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Magnetic interference P85D - Compass and DJI Drone

AllDigital

Member
Feb 27, 2013
63
170
SoCal
So, here is a new one for me. I've got a new DJI Phantom 3 drone. For the past 3-4 weeks it has been working well, but occasionally throwing compass errors on start-up. After a long drive today, I couldn't get the compass corrected at all to start up the drone (in the middle of a field). After some research online, I discovered that if the compass becomes exposed to a huge magnetic field it needs to be degaussed and the IMU and compass on the drone needs recalibrating. It took a LOT of degaussing to get it back to normal, but it got me thinking... what caused it?

When I travel with the drone it is in a nylon case in my trunk, right above the rear coil on my P85D. Hmmm. That might be causing a magnetic field. So, I did a bunch of tests. Using a standard field compass in liquid, when I put it in the car in the back it pegs the needle to the floor (suspended in liquid) and the compass needle won't move -- with the car off. I have also found significant compass interference, just by putting it in the passenger seat, passenger floor (front coil?) and moderate amounts around the car. In a drive test, the rear compass test stays pegged while driving, turning, u-turning, etc. Not surprising, given what lies a foot away, but makes me realize that anything that is magnetic sensitive (e.g. a precision drone) might need to be shielded. I couldn't find a reliable place in the car (besides the drivers seat) without any compass interference.

To test my theory, I took the degaussed drone five miles away in another car (one of those ICE cars) and no issue on start-up. Then I took it to the same field in the back of my Tesla and it needed compass calibration three times to get it started.

I know there are other threads discussing EMF, but does anyone have a good solution to shield sensitive equipment in the back of a P85D? I can't be seen flying my drone and driving a gas vehicle.
 

siucity

Button Pusher
Feb 18, 2015
407
208
SF North Bay, CA
I have a DJI Phantom 3 Pro, and I've traveled with it in a case (regular DJI case) in the frunk. Haven't had issues starting it up. Are you experiencing issues when it's stored in the frunk too?
 

ecarfan

Well-Known Member
Sep 21, 2013
19,198
13,846
San Mateo, CA
I have a DJI Phantom 3 Pro, and I've traveled with it in a case (regular DJI case) in the frunk. Haven't had issues starting it up.

And you have a Dual Motor car. Interesting. Apparently the EMF is weaker due to the smaller, less powerful motor in front.
 

MarkS22

Member
Apr 6, 2015
796
1,985
Morris County, NJ
Hmm. I've traveled quite a bit with an Inspire in the back of my P85D, both in the case and out and a couple times in the front seat. Never had any issues like this. Maybe the Inspire has better shielding? I do have an older Phantom that I could test.
 

Denarius

Active Member
Apr 27, 2013
1,378
84
Utah
I always keep my DJI Phantom 3 in the trunk of my P85D, I store it in a pelican hard case and have never had any compass issues. I only calibrate if I've driven > 20 miles from the spot I last used it.
 

jeffro01

Active Member
Jan 30, 2013
2,676
1,926
Teller County CO
OT: Agreed the registration requirement is silly, but the problem of irresponsible drone owners interfering with aircraft is not.

If people could just be responsible adults then drone registrations wouldn't be needed... Unfortunately it's only a matter of time before some idiot's drone gets sucked into a commercial airliner jet engine and then things will really get ugly from there...

Jeff
 

choatie88

Member
Dec 2, 2015
19
0
NYC, NY
If people could just be responsible adults then drone registrations wouldn't be needed... Unfortunately it's only a matter of time before some idiot's drone gets sucked into a commercial airliner jet engine and then things will really get ugly from there...

Jeff

c.f. autopilot, etc etc
 

pilotSteve

Active Member
Jul 14, 2012
1,467
1,330
Prescott Az
OT: Agreed the registration requirement is silly, but the problem of irresponsible drone owners interfering with aircraft is not.

Not to go too far off topic (I have a DJI Phantom 3 so next time I take it traveling in my S85 I'll carry it in the trunk). HOWEVER I have serious concerns about the FAA's "registration" of drones. At the least its self-incrimination and quite possibly illegal anyhow. Consider reading The Problems with Mandatory Drone Registration - sUAS News.
 

AllDigital

Member
Feb 27, 2013
63
170
SoCal
Back on topic... I might have an overly sensitive DJI or something else might be going on, but the compass test I did in the car clearly indicates a significant magnetic field, even when off and parked. Enough to peg the compass flat. I'm sure the DJI sensor is more sensitive than an old liquid filled Boy Scout compass, so I would assume the DJI component compass is also "pegged" in place when I'm driving around. I'm going to experiment with a Mu Metal shield in the case to see if it helps.

On the side topic of registration... I'm registered and I also think it is necessary. Interesting that it isn't drone registration it is pilot registration. The reg process doesn't even ask if you own a drone, the make or model. So, it is more analogous to a drivers license than a car registration, although you are supposed to put your reg id on all your drones. I didn't used to think it was necessary, but after flying the DJI for a while, it has become obvious that the tech has matured to a point where any 10 year old could fly a drone miles away and at thousands of feet high without any training. The price point will drop rapidly and millions could ship, creating real hazards and irresponsibility without some accountability. The next 3-5 years will be interesting as the FAA, cities and states struggle to find a balance. An HOA community near me just banned drones, which is funny, since they don't own or govern the skies above -- like banning airplanes above your property. A legal Wild West for a while.
 

kennybobby

Member
Sep 14, 2014
478
36
Heart o' Dixie
Back on topic... I might have an overly sensitive DJI or something else might be going on, but the compass test I did in the car clearly indicates a significant magnetic field, even when off and parked. Enough to peg the compass flat. I'm sure the DJI sensor is more sensitive than an old liquid filled Boy Scout compass, so I would assume the DJI component compass is also "pegged" in place when I'm driving around. I'm going to experiment with a Mu Metal shield in the case to see if it helps.

Does it do this on the right side of the trunk toward the inverter, or on the left side toward the motor? Can you try the compass test underneath the car to pinpoint the source both when off and on--i would guess that it will be in the vicinity of the inverter.

The large cables to the inverter make a dc current loop that creates a magnetic field, which it sounds like the North pole is pointing down.

Any iron or magnetic steel sheet will work as a faraday cage to shield the magnetic field.
 

MITE46

Member
Aug 26, 2014
185
384
Los Altos / San Marino
I have the same issue with Phantom 3 pro in hard case...but I tested it with another identical setup, same exact model and case, and the 2nd one didn't have issues. This is right on top of the rear axle in the trunk.
 

andrewket

Well-Known Member
Dec 20, 2012
5,704
1,525
I have a DJI Phantom 3 Pro, and I've traveled with it in a case (regular DJI case) in the frunk. Haven't had issues starting it up. Are you experiencing issues when it's stored in the frunk too?

I carried a Phantom 2 in a hard case in the frunk of my P85+ for months, and now a phantom 3 is a soft case in the trunk of my P85D and have not had any issues with the compass.
 

asudan

Member
Oct 16, 2015
128
13
Phoenix, AZ
If people could just be responsible adults then drone registrations wouldn't be needed... Unfortunately it's only a matter of time before some idiot's drone gets sucked into a commercial airliner jet engine and then things will really get ugly from there...

Airplanes are designed to handle bird strikes from MUCH larger birds than these drones they are trying to register. This isn't the issue My DJI will not even fly near enough to an airport to be an issue and the smaller drones are really no issue.

This is about control. It is about making a list, etc. Government oversight. It has nothing to do with drones being sucked into jet engines.
 

jeffro01

Active Member
Jan 30, 2013
2,676
1,926
Teller County CO
Airplanes are designed to handle bird strikes from MUCH larger birds than these drones they are trying to register. This isn't the issue My DJI will not even fly near enough to an airport to be an issue and the smaller drones are really no issue.

This is about control. It is about making a list, etc. Government oversight. It has nothing to do with drones being sucked into jet engines.

You couldn't possibly be more wrong but don't let facts get in the way of your anti-government sentiment. Drones should be outright banned and they eventually will be if the current behavior issues some drone owners seem to already have. I know a fair share of pilots, some fly for well known commercial airlines and I can assure you they are extremely concerned about this scenario. The risk is even greater when talking about smaller aircraft like helicopters and such.

The way this should work is you are not allowed to fly at all until you've proven you can responsibly operate your drone, much like a car or any other aircraft out there.

Jeff
 

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