Spooky Action at a Distance

[Aeroworks]

My new mavic as if 1 week ago has a weird thing with mag interference. It flies great and have had no issues. But whenever i turn and face northeast i get an interference message. When i yaw to another direction it clears up. Happens everytime i fly. I wouldn't think the interference detection would be so directional.

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[erkme73]

My new mavic as if 1 week ago has a weird thing with mag interference. It flies great and have had no issues. But whenever i turn and face northeast i get an interference message. When i yaw to another direction it clears up. Happens everytime i fly. I wouldn't think the interference detection would be so directional.

Sent from my SAMSUNG-SM-G935A using MavicPilots mobile app

IF it is related to the rear compass noise issue I just described, then I suspect that cold be attributed to the current/load on a given motor. I suppose it could be that turning in one direction causes more noise than in another. Given that yawing clockwise increases RPM on a different pair of motors than going counter-clockwise. Pull down your DAT file from the aircraft, upload it to dropbox or google drive, and paste a link to it here, calling @BudWalker's attention.

 

[Aeroworks]

The thing is if i hover with no input the mag interferance doesnt go away. When i turn another direction and hover it goes away. I would say unrelated to the motors.

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[erkme73]

The thing is if i hover with no input the mag interferance doesnt go away. When i turn another direction and hover it goes away. I would say unrelated to the motors.

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Could be. Since I found success with my troubles (thanks to budwalker), now anytime some says they see an inteference warning, I immediately assume they have the same issue. Kinda like when the only tool in your tool bag is a hammer, all you see is nails.

Still, I'd ask budwalker if he's interested in looking at your DAT. The guy is a genius and has been able to help identify which sensors/variables are acting wonky. Maybe not why, but it's certainly better than guessing - and it provides a little more to go on, should you choose to contact DJI about it.

 

[BudWalker]

The thing is if i hover with no input the mag interferance doesnt go away. When i turn another direction and hover it goes away. I would say unrelated to the motors.

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This actually could be a compass calibration issue. Contrary to popular belief compass calibration issues are quite rare. I'd really like to see the .DAT for one of these flights. A flight where the Mavic is rotated through 360 degrees would be especially informative.

To see how to retrieve the .DAT look here. It's be large so you'll have to Dropbox or GoogleDrive it and provide the link.

 

[BudWalker]

@Aeroworks I'd understand you might be reluctant to do another flight just to get a 360 degree rotation that I described. You could instead do a "flight" without using the motors. Place it on the ground, turn it on and wait for it to acquire enough satellites for GPS mode. Pick it up, hold at arms length and do two 360 degree rotation. Then power off. That should provide the data we need.

 

[Willik]

It depends on what you consider "fixed". The short answer is yes. The new firmware has the flight controller switch from the rear compass to the redundant front compass if it gets too noisy. That should eliminate the compass and gps data discrepancies. It will also trigger a "strong magnetic interference" warning on the app while flying.

IMHO, the reason why I consider this a software fix to a hardware problem is because the firmware only addresses the symptoms, not the cause. The cause is the higher current giving off too much RF noise under full throttle. DJI 'repaired' my unit (replacing it with another MP), and subsequent flights showed that the noise was significantly reduced on the rear compass. Enough that it never switches to the front. It also cured the TBE issue, and I get no interference warnings. The rumored hardware fix is better shielded/twisted wires to help reduce the RF noise.

The reason DJI has two compasses is for redundancy. If the normal operating parameters have the flight controller switching from the rear to the front, that redundancy is gone.

I have no idea at what point this issue was addressed from a build/manufacturing standpoint. I can only imagine that the currently produced units have the proper shielding and will perform as my replacement unit does. At some point, whenever that change occurred - say after SN 150XXXX - you're safe. I don't think DJI would acknowledge the issue, let alone at what SN the improvement was implemented. So just speculation on my part.

That said, if I had a new unit now, the acid test would be to fly it with the latest firmware, balls-out in sport mode, as aggressively as possible for as long as possible. If you see no interference warnings, you're hardware is probably current and OK. You can also take the DAT file generated from that aggressive flight and have @BudWalker look at it for compass noise.

Thanks for precise explanation. I will try to stay in P mode... Luckily no urgent need for sport mode when turning vids. On the other hand it s*cks when we know about the issue what DJI cant solve with FW up.

 

[erkme73]

Thanks for precise explanation. I will try to stay in P mode... Luckily no urgent need for sport mode when turning vids. On the other hand it s*cks when we know about the issue what DJI cant solve with FW up.

I would not just 'live with it' if you know you have the issue. Test it out thoroughly now while you have warranty. Besides, there are circumstances where you may have no choice but to use sport mode - i.e. strong headwinds. That's not the time to find out it's a problem.

 

[leesmavic]

@Aeroworks I'd understand you might be reluctant to do another flight just to get a 360 degree rotation that I described. You could instead do a "flight" without using the motors. Place it on the ground, turn it on and wait for it to acquire enough satellites for GPS mode. Pick it up, hold at arms length and do two 360 degree rotation. Then power off. That should provide the data we need.

Now that is a cool way of diagnostics! I wonder if high current compass interference in sports mode during high load on the motors can be tested without actual flying as well. Can it?

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[BudWalker]

Now that is a cool way of diagnostics! I wonder if high current compass interference in sports mode during high load on the motors can be tested without actual flying as well. Can it?

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Dunno. The Mavic could be run without props. But, it's unclear if running at max speed without a load would result in a high enough current.

 

[leesmavic]

Dunno. The Mavic could be run without props. But, it's unclear if running at max speed without a load would result in a high enough current.

Any way we can test that? I'm willing to do whatever it takes with it to be more confident in it when flying. I really hate the feeling that I can't trust it. Too afraid to loose it to test in action as I'm not experienced at operating at all.

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[BudWalker]

Any way we can test that? I'm willing to do whatever it takes with it to be more confident in it when flying. I really hate the feeling that I can't trust it. Too afraid to loose it to test in action as I'm not experienced at operating at all.

Sent from my XT1572 using MavicPilots mobile app

You could measure the noise on the back compass but that isn't the whole story. The issue is does that noise impact the compass enough to negatively affect the flight controller. The compass data has both an offset and gain that aren't known precisely and probably is different for each Mavic.

 

[Tomasz]

BudWalker
I am having also issues with sudden switch to ATTI, and i would like to know whether I need to send my bird for reparation (better compass/EM shielding) or software can fix it,
Therefore I am volunteer for in flight test to provide you data needed to confirm your suspicions/my problems.
Could you please describe 'test design' (i.e.: what I shall do before the flight, during it and after).

 

[BudWalker]

BudWalker
I am having also issues with sudden switch to ATTI, and i would like to know whether I need to send my bird for reparation (better compass/EM shielding) or software can fix it,
Therefore I am volunteer for in flight test to provide you data needed to confirm your suspicions/my problems.
Could you please describe 'test design' (i.e.: what I shall do before the flight, during it and after).

If the switch to ATTI occurs after running in Sport mode with either max elevator or max throttle then it's likely you have the back compass issue. In this case it's best that you talk to DJI Support.

Otherwise we need to look at the .DAT for one of those flights where the unexplained switch to ATTI occurred. Look here to see how to retrieve that .DAT. The .DAT is on the Mavic, it's not the .dat on the tablet. It'll be large so you'll need to Dropbox or GoogleDrive it and then provide the link.

 

[Tomasz]

If the switch to ATTI occurs after running in Sport mode with either max elevator or max throttle then it's likely you have the back compass issue. In this case it's best that you talk to DJI Support.

Otherwise we need to look at the .DAT for one of those flights where the unexplained switch to ATTI occurred. Look here to see how to retrieve that .DAT. The .DAT is on the Mavic, it's not the .dat on the tablet. It'll be large so you'll need to Dropbox or GoogleDrive it and then provide the link.

Thanks for reply, I have already two .DAT files when ATTI was triggered, I will upload them over the weekend.
But what I offered is to do a test flight following certain behawior (i.e. Max throttle in P-mode, 360 rotation in both direction, than s-mode ....)
So if someone is interested in results from such experiment I can perform it on my Mavic.

PS. I uploaded flight records to DJI cloud and reported the problem, and they asked me to sent bird for inspection/repair.

 

[Vlakvark]

My experience since 10th November 2016: My MP has done 234 active flights with DJI Go, DJI Go 4 and Litchi (mostly "waypoint" with the latter). Total distance: 376 km. On only about 3 occasions my MP switched to Atti mode and started TBE-ing, when in "hold" mode. Each time I could "fly it out" with forward throttle, and land comfortably afterwards, back in GPS Atti mode. I have never flown in S mode.

Importantly, though, every TBE event was associated with wind gusts between 11.8 m/s (26.4 mph) and 16.95 m/s (37.92 mph) ( that's also, respectively, 70951.9 and 101918.19 furlongs per fortnight! [emoji851]).

Thankfully, the only thing it ever collided with, was the occasional bug in the sky, so, it's still flying with it's original set of props and is still looking brand new, after wiping the bug juice off (touch wood!)

Hopefully, all this info means something to someone!







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[BudWalker]

Thanks for reply, I have already two .DAT files when ATTI was triggered, I will upload them over the weekend.
But what I offered is to do a test flight following certain behawior (i.e. Max throttle in P-mode, 360 rotation in both direction, than s-mode ....)
So if someone is interested in results from such experiment I can perform it on my Mavic.

PS. I uploaded flight records to DJI cloud and reported the problem, and they asked me to sent bird for inspection/repair.

Not sure what you need from me. I thought it was help diagnosing the unexplained switch to ATTI. If so, it's premature to be thinking about designing a test to uncover more details about the switch to ATTI. Probably won't need a test.

If it's a test to learn more about the back compass issue we already know quite a bit. If we're trying to develop a test that can be used by pilots to confirm they don't have the back compass issue then, IMHO, that's not a good idea. It's one thing to determine that an incident was caused by a noisy back compass. Determining that the back compass noise level won't ever cause an issue is much different problem. There is the real possibility any test developed could be incorrect. Or, misunderstood and not applied or interpreted correctly.

I understand people waited a long time for their Mavic and don't want to relinquish it for an evaluation/repair trip to DJI support. They would much rather know if that's really necessary before sending it off. This will be my first negative comment about DJI but they really could be doing a much better job communicating about the back compass issue. One thing pilots can do is contact @Ed Windham about this.

 

[Tomasz]

Not sure what you need from me. I thought it was help diagnosing the unexplained switch to ATTI. If so, it's premature to be thinking about designing a test to uncover more details about the switch to ATTI. Probably won't need a test.

If it's a test to learn more about the back compass issue we already know quite a bit. If we're trying to develop a test that can be used by pilots to confirm they don't have the back compass issue then, IMHO, that's not a good idea. It's one thing to determine that an incident was caused by a noisy back compass. Determining that the back compass noise level won't ever cause an issue is much different problem. There is the real possibility any test developed could be incorrect. Or, misunderstood and not applied or interpreted correctly.

I understand people waited a long time for their Mavic and don't want to relinquish it for an evaluation/repair trip to DJI support. They would much rather know if that's really necessary before sending it off. This will be my first negative comment about DJI but they really could be doing a much better job communicating about the back compass issue. One thing pilots can do is contact @Ed Windham about this.

Thanks @BudWalker I got your point, and you are right the last think which I want to do after 2 months of waiting is to send away my new bird for a few weeks.
Here are my logs from two flights:
Dropbox - Flight logs
The smaller one is test flight where I managed to observed ATTI switch after 2 mins of different maneuvers.

The bigger one was normal flight when at the end last 1-2 mins bird switched to ATTI. If you could analyse them to determine the most probable reason would be great.

And many thanks for meaningful input into this discussion

 

[BudWalker]

Thanks @BudWalker I got your point, and you are right the last think which I want to do after 2 months of waiting is to send away my new bird for a few weeks.
Here are my logs from two flights:
Dropbox - Flight logs
The smaller one is test flight where I managed to observed ATTI switch after 2 mins of different maneuvers.

The bigger one was normal flight when at the end last 1-2 mins bird switched to ATTI. If you could analyse them to determine the most probable reason would be great.

And many thanks for meaningful input into this discussion

Your Mavic appears to have the gpsHealth problem. gpsHealth is not the same as number of satellites. gpsHealth has a range of 0 to 5 and 4 or 5 is required for GPS to be used for navigation.

In FLY045 gpsHealth drops from 5 to 1 twice, each time causing the switch to ATTI

In FLY064 this happens once

It's normal for the gpsHealth to start at 0 at batteryOn but then increase to 5 as the gps acquires satellites. There is no apparent reason for the drop from 5 to 1; note the satellite count doesn't drop.

IMHO this almost certainly a hardware problem. In all the P3 flights I've looked at this never happened. I must've seen 6 or 7 Mavics with this gpsHealth issue.

 

[Tomasz]

Your Mavic appears to have the gpsHealth problem. gpsHealth is not the same as number of satellites. gpsHealth has a range of 0 to 5 and 4 or 5 is required for GPS to be used for navigation.

In FLY045 gpsHealth drops from 5 to 1 twice, each time causing the switch to ATTI
View attachment 4621
In FLY064 this happens once
View attachment 4620
It's normal for the gpsHealth to start at 0 at batteryOn but then increase to 5 as the gps acquires satellites. There is no apparent reason for the drop from 5 to 1; note the satellite count doesn't drop.

IMHO this almost certainly a hardware problem. In all the P3 flights I've looked at this never happened. I must've seen 6 or 7 Mavics with this gpsHealth issue.

@BudWalker thanks for prompt analysis, so it means that I will need to send it to service. I will have last few flights over the WE before that.