Hello,

I am trying to use a Phantom 4 Pro to fly photogrammetry surveys where I need it to stay at a constant altitude the whole time.

Unfortunately when flying it is continually losing altitude slowly the whole time, but it doesn't realise this. On the app it will list the altitude as constant, but if I hover the drone just above the horizon I can watch as it slowly descends below the horizon and then keeps descending until I touch the control to make it fly up again. At altitudes of around 1-1.5 meters it holds its altitude well, which suggests the VPS is working properly, it's just at any altitude higher than this it's constantly descending.

So if I'm trying to fly a drone survey at 100m above the ground, about 10mins into the survey it has already dropped to ~50m but still thinks it's flying at 100m.

I have updated the firmware, calibrated the IMU, compass and the VPS, cleaned the VPS sensors, everything I can think of. But unfortunately the issue still persists. Does anyone have any suggestions as to what is causing this issue or what a potential fix might be please?

Thanks a lot.

At an altitude of 100 metres the VPS should have no effect since it only has a range of 10 metres.
Does the drone lose altitude in ordinary flight or just when flying a survey flight with special software?
If it loses height in normal flight, post flight data to see if there are any clues in there.
Does it lose height if you attempt a survey flight at constant height relative to the launch point?

Labroides Posted at 5-28 14:46
At an altitude of 100 metres the VPS should have no effect since it only has a range of 10 metres.
Does the drone lose altitude in ordinary flight or just when flying a survey flight with special software?
If it loses height in normal flight, post flight data to see if there are any clues in there.

Hi Labroides, thanks a lot for your reply and sorry for my (very) late response.  The drone loses altitude in ordinary flight as well as when flying with special software. It does also lose height when attempting a survey flight at constant height relative to take off point.

I've sent you some flight data - if you're able to offer any advice that would be much appreciated. Thanks a lot!