I've got a fair sized quad, 6 Kg and 4 Turnigy G46 motors an 15x8 props.
I've been several months more than 3, (just weekends) tryung to get loiter working properly.
I THINK I have position hold OK now, but altitude hold just isn't doing it for me.
I use the CRIUS V1.0 all in one and megapirate 2.7.4
At one point it seemed to be working, but put it in a slight wind and forget it. Just talking P gains, with the hold gain at 2.4 and the alt rate gain at 0.11, it would slowly drop down about 4 meters, and then near the bottom, zoom up to the altitude where it should be, but there it cuts power and starts dropping down again.
I decided to put it back to where it seemed to work better before, alt hold gain, 0.43 and alt rate gain at 0.33. Seems better, but I have to have it perfectly stabalized before puting in to loiter. If it's off by a bit, it drops like before, and zooms back up again after about 3 meters or so.
I the last test, I had done a first test which did as I described, I flipped it into stab before it fell too far. Got it back to a good position and stable again, then flipped to loiter again, Again it dropped a little and then shot of, as though it was in RTL mode. The cycling mentioned before doesn't very throttle all that much, but this last move cranked the throttle up to about 60%, and it headed of to a very definite direction, like it thought it knew where it was going.... in any case it wasn't heading for home.
Flipped to stab and got control back.
From time to time, it has beetled off before, but usually early in a test. I found that you need to give a good three minutes for the GPS to stabalize on a home position. So now I wait for a good lock before I start any tests, and also, on this occasion, the first test of loiter didn't beetle off.
No-one at "another forum" could help.