My Mavic Pro's GPS went bad!!

[FlyingFilmmaker]

So from my previous thread, my MP1 has been drifting to the side when flying (not hovering) but the direction of the drift is tied to the compass directions (North South East West) rather than the orientation of the drone. (Here's the link to my previous post for a more complete description. Drone not flying straight after crash and repair)

After a lot of testing and thinking, I narrowed it down to the compass and GPS with the compass being unlikely since it looks fine in the app and calibrates normally. This pretty much left the GPS, but that seemed pretty unlikely.

So, to test it I decided to take off before it got a GPS lock and see if it flies straight in vision mode. I took off immediately after IMU initialization, and it flew perfectly straight until it acquired the GPS signal. In fact, I was flying backwards when it got GPS and I could see it deviate to the left at the same time the rear light flashed to signal GPS lock.

So it appears that the GPS is at fault. I took the top cover back off today, looked at the wires (nothing was unusual), unplugged the GPS, plugged it back in, reassembled, and took for a test flight. Same thing.

Apparently the GPS unit is either bad or has a bad connection. Seems VERY strange that it would cause the drone to drift but not give ANY errors, but that's what's happening.

I guess the next thing to do is to get a new GPS unit. Hopefully that will fix it. Getting tired of my drone not working.

Has anyone else had GPS issues that made their drone do weird things?

 

[old man mavic]

it could be that its the connector from the GPS ,unit that stays in the top of the case when you remove it from the main control board ,check to see if there are any bent pins as its fiddly to plug it in while holding both the main body and the top as you connect it

 

[FlyingFilmmaker]

it could be that its the connector from the GPS ,unit that stays in the top of the case when you remove it from the main control board ,check to see if there are any bent pins as its fiddly to plug it in while holding both the main body and the top as you connect it

I looked at the connection, looked fine. Didn't looks specifically for bent pins but I think I would have noticed it. I simply set the main body on a desk so it's not quite as hard.

 

[old man mavic]

I looked at the connection, looked fine. Didn't looks specifically for bent pins but I think I would have noticed it. I simply set the main body on a desk so it's not quite as hard.

no worries just trying to think of issues it might be guess the only thing to do is try a new GPS unit and see if that fixes it,other than that its an issue with the IMU not correlating the info from the various units in the drone and matching what the GPS unit is telling it,just one thing is the height that the deviation to the flight path happens above the downwards sensor range or only when you are within range of the sensors, as GPS positioning takes over above around 35 ft

 

[Flygmaskin]

How do the flight logs look? Any anomalies there or anything that might help you isolating the issue? You could post a.txt from the mobile device and a .dat from the AC.

Interesting to see the changes in the logs when GPS kicks in. Also, there are geniuses here at the forum that might see something in the logs.

 

[FlyingFilmmaker]

no worries just trying to think of issues it might be guess the only thing to do is try a new GPS unit and see if that fixes it,other than that its an issue with the IMU not correlating the info from the various units in the drone and matching what the GPS unit is telling it,just one thing is the height that the deviation to the flight path happens above the downwards sensor range or only when you are within range of the sensors, as GPS positioning takes over above around 35 ft

Deviation/drift happens at any altitude you fly at from 10 feet to 400 feet.

 

[FlyingFilmmaker]

How do the flight logs look? Any anomalies there or anything that might help you isolating the issue? You could post a.txt from the mobile device and a .dat from the AC.

Interesting to see the changes in the logs when GPS kicks in. Also, there are geniuses here at the forum that might see something in the logs.

Might try to get those. Never had much success getting flight logs before though.

 

[Flygmaskin]

Might try to get those. Never had much success getting flight logs before though.

I think someone might be able to help you from those logs.

Not to hard to obtain.

 

[lannes]

Might try to get those. Never had much success getting flight logs before though.

Just follow the instructions and post the link here

DJI Flight Log Viewer | Phantom Help

Upload and view flight logs from your DJI drones

www.phantomhelp.com

 

[Dave Maine]

It sounds like a conflict between the ac compass and the GPS data. The flight controller integrates data from both of them and calculates the commands for directional control from that. When you take off, does the drone compass heading match the tablet heading and your actual orientation? Magnetic disturbances at the takeoff point cause the compass orientation to be wrong, either a little bit or a lot. Large differences lead to crashes.

 

[sar104]

So from my previous thread, my MP1 has been drifting to the side when flying (not hovering) but the direction of the drift is tied to the compass directions (North South East West) rather than the orientation of the drone. (Here's the link to my previous post for a more complete description. Drone not flying straight after crash and repair)

After a lot of testing and thinking, I narrowed it down to the compass and GPS with the compass being unlikely since it looks fine in the app and calibrates normally. This pretty much left the GPS, but that seemed pretty unlikely.

So, to test it I decided to take off before it got a GPS lock and see if it flies straight in vision mode. I took off immediately after IMU initialization, and it flew perfectly straight until it acquired the GPS signal. In fact, I was flying backwards when it got GPS and I could see it deviate to the left at the same time the rear light flashed to signal GPS lock.

So it appears that the GPS is at fault. I took the top cover back off today, looked at the wires (nothing was unusual), unplugged the GPS, plugged it back in, reassembled, and took for a test flight. Same thing.

Apparently the GPS unit is either bad or has a bad connection. Seems VERY strange that it would cause the drone to drift but not give ANY errors, but that's what's happening.

I guess the next thing to do is to get a new GPS unit. Hopefully that will fix it. Getting tired of my drone not working.

Has anyone else had GPS issues that made their drone do weird things?

This problem is completely trivial to diagnose. At the simplest level, does the compass indication on the app show the aircraft pointing in the right direction, and if you pick it up and rotate it, does the display (either map or compass rose) see the rotation properly? Next - how many satellites is it indicating as locked, and does it show the correct location on the map? If you pick it up and move it does it move properly on the map?

Beyond that, one glance at the flight logs will give the definitive answer and end all speculation. That said, it is most unlikely to be a GPS problem - if that were the case then it would not go into P-GPS mode. It's far more likely to be a compass problem, which is easily fixed.

 

[FlyingFilmmaker]

This problem is completely trivial to diagnose. At the simplest level, does the compass indication on the app show the aircraft pointing in the right direction, and if you pick it up and rotate it, does the display (either map or compass rose) see the rotation properly? Next - how many satellites is it indicating as locked, and does it show the correct location on the map? If you pick it up and move it does it move properly on the map?

Beyond that, one glance at the flight logs will give the definitive answer and end all speculation. That said, it is most unlikely to be a GPS problem - if that were the case then it would not go into P-GPS mode. It's far more likely to be a compass problem, which is easily fixed.

I will try to get flight logs up soon. The compass indicator does point the right direction, but I haven't tried rotating it to see if it displays the movement. It shows at least 10 satellites when it's on the ground which is about normal in our narrow valley (both with the Mavic and P3A). I haven't looked at the map while moving so that's something I'll check as well and report back. I thought I had pretty much ruled out a compass problem since I've recalibrated that several times with no change and the indicators in the app look normal, but I really don't know. As I said I'll try to get some logs up for inspection.

 

[FlyingFilmmaker]

Here are the flight logs from the flight where I was flying first in ATTI/VISION then went to GPS. The GPS portion of the flight is pretty short since I was just doing a test.

AC flight log. DJI_ASSISTANT_EXPORT_FILE_2020-07-06_12-55-55.DAT

And the TXT log from DJI GO 4.

I'll try to do the compass and GPS tests with the app today.

Thanks so much everyone for the help on this!!

 

[BudWalker]

Here are the flight logs from the flight where I was flying first in ATTI/VISION then went to GPS. The GPS portion of the flight is pretty short since I was just doing a test.

AC flight log. DJI_ASSISTANT_EXPORT_FILE_2020-07-06_12-55-55.DAT

And the TXT log from DJI GO 4.

I'll try to do the compass and GPS tests with the app today.

Thanks so much everyone for the help on this!!

FLY170 is showing that GPS_ATTI was in effect 43 secs before navHealth had reached 4 (out of 5). That's not right. While that's being looked at can you do a test? After power up wait for gps indicator on the controller to reach 4. Then launch and see if you still see the problems you described.

 

[BudWalker]

@DroneFilmmaker I had another read of your original post. (I hate it when others don't carefully read all the posts before commenting. ) The "problem" you're seeing is normal. If launch occurs before navHealth (or gpsLevel) reaches 4 the vision system and not GPS is being used for attitude control. When the switch from vision to GPS is made there will be some minor adjustments. It isn't seamless.

At least with the Mavic GPS_ATTI really means that either GPS or the vision system is being used for attitude control.

 

[FlyingFilmmaker]

@DroneFilmmaker I had another read of your original post. (I hate it when others don't carefully read all the posts before commenting. ) The "problem" you're seeing is normal. If launch occurs before navHealth (or gpsLevel) reaches 4 the vision system and not GPS is being used for attitude control. When the switch from vision to GPS is made there will be some minor adjustments. It isn't seamless.

At least with the Mavic GPS_ATTI really means that either GPS or the vision system is being used for attitude control.

I gave it a try with letting the navHealth go to 4 before take-off and the issue is still there. If you read the other post I linked to the problem isn't that it adjusts direction when getting GPS lock but that it flies about 20 degrees (just an estimate) off from straight forward when in GPS mode. Here's a full description from the other thread. Drone not flying straight after crash and repair

 

[BudWalker]

I gave it a try with letting the navHealth go to 4 before take-off and the issue is still there. If you read the other post I linked to the problem isn't that it adjusts direction when getting GPS lock but that it flies about 20 degrees (just an estimate) off from straight forward when in GPS mode. Here's a full description from the other thread. Drone not flying straight after crash and repair

Can you provide both the .txt and .DAT for that flight then.

 

[FlyingFilmmaker]

This problem is completely trivial to diagnose. At the simplest level, does the compass indication on the app show the aircraft pointing in the right direction, and if you pick it up and rotate it, does the display (either map or compass rose) see the rotation properly? Next - how many satellites is it indicating as locked, and does it show the correct location on the map? If you pick it up and move it does it move properly on the map?

Beyond that, one glance at the flight logs will give the definitive answer and end all speculation. That said, it is most unlikely to be a GPS problem - if that were the case then it would not go into P-GPS mode. It's far more likely to be a compass problem, which is easily fixed.

After uploading the logs I just took the drone out and tested both of these. The compass point right where it should and the indicator in the app rotates like it should when I pick it up and rotate it. The GPS shows the correct location on the map and if I move it, the little arrow on the map moves where I go. And it had 10 satalites.

 

[FlyingFilmmaker]

Can you provide both the .txt and .DAT for that flight then.

This flight had that problem as well after it got the GPS lock, but I can get flight logs for a longer flight with GPS as well if that's needed.

 

[sar104]

I gave it a try with letting the navHealth go to 4 before take-off and the issue is still there. If you read the other post I linked to the problem isn't that it adjusts direction when getting GPS lock but that it flies about 20 degrees (just an estimate) off from straight forward when in GPS mode. Here's a full description from the other thread. Drone not flying straight after crash and repair

All the issues in the flight that you posted were due to insufficient GNSS satellite reception.





In terms of compass data, compass 0 was active and the magnetic data look good enough not to have cause the problem.