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P4 lost GPS signal in rural flight also lots of warnings
635 33 2018-1-6
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skyguy17
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Hi Fellow P4 pilots,

After the Red Green LED issue in November (from new) I have only ventured out on a few flights when the weather in the UK is kind enough.  Today I took it to a local very rural location to film the winter scene (it was misty) around noon.

The flight was far away from external RF sources (ie no town within miles) and I shot some nice views of the local water meadow and forest, at an altitude of between 120ft to 240ft.  During this flight I picked up a number of warnings about Yaw and even lost GPS signals for a while (though the AC was in sight of me).  I'm running the latest Firmware on the RC, AC and iOS device is using DJI Go 4 ver 4.1.20.

Before this flight I updated iOS app and carried out a full IMU and Compass calibration.

The fact the AC lost GPS is a big concern and I'm wonder again if the current Firmware on the P4 is actually stable
!  

Here is my log file (zipped up) if anyone or DJI support can give me a clue what the issue is?  

As this is an expense bit of kit I worried about fly aways and return to home failures!  Thanks guys....



DJIFlightRecord_2018-01-06.zip

756.14 KB, Down times: 3

2018-1-6
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ALABAMA
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Can't make heads or tails of that.     Go here and follow directions         http://www.phantomhelp.com/logviewer/upload/
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skyguy17
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ALABAMA Posted at 2018-1-6 08:43
Can't make heads or tails of that.     Go here and follow directions         http://www.phantomhelp.com/logviewer/upload/

Thanks Alabama, did the ZIP not work? Are you not able unZIP the file to the original TXT?

I tried the source flightlog [.TXT] file in "phantomhelp" and it shows same as Airdata UAV.  The errors occur around 10min and 11 sec into the flight.
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ALABAMA
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Unzipped, but just Chinese jibberish.
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skyguy17
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ALABAMA Posted at 2018-1-6 08:55
Unzipped, but just Chinese jibberish.

It's probably because I using an iMac and used the built in compress feature.  Let me try and PC zip instead.
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skyguy17
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ALABAMA Posted at 2018-1-6 08:55
Unzipped, but just Chinese jibberish.

Hi Alabama, have run it through winzip, tell me if this works for you?  Cheers ...
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Aardvark
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You could always try DJI Go 4 V4.1.22, it came out about four days ago.

A view of the Phantomhelp results would provide some details maybe as to what may have happened to generate the errors. Follow Alabamas link above, it explains what is needed. Phantomhelp displays the data in a format that is easy to read and understand.

Which iOS device are you using ?
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skyguy17
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Aardvark Posted at 2018-1-6 09:33
You could always try DJI Go 4 V4.1.22, it came out about four days ago.

A view of the Phantomhelp results would provide some details maybe as to what may have happened to generate the errors. Follow Alabamas link above, it explains what is needed. Phantomhelp displays the data in a format that is easy to read and understand.

Hi Aardvark,

I'm running the App on an iPad Air 1. The App is up to date according to the apple store, on the App store it states 4.1.22 but within the DJI GO 4 app and the "About" menu it says ver is 4.1.20? Odd??

The errors start about 10min into the flight, GPS tab shows 16 Satellites are seen, no other clue in the file that I can see. I've upload a new ZIP file.  Not sure what else I should be looking for?
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Aardvark
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skyguy17 Posted at 2018-1-6 09:44
Hi Aardvark,

I'm running the App on an iPad Air 1. The App is up to date according to the apple store, on the App store it states 4.1.22 but within the DJI GO 4 app and the "About" menu it says ver is 4.1.20? Odd??

"I'm running the App on an iPad Air 1. The App is up to date according to the apple store, on the App store it states 4.1.22 but within the DJI GO 4 app and the "About" menu it says ver is 4.1.20? Odd??"

I wonder if an uninstall and reinstall might help, my 'About' shows V4.1.22, I wonder if there's been a glitch during installation ?

If you post the phantomhelp file here then there are one or two that are very good at flight analysis that may be able to give a clue.
I already have a suspicion, you say you calibrated the compass, there is a slight chance of a bad compass calibration conflicting with the GPS data.
2018-1-6
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Why would anything to do with the app or the RC have anything to doo with the AC losing GPS signal? It can only be down to the GPS receiver and software using it in the aircraft. Unless there is GPS jamming and or selective availability turned off GPS is very stable certainly out in the open with unrestricted view of the sky.
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Aardvark
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PeteHB Posted at 2018-1-6 10:08
Why would anything to do with the app or the RC have anything to doo with the AC losing GPS signal? It can only be down to the GPS receiver and software using it in the aircraft. Unless there is GPS jamming and or selective availability turned off GPS is very stable certainly out in the open with unrestricted view of the sky.

He says that the GPS data reports 16 satellites, so something is causing Application to report an error.

Edit:- thats why its best to see the facts in the data, saves speculation.
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skyguy17
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Aardvark Posted at 2018-1-6 09:58
"I'm running the App on an iPad Air 1. The App is up to date according to the apple store, on the App store it states 4.1.22 but within the DJI GO 4 app and the "About" menu it says ver is 4.1.20? Odd??"

I wonder if an uninstall and reinstall might help, my 'About' shows V4.1.22, I wonder if there's been a glitch during installation ?

Hi Aardvark, OK am I being thick?

I've uploaded the TXT log file as zip which holds the flight info at the start of this thread. Phantomhelp only lets me export a KML or CSV neither of which I can load on this forum (it would seem). When you say you want the file from PhantomHelp what do you mean? Cheers...
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skyguy17
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This is what Airdata UAV is showing me
2018-1-6
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Aardvark
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skyguy17 Posted at 2018-1-6 10:22
Hi Aardvark, OK am I being thick?

I've uploaded the TXT log file as zip which holds the flight info at the start of this thread. Phantomhelp only lets me export a KML or CSV neither of which I can load on this forum (it would seem). When you say you want the file from PhantomHelp what do you mean? Cheers...

Just copy the address of the page it displays the record on in phantom help and post as a link here. That's it really.
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Aardvark
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skyguy17 Posted at 2018-1-6 10:22
Hi Aardvark, OK am I being thick?

I've uploaded the TXT log file as zip which holds the flight info at the start of this thread. Phantomhelp only lets me export a KML or CSV neither of which I can load on this forum (it would seem). When you say you want the file from PhantomHelp what do you mean? Cheers...

Here's another thread containing a phantom help file, you'll see what I mean there https://forum.dji.com/forum.php? ... &fromuid=154551
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skyguy17
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Aardvark Posted at 2018-1-6 10:52
Just copy the address of the page it displays the record on in phantom help and post as a link here. That's it really.

http://www.phantomhelp.com/logviewer/CT2R9MAD74WH8CV4T1JV/#

OK here it is !  Very interested to know what caused this, I've been watching on the iPad , which I have recorded off the screen as well. Might post this later...
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Labroides
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PeteHB Posted at 2018-1-6 10:08
Why would anything to do with the app or the RC have anything to doo with the AC losing GPS signal? It can only be down to the GPS receiver and software using it in the aircraft. Unless there is GPS jamming and or selective availability turned off GPS is very stable certainly out in the open with unrestricted view of the sky.

Your Phantom never lost GPS signal.
The GPS system was working just find.
But the flight data shows a Yaw Error starting at 10:11.5.
The compass data was conflicting with GPS data.
The flight controller was unable to deal with two sets of conflicting data and as it can't fly without the compass, it ignored GPS data.
The cause of the yaw error is uncertain but since you mentioned (unnecessarily) recalibrating the compass and IMU before the flight, that is an obvious point to be suspected.
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Labroides
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PeteHB Posted at 2018-1-6 10:08
Why would anything to do with the app or the RC have anything to doo with the AC losing GPS signal? It can only be down to the GPS receiver and software using it in the aircraft. Unless there is GPS jamming and or selective availability turned off GPS is very stable certainly out in the open with unrestricted view of the sky.

He never lost GPS signal.
See post 17 for details
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Genghis9
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Before assuming anything...exactly why did you perform both a compass calibration and an IMU calibration?
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skyguy17
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Genghis9 Posted at 2018-1-6 21:46
Before assuming anything...exactly why did you perform both a compass calibration and an IMU calibration?

I had read on the forum that if you move to a new location then doing an IMU and compass calibration was good practise.  Was I wrong?

On a couple of flights filmed the camera looked as if it was turned slightly to the right when the P4 was traveling straight ahead, giving the impression I was filming on a slight diagonal. I thought carrying out both might be helpful and allow the gimbal to center the image better.

I have not calibrated the AC since purchase, however why should the two calibrations be a problem? Is this not the purpose of these to improve flight stability and location finding? Cheers .....
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skyguy17
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Labroides Posted at 2018-1-6 16:36
He never lost GPS signal.
See post 17 for details

Then the iOS app is showing something different look at the GPS signal level they have drop away.  I have taken this picture from the iPad when replaying the flight at the point the warnings occur.

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Labroides
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skyguy17 Posted at 2018-1-7 00:29
I had read on the forum that if you move to a new location then doing an IMU and compass calibration was good practise.  Was I wrong?

On a couple of flights filmed the camera looked as if it was turned slightly to the right when the P4 was traveling straight ahead, giving the impression I was filming on a slight diagonal. I thought carrying out both might be helpful and allow the gimbal to center the image better.

I had read on the forum that if you move to a new location then doing an IMU and compass calibration was good practise.
You'll find a lot of misinformation on the forum and recommending to recalibrate compass and/or IMU frequently is misinformation.
why should the two calibrations be a problem? Is this not the purpose of these to improve flight stability and location finding?
If your Phantom flies straight (instead of big curves and it hovers without slowly spiraling, your compass is just fine and nothing will improve it.
Location comes from GPS and there's nothing you can do to improve that either.
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Labroides
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skyguy17 Posted at 2018-1-7 00:35
Then the iOS app is showing something different look at the GPS signal level they have drop away.  I have taken this picture from the iPad when replaying the flight at the point the warnings occur.

[view_image]

The flight data shows that the number of GPS sats locked didn't drop.
There's no such thing as a weak GPS signal when your Phantom is up with an unobstructed sky view.
The "weak GPS" message is poorly worded and is drawing your attention to the fact that the Phantom is in atti mode because the flight controller is ignoring GPS data.
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skyguy17
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Labroides Posted at 2018-1-7 01:18
I had read on the forum that if you move to a new location then doing an IMU and compass calibration was good practise.  
You'll find a lot of misinformation on the forum and recommending to recalibrate compass and/or IMU frequently is misinformation.
why should the two calibrations be a problem? Is this not the purpose of these to improve flight stability and location finding?

Hi Labroides,

Thanks for your comments, so I have carried out these two calibrations and I'm getting these warnings now, what recommendations do you have to remove these warning messages.

Agree with your comments GPS is position and compass is heading information they should be complimentary rather conflicting the flight.  What intrigues me is why is this happening?
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Aardvark
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skyguy17 Posted at 2018-1-7 01:35
Hi Labroides,

Thanks for your comments, so I have carried out these two calibrations and I'm getting these warnings now, what recommendations do you have to remove these warning messages.

First thing to check would be to make sure the DJI Go 4 installation was good, you said it was reporting it as V4.1.20 after upgrading to V4.1.22. I wonder if a calibration of RC may help (App' or RC sending incorrect command ? Just a thought really).

If the CSV file (from your phantomhelp screen) is loaded into a spreadsheet you'll see a bit more data. And curiously there seems to be some 'rudder' (yaw) input from the control sticks just as the problem starts. Whether that had anything to do with initiating the problem, or in reaction to it I don't know. Is there any possibility it could've been a bird strike, being a nature reserve ?
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Aardvark
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Genghis9 Posted at 2018-1-6 21:46
Before assuming anything...exactly why did you perform both a compass calibration and an IMU calibration?

Unfortunately the P4 manual still shows conflicting information regarding the compass calibration on Pages 56 & 57. This has not been updated since last July at the last official firmware release.
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skyguy17
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Aardvark Posted at 2018-1-7 05:55
First thing to check would be to make sure the DJI Go 4 installation was good, you said it was reporting it as V4.1.20 after upgrading to V4.1.22. I wonder if a calibration of RC may help (App' or RC sending incorrect command ? Just a thought really).

If the CSV file (from your phantomhelp screen) is loaded into a spreadsheet you'll see a bit more data. And curiously there seems to be some 'rudder' (yaw) input from the control sticks just as the problem starts. Whether that had anything to do with initiating the problem, or in reaction to it I don't know. Is there any possibility it could've been a bird strike, being a nature reserve ?

I have uninstalled the DJO Go 4 app as the update did not appear to have installed on the iPad correctly, though the App Store reported it had. I'm now running on the iOS device 4.1.22 as reported in the App.

As far as a bird strike, looking at the video footage there is no camera wobble to indicate anything happened like that and I also looked up at the P4 when the GPS warning popped up and did not spot anything near the AC.

I have done another compass calibration running the new app. It shows up as "Excellent", its a little too windy just now to try her out but might take it up if the wind drops this evening or tomorrow.  Thanks ...

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Aardvark
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skyguy17 Posted at 2018-1-7 06:34
I have uninstalled the DJO Go 4 app as the update did not appear to have installed on the iPad correctly, though the App Store reported it had. I'm now running on the iOS device 4.1.22 as reported in the App.

As far as a bird strike, looking at the video footage there is no camera wobble to indicate anything happened like that and I also looked up at the P4 when the GPS warning popped up and did not spot anything near the AC.

A few easy test flight should indicate if anything really broken. Now that compass well calibrated the general consensus is that it should not need doing again until advised by system, or investigating some erratic flight behaviour. Just as a thought, have you calibrated the visual sensors yet using Assistant 2, occasionally some erratic flight behaviour has been resolved after 'Sensor' calibration ?
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Genghis9
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skyguy17 Posted at 2018-1-7 00:29
I had read on the forum that if you move to a new location then doing an IMU and compass calibration was good practise.  Was I wrong?

On a couple of flights filmed the camera looked as if it was turned slightly to the right when the P4 was traveling straight ahead, giving the impression I was filming on a slight diagonal. I thought carrying out both might be helpful and allow the gimbal to center the image better.

I am not here to judge you, as mentioned, there is a lot of information out there and here which is not accurate or up to date or both.  In this case the current accepted and best practice is to not perform either of those calibrations unless the system says to do so.
Unfortunately, even your outdated manual works against you, as Aardvark points out it still states doing a compass calibration is acceptable practice.  However, current manuals state what I've just indicated above.  
Now this does not mean you can't do these calibrations, but there is some risk in doing so.  Whenever these calibrations are done you run the risk of introducing error in to the system.  Meaning, there is a distinct possibility you may have incorrectly performed either or both calibrations and caused errors to be introduced in to the system.  If that is the case, and I couldn't tell you one way or the other if you did, then you can attempt to recalibrate again.  
If you do, I can tell you that you need to perform these calibrations as precisely as possible.  You have to take every precaution and follow the procedures exactly as stated.  This means ensuring no metal around, no magnetic interference of any kind (within reason of course) and in the case of the IMU that it is done on as perfect a level platform as possible in all axis.  Individuals like Labroides and Aardvark have got knowledge and experience with these actions and can better advise you than I.  Also there are others that can help, a member named Endotherm is very meticulous about reviewing your flight log and can explain your results thoroughly.
Wish you all the luck
Your only other option is to send it back to DJI for them to correct or fix.
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Genghis9
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Aardvark Posted at 2018-1-7 06:05
Unfortunately the P4 manual still shows conflicting information regarding the compass calibration on Pages 56 & 57. This has not been updated since last July at the last official firmware release.

Yes I suspected that was the case...I really wish DJI would spend some time cleaning up their past documents as much as they spend changing everything else now and beyond...wishful thinking I guess
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skyguy17
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Thanks for everyone helping me out this weekend, some useful suggestions. Agree the manual is very misleading as it says specifically in the text you should do a compass calibration if your location has changed and should be part of your pre-flight checks. [Page 56 in ver 1.6 of the pdf manual]

I'm still not fully sure why the Yaw and GPS errors occurred, they also happened +10mins into the flight and I was returning the AC to the Home point manually as I was about to bring it down using RTH button.  If the Compass and IMU calibrations had failed I would have assumed these errors would have happened as soon as I launched the P4.

@DJI Support - please can you look at my up loaded log file and see if you make a comment from these as to why the error messages occurred?

For those interested, here is the data from Phantomhelp as the raw values, the Yaw error occurred at 10m 11.5s in the log.




Once again thanks to all for your comments !!
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Genghis9
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skyguy17 Posted at 2018-1-8 01:52
Thanks for everyone helping me out this weekend, some useful suggestions. Agree the manual is very misleading as it says specifically in the text you should do a compass calibration if your location has changed and should be part of your pre-flight checks.

I'm still not fully sure why the Yaw and GPS errors occurred, they also happened +10mins into the flight and I was returning the AC to the Home point manually as I was about to bring it down using RTH button.  If the Compass and IMU calibrations had failed I would have assumed these errors would have happened as soon as I launched the P4.

To clarify some things
First, no one has said or indicated that the calibrations completely failed.  Rather we are inferring that by performing these calibrations that some error may have been introduced in to your system which caused the errors.  However, it is also possible that your drone is malfunctioning on its own, but lacking further information it is most likely due to the first assertion.  
Lastly, a little background information to consider about the compass calibration.  At least one of the reasons for the manual indicating the need for a calibration when changing locations was to compensate for a change in declination.  However, as typical with the manuals DJI writes they did not fully explain why the calibration was needed, just a simple statement about changing locations.  To many they assumed, incorrectly, that just changing locations by a few feet or a few blocks was enough to require the calibration.  However, a change in declination (difference between magnetic north and true north) only really matters navigationally speaking, when one changes their location by several hundred miles for that change to significantly matter.  Now with the coupling of GPS and a sensitive compass system the need for this calibration is mostly unnecessary unless there are other factors the system determines to require an adjustment or correction.
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Aardvark
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skyguy17 Posted at 2018-1-8 01:52
Thanks for everyone helping me out this weekend, some useful suggestions. Agree the manual is very misleading as it says specifically in the text you should do a compass calibration if your location has changed and should be part of your pre-flight checks.

I'm still not fully sure why the Yaw and GPS errors occurred, they also happened +10mins into the flight and I was returning the AC to the Home point manually as I was about to bring it down using RTH button.  If the Compass and IMU calibrations had failed I would have assumed these errors would have happened as soon as I launched the P4.

You seem to have things in hand, I'll post my calibration reminder list. If there are any you've not done as yet it may help. i.e. your compass should be good :-)

There are five calibrations on the P4:-

1) Sensors (Using DJI Assistant 2 v1.2.0, latest version), usually done just after update on Assistant 2.

2) IMU (level surface, make sure it's had time to cool down if it's been powered up, say half an hour at lowest ambient temperature, a cool evening or air conditioned room below 10 degrees C helps speed up aircraft initialisation).  
(Note:-Using the newer '3D' IMU calibration routine, my last two IMU calibrations have been done at about 20C ambient air temperature. The subsequent IMU warm up time when aircraft is first powered up and initialising does not seem to have been adversley affected, and warm up time is a few seconds at most.)

3) Gimbal (just after IMU).

4) RC sticks (with aircraft off).

5) And compass (in an open area (not over steel reinforced concrete), away from ferrous materials or electromagnetic interference). Get one good calibration, and that should be all that is needed until informed by system or erratic flying that needs investigation. Note that any ferrous metals very close to legs (steel frame in desk, cutlery in kitchen drawer, windowsill strengthening etc) will generate a 'compass error', this does not mean compass needs recalibration. just move the aircraft away from source of interference.
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Aardvark
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Genghis9 Posted at 2018-1-8 04:02
To clarify some things
First, no one has said or indicated that the calibrations completely failed.  Rather we are inferring that by performing these calibrations that some error may have been introduced in to your system which caused the errors.  However, it is also possible that your drone is malfunctioning on its own, but lacking further information it is most likely due to the first assertion.  
Lastly, a little background information to consider about the compass calibration.  At least one of the reasons for the manual indicating the need for a calibration when changing locations was to compensate for a change in declination.  However, as typical with the manuals DJI writes they did not fully explain why the calibration was needed, just a simple statement about changing locations.  To many they assumed, incorrectly, that just changing locations by a few feet or a few blocks was enough to require the calibration.  However, a change in declination (difference between magnetic north and true north) only really matters navigationally speaking, when one changes their location by several hundred miles for that change to significantly matter.  Now with the coupling of GPS and a sensitive compass system the need for this calibration is mostly unnecessary unless there are other factors the system determines to require an adjustment or correction.

A clear and consise reply there :-)
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