GPS Compass Error whilst in flight

[SuperRC]

Thanks guys. I'll try and extract this,. DAT file in the next couple of days. And I'll add a link to this thread.

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[SuperRC]

The records on the drone are the .DAT files. They have a lot more info and sometimes yield the cause in this type of incident. For info on how to retrieve a .DAT go here That page also contains info on picking the right .DAT. It will be large and can't be uploaded here. Instead, you'll need to create a Dropbox link (or equivalent) and post that here.

If the other pilots in this thread with a similar incident would like to post their .DAT I'd be glad to take a look those as well.

Thanks guys. I'll try and extract this, .DAT file in the next couple of days. And I'll add a link to this thread.

Sorry ... HealthyDrones only ever shows a brief summary but no details at all.
It never shows compass errors and isn't suitable for investigating an incident.

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[Monico Garza]

I had the same thing happen to me since the last firmware upgrade. Before this last time it happened when I flew by a train full of metal of course I knew then what caused it. These last 2 times it was in the air about 200ft in open field after a few seconds it fixed itself never had any issues but I am wondering why this has happened recently and it seems like I am not the only one that's having the problem.


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[robinb]

Ok, I have the dat file off the drone, where / how to view it ?

thanks

 

[robinb]

So tried to convert DAT to a csv file, but no luck in getting the csv to upload to the phantom log viewer or healtydrones

Help !

The DAT file is here.

Dropbox - FLY135.DAT

 

[BudWalker]

So tried to convert DAT to a csv file, but no luck in getting the csv to upload to the phantom log viewer or healtydrones

Help !

The DAT file is here.

Dropbox - FLY135.DAT

I didn't see this until just now. I'm not sure how you converted to .csv. I loaded the .DAT into CsvView which then converts the .DAT to a .csv and then visualizes that .csv. CsvView can be obtained by going here.

My analysis of this incident is not all that informative. I'll do some speculation to make up for that

Shown are the values for Yaw and magYaw. Yaw is the Flight Controller's notion of the AC heading. Yaw is derived mostly from the IMU values. Yaw is the value you see in the form of a red triangle presented by the DJI Go App. magYaw is a diagnostic computed by DatCon which CsvView uses to convert the .DAT. Unlike Yaw, magYaw is computed from the current value of the magnetometers.

At time 68.1867 the values of Yaw and magYaw separate, the FC declares a YAW_ERROR_LARGE and presents that as a "compass error" in the Go App. The problem is that the separation is not very large. In addition, there is no apparent cause for the separation. Two points should be emphasized. magYaw is a diagnostic computed by DatCon. At best it's a proxy for some calculations done by the P3. Secondly, there are many variables that DatCon doesn't know about.

I'm not a DJI engineer writing the code for the P3 FC so the following is just speculation on my part. The FC can't always be correct and has to always be looking for indications of possible problems. In particular, if it's possible the heading is incorrect then it doesn't want to use that heading to navigate. But, it's impossible for any algorithm to detect an incorrect heading with 100% accuracy. You have to choose - err on the side of not detecting a problem, or err on the side of false positives.

I get the impression that, with every FW update, the trend is toward more false positives and less undetected heading errors. Personally, I think this is the right trend. I've adopted the perspective that an occasional mid-flight "compass error" is the P3 saying "I'm confused, can you fly this thing in ATTI mode until I get it figured out". Not that there is a serious issue that needs fixing.

There is an exception. If the Go App is saying "compass error" then DON'T initiate an RTH. The P3 is telling you that it's not sure about it's heading value. If you initiate an RTH it will use whatever that heading value is to navigate back home - probably in the wrong direction.

 

[robinb]

Hi, thanks Bud

I used 2 methods to obtain a csv file, an online converter and an app. Both resulted files failed to load on the 2 mentioned websites.

Its all a bit odd, I took off fairly quickly and moving forward and increased hight to 80m.
At about 700m away I got the error message.
I turned drone around and flew it in atti mode.
Just at point of getting home it reverted to GPS mode.

Obvious I would not initiate RTH (in fact never have) as I could see drone did not know its location. Until it got close to me.

Bit concerning that the only time it did it before was very brief, this was a lot longer etc.

So other than Yaw error is there anything else ?

thanks

 

[BudWalker]

@robinb,
I seem to have omitted a critical point. YAW_ERROR_LARGE is the "compass error". When YAW_ERROR_LARGE happens that gets presented in the Go App as a compass error. (COMPASS_ERROR_LARGE and SPEED_ERROR_LARGE also get presented as a "compass error"). There is a root cause that caused both the magYaw/Yaw separation and the YAW_ERROR_LARGE. But, DatCon isn't smart enough to tell us that root cause.

You didn't say which app you used to convert the .DAT to a .csv. The only app that I know that does this is DatCon. Neither PhantomHelp or HealthyDones will accept a .csv generated by DatCon. However, CsvView will accept the .csv generated by DatCon and TXTlogToCSVtool (a .txt to .csv converter). The next version will also accept Litchi .csv log files and the Typhoon H .csv log files.

I took the liberty using your post to make the point to the forum at large about not initiating the RTH in the presence of a "compass error".

You could retrieve the .DAT from the other flight with the compass error. It might be more informative.

 

[robinb]

I used datcon to generate CSV file and another online website (www.mapsmadeeasy.com) but as you said healthy drones and the pp site can't view them.

I had not not across css view app until you mentioned it earlier,

I run Mac so I don't have ready access to widows computer.

I would need to go back through my flights to see if I can recall date of last time I had the error, again it was whilst airborne, not as high but probably 500 m away, it was quite brief error. I have done quite a few flights between.

Bit odd, anything come to mind that would cause this ?

Thanks

 

[robinb]

ok, got cssview on another pc running.

Not sure I really understand what its telling me.

 

[robinb]

Here is the other file when i had the error before.
Looks like there is also compass error at the end of flight, I did not see this as I was coming into land and watching the drone.

Dropbox - FLY132.DAT

 

[BudWalker]

@robinb,
I looked at your FLY132. I think you'll like this one better. I do. It's clear what happened. There were two "compass error" incidents. Both were caused by geomagnetic distortion at the launch/termination site. This could be caused by ferrous material such as a culvert under the roadway at the launch/termination site.

Before launch the magnetometer values where incorrect because of the geomagnetic distortion. Yaw was initialized with this incorrect value. When the P3 launched the P3 cleared geomagnetic distortion ad the magnetometers became correct. But, Yaw didn't change because the gyros didn't report any rotation. This Yaw/magYaw separation can be seen here.

It's a little unusual that the YAW_ERROR_LARGE (i.e., compass error) didn't indicate until 20 secs later.

The second compass error incident was in the form of a COMPASS_ERROR_LARGE that occurred when the P3 was brought back to the geomagnetic distortion. As the P3 lost altitude there was change in the magnetometers along with the Yaw/magYaw separation.

The incident in the flight is unrelated to the incident in the other flight (FLY135) we've been looking at.

 

[robinb]

Ok, thanks

I did not get any warning about compass until I was airborne and some distance away from me.
In past if there has been something large metallic I have seen warning on screen.
Thats not to say it did not happen or there was not something underground.
I had a friend with me that day flying his p3 advanced and he did not mention anything about warning on his but I will double check with him later today.

I was not too worried about the flight as the error was brief, the original flight from the other day still bothers me.

Wish I knew the root cause of problem.

 

[BudWalker]

Ok, thanks

I did not get any warning about compass until I was airborne and some distance away from me.
In past if there has been something large metallic I have seen warning on screen.
Thats not to say it did not happen or there was not something underground.
I had a friend with me that day flying his p3 advanced and he did not mention anything about warning on his but I will double check with him later today.

I was not too worried about the flight as the error was brief, the original flight from the other day still bothers me.

Wish I knew the root cause of problem.

FLY132 and FLY135 have different "compass error" problems. They are unrelated. They do not share a common root cause.

In FLY132 the cause is a distortion in the geomagnetic field at the launch/landing site. The P3 can't know if the field is distorted. But it does know the intensity of the field. This is the magMod value that you should check before launch and confirm that it is in the range [1400, 1600]. The P3 requires that magMod be within [1200, 2000] (I think this right) and will prevent motorStart otherwise.

The problem is that the field can be distorted but the magMod (intensity) is within limits. At the beginning of FLY132 magMod was 1449 which is within the acceptable range.

At the end of FLY132, just a few meters away, magMod was 4373. The P3 would have prevented motorStart at this location.

FLY132 and FLY135 have different "compass error" problems. They are unrelated. They do not share a common root cause.


FLY132 and FLY135 have different "compass error" problems. They are unrelated. They do not share a common root cause.

 

[John@egl-i]

I experienced this, mentioned it to the landowner and discovered there was a buried tractor just below the grass!....don't you just love farmers....Panic over!....will now be my default diagnosis, rather than investing in a metal detector.

 

[Mocho]

I experienced this, mentioned it to the landowner and discovered there was a buried tractor just below the grass!....don't you just love farmers....Panic over!....will now be my default diagnosis, rather than investing in a metal detector.

You don't need a metal detector if your ph/tablet device contains a magnetometer. Just get a metal detector app and place your device on the ground to see if there is anything magnetic under you.

First discovered such an app when I was trying to find the main water shut off to the house, which was under the lawn.
I didn't have access to a metal detector but recalled my iPhone has a magnetometer built in, sure enough there was an app for that I did find the exact spot for my shut off valve

 

[robinb]

FLY132 and FLY135 have different "compass error" problems. They are unrelated. They do not share a common root cause.

In FLY132 the cause is a distortion in the geomagnetic field at the launch/landing site. The P3 can't know if the field is distorted. But it does know the intensity of the field. This is the magMod value that you should check before launch and confirm that it is in the range [1400, 1600]. The P3 requires that magMod be within [1200, 2000] (I think this right) and will prevent motorStart otherwise.

The problem is that the field can be distorted but the magMod (intensity) is within limits. At the beginning of FLY132 magMod was 1449 which is within the acceptable range.
View attachment 64474
View attachment 64475

At the end of FLY132, just a few meters away, magMod was 4373. The P3 would have prevented motorStart at this location.
View attachment 64476
View attachment 64477


FLY132 and FLY135 have different "compass error" problems. They are unrelated. They do not share a common root cause.


FLY132 and FLY135 have different "compass error" problems. They are unrelated. They do not share a common root cause.

Thanks Bud for your help.
I find interpreting the logs hard as its just a mass of numbers to me.
In a few days will take to air again, see what happens.

 

[SuperRC]

The records on the drone are the .DAT files. They have a lot more info and sometimes yield the cause in this type of incident. For info on how to retrieve a .DAT go here That page also contains info on picking the right .DAT. It will be large and can't be uploaded here. Instead, you'll need to create a Dropbox link (or equivalent) and post that here.

If the other pilots in this thread with a similar incident would like to post their .DAT I'd be glad to take a look those as well.

Hi Bud,
I have downloaded the .DAT file for the date I did the flight and got the compass error.

After reviewing the video I noticed the compass error came up when i was close to some power lines, but well clear of them. This has not happened before, so to test it, today I did a flight from another location and flew in very close proximity to those same powerlines, there was no compass error.

Anyway, here is a link to the .DAT file for the flight with the compass error.

Dropbox - FLY136.DAT

Cheers

 

[BudWalker]

Hi Bud,
I have downloaded the .DAT file for the date I did the flight and got the compass error.

After reviewing the video I noticed the compass error came up when i was close to some power lines, but well clear of them. This has not happened before, so to test it, today I did a flight from another location and flew in very close proximity to those same powerlines, there was no compass error.

Anyway, here is a link to the .DAT file for the flight with the compass error.

Dropbox - FLY136.DAT

Cheers

The compass error in this flight is even more of a mystery than @robinb 's first flight (FLY135). I checked all of the values that DatCon knows about. The only thing I found was abrupt roll and gyroZ values at the time (85 secs) of the compass error.

I've seen this in other flights where gusty wind conditions generate sensor values the FC didn't predict. The roll and gyro values were not accompanied by stick inputs. However, in those flights the sensor deviations were much larger. Although in this flight there were other instances with large values for roll and gyroX these happened while the A/C was on the ground and not moving. BTW, I ran DatCon at 200 Hz and submitted that .csv to CsvView.

Believe it or not I had a flight very similar to this. The compass error was accompanied with an abrupt change in roll and gyroX values. And, it occurred close to some power lines. I have since flown close to those power lines many times attempting to recreate the problem. Nothing - I've had to conclude the power lines were just a coincidence. I've not had an unexplained compass error in the roughly 90 flights since that incident.

My advice? If this is an isolated incident treat it as a false positive as I described in post #26. But, if it's a common occurrence maybe it's time for a trip to DJI repair.

 

[SuperRC]

Hi Bud,
Thanks very much for the analysis. Some of it makes sense, however some is beyond the level of my knowledge. Lol
I just want to note, that when I got the compass error and yawned the aircraft to return, the camera gyro had some massive roll (about 20 degrees), then eventually levelled itself out after about 20 seconds. Not sure if this is anything to do with false roll and gyro values.

Do you mind if I send you my. DAT file from the last flight I did where I didn't have an issue? I'll have to send it to yo in Thursday as that's when I'll get home from work. The funny thing with this one is that I did not have any errors or indications when I flew near the power lines, however when I uploaded my file to healthy drones, it shows the track where I flew near the power tower (W-X) as red weak signal.
On the map you can visually see the power lines, however the red weak signal only came when I flew over the power tower. When I flew near the actual lines (D) it doesn't show any signal degradation, all green.
Here is the link to healthy drones:

HealthyDrones.com - Innovative flight data analysis that matters

Cheers


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