Mavic First Flight Uncontrolled - Magnetic Interference

[erkme73]

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.
View attachment 2503
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.

View attachment 2505
View attachment 2507
View attachment 2508
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.

I'm developing a man-crush on you...

 

[BudWalker]

I'm developing a man-crush on you...

....this could be tricky...don't wanna say the wrong thing....lemme think some....

 

[erkme73]

....this could be tricky...don't wanna say the wrong thing....lemme think some....

No worries. It's the benign, non-stalking kind of crush...

 

[Manfrenjensen]

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.
View attachment 2503
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.

View attachment 2505
View attachment 2507
View attachment 2508
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.

Hi,
Total novice here. I have been flying mine for a total of one day. I'm trying to understand this response as best I can. Is the moral of the story here that the pilot pretty much did things as he should but sometimes **** just happens? In other words, he calibrated correctly, flew it correctly, etc... but that unexpected magnetic distortions at a certain height/distance caused the incident and there wasn't much he could do to about it?

I live on the edge of a subdivision with 3/4 acre lots. In other words, it's a not a very dense urban area with big buildings/apartments, etc. Behind my house is wide open fields with no structures. I thought just going right behind my fence would be fine. But I'm always getting "mag" warnings. However, so far, it has not caused any problems... I've had several successful flights. In fact, the only scary moment I've had was when I went to another location... which was really wide open with very few houses (and had NO mag warnings) and this was the only time the controller lost connection (and the mavic was very close to me!) and the mavic automatically kicked into RTH mode... scared the bejeezus out of me. I have NO idea why that happened there, but I promptly left the area.
Anyway... does it sound like flying behind my house is a dumb idea? I've seen several videos of people flying mavic in much denser urban areas. This is really surprising me that I have already had these warnings and one scary moment.

 

[Manfrenjensen]

Allrighty then.... well anyway, on my 2nd day of flying in the same place, no problems at all (not even mag interference warning).

 

[BudWalker]

Hi,
Total novice here. I have been flying mine for a total of one day. I'm trying to understand this response as best I can. Is the moral of the story here that the pilot pretty much did things as he should but sometimes **** just happens? In other words, he calibrated correctly, flew it correctly, etc... but that unexpected magnetic distortions at a certain height/distance caused the incident and there wasn't much he could do to about it?

I live on the edge of a subdivision with 3/4 acre lots. In other words, it's a not a very dense urban area with big buildings/apartments, etc. Behind my house is wide open fields with no structures. I thought just going right behind my fence would be fine. But I'm always getting "mag" warnings. However, so far, it has not caused any problems... I've had several successful flights. In fact, the only scary moment I've had was when I went to another location... which was really wide open with very few houses (and had NO mag warnings) and this was the only time the controller lost connection (and the mavic was very close to me!) and the mavic automatically kicked into RTH mode... scared the bejeezus out of me. I have NO idea why that happened there, but I promptly left the area.
Anyway... does it sound like flying behind my house is a dumb idea? I've seen several videos of people flying mavic in much denser urban areas. This is really surprising me that I have already had these warnings and one scary moment.

Sorry I didn't get around to responding to this yesterday. If there is a moral to the story it's don't launch from a site where there could be buried ferrous material. If you gotta, then hand launch it from as high as you can. I also mentioned in that post you can look at the red triangle on the Go App display and see if it's pointing in the correct direction prior to launch.

I'm not sure what you mean by a "mag" warning. Could you be more specific?

There have been several incidents recently where there was a disconnect between the RC and Mavic while at close range. In one that I'm aware of (New to Mavic, lost conection between remote and drone. ) there was an OUTOF_CONTROL_GOHOME triggered which, apparently, is different than an RTH.

 

[Manfrenjensen]

Sorry I didn't get around to responding to this yesterday. If there is a moral to the story it's don't launch from a site where there could be buried ferrous material. If you gotta, then hand launch it from as high as you can. I also mentioned in that post you can look at the red triangle on the Go App display and see if it's pointing in the correct direction prior to launch.

I'm not sure what you mean by a "mag" warning. Could you be more specific?

There have been several incidents recently where there was a disconnect between the RC and Mavic while at close range. In one that I'm aware of (New to Mavic, lost conection between remote and drone. ) there was an OUTOF_CONTROL_GOHOME triggered which, apparently, is different than an RTH.

Very good info, thanks!!
The "mag warning" I was referring to, displays on screen as "mag interf"... which I believe means magnetic interference. On my first day flying it behind my house (with houses nearby on one side, but wide open space on the other side), I was frequently getting that warning. On my second day flying in the same place, I got no such warnings.

 

[BudWalker]

Very good info, thanks!!
The "mag warning" I was referring to, displays on screen as "mag interf"... which I believe means magnetic interference. On my first day flying it behind my house (with houses nearby on one side, but wide open space on the other side), I was frequently getting that warning. On my second day flying in the same place, I got no such warnings.

The "mag warning" came while in the air? At what altitude?

 

[Manfrenjensen]

The "mag warning" came while in the air? At what altitude?

Hmm... good question.
I remembered it happening all over the place (on the ground and all different altitudes). But, I just asked my two boys who were flying with me...
One said "only on the ground, maybe once in the air".
The other said, "it also happened sometimes in the air".

Haha.. so, I guess not very reliable info. I will have to pay better attention to that next time.

We were launching from a dirt road. But now that you mention it, I think there is a metal utility pipe that runs under it. So that may explain a lot.

 

[BudWalker]

Hmm... good question.
I remembered it happening all over the place (on the ground and all different altitudes). But, I just asked my two boys who were flying with me...
One said "only on the ground, maybe once in the air".
The other said, "it also happened sometimes in the air".

Haha.. so, I guess not very reliable info. I will have to pay better attention to that next time.

We were launching from a dirt road. But now that you mention it, I think there is a metal utility pipe that runs under it. So that may explain a lot.

Can you retrieve the .DAT for one of those flights that had the mag interference? To see how go here. It'll be large so you'll need to Dropbox it and post the link.

 

[Manfrenjensen]

Can you retrieve the .DAT for one of those flights that had the mag interference? To see how go here. It'll be large so you'll need to Dropbox it and post the link.

Thanks for the link. I got in there to look at the files but unfortunately it appears the files from that day (12/26) are no longer there. There is only one from the last flight of that day (which was at night and real short with no problems) and onward.
So, I guess it must start removing the older ones based on elapsed time or storage space?

 

[BudWalker]

Thanks for the link. I got in there to look at the files but unfortunately it appears the files from that day (12/26) are no longer there. There is only one from the last flight of that day (which was at night and real short with no problems) and onward.
So, I guess it must start removing the older ones based on elapsed time or storage space?

Yes. But, it seems you may have another of these events and you can retrieve the .DAT from that one if you're still interested.

 

[Manfrenjensen]

I'm definitely still interested. But all of the issues & warning I described were on 12/26 (that data is gone). I didn't have any problems at all yesterday... and I haven't flown yet today.
In other words, I don't think I have any .DAT files from problem flights. I assume that's what you were asking for? Sorry, if I'm misunderstanding something.
I will fly again in a few minutes and will post here if it happens again. Thanks for offering to take a look.

 

[erkme73]

@Manfrenjensen - next flight, GUN IT hard. Go to sports mode and go full throttle back and forth.

 

[Manfrenjensen]

@Manfrenjensen - next flight, GUN IT hard. Go to sports mode and go full throttle back and forth.

haha.. why?? Somehow that sounds like a recipe for disaster.

 

[erkme73]

Completely serious. If your problem is related to the motor load induction of noise on the rear compass like so many of us have experienced, you may only see the warnings under those conditions. Try to keep the RPM and motor load high, and if your unit is sensitive to interference you'll see the warnings after a few seconds.

 

[Manfrenjensen]

Completely serious. If your problem is related to the motor load induction of noise on the rear compass like so many of us have experienced, you may only see the warnings under those conditions. Try to keep the RPM and motor load high, and if your unit is sensitive to interference you'll see the warnings after a few seconds.

Interesting! If confirmed, is that considered a defect that DJI would assist with?

 

[erkme73]

Interesting! If confirmed, is that considered a defect that DJI would assist with?

I can't speak for DJI, and can only address my specific instance, but after viewing my DAT and seeing the noise created by the higher motor loads, they wanted my unit back for repair/replacement. It's currently en route back to me. I fully intend to put a hurting on the loads and get my DAT to @BudWalker for a before-after comparison.

Once DJI determined that the induced interference caused the rear compass to get wonky, they updated the firmware to force the flight controller to switch to the unaffected front compass. That has prevented the dreaded toilet-bowl effect (TBE) that can cause a perceived loss of control, but anytime that happened, the app would indicate magnetic interference. Thus, the latest firmware really exposed the issue on devices where the operators may not have know they even had a problem.

If you see the magnetic interference message during flight, and you get it repeatedly when going full throttle, I would suggest you contact DJI and let them know. @BudWalker will have to address this himself, but I would guess he too would be interested in seeing a copy of your DAT so he can analyze the interference patterns.

I'm reluctant to say this is a known hardware issue. But, given these facts, you can draw your own conclusion.

 

[Manfrenjensen]

I can't speak for DJI, and can only address my specific instance, but after viewing my DAT and seeing the noise created by the higher motor loads, they wanted my unit back for repair/replacement. It's currently en route back to me. I fully intend to put a hurting on the loads and get my DAT to @BudWalker for a before-after comparison.

Once DJI determined that the induced interference caused the rear compass to get wonky, they updated the firmware to force the flight controller to switch to the unaffected front compass. That has prevented the dreaded toilet-bowl effect (TBE) that can cause a perceived loss of control, but anytime that happened, the app would indicate magnetic interference. Thus, the latest firmware really exposed the issue on devices where the operators may not have know they even had a problem.

If you see the magnetic interference message during flight, and you get it repeatedly when going full throttle, I would suggest you contact DJI and let them know. @BudWalker will have to address this himself, but I would guess he too would be interested in seeing a copy of your DAT so he can analyze the interference patterns.

I'm reluctant to say this is a known hardware issue. But, given these facts, you can draw your own conclusion.

Wow. Very interesting. OK, I'm going to try that today and post the results here.
I have not had a single warning or disconnect issue since the 1st day... even flying in the same areas.
So strange. But I'm curious, so I'm going to give this a try just in case.

 

[frankiez]

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

How do recalibrate the compass? I looked at the compass setting and it didnt have the box telling me that it needs calibrating. I had heard someone say they calibrate it every time they fly it.

sent from my Galaxy Note4