situation. It happened all three flights near the same spot! No where else on the flights except at takeoff on two of the flights. I used same drone today at two different locations with no problem. I have used same drone at multiple flights before this with only one incident where I tried taking off from a metal grate. So my only conclusion is that there was some type of environmental interference inthat area. If by chance I get hired to film more properties there I am going to be sure I take my old compass and see what happens! One thought comes to me just now! Were there sever sun spots that day?

 

[Meta4]

So my only conclusion is that there was some type of environmental interference in that area.

But that conclusion isn't correct.
If there was something in the ground that set the compass off, the compass would be going of all the way to 300 feet.
When you are 300 feet up, nothing on the ground is going to have any effect on your compass.
This ship is almost 1000 ft long and made of steel.
It's carrying 2000+ steel containers but you could fly quite a lot closer before your compass would complain:

One thought comes to me just now! Were there sever sun spots that day?

Even if the sunspots were purple, they still won't make any difference to your compass.

 

[slup]

Right but first shut everything down, phone tablet and rc then move 10 or 15 feet and restart everything

It's enough to just power cycle the AC at the new take off spot ... that will trigger a new initialization of the IMUYaw according to compass values. Nothing coming from the tablet or RC will affect that ...

As a side note it's also worth mentioning, as it's a M2P that the OP have ... the M2 models aren't equal prone to create an uncontrollable situation coming from a yaw error as other models. This as a wrongly initialized IMUYaw due to a magnetic disturbed compass will re-initialize when the compass leave the magnetic field up higher ... but this correction only take place if the AC isn't moved after the power on & the first IMUYaw initialization.

 

[Trackerputnam]

I understand most of which others have said! That all makes total sense! But it did happen! I did not change my take off or landing spot. I did not walk around with the controller while drone was in flight! I was in an off grid area though! Perhaps the drone was visible to one of the two compounds in the area? Maybe something they had? Anyway, nothing bad happened, the drone came home and landed, my client loved the pictures! I just found it interesting!

 

[Meta4]

I understand most of which others have said! That all makes total sense! But it did happen!

Yes .. it happened, but not for the reason that you guessed.
Perhaps @sar104 can come up with an explanation?

I did not change my take off or landing spot.

Did you launch from where you had the compass warning?

I did not walk around with the controller while drone was in flight!

It wouldn't matter if you did.

I was in an off grid area though! Perhaps the drone was visible to one of the two compounds in the area? Maybe something they had?

Nothing on the ground can affect your compass when you are 300 feet in the air.

 

[sar104]

Yes .. it happened, but not for the reason that you guessed.
Perhaps @sar104 can come up with an explanation?

Did you launch from where you had the compass warning?

It wouldn't matter if you did.

Nothing on the ground can affect your compass when you are 300 feet in the air.

Rock, including granite, can be ferromagnetic if it contains significant quantities of iron, but I doubt that was the cause here. Without seeing a log file there's really no way to figure out what was going on. That said, since it was a Mavic 2, my first guess would be that the power up interference messages were related to the time/distance requests for compass calibration, not to actual interference. That doesn't explain the compass errors in the air however, and those may well be unrelated since compass interference messages and compass error messages are completely different.