I'm making a quadcopter(wheelbase 1200mm) with 4 30" props(30x8).
FC I'm using is DJI's NAZA m V2 and it's been working well in most case except near ground.
The problem is fluctuating altitude near ground(about 1 meter or less). Once the a/c goes up, everything works well.
I thought it is because of the ground effect but the a/c fly very well in certain configuration especially when frame cover is opened.
The frame is a rectangular box(250x250x50mm) and it is mostly closed except there is 13mm hole where wires go thru in the bottom and the top is covered by a plastic plate fastened by 4 screws.

I've tested so many configurations and it only works when the cover is opened.
I tried to lift the cover up a bit about 5mm and it is not working.

To check what's going on, iOSD was used.
I was expecting pressure is a key factor and the graph shows that the pressure fluctuate about 1.5~2 m.
I wish I can filter that signal but there is no way that I can control the pressure sensor in my knowledge.

Do you have any comments on this problem?
Thank you for reading this thread.

[ATTACH]2170439[/IMG]