I fly a lot over the sea. Yesterday evening I was using zoom at 2.7K res, when the aircraft stated behaving very oddly.   When I tried to fly it back towards me I noticed it was going very slow, like it was in tripod mode, even though it wasn't.  When I zoomed back out it speeded up again.   Now that I had the aircraft close to me and over land, I tried climbing only for the aircraft to slow down again.   I landed the aircraft but I noticed ground detection was turned off.   I retest today.  May only need a boit

Was the camera pointing straight down, or looking ahead?

Labroides Posted at 7-11 07:56
Was the camera pointing straight down, or looking ahead?

It was pointing ahead.   So when it wasn't coming back I zoomed out to 1:1 and it seemed to speed up.   So, I flew it around close to me fir a while in normal mode and it slowed down again.  I then put it in sports mode, it then speeded up.   I started get worried by now so I thought it best to land.  During landing it was not detecting the ground, but it landed OK.  I presumes it was a glitch.  I will test it when it stops raining.   I will do this over land to play safe.  

Was during bluehour? During bluehour snsors tend  to malfunction and the drone slows down and sometimes stops, just switch to sportmode till it's darker.

Huginn Kenningar Posted at 7-11 14:32
Was during bluehour? During bluehour snsors tend  to malfunction and the drone slows down and sometimes stops, just switch to sportmode till it's darker.

Whats the blue hour?

john.motchbtconnect.com Posted at 7-11 14:35
Whats the blue hour?

Darker end of twilight. Switching to Sport mode turns off the obstacle avoidance sensors.

john.motchbtconnect.com Posted at 7-11 08:41
It was pointing ahead.   So when it wasn't coming back I zoomed out to 1:1 and it seemed to speed up.   So, I flew it around close to me fir a while in normal mode and it slowed down again.  I then put it in sports mode, it then speeded up.   I started get worried by now so I thought it best to land.  During landing it was not detecting the ground, but it landed OK.  I presumes it was a glitch.  I will test it when it stops raining.   I will do this over land to play safe.

" During landing it was not detecting the ground, but it landed OK."

Did the bottom light come on?

Hello there john.motchbtconnect.com. I am sorry for the trouble this has caused and thank you for reaching out. Just a reminder that when flying above the water, the vision positioning function will turn off automatically and only the GPS and barometer are used for positioning, if affected by the accuracy range, and an accident might happen. In addition I will also post a DJI Forum thread on How to Fly Safely Over Water. Thank you.

https://forum.dji.com/thread-181878-1-1.html

What was your heght when passing over water?

Perhaps check your log file http://phantomhelp.com/logviewer/

FB: GeoDrone4K Posted at 7-11 22:34
What was your heght when passing over water?

I was at least a 100ft above the water.    I fly over water all the time but never seen this problem before.   Weather permitting I give it a good test today

DJI Stephen Posted at 7-11 19:22
Hello there john.motchbtconnect.com. I am sorry for the trouble this has caused and thank you for reaching out. Just a reminder that when flying above the water, the vision positioning function will turn off automatically and only the GPS and barometer are used for positioning, if affected by the accuracy range, and an accident might happen. In addition I will also post a DJI Forum thread on How to Fly Safely Over Water. Thank you.

https://forum.dji.com/thread-181878-1-1.html

I checked the notifications in uav data and it changed quite a few times to "mode changed to detour".    Which I think means obstacle avoidance has kicked in.   I was well about the sea, but lower than I normally fly.   Also it was evening, 2 hours before sunset so the sun was low in the sky.   Maybe the low sun was reflecting off the water which was causing the obstacle avoidance to kick in.  I presume it slows down when mode changed to detour.    The UAV DATA app is a must app to have and its only £6pm for full functionality.   If I ever lose the drone I'm banking on uav data to provide the loss evidence for my insurance.

I should add I never fly lower than 40ft above water as I know the risks.  

john.motchbtconnect.com Posted at 7-12 01:53
I was at least a 100ft above the water.    I fly over water all the time but never seen this problem before.   Weather permitting I give it a good test today

Rise over 120 ft and sensors will not "see" the water.