Mavic First Flight Uncontrolled - Magnetic Interference

beachcombing · Dec 13, 2016

I got my Mavic yesterday. It was raining so I could fly, but I updated the firmware and calibrated the compass and IMU.

I'm not a novice. I have a Phantom 3 Professional and had a Phantom 2 Vision + before that and harebve flown numerous flights with no issues.

Today, I took the Mavic out at lunch to test fly it since the clouds briefly cleared.

The first time I went up about 15 feet and immediately got a warning that said "Warning:Compass Interference. Temp Max Altitude: 16FT" and a few seconds later I got "FORCE LANDING". Note that I had a good GPS signal when I took off.

So I shut everything down and restarted the controller and the Mavic. The DJI Go app said to calibrate the compass so I did that, got a good GPS signal and took off. I only got about 15 feet high before the Mavic took off sideways. I tried full down throttle and it would not come all the way down and went screaming fast toward the street. Thankfully, it missed the trees and the cars in the street and landed without any damage.

Here's the Healthy Drones data.
HealthyDrones.com - Innovative flight data analysis that matters
Here's the video.

I moved over to the other side where there was a little bit more room, but I kept getting interference when I got to about 50 feet.
HealthyDrones.com - Innovative flight data analysis that matters

Note that I have flown my Phantom 3 in this exact spot with absolutely no problems.

Any ideas?

msinger · Dec 13, 2016

Since you're a seasoned pilot, I'm guessing you know most sidewalks are chock-full of metal. Did you calibrate the compass on the sidewalk too?

beachcombing · Dec 13, 2016

I was in the grass calibrating the compass. Also around here the sidewalks typically are not reinforced with steel. And if they are, it's usually a wide 6" grid. And the calibration of the compass went fine. And lastly, when I moved to the other spot, I took off from asphalt on the plaza. No steel it. And I was getting the "interference" message when I was 50 feet in the air. But the message would go away if I came down a bit in altitude.

msinger · Dec 13, 2016

I would try recalibrating the compass away from all possible sources of magnetic metal. And, then try taking off in the same location.

beachcombing · Dec 13, 2016

Cool. Thanks. I'm going to take it out to a park away from everything and try it. This was certainly a crazy/scary experience. It seems crazy too that it could be that sensitive (based on similar reports). Never had anything close to this much interference reported with any of my Phantoms.

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msinger · Dec 13, 2016

Yes, sir. It looks like you got away unscathed though.

laura schlenker · Dec 13, 2016

That did looks scary, I bet your heart was in your throat.

4wd · Dec 14, 2016

You can check the sensors in the app beforehand, I wouldn't expect to see such odd behaviour unless one of the two was way out - which might happen if calibrated when folded or something was wrong with one.

Kilrah · Dec 14, 2016

beachcombing said:
And I was getting the "interference" message when I was 50 feet in the air. But the message would go away if I came down a bit in altitude.

There couldn't be anything telling you more clearly that there was actually stuff in the ground.

beachcombing · Dec 14, 2016

Kilrah said:
There couldn't be anything telling you more clearly that there was actually stuff in the ground.

Not sure I understand what you are saying. I didn't get the message when I was on the ground. I kept getting it as I hit 50 feet up. But the message would clear if I came back down a little. And this was when I launched from the asphalt area.

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Kermit215 · Dec 14, 2016

I'd be interested to see a screenshot of the compass interference at the takeoff point.

Mako79 · Dec 14, 2016

beachcombing said:
I got my Mavic yesterday. It was raining so I could fly, but I updated the firmware and calibrated the compass and IMU.

I'm not a novice. I have a Phantom 3 Professional and had a Phantom 2 Vision + before that and harebve flown numerous flights with no issues.

Today, I took the Mavic out at lunch to test fly it since the clouds briefly cleared.

The first time I went up about 15 feet and immediately got a warning that said "Warning:Compass Interference. Temp Max Altitude: 16FT" and a few seconds later I got "FORCE LANDING". Note that I had a good GPS signal when I took off.

So I shut everything down and restarted the controller and the Mavic. The DJI Go app said to calibrate the compass so I did that, got a good GPS signal and took off. I only got about 15 feet high before the Mavic took off sideways. I tried full down throttle and it would not come all the way down and went screaming fast toward the street. Thankfully, it missed the trees and the cars in the street and landed without any damage.

Here's the Healthy Drones data.
HealthyDrones.com - Innovative flight data analysis that matters
Here's the video.

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

I moved over to the other side where there was a little bit more room, but I kept getting interference when I got to about 50 feet.
HealthyDrones.com - Innovative flight data analysis that matters

Note that I have flown my Phantom 3 in this exact spot with absolutely no problems.

Any ideas?

The phantom series is totally different to the Mavic. I think the Mavic is more sensitive.
I would never calibrate my compass near where you flew. That place is full of large buildings, rebar etc.
I would take it to an open grassy field and do the dance there and never do it again unless I travelled a certain distance.
If I get a compass interference at the flight location, I would move a few meters away or hand/card board box launch.
A compass warning does not mean you need to compass dance. It just means there is interference near.

BudWalker · Dec 14, 2016

beachcombing said:
I got my Mavic yesterday. It was raining so I could fly, but I updated the firmware and calibrated the compass and IMU.

I'm not a novice. I have a Phantom 3 Professional and had a Phantom 2 Vision + before that and harebve flown numerous flights with no issues.

Today, I took the Mavic out at lunch to test fly it since the clouds briefly cleared.

The first time I went up about 15 feet and immediately got a warning that said "Warning:Compass Interference. Temp Max Altitude: 16FT" and a few seconds later I got "FORCE LANDING". Note that I had a good GPS signal when I took off.

So I shut everything down and restarted the controller and the Mavic. The DJI Go app said to calibrate the compass so I did that, got a good GPS signal and took off. I only got about 15 feet high before the Mavic took off sideways. I tried full down throttle and it would not come all the way down and went screaming fast toward the street. Thankfully, it missed the trees and the cars in the street and landed without any damage.

Here's the Healthy Drones data.
HealthyDrones.com - Innovative flight data analysis that matters
Here's the video.

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

I moved over to the other side where there was a little bit more room, but I kept getting interference when I got to about 50 feet.
HealthyDrones.com - Innovative flight data analysis that matters

Note that I have flown my Phantom 3 in this exact spot with absolutely no problems.

Any ideas?

Could we take a look at the .DAT file that's on the Mavic itself, not the tablet. There is a lot more info than what's available in the .txt you submitted to HD. The .DAT will have data on both compasses. To see how to retrieve the .DAT go here. It'll be large so you'll have to Dropbox it and post the link.

DesertWindAero · Dec 14, 2016

beachcombing said:
I got my Mavic yesterday. It was raining so I could fly, but I updated the firmware and calibrated the compass and IMU.

I'm not a novice. I have a Phantom 3 Professional and had a Phantom 2 Vision + before that and harebve flown numerous flights with no issues.

Today, I took the Mavic out at lunch to test fly it since the clouds briefly cleared.

The first time I went up about 15 feet and immediately got a warning that said "Warning:Compass Interference. Temp Max Altitude: 16FT" and a few seconds later I got "FORCE LANDING". Note that I had a good GPS signal when I took off.

So I shut everything down and restarted the controller and the Mavic. The DJI Go app said to calibrate the compass so I did that, got a good GPS signal and took off. I only got about 15 feet high before the Mavic took off sideways. I tried full down throttle and it would not come all the way down and went screaming fast toward the street. Thankfully, it missed the trees and the cars in the street and landed without any damage.

Here's the Healthy Drones data.
HealthyDrones.com - Innovative flight data analysis that matters
Here's the video.

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

I moved over to the other side where there was a little bit more room, but I kept getting interference when I got to about 50 feet.
HealthyDrones.com - Innovative flight data analysis that matters

Note that I have flown my Phantom 3 in this exact spot with absolutely no problems.

Any ideas?

Are there transit tunnels under that area?

beachcombing · Dec 14, 2016

There are no transit tunnels or transit of any kind in that area. The interstate tunnel goes under there (regular vehicular traffic) but it's at least 50 feet below ground at that point because it goes under the river and the river is 50 - 60 feet deep to accommodate aircraft carriers going to the shipyard.

Here are the DAT files. I think these are the correct flights. There were only three flight records from that day. And the first one had a really small file size.
Dropbox - DJI_ASSISTANT_EXPORT_FILE[2016-12-14 21-50-02].DAT
Dropbox - DJI_ASSISTANT_EXPORT_FILE[2016-12-14 21-42-57].DAT

Thanks for checking them out.

erkme73 · Dec 15, 2016

Work your magic, @BudWalker... My MP started its journey to Carson today thanks to your analysis....

ziggys · Dec 15, 2016

T

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Random155 · Dec 15, 2016

Holy ****!!!! You are one lucky guy. You missed signs, trees and several cars. Not sure how to help, but I can say, sidewalks dont have rebar in them, as they are not used for structure. However calibrating the compass in a big open field away from any interference is always recommended. Good luck with your next flight.

Kilrah · Dec 15, 2016

beachcombing said:
Not sure I understand what you are saying. I didn't get the message when I was on the ground. I kept getting it as I hit 50 feet up. But the message would clear if I came back down a little. And this was when I launched from the asphalt area.

The ground was disturbed (which prompted you to calibrate). You calibrated, therefore calibrating for that disturbance, so no more warning. Flying up you get out of the bad magnetic enviromnent for which you calibrated for so the calibration is now wrong and you get the warning. Fly back down you get in the disturbance again and thus the warning disappears.
If you get a compass warning after flying away from a place you calibrated at it's a dead proof that this location was disturbed and unsuitable for calibrating, you should stop and land right now, and don't fly again before calibrating in a good location.

If you have a known good calibration (i.e. you don't have any warnings nor problems in most places you're usually flying in) the app prompting to calibrate has 90% chance of actually meaning "this location is bad". You should NOT fly from there and even less actually calibrate there.

BudWalker · Dec 15, 2016

beachcombing said:
There are no transit tunnels or transit of any kind in that area. The interstate tunnel goes under there (regular vehicular traffic) but it's at least 50 feet below ground at that point because it goes under the river and the river is 50 - 60 feet deep to accommodate aircraft carriers going to the shipyard.

Here are the DAT files. I think these are the correct flights. There were only three flight records from that day. And the first one had a really small file size.
Dropbox - DJI_ASSISTANT_EXPORT_FILE[2016-12-14 21-50-02].DAT
Dropbox - DJI_ASSISTANT_EXPORT_FILE[2016-12-14 21-42-57].DAT

Thanks for checking them out.

There were three flights included in the posted .DAT files. The second flight corresponds to the video in the first post. In summary, the Mavic was launched from a geomagnetically distorted site causing the Yaw (heading) to be incorrect. This incident is similar to some P3 incidents that I've looked at. Here is a recent one.

The Mavic gets it's heading info from a combination of sensors; mostly the gyros, then the accelerometers. Shortly after batteryOn the Flight Controller initializes the Yaw value based on the compass magnetometers but after that it's info coming from the gyros and accelerometers that determine Yaw. After this the magnetometers have only a small effect on the value of Yaw.

If the launch site is geomagnetically distorted the Yaw value will be incorrect because of the effect on the magnetometers. When the Mavic has cleared the effects of the geomagnetic distortion the compass/magnetometers become correct, BUT the Yaw is being determined by the gyros which hasn't changed.

That's what happened in this incident.

magYaw is a diagnostic value calculated by DatCon from the magnetometer data. Here, magYaw and Yaw (the value that the Mavic uses for heading) are the same incorrect value until the Mavic launches at time 3.2 secs. Then magYaw (blue line) changes to -134, the correct value, BUT Yaw (green line) stays at the old, incorrect, value of -115. I looked at the video to confirm that magYaw is correct.

The Mavic is different from the P3 in that the P3 would have switched to ATTI because it has to assume that it's possible Yaw is incorrect. The Mavic did not switch to ATTI but from pilot's description appears to taken a different strategy. I haven't seen enough Mavic incidents to know if the Mavic was trying to navigate at this point. From looking at the control inputs and motor speeds my best guess is that the Mavic was attempting to both navigate and respond to control inputs.

At time 15.38 the only control input is full negative throttle but the Mavic proceeded across the traffic circle. In the GoogleEarth view the AC location is shown as an A. The blue line is the magYaw value and the green line is the Yaw value.

This incident was not caused by a compass calibration problem. It was all due to the geomagnetic distortion at the launch site. Note that the magYaw/Yaw stops separating when the Mavic reaches 1.6 meters. If the pilot had hand launched higher than 1.6 meters there would not have been an incident. The effect of a compass calibration is to compensate for onboard magnetic distortions. A compass calibration does not compensate or know about local or regional geomagnetic distortions. All the compass calibration needs is a geomagnetic field that 1) isn't distorted within the confines of the compass dance and 2) has a strength that isn't drastically different from the launch site. The pilot achieved this in the flight previous to this one.

Unfortunately, checking the magMod value isn't much use in detecting this situation before launch. The geoMagnetic field is distorted but it's strength hasn't changed enough to notice. The only way to really detect this kind of problem is to eyeball the Mavic, know which way it's pointing, and check that with the red arrow in the display. Having said that, I'll also add that I never do this.