Maiden Flight -GPS issue

[Leigh]

OK so first chance to fly again today and have good news.Applied the update .04 on Thursday and tested in a new location today, same as before lost GPS lock within about the first minute and dropped to OPTI, I carried on flying and though it did reconnect it dropped 10 more times in the 10 minute flight.Then changed location again but this time I calibrated the compass, first time calibration failed due to interference second time was fine, only this time when I took off it didn't loose GPS lock at all for the 20 minute flight nor the subsequent two other 20 minutes flights !!!! Very pleased.

 

[Bunny Too]

Nice, hopefully that is a fix.
Regards,
-d.

 

[Mavicsailor]

OK so first chance to fly again today and have good news.Applied the update .04 on Thursday and tested in a new location today, same as before lost GPS lock within about the first minute and dropped to OPTI, I carried on flying and though it did reconnect it dropped 10 more times in the 10 minute flight.Then changed location again but this time I calibrated the compass, first time calibration failed due to interference second time was fine, only this time when I took off it didn't loose GPS lock at all for the 20 minute flight nor the subsequent two other 20 minutes flights !!!! Very pleased.

Leigh,

That's great to hear!

There are many theories out there on what causes the GPS health to suddenly drop. Luckily, in your case it sounds as simple as a clean compass calibration. One of the other theories is high current when in sport mode flying aggressively, or possibly in GPS Atti mode with a combination of sticks at the same time also drawing excessive current.

Maybe this high current also throws off the compass. Makes sense. By chance when you were having this problem, did you look at the sensors to assure very low numbers from the compass? I look at mine while at hover and they typically bounce around 20 or less. If I put the AC near something that may effect a compass, the number goes up. If the compass is out of calibration, or interference either external or internal to the AC throws it out further, the GPS and compass may not agree. Seems strange that when this happens the problem would show as a drop in GPS health.

 

[Leigh]

I looked at the sensor readings for both compass and IMU but only on the ground and not in flight both were green and really low numbers both before and after compass calibration


Sent from my iPhone using MavicPilots

 

[jackgarner]

I looked at the sensor readings for both compass and IMU but only on the ground and not in flight both were green and really low numbers both before and after compass calibration


Sent from my iPhone using MavicPilots

Actually... would you mind uploading one of your new .dat files along with the old ones? I would like to see if there is anything different that could be causing the gps errors

 

[Leigh]

Actually... would you mind uploading one of your new .dat files along with the old ones? I would like to see if there is anything different that could be causing the gps errors

Ok just uploaded to the same Dropbox folder, flight 32 should be the bad one with lots of GPS drops and 35 should be the good flight with none

 

[jackgarner]

Alright.. =( I've been looking ~ an hour for some sort of correlation and I found a spike in the pwm the moment gps health drops

I'm not sure if I'm grasping at straws here or if this is something for DJI to take a look at.. maybe a surge is causing the gps to cut? but then the number of satellites should also drop... @BudWalker What do you think?
(flight 32)




(this is my flight)

 

[Mavicsailor]

A YouTube video showing the Mavic tear down (I believe by Drone Valley) pointed out a ferrite choke on the wire leading to the GPS module. This would indicate that the gps module is very susceptible to noise, and they are attempting to filter it out. Your theory on a spike, above and behind normal noise, may be correct.

 

[jackgarner]

A YouTube video showing the Mavic tear down (I believe by Drone Valley) pointed out a ferrite choke on the wire leading to the GPS module. This would indicate that the gps module is very susceptible to noise, and they are attempting to filter it out. Your theory on a spike, above and behind normal noise, may be correct.

Time to buy a lottery ticket!!

(back to reality.. lol) If this is a hardware issue we could be in for some serious trouble =(

 

[Mavicsailor]

I couldn't find the one from Drone Valley, but the GPS choke was referenced in this video.

So many theories on what is causing this drop in gps health, that leads to ATTI. I have to wonder if DJI is still trying to figure it out, or maybe they known what's causing it and are now trying to engineer a solution. Hopefully there is a firmware fix, and it's not a design flaw that can't be corrected without being returned.

Drone Valley pointed out the attention to detail DJI engineers built into the Mavic with making sure the soldier connections were rounded and not pointed. He stated that pointed connections could act like small antennas dispursing RF noise. Could this be something as simple as a few pointed connections because of poor QC?

This dropping GPS health in combination with the inability to sometimes control the AC in Atti is concerning.

 

[BudWalker]

View attachment 6680
View attachment 6688

Alright.. =( I've been looking ~ an hour for some sort of correlation and I found a spike in the pwm the moment gps health drops

I'm not sure if I'm grasping at straws here or if this is something for DJI to take a look at.. maybe a surge is causing the gps to cut? but then the number of satellites should also drop... @BudWalker What do you think?
(flight 32)
View attachment 6682
View attachment 6683


(this is my flight)

View attachment 6684
View attachment 6686

I didn't see this until just now. The notification system doesn't seem to always work right.
Anyway, FLY032 pertains to the middle two plots. Looking closer (zooming in) at one of those gpsHealth drops it seems the motor commanded (that's the PWM signal) occurs after the the gpsHealth drop.


Seems to be a common occurrence when gpsHealth drops. I'll speculate that the AC wants to make speed or attitude adjustments as a result of the gpsHealth drop. But, that doesn't seem to be very compelling.

This business of the gpsHealth drop is quite puzzling to me. gpsHealth is one of the few values for which there is at least some DJI documentation; both in the SDK docs as well as the decompiled Go App. It exists on the P3 and there has never been any reason to think it means anything other than GPS signal quality. Likewise, on the Mavic gpsHealth will decrease slowly when you expect; e.g. when the numSats starts to decrease because of an obstructed sky view.

But, this sudden drop from 5 to 1 is entirely different.

I forgot who speculated that it might be an indication that the FC thinks there is an inconsistency in the values derived from the compass and GPS values. DJI has a history of reporting errors with misleading labels.The P3 reports a compass error in the Go App when nonGPSCause has a value of SPEED_ERROR_LARGE, YAW_ERROR_LARGE, or COMPASS_ERROR_LARGE. The first 2 have nothing to do with the compass. The Mavic also has a nonGPSCause value that I check when there is a gpsHealth issue. But, there isn't any correlation.

There have been reported cases of a compass calibration fixing the gpsHealth drop issue. And, it's happened enough times to suppose there is a cause and effect relationship. It's very difficult for me to accept this. IMHO the bad compass calibration scenario is an urban myth that has been repeated so many times by so many that it's just assumed to be correct. All the fly away incidents that I've looked at have never been because of a compass calibration issue. Is it possible that during a compass calibration the Mavic is also calibrating the GPS receiver? Not too compelling, but it's all I got.

 

[ScrappyMavic]

I didn't see this until just now. The notification system doesn't seem to always work right.
Anyway, FLY032 pertains to the middle two plots. Looking closer (zooming in) at one of those gpsHealth drops it seems the motor commanded (that's the PWM signal) occurs after the the gpsHealth drop.
View attachment 6832
View attachment 6833
Seems to be a common occurrence when gpsHealth drops. I'll speculate that the AC wants to make speed or attitude adjustments as a result of the gpsHealth drop. But, that doesn't seem to be very compelling.

This business of the gpsHealth drop is quite puzzling to me. gpsHealth is one of the few values for which there is at least some DJI documentation; both in the SDK docs as well as the decompiled Go App. It exists on the P3 and there has never been any reason to think it means anything other than GPS signal quality. Likewise, on the Mavic gpsHealth will decrease slowly when you expect; e.g. when the numSats starts to decrease because of an obstructed sky view.

But, this sudden drop from 5 to 1 is entirely different.

I forgot who speculated that it might be an indication that the FC thinks there is an inconsistency in the values derived from the compass and GPS values. DJI has a history of reporting errors with misleading labels.The P3 reports a compass error in the Go App when nonGPSCause has a value of SPEED_ERROR_LARGE, YAW_ERROR_LARGE, or COMPASS_ERROR_LARGE. The first 2 have nothing to do with the compass. The Mavic also has a nonGPSCause value that I check when there is a gpsHealth issue. But, there isn't any correlation.

There have been reported cases of a compass calibration fixing the gpsHealth drop issue. And, it's happened enough times to suppose there is a cause and effect relationship. It's very difficult for me to accept this. IMHO the bad compass calibration scenario is an urban myth that has been repeated so many times by so many that it's just assumed to be correct. All the fly away incidents that I've looked at have never been because of a compass calibration issue. Is it possible that during a compass calibration the Mavic is also calibrating the GPS receiver? Not too compelling, but it's all I got.

Could it just be, @BudWalker , that any type of pitch/roll/TBE oscillations originating from mayYaw mismatch from Yaw will drive the gpsHealth to 1 as it switches to ATTI mode. In this case the GPS data was fine, but the unstable control loop generated large enough errors for flight controller to know something was wrong. Since it doesn't know for sure GPS was not the cause, and for safety, it considers gpsHealth is low.

In a separate post here I show how much my magYaw to Yaw alignment improved by simply using "nose down" on last compass calibration instead of "nose sideways". I'm curious if others have better Yaw alignment and less ATTI issues by using "nose down".

 

[BudWalker]

Could it just be, @BudWalker , that any type of pitch/roll/TBE oscillations originating from mayYaw mismatch from Yaw will drive the gpsHealth to 1 as it switches to ATTI mode. In this case the GPS data was fine, but the unstable control loop generated large enough errors for flight controller to know something was wrong. Since it doesn't know for sure GPS was not the cause, and for safety, it considers gpsHealth is low.

In a separate post here I show how much my magYaw to Yaw alignment improved by simply using "nose down" on last compass calibration instead of "nose sideways". I'm curious if others have better Yaw alignment and less ATTI issues by using "nose down".

Just responded to the sideways compass dance thread you started.

I think this is great! Especially the graphical presentation

Some additional things I've noticed about the gpsHealth-drops-to-1 issue. It often, not always, will come right after an abrupt roll and/or pitch change. gpsHealth will drop to 1 between 1 and 2 seconds later. The switch to ATTI then comes after another 0.5 seconds.

Your posts caused me to take another look at some other gpsHealth-drops-to-1 incidents. One thing I noticed is that magYaw seems to have a bug that shows up under high gyroX and gyroY rates. It's just the Mavic version that's broke. Extreme pitch and roll isn't a problem it's just when they are changing fast. I'll have a look.

Another thing I noticed is this flight that had multiple gpsHealth-drops-to-1 incidents. It seems to exhibit a Yaw/magYaw behavior that would be expected from a bad compass calibration


Also in this flight the Mavic landed and sat still on the ground for 330 secs. Initially, the magYaw/Yaw separation was 34 and slowly changed to 16

I think this is the FC correcting the Yaw value based on the info it was getting from the compass.

 

[beach_Dr]

Hi
New here and new to drones in general. I have about 2 1/2 hours flying time on my Mavic. In the last week, dropped to Atti mode 3x in 1 flight, 8 times in next flight - I upgraded to latest firmware (on 2 March) and recalibrated compass before the flight with 8 drops. All events have been in sport mode. Most drops are less than 5 seconds, but last drop on the most recent problem flight lasted about 30sec, with drone drifting badly in Atti until I dropped altitude enough and brought it in from over the ocean onto land for vision sensors to kick in.

I've obviously been scouring the forum for posts on the GPS subject.

DJI have just suggested flying from another location, or sending in for service if problem continues (How many times must it happen before it is considered service worthy?). Has anyone with these problems sent their MP in for service and had the GPS issue successfully fixed?
I again recalibrated compass have done 2 short flights today (very windy), did not enter sport mode, and the MP behaved as well as could be expected in the wind.

 

[Mavicsailor]

Hi
New here and new to drones in general. I have about 2 1/2 hours flying time on my Mavic. In the last week, dropped to Atti mode 3x in 1 flight, 8 times in next flight - I upgraded to latest firmware (on 2 March) and recalibrated compass before the flight with 8 drops. All events have been in sport mode. Most drops are less than 5 seconds, but last drop on the most recent problem flight lasted about 30sec, with drone drifting badly in Atti until I dropped altitude enough and brought it in from over the ocean onto land for vision sensors to kick in.

I've obviously been scouring the forum for posts on the GPS subject.

DJI have just suggested flying from another location, or sending in for service if problem continues (How many times must it happen before it is considered service worthy?). Has anyone with these problems sent their MP in for service and had the GPS issue successfully fixed?
I again recalibrated compass have done 2 short flights today (very windy), did not enter sport mode, and the MP behaved as well as could be expected in the wind.

Most of the issues with sport mode and the RF noise, sometimes produced at high currents, have been resolved with the twisting of the wires done at the factory, or a FW fix where it switched compasses. (Mavics manufactured sometime after 12/1/16 had the HW fix I believe ). Others have made the modification themself thanks to research from some very creative members on this forum. Maybe start another thread to discuss this and post the problem Dat file downloaded from Mavic. It would be interesting to look at this if your Mavic was purchased after the factory fix.

 

[beach_Dr]

Thanks will do. Slow internet - should have DAT file uploaded by the morning, will post new topic then

 

[misskimo]

Can you upload your log to PhantomLogViewer?

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

I tried to upload too the link but dont work