I had a small DJI F450 quad with an APM 2.5-kit (3DR APM 2.5, 3DR GPS/Compass uBlox 7, 3DR PM, 3DR Telemetry) and with firmware 3.2.1 (the latest for APM). LiPo between plates, APM on top, GPS on mast, gimbal under. It worked perfect in all flight modes.
I moved the APM-kit over to a DJi F550 and reprogrammed it (ArduPlane then ArduCopter 3.2.1 for hexa). APM between plates, LiPo on top, GPS on mast and gimbal under. It works splendid in Stabilize mode. In Alt Hold and Loiter it starts to throttle irregularly and goes side to side a little all the time (seems it corrects the sudden throttle changes). It sinks slowly until it would hit the ground, it raises a few meters, …
Last time I flew I had 12+ satellites.
It is compass calibrated.
I have had problems with wind disturbing the barometer so I have put “foam” around the APM like walls and that have worked good with all multicopters with APM. Even the sun may disturb the APM, but thats impossible on this one. I have flown the DJI 550 in days where there is no sun or wind att all.
In stabilize mode it uses the gyroscope and the accelerometers.
In altitude hold it uses the same plus the barometer, right?
In Loiter mode it uses the above plus GPS and Compass, right?
Therefore I guess its the barometer that is the first problem.
I have moved the telemetry out under an arm, it interferred.
I use Futaba FASST.
All cables are twisted.
I have the same problem without the gimbal and without the rectractables.
And yes, compass-callibration between any changes in hardware.
I have built 10+ multicopters from 450- to 680-sizes with APMs, Pixhawks and they works fine.
The only difference I can come up to is that the things are in different places. !? Its the same material of frame, same motors, same ESCs, same APM-kit, same RC, UBEC, …
Any suggestions what I should do? Is it just interferrence?! What to do i it is?