I’ve built a couple of quads using Crius AIO Pro flight controllers with ArduCopter 3.0.1 R4 firmware and they work well. Now I’ve built one with an APM 2.6 clone and although it flies OK in STABILIZE mode it does not hold its position in LOITER. The firmware is ArduCopter 3.2.1 with default settings. The compass reads correctly. In a recent test it drifted about 75 meters in 3 minutes in a roughly straight line. I think the wind would have carried it further than that so I suppose it was trying. The log confirms that it was in LOITER and it had 10 satellites and the HDOP was 1.62 meters. I’ve also tried RTL and it worked, but there was a delay of about 5 seconds (10 meters) before starting to return.
I would be glad of any advice.