Hi All,

I've got a very powerful quad build going on here and have finally managed to get it flyable in Stabilize. After AutoTune failed to tune it to a point where any significant roll or pitch commands would prevent it from "flipping out", I have lowered the PIDs and now she is flying like a dream... in Stabilize Mode.

What is happening now is that Altitude Hold and Loiter are unable to maintain a consistent altitude. When I keep the Quad hovering in place (either by manually doing so or using loiter), I get an altitude change of +/-1-2Meters. This is a bit of an issue but even more so is that when I fly it laterally, it looses altitude quickly and all of a sudden pitches/rolls violently then shoots up into the sky where I have to quickly change over to Stabilize to correct as some of the pitching is close to 90 degrees!

Here are the current PIDs that I have which allow me to fly nicely in Stabilize:

Here are the Specs on the quad:

Motors: T-Motor 3520-11 400KV

ESCs: Phoenix Edge Lite 50AMP

Props: 14x4.7 APC SlowFly

APM Version: 2.6 with Firmware Version 3.1

Here is what I am seeing in my log with regard to the sudden, not expected and not requested, altitude changes while flying in Loiter and Altitude Hold:

The logs are attached to this post but as you can see above, right in the middle of the flight before I switch to Stabilize, the altitude starts climbing QUICKLY! Also, at this point, the copter is pitching and rolling out of control hence the switch to Stabilize. In the next Altitude Hold attempt, you can see the copter starts climbing on its own again and cannot maintain altitude whenever in a mode that requests altitude hold!

The APM is sitting on Alpha Gel to reduce Vibration and is also covered in a dark soft foam to keep the light off the barometer and to protect the APM.

Please, any help would be greatly appreciated! We've been trying to get this thing flying properly for some time now and though it flies fine in Stabilize, we want to fly without this erratic behavior in Altitude Hold and Loiter. I foresee this issue being present in AUTO mode too because it seems to be linked to the Barometer and don't want to lose this heavy and powerful quad.

Thanks in advance to anyone who can help!

Kind regards,

Oliver Volkmann

Micro Aerial Projects L.L.C.

2014-01-27 11-52.kmz

2014-01-27 11-52.log

2014-01-27 11-52.log.gpx