Spooky Action at a Distance

[Vlakvark]

This drop out of GPS mode and "toilet-bowling" has happened to me twice in the last few days, while flying manually with DJI Go as well as the Litchi app. (I'm using iPhone 6 as well as lPad mini). While toilet-bowling and drifting it seemed to hold the altitude well. After a short fight, it recovered and stabilized. In subsequent flights it was Ok! I get the idea these incidents were associated with unexpected wind gusts, although, generally, it was not windy at all. DJI support recommended an IMU calibration followed by a compass calibration, which I intend to do a.s.a.p!


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[BudWalker]

Hi All,

Well, I had my first problem with the mavic a few days ago. I've made about 30 flights so far without incident, it's a fantastic machine. I was flying around a lake far from power lines and using tap-fly as sort on an autopilot so I could concentrate on camera settings. I began getting yaw drift, to the point where I was almost flying sideways, as I could tell from the video feed. The rest of this story is told after reviewing the flight log many times. I then began heading back toward my home point, at which time I got the message "weak GPS signal". It had been showing 18 satellites, and still did, although the strength bars went down to 2 and turned red. The aircraft went into ATTI mode, as it should have, but began flying backwards and drifting sideways while maintaining an altitude of 150 feet. I made sure tap-fly mode was off. When I saw that the mavic was pointed in my general direction I pushed the right stick forward 100 % and got it back above me. I let go of both sticks and it began "toilet bowling", moving in circles above me without any input. I saw that the satellite strength bars were increasing and soon I had control back and was able to land.

I know that the yaw drift was probably from a bad compass calibration. I had just calibrated it at the park and there were frisbee golf goals not too far away, they may have caused a problem so my bad on that. However, after reading countless posts about the sudden loss of gps, and my own experience, I think the mavic does have a flaw. I think the gps unit is faulty and prone to sudden gps loss. I can understand going from 18 satellites to 10, but going from 18 to 0 in an instant in open country has got to be the gps unit. I don't know how to upload my flight log, if anyone knows how, let me know.View attachment 1613View attachment 1613View attachment 1614

Would it be possible to get the .DAT from this flight? If so, then it may be possible to determine the cause of the incident in this flight. The .DAT is on the Mavic Pro itself. To retrieve it use DJI Assistant 2 and go to the Flight Record tab. After confirming that it's OK to put the Mavic in Flight Data mode a list containing the recent flights will appear. Select just the Flight Control File of the incident flight and then press Save To Local. Ultimately a file with a name something like DJI_ASSISTANT_EXPORT_FILE[2016-10-27 22-40-28].DAT will be created. That file can't be attached here so you'll have to Dropbox it and post the link.

I'll use DatCon to convert this .DAT to a .csv file. If you've been on PhantomPilots P3 forum you may know about DatCon which reads and converts the P3 .DAT files. DatCon has been extended to work with Mavic .DAT files. I plan to relaease it in a week or so. But, I wanted to look at your incident while there is still the opportunity to retrieve that .DAT

 

[Sky Captain]

BudWalker, I will work on getting the DAT file out and will post it here, thanks

 

[mattmjm]

Edit: TBE = Toilet Bowl Effect

Also, what are the appropriate steps to notify DJI? Is there an official Email address?

I have posted about this issue in the forums, but not sure if that is going to be good enough.

 

[J3ffrey]

This IS NOT GOOD to see these stories popping up almost everyday. I may just flip mine on ebay for a small profit and never fly drones again.

I can tell you it is SCARY as heck when your drone takes off flying with no control from your sticks... it happened to me while filming almost 80 People in the water below during a dive in FL... for the 20 or so seconds it was out of control it was probably the scariest moments of my life just waiting to see if it ended up smacking a boat, or a kid/person in the water. Luckily it crashed south of the dive site and didn't hit anyway. Have never flown another drone near people since... was hoping the mavic wouldn't have this issue. Btw the drone that crashed went up about 150 feet and then flashed "GPS fail" and took off on it's own.. it was a blade chroma 4k

 

[Vlakvark]

Edit: TBE = Toilet Bowl Effect

Also, what are the appropriate steps to notify DJI? Is there an official Email address?

I have posted about this issue in the forums, but not sure if that is going to be good enough.

I logged in to Dji Support and started a "chat". They were very responsive and helpful. Finally an IMU- followed by a Compass calibration was recommended for my gps loss and toilet bowling problem. That seems to have helped, but it's still too soon to tell conclusively.


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[Vlakvark]

Would it be possible to get the .DAT from this flight? If so, then it may be possible to determine the cause of the incident in this flight. The .DAT is on the Mavic Pro itself. To retrieve it use DJI Assistant 2 and go to the Flight Record tab. After confirming that it's OK to put the Mavic in Flight Data mode a list containing the recent flights will appear. Select just the Flight Control File of the incident flight and then press Save To Local. Ultimately a file with a name something like DJI_ASSISTANT_EXPORT_FILE[2016-10-27 22-40-28].DAT will be created. That file can't be attached here so you'll have to Dropbox it and post the link.

I'll use DatCon to convert this .DAT to a .csv file. If you've been on PhantomPilots P3 forum you may know about DatCon which reads and converts the P3 .DAT files. DatCon has been extended to work with Mavic .DAT files. I plan to relaease it in a week or so. But, I wanted to look at your incident while there is still the opportunity to retrieve that .DAT

Thanks for your offer to investigate my problem! I'm trying to install DJI Assistant 2 on my Macbook Air, but haven't got it right yet! Meanwhile I've formatted the SD Card on the Mavic Pro. Could that have killed the .DAT files?

 

[BudWalker]

Thanks for your offer to investigate my problem! I'm trying to install DJI Assistant 2 on my Macbook Air, but haven't got it right yet! Meanwhile I've formatted the SD Card on the Mavic Pro. Could that have killed the .DAT files?

Negatory. The .DAT will still be there. The SD card that you formatted contains the flight videos. The .DATs are on a separate SD card.

When you extract the data don't include the Vision Module data - just the Flight Control data. DatCon doesn't know about the VM data. Also, you can include the FC from more than one flight.

 

[Freeky Reeky]

keep us posted sky captain .
thx for your update .

 

[BudWalker]

I looked at the .DAT for a incident that @erkme73 provided. I'm posting the results here since that incident is very similar to the ones being discussed in this thread. I'll describe what happened but since this is my first Mavic incident I can only speculate why it happened.

This was a ToiletBowling incident which happened here.



It appears to me that switching to Sport mode caused the Z axis magnetometer to become noisy.

The magZ noise is actually pretty severe with a minimum of 35 and a maximum of 1800. I've not seen anything like this on the P3.

DatCon has a computed field called magYaw that is the heading computed from the magnetometers and is different than Yaw which comes from the Flight Controller. Usually, magYaw is the same as Yaw. When the Z magnetometer became noisy magYaw began to separate from Yaw.

The Yaw/magYaw separation had been 5 degrees but slowly grew to 30 degrees at 850 secs when ToiletBowling was obvious.

With the P3 this amount of Yaw/magYaw separation often leads to a nonGPSCause error (presented as a compass error in the DJI Go App) and a switch to ATTI mode. In this incident there was no switch to ATTI mode. I'll speculate that the ToiletBowling actually started at 823 but didn't become apparent until 848 secs when the pilot removed control stick input. At this point the Mavic should've just hovered without stick input but was moving (ToiletBowling).

I'm speculating the magZ noise was caused, at least partly, by the switch to Sport mode. I've asked @erkme73 if the other ToiletBowling incidents happened only after a switch to Sport mode.

A compass calibration issue can be seen by looking at the behavior of Yaw and magYaw. There was no indication of a compass calibration issue in this flight.

The .csv used here has been attached here as a .zip for those interested in looking this incident.

 

[erkme73]

I looked at the .DAT for a incident that @erkme73 provided. I'm posting the results here since that incident is very similar to the ones being discussed in this thread. I'll describe what happened but since this is my first Mavic incident I can only speculate why it happened.

This was a ToiletBowling incident which happened here.
View attachment 1711


It appears to me that switching to Sport mode caused the Z axis magnetometer to become noisy.

The magZ noise is actually pretty severe with a minimum of 35 and a maximum of 1800. I've not seen anything like this on the P3.

DatCon has a computed field called magYaw that is the heading computed from the magnetometers and is different than Yaw which comes from the Flight Controller. Usually, magYaw is the same as Yaw. When the Z magnetometer became noisy magYaw began to separate from Yaw.

The Yaw/magYaw separation had been 5 degrees but slowly grew to 30 degrees at 850 secs when ToiletBowling was obvious.

With the P3 this amount of Yaw/magYaw separation often leads to a nonGPSCause error (presented as a compass error in the DJI Go App) and a switch to ATTI mode. In this incident there was no switch to ATTI mode. I'll speculate that the ToiletBowling actually started at 823 but didn't become apparent until 848 secs when the pilot removed control stick input. At this point the Mavic should've just hovered without stick input but was moving (ToiletBowling).

I'm speculating the magZ noise was caused, at least partly, by the switch to Sport mode. I've asked @erkme73 if the other ToiletBowling incidents happened only after a switch to Sport mode.

A compass calibration issue can be seen by looking at the behavior of Yaw and magYaw. There was no indication of a compass calibration issue in this flight.

The .csv used here has been attached here as a .zip for those interested in looking this incident.

Buy this man a beer. No, a case of beer. Scratch that. Buy him a frigging brewery. Since I had no reason to suspect P-mode to S-mode operation was involved, I honestly could not recall if I've ever had the TBE during either mode exclusively. However, since Bud asked me that question, I've moved 700 miles north to middle-TN where there is nothing but open forest and cliff formations. I flew about 22k feet on my first (and so far only) flight. The first 19 minutes (or so) were exclusively p-mode. I had several hovers and zero TBEs. As I started my trip back to the homepoint, I switched to s-mode to get back quicker. Immediately thereafter, it felt like there were rubber bands pulling the MP in every direction as I tried to fly a straight line back to the homepoint. It was flying like I had a BAC of .30.

It kept switching back and forth between ATTI and GPS, and putting it back in P-mode did NOT stop the TBE. Whenever I let go of the sticks, it started drift FAST. When I managed to get it close to the homepoint, and the altitude was low enough for the VPS to lock, it became rock solid. Up until that moment, I was puckering with max sphincter power.

I am SO grateful to Bud for putting so much effort an time into analyzing this. Who knows what DJI is doing internally, but what they told me seemed like they have zero grasp of (or interest in) solving the problem. They dismissed this as flying in the dark and interference. I should fly during the day and launch from a different home point. Riiight...

 

[niclariv]

Please tell DJI so they can fix the transition to sport mode if that's the cause of this for everyone


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[Sky Captain]

BudWalker, when I try to access the dat files with DJI assistant 2, I just get a spinning wheel but they never show up.

 

[erkme73]

Just a couple more data points... I flew my MP two more times since my worst case of TBE yet. Keeping it in GPS mode the entire time, I had NO wandering/TBE for either flight.

 

[niclariv]

If you happen to switch to sport mode and see this happen again, it would be helpful to know if toggling the sport mode switch back to normal makes the Mavic get back under control


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[erkme73]

If you happen to switch to sport mode and see this happen again, it would be helpful to know if toggling the sport mode switch back to normal makes the Mavic get back under control


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In my case it has not. Once the TBE starts, the MP develops distinct arcs in every direction of travel. The GPS may return, at which point precise control returns, but it doesn't last. After a few seconds to maybe a minute, it switches back to ATTI - along with another warning that the satellite signal is off and to use caution - and the wobbling returns. The only thing that seems to snap it out is when the craft is low enough to get a VPS lock. Then it's rock solid again. Of course, shutting it off, and starting all over makes it fly like a dream - until switched back to sports mode.

 

[niclariv]

In my case it has not. Once the TBE starts, the MP develops distinct arcs in every direction of travel. The GPS may return, at which point precise control returns, but it doesn't last. After a few seconds to maybe a minute, it switches back to ATTI - along with another warning that the satellite signal is off and to use caution - and the wobbling returns. The only thing that seems to snap it out is when the craft is low enough to get a VPS lock. Then it's rock solid again. Of course, shutting it off, and starting all over makes it fly like a dream - until switched back to sports mode.

Has it flown reliably for you every time you don't use sports mode? And does the switch to sports mode make it screw up every time? If so I bet that will be really helpful for DJI to solve with a firmware update - and good for everyone else to know to just avoid sports mode for now and they'll be good to go.


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[erkme73]

Has it flown reliably for you every time you don't use sports mode? And does the switch to sports mode make it screw up every time? If so I bet that will be really helpful for DJI to solve with a firmware update - and good for everyone else to know to just avoid sports mode for now and they'll be good to go.


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Up until today when BudWalker pointed out what triggered the TBE for the flight he analyzed, I had no clue that I should be paying attention to what mode I was in. Everyone was barking "it's a bad compass data" and "you need to be butt nekkid in the center of a baseball field to get a good compass calibration" - so that's what I focused on. Now that I know there's a correlation with the mode being switched to sports, I can say YES. Granted I've only had three or four flights, but in each case staying in P-mode meant zero TBEs. Switching to S-mode, each flight experienced TBE. Might just be correlation (and not causation) but I'm certainly paying attention now.

 

[BudWalker]

If you happen to switch to sport mode and see this happen again, it would be helpful to know if toggling the sport mode switch back to normal makes the Mavic get back under control


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If the theory proves to be correct then switching back to normal mode won't have an immediate effect. When the switch to Sport mode occurs the Yaw/magYaw separation isn't immediate. It gradually increases until TBE occurs. After switching back to normal mode the return to a normal Yaw/magYaw separation will also be gradual.

 

[erkme73]

If the theory proves to be correct then switching back to normal mode won't have an immediate effect. When the switch to Sport mode occurs the Yaw/magYaw separation isn't immediate. It gradually increases until TBE occurs. After switching back to normal mode the return to a normal Yaw/magYaw separation will also be gradual.

Well, the DAT I'm uploading now (2.5 hrs to go) will show 90% of the flight in P-mode. I switch to S-mode to get back to homepoint - but what should have been a straight line back looked like a drunkard trying to walk a line. When I got back to within the final minute or two, I'd switched back to P-mode, but the wild TBE was worse than ever. It settled just before landing - which I attributed to getting closer to the ground where VPS took over - but maybe it was the merging of the Yaw/magYaw as you described it.

I tell you one thing, if not for investigating this, or emergency need, I will not willingly switch back to to S-mode. How do we get DJI involved to get this addressed?