Maiden Flight -GPS issue

[Leigh]

Ok my first flight everything went as it should got GPS lock on 17 Satellites took off in Beginner mode and within a minute lost GPS lock and it fell back on opti showing week GPS signal with 17 Satellites still so I landed.
This happened all 3 times I tried so stopped flying till I know what happened.

Any ideas guys?


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[Cyberpower678]

Can you upload your log to PhantomLogViewer?

https://www.phantomhelp.com/LogViewer/Upload/

 

[Mavicsailor]

Ok my first flight everything went as it should got GPS lock on 17 Satellites took off in Beginner mode and within a minute lost GPS lock and it fell back on opti showing week GPS signal with 17 Satellites still so I landed.
This happened all 3 times I tried so stopped flying till I know what happened.

Any ideas guys?


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There have been multiple reports of GPS health (5 bars top) suddenly dropping from full strength to none, while maintaining a high level of satellites. At this point it drops (less than 4 bars) into Atti mode where the flight characteristics seem to very considerably from pilot to pilot. Luckily yours was close enough to the ground to maintain control using the optical sensors for position.

Hopefully DJI is working on solving this mystery. The interesting thing is how quickly the health drops. One would think it might drift a bit as do the number of satellites, but not drop to 0 suddenly. It's understandably a reason for much concern. In some situations this has and can lead to crashes. To date, there appear to be multiple theories, but no hard solutions from DJI.

Given the repeatability of yours it may be best to send it back under warranty. Sounds like the GPS receiver may be marginal at best. Possibility even something as simple as pointy soldier points (bad QC)creating mini antennas generating increased RF that would decrease the GPS SNR. Even then, not sure why it would suddenly drop off.

 

[larkin]

I suspect it's a software issue or it's an unfixable hardware issue. The GPS on this thing is for sure it's weakest point. You just have to change location. Any potential for magnetic interference where you are in? This has happened to me but always during a semi low hover close to metal on objects, like a parking structure or in my home.

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[Leigh]

Here are some of the logs thanks
Phantom Log Viewer - PhantomHelp.com
Phantom Log Viewer - PhantomHelp.com

 

[Leigh]

Not tried a different location yet, dont think there was much chance of magnetic interference, this was at a low hover as you can see from the logs just took off , sat at a meter up from take off point and GPS was locked , moved forward about 3 meters and hovered, then watched is switch to Opti, waited about a minute or two to see if it would lock again, it didn't so reversed it back to the take off point and landed it, repeated this 4 or 5 times in beginner mode and normal mode, same result everytime, have done anything to the drone out the box , no compass or IMU calibrations, already on the latest software.

 

[Mavicsailor]

Not tried a different location yet, dont think there was much chance of magnetic interference, this was at a low hover as you can see from the logs just took off , sat at a meter up from take off point and GPS was locked , moved forward about 3 meters and hovered, then watched is switch to Opti, waited about a minute or two to see if it would lock again, it didn't so reversed it back to the take off point and landed it, repeated this 4 or 5 times in beginner mode and normal mode, same result everytime, have done anything to the drone out the box , no compass or IMU calibrations, already on the latest software.

Leigh,

It would be most helpful if you could pull the .dat file directly from the mavic using DJI assist. That gives much more to work with using CsvViewer written by BudWalker. (Thanks again!) As the file is large, you will need to use dropbox or similar. Even with this I'm not sure if much can be learned in these GPS health drop reports using the .dat file from the Mavic.

BudWalker, have you been able to identify anything that is unique to these situations other than the GPS health shown as suddenly dropping? Maybe abnormally high noise in any of the readings that might affect the GPS SNR and consequently the health of the Signal quality ?

 

[Leigh]

I'll get the .dat files shortly if you think it might help.Just performed a very basic test in the back yard, didn't fly as the light was fading but I powered up and got a GPS lock then when to pick it up and lost the lock (I assume if your palm is over the top of the drone it blocks the signal?) moved my hand underneath and it locked again then walked it around the yard it is held the lock (Sats went from 9 originally to 12 eventually)

 

[Mavicsailor]

The GPS module is in the back of the Mavic so if that's blocked the satellites will go down. For these issues the focus is more on the GPS Health as indicated by the 5 bars next to the GPS satellite number. The health is what determines if the Mavic drops into Atti mode where it will not lock into position unless aided by the downward optical sensors. (Opti)

Can't promise anything in the .dat file will point to a problem other than it dropping gps health which we already know. If you try it in another location ruling out interference and it still has this problem, you may want to call support and start the preparation for return, or just return it to the place of purchase and get another one. They seem to be more available now in many outlets.

 

[Leigh]

Dropbox - Leigh Mavic Logs

Ok that should work hopefully.Thanks for your help, won't get chance to fly again till next weekend but will try a new location, I guess then I'll know if I need to make a return. It came direct from DJI.

 

[TopGun]

If I read the logs correctly, you were in ATTI for (only) a fraction of a second on both logs.

FWIW I have flown on the other side of the A30 in the crabtree plantation (is that correct name) with no issues. However, I dont think a blip of less than a second would have registered with me.

 

[Leigh]

Yes I saw that too but that wasn't my experience, on all occasions took off with GPS lock and hovered for a minute or so then went forward in a straight line 3 - 5 meters with lock still then it drifted to the left as if blown by wind just slightly and then went to opti mode and remained hovering and stable, I held it there for a minute to see if GPS lock came back , it didn't and I reversed it back to landing spot and landed.When I lost GPS lock I could see I retained 17 Sats but the GPS signal went from full to 1 or 2 bars I think.


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[SkyRider]

Did you calibrate the compass? Unless something has changed, if the compass and gps disagree enough, this can happen. Try a good compass calibration far from anything metal and see if that helps.

 

[larkin]

Flying indoors?

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[Leigh]

No not calibrated compass at all (conflicted comments about when to do it so waiting for it to tell me) but also read that this may help will find new location and calibrate next chance I get.


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[Leigh]

Outdoor flight not sure I'd ever trust a flight indoors, not really got the space at home


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[Leigh]

Yes I saw that too but that wasn't my experience, on all occasions took off with GPS lock and hovered for a minute or so then went forward in a straight line 3 - 5 meters with lock still then it drifted to the left as if blown by wind just slightly and then went to opti mode and remained hovering and stable, I held it there for a minute to see if GPS lock came back , it didn't and I reversed it back to landing spot and landed.When I lost GPS lock I could see I retained 17 Sats but the GPS signal went from full to 1 or 2 bars I think.


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Just noticed you can play back a video of the flights in flight list on the DJI app, they show my experience in that it went into Opti mode and didn't go back to GPS lock.Anyone know why logs show briefly in Atti mode then back to GPS but flight list and my experience showed it didn't return to GPS?


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[TopGun]

Mine insisted on a compass calibration when it was new from the factory which made perfect sense as it was made thousands of miles away somewhere in the far east.
I would 100% do a compass calibration and wonder why it did not insist before your first flight. Mine did.

After the first time I have been 40 or 50 miles to Southampton and I don't re calibrate with no adverse effect.

 

[jackgarner]

Here is one of my flight logs where the gps drops (300 feet in the air so no interference)


Here is your flight log (flight 10) Looks exactly the same... This is definitely something DJI needs to fix

 

[Leigh]

So having read a few threads on this forum about this issue am I looking at a hardware issue if so as it has only flown 5 meters I should be able to ask for an new unused replacement (I have refresh too) or should I try the compass calibration and a new location first ? Has anyone had this problem resolved by replacing their Mavic?


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