Temporary sinking, any ideas?

[Nicodema]

Hi

This is my first post, but I have been building and flying multicopters for around 7 years, from MK, through APM to now a hex with Naza and the Phantom 2.

I had an odd flight last weekend and I'm puzzled what the problem was. This was the second flight of the session, starting with a full battery. I got a full lock with 10 satellites, green flashes, then waited around a minute after that, before take off.

Throttle seemed fine, but I did notice a slight downward drift on centre stick. Not enough to worry about, but I wondered if the cold air was having an effect. This was a fairly cold (~6 deg C) but fine day.

After a few minutes of flying, first in ATTI, then in GPS mode, the phantom started to slowly sink during forward flight. Once this had started, it would not respond to up throttle, but would respond to down.

Once I had landed, I turned the battery off, waited 10 secs or so then turned it back on again. It flew without incident after that and was happy to hold altitude.

It almost seemed as if the max height limit was coming into play much lower than it should have done, as if maybe the altimeter was way off calibration.

Anybody else had this behaviour?

 

[Hughie]

At what kind of height were you experiencing this ?

 

[Nicodema]

Around 10m. No higher than 15m. Then the effect continued all the way down to the ground.

 

[Hughie]

Are you gains set to the default factory settings ?

 

[Nicodema]

Yes they are. And I would reiterate that this was aberrant behaviour, not the usual flight characteristics. Very puzzling.

 

[EMCSQUAR]

I would clean battery post (all four) It sounds like voltage resistance and also open lid and check all cold soldered joints. I suspect "smart battery" is giving false readings.

It sounds very similar to a situation if you were to disable battery warnings, when battery reaches threshold P2s are notorious for slowly dropping. I ran P2 down to 9.9v and it barely flew during a test.

 

[Nicodema]

Good point. not sure if it's the reason, but a good precaution. I did one of my packs with a contact cleaner pen. I may not have done the other one. Will do both again.

 

[SteveMann]

Was the wind gusty? This can confuse the barometric altimeter which is how the Phantom maintains altitude.

 

[Nicodema]

No Steve, conditions were very still.

I read through a few pages of the thread about early auto landing batteries and I wonder if it was trying to do that on one of my packs. Either due to a poor connection or internal issues. Oh well, something to monitor.