My P4P started acting funny yesterday. GPS would 'fail' with 16 sats locked on. This would happen on and off. There would be 16 sats but the GPS signal strength indicator would alternate between full reception and one red bar. Firmware and RC are up-to-date. There could be a loose connection or the module is faulty. I am traveling and the flight log is huge (several hundred MB) but I don't think it will say anything more than what I've just describle.


Totally clear skies and relatively calm air has allowed me to fly in ATTI mode at close ranges with direct LOS without concern of flyaway. However, I'm not going to tempt fate and ground the aircraft for now.
There is no error message on the diagnostics for the GPS but I did get a warning about an IMU error. Warning [IMU] heading exception'
The bias and gyro readings were fine after a restart and I calibrated again anyway. (edited 5-4-2017 ; but not a 'cold' recal which is why it didn't help, see later down this thread)
This aircraft is new and has not been damaged in any way. Another aircraft has no problems in the same area.
Would be grateful for suggestions from the usual experts on this forum

(see the solution to this at the end; the problem was really related to the IMU requiring re-calibration)

Well, you can try to "renew" the firmware after connecting via DJI Assistant. They have the new version of it, which has been launched yesterday I believe. Also, try to reset all the settings in the app, calibrate the IMU and the compass and then try to fly it in P mode. If you see no change you will probably need to contact DJI's technical support. I suppose you are not trying to fly within any NFZ.

piowoc73 Posted at 2017-3-8 17:03
Well, you can try to "renew" the firmware after connecting via DJI Assistant. They have the new version of it, which has been launched yesterday I believe. Also, try to reset all the settings in the app, calibrate the IMU and the compass and then try to fly it in P mode. If you see no change you will probably need to contact DJI's technical support. I suppose you are not trying to fly within any NFZ.

Thanks. I did all of those.  I don't fly in NFZs.

The thing that bugs me is that the problem is intermittent. I get full sats on take-off and within seconds, even with 13 or 14 indicated sats, it says I've lost GPS contact. I probably have a faulty GPS receiver but its unusual for a piece of electronics to fail this way, its usually all or none. Perhaps the GPS antenna, is somehow faulty. If it continues, I'll send the aircraft in.

Thanks for responding.

And no, I'm NOT in Saudi Arabia. I'm using a VPN and this messes up the IP locator...

Mike-the-cat Posted at 2017-3-9 02:55
Thanks. I did all of those.  I don't fly in NFZs.

The thing that bugs me is that the problem is intermittent. I get full sats on take-off and within seconds, even with 13 or 14 indicated sats, it says I've lost GPS contact. I probably have a faulty GPS receiver but its unusual for a piece of electronics to fail this way, its usually all or none. Perhaps the GPS antenna, is somehow faulty. If it continues, I'll send the aircraft in.

You may check the following website of UAV Forecast: http://www.uavforecast.com/#/faq
They outline some GPS anomalies there and how they may influence the drone's GPS system.
I like this app, because it gives you an estimate on how many sats to expect at any given time and location.

It looks like solar activity was fairly bad on March 5, but decent on the 6-8th, still might want to check for your area. Also, check to see if there was any GPS testing in the areas you were flying. The government does so every now and then and it is posted in NOTAMs for pilots to be aware of GPS issues.

piowoc73 Posted at 2017-3-9 07:23
You may check the following website of UAV Forecast: http://www.uavforecast.com/#/faq
They outline some GPS anomalies there and how they may influence the drone's GPS system.
I like this app, because it gives you an estimate on how many sats to expect at any given time and location.

Thanks to you and LW UAS for responding,  but I don't think solar activity is the issue here.  My I2 has not given the same issues flying over the same territory. DJI might want to comment on this. Perhaps the I2 has a more sensitive GPS?

The truth is that my P4P GPS system is probably at the threshold of passing QC for reasons that are not clear still.

The wind is still dead calm today so there isn't much drift even in ATTI mode. Was able to stay on GPS mode 70% of the time on the P4P today to get good footage. On sunny days with good light, honestly this bird gives images that make it not worth carrying the I2 unless I want to do some specialty shots with a 25mm or 45mm lens. So much faster to set up and easier to lug around when walking...

It is a faulty GPS, like you surmised. Open a support ticket, and get it fixed before you have a worse problem.

Maxxgold Posted at 2017-3-9 15:29
It is a faulty GPS, like you surmised. Open a support ticket, and get it fixed before you have a worse problem.

Thanks Max. I will take your advice and be safe.

The problem was that the IMU needed calibration. Once I did this the GPS problem went away.

So... if you see the message 'Warning [IMU] heading exception' you should calibrate the IMU. Interestingly, at startup the IMU warmed up as usual and under the 'sensors' menu the bias and gyroscope readings were fine....

LW UAS Posted at 2017-3-9 11:43
It looks like solar activity was fairly bad on March 5, but decent on the 6-8th, still might want to check for your area. Also, check to see if there was any GPS testing in the areas you were flying. The government does so every now and then and it is posted in NOTAMs for pilots to be aware of GPS issues.

"It looks like solar activity was fairly bad on March 5"
'Although this comes up in forums all the time,there  have never been any cases of solar activity affecting Phantom owners.
If it did, you'd find hundreds or thousands experiencing problems as well as all kinds of other GPS users.

Mike-the-cat Posted at 2017-3-14 03:36
The problem was that the IMU needed calibration. Once I did this the GPS problem went away.

So... if you see the message 'Warning  heading exception' you should calibrate the IMU. Interestingly, at startup the IMU warmed up as usual and under the 'sensors' menu the bias and gyroscope readings were fine....

I doubt that a IMU-calibration can solve your problem. Calibration of an IMU will not change anything to the number of satellites your GPS unit (both !) can and will receive. I think the earlier diagnosis of faulty GPS or a faulty connection of the GPS is a more probable cause and should be investigated by DJI.

I agree with Labroides that 'solar activity' is certainly NOT involved here as it never is.

PhanFran Posted at 2017-3-14 10:21
I doubt that a IMU-calibration can solve your problem. Calibration of an IMU will not change anything to the number of satellites your GPS unit (both !) can and will receive. I think the earlier diagnosis of faulty GPS or a faulty connection of the GPS is a more probable cause and should be investigated by DJI.

I agree with Labroides that 'solar activity' is certainly NOT involved here as it never is.

Thanks for your response but this is EXACTLY my point.

The message seems to say that there is a GPS failure (not really since the minimum satellites locked on was 11 and most of the time it was 15...)

The message to focus on was the transient 'IMU exception'. I hike so it was possible that even in the padded bag, a jump or a sudden turn during transport could have upset the IMU.

I've flown multiple flights since the IMU calibration and there are no issues. I will make a separate post on this matter and have edited the post you are quoting to reflect the central issue.

I do agree the worry about 'solar activity' is grossly over-rated.

Mike-the-cat Posted at 2017-3-15 16:40
Thanks for your response but this is EXACTLY my point.

The message seems to say that there is a GPS failure (not really since the minimum satellites locked on was 11 and most of the time it was 15...)

Imu calibration is the problem???

Imu calibration is the problem??

tx mike ,problems result

fansca0f4ad2 Posted at 2017-3-18 15:02
tx mike ,problems result

Huh - I think your computer went to sleep there....

Mike-the-cat Posted at 2017-3-14 03:36
The problem was that the IMU needed calibration. Once I did this the GPS problem went away.

So... if you see the message 'Warning  heading exception' you should calibrate the IMU. Interestingly, at startup the IMU warmed up as usual and under the 'sensors' menu the bias and gyroscope readings were fine....

I got this issue on my third flight with a brand new P4P.  Not very reassuring at all.  Did you get the error again after the IMU Calibration?

yoengel Posted at 2017-3-24 06:07
I got this issue on my third flight with a brand new P4P.  Not very reassuring at all.  Did you get the error again after the IMU Calibration?

Nope. The bird has been flying well since.

yoengel Posted at 2017-3-24 06:07
I got this issue on my third flight with a brand new P4P.  Not very reassuring at all.  Did you get the error again after the IMU Calibration?

Aloha yoengel,

     Make sure your Phantom is on a measured, level surface and away from interference when you do your IMU calibration.  Be sure to check the IMU report after the calibration to see if you have to do it again.

     Hope this helps!

Aloha and Drone On!

Cetacean Posted at 2017-3-25 02:36
Aloha yoengel,

     Make sure your Phantom is on a measured, level surface and away from interference when you do your IMU calibration.  Be sure to check the IMU report after the calibration to see if you have to do it again.

Aloha Cetacean,

I thought for IMU calibration, we just need a flat surface, do we need it to be away from interference as well?  Finding a level table in the middle of a park is not easy.

Mahalo!

yoengel Posted at 2017-3-25 10:48
Aloha Cetacean,

I thought for IMU calibration, we just need a flat surface, do we need it to be away from interference as well?  Finding a level table in the middle of a park is not easy.

Aloha yoengel,

     It is not that demanding, although some really do have a hard time finding a place without interference.  At least in my case, when I start up my system, I get an interference report for Radio Channel Quality (below IMU and Compass).  This is how I know if I can do a proper IMU calibration.

     So, if you are in your yard, or other favorite launch spot, bring a board, something for shimming and a level.  (You can practice getting the board level in a close grassy spot.)  Then once it is set up, do the IMU calibration.  In my yard, I have a picnic table that is leveled with shims and a plastic launch stand that is leveled to.

     Hope this helps!

Aloha and Drone On!