Hi,

I've been experiencing trouble-free flight with the Phantom 4 until yesterday. While flying and shooting still photography I was hovering and composing a shot, when suddenly the Phantom starting to move quite quickly in a arc without any input from the controls. I was able to regain control, but the controls were difficult - I could get it to change course, but it would just continue on this course (sort of arcing around) when I returned the controls to neutral.

I was able to bring it back and it seemed once it was close to the ground it stabilized. After hovering in front of me I tried to increase altitude. Once at about 60 feet it started to behave erratically again. So I just brought it down. There was no indication in the DJI Go app that anything was wrong - good signal, good GPS, etc. On landing however the App reported a Vision System Error (f00000). Although it was calm on the ground, it's possible it was windy at 280ft. But it seems unlikely that it would be significantly windier at 60 feet directly above me at the end of the flight.

Here's a Healthy Drones log: HealthyDrones.com - Innovative flight data analysis that matters. The squigly path on both ends of the flight are the problems. I'm not sure if the report shows input control, but in the Go App log viewer it's clear there is no input from the control when it starts moving.

I got DJI support on chat when I got home and they had me do vision, IMU, Controller calibration and told me I should be good.

But am I? Because I don't know why this happened, I'm not confident it won't happen again, and in a different environment this could be catastrophic.

Any ideas on cause or prevention?

My first thought is that the compass needs calibrated, preferably in an open grass area.

Aardvark Posted at 2016-8-22 03:50
My first thought is that the compass needs calibrated, preferably in an open grass area.

Thanks Aardvark. I calibrated before I flew and I was on a wide open, flat river bank. It's possible that I got a bad calibration. If so, it would be nice to have a way of telling if the calibration is off before experiencing erratic behavior.

A tip to determine wind speed @ any height... hover, then flip too Attitude mode, the speed its traveling will be the wind speed, and you'll kno which direction the wind is blowing

"A        00m 00s        0.0 ft        0 ft        Mode        Mode changed to GPS_Atti"
The aircraft went into atti mode, maybe this caused your issue as it flew with the wind. and it was gps_atti, meaning your rc were in p-mode. thats all i saw, and it says it happened at the very beginning of the flight. ¯\_(ツ)_/¯

Bilzc10 Posted at 2016-8-22 04:57
"A        00m 00s        0.0 ft        0 ft        Mode        Mode changed to GPS_Atti"
The aircraf ...

I was under the impression gps_atti was equal to P mode. When I look at past logs they all start with "Mode changed to GPS_Atti" Do yours not?

mark82 Posted at 2016-8-21 17:15
I was under the impression gps_atti was equal to P mode. When I look at past logs they all start w ...

They probably do. The aircraft probably starts in p-atti until it connects to some satellites.

Bilzc10 Posted at 2016-8-22 06:42
They probably do. The aircraft probably starts in p-atti until it connects to some satellites.

I can't find any reference to another mode in any of my logs. What should the logs say once it's connected to satellites and operating in true P mode? It seems like entering and staying in gps_atti mode is the norm based on other logs I've found online.

I have had the exact same scenario happening with mine 2 of the last times 10 or so times I've used it. It flies great, as normal - I can run a bit of a track, do some figure8's to test it. fly higher fully controlled and then it will start making these wide arcs seeming to be out of control.
I've been in P mode with full GPS. Any ideas?

kimballv@chelph Posted at 2016-8-22 10:49
I have had the exact same scenario happening with mine 2 of the last times 10 or so times I've used  ...

Usually, this is a symptom of a poor compass calibration, try doing it again, away from any metal.

Geebax Posted at 2016-8-22 09:24
Usually, this is a symptom of a poor compass calibration, try doing it again, away from any metal.

Thanks Geebax. Is there any way to diagnose a poor calibration before you fly? I was on a wide river bank in Alaska. I calibrated before flight and all looked good. The closest obvious metal was a bridge about a 1/4 - 1/2 mile away.

mark82 Posted at 2016-8-22 13:26
Thanks Geebax. Is there any way to diagnose a poor calibration before you fly? I was on a wide riv ...

It is not the metal that is obvious, it is metal on your person, or pipes in the ground, or steel reinforcing bar.

It looks like a compass error at that time. Please try to calibrate the compass in an open area. What's more, you can also use DJI Assistant 2 to download the flight data flie from the drone and send it to support.us@dji.com for data analysis.

to clarify, you said you were on a river bank...  Were you flying over the river and if so at what altitude?  Could the VPS sensors have caused this erratic behavior?