I have an APM2.5+ with the Mediatek 3329 V2.0.
My octocopter flies well in stab, but has very strange behavior in Loiter and RTL. At first I was sure it was just me not beeing able to dial in the PIDs, but me and an APM-using friend have spent weeks with it now. Two days ago, I got it Loitering pretty perfect by changing the Loiter-I to 0.1 (BIG octocopter) and Loiter-P to 2.
I was so happy! RTL also worked as expected. I even changed the values back to confirm that it again would start to misbehave, and it did! Overshooting, going back and forth etc, just way off target by 10-meters and generally acting confused. Then the batteries ran out.
The next day I set the values back to what had worked so well the day before.
But now, it was bad again. Acting differently though. I took it up to about 10 meters, about 20 meters away from me. Looking at Mission planner and the log, it shows that I had left the park area (green) and flown all the way to the housing area, over 100 meters away. Still, I had at least 9 satellites! This went on for minutes? Not just a glitch.
Anyway, I'm thinging my Meditek is up to no good, and that might be why Loiter and RTL are so bad too.
In the pic below, not that I was never outside the inner half of the white cirle.
Hoping someone can take a look at the logs and maybe find something wrong. I don't mind buying a better GPS if I know that it will help.