I have my rebuilt F550 pretty well balanced but when I kick it into ATTI mode it noticably pitches forward and start to travel quickly  in that direction.

I've even tried mounting the battery further back to counter the effect but the 550 seems hell-bent on pitching forward.

I re-calibrated both the compass and the IMU.

I have recently installed the e300 propulsion kit (which is pretty impressive on the noise reductions)

Could it have something to do with the gains?

Any input is greatly appreciated.

Are the symptoms Holds in GPS mode but pitches forward in Attitude mode.  If so I would look at your elevator trims in the radio and the Radio calibration in the Naza Assistant.
If it is holding in GPS compass and IMU should be OK.  Just make sure IMU is done a level surface.  I use a bubble level sometimes to confirm for calibration.

joe@heliflightc Posted at 2015-5-1 21:11
Are the symptoms Holds in GPS mode but pitches forward in Attitude mode.  If so I would look at your ...

Ahhhh Elevator trims... I will check that.

THANKS!

doug.dougjohnso Posted at 2015-5-2 06:58
Ahhhh Elevator trims... I will check that.

THANKS!

I checked the trims and I could definitely trim it back far enough to stop the forward atti movement. But then it runs backward in GPS mode. LOL.

It MUST be a balance thing. I'll have to try to rebalance it.

It can be quite surprising how much an offset in balance can affect the flight characteristics especially if it's quite a heavy rig.

I fly with differing payloads on my relatively heavy F550 (AUW about 2.7kg). The left to right balance very rarely changes but the front to back balance requires constant adjustment depending on the battery packs I'm using. I have the AeroXcraft landings skids on my F550 and this allows me to slide both the gimbal position and the battery cradle back and forth to achieve a perfect balance for different battery configurations.

Regards

Nidge

doug.dougjohnso Posted at 2015-5-2 07:27
I checked the trims and I could definitely trim it back far enough to stop the forward atti moveme ...

This sound like the level was off during IMU calibration or a significant weight imbalance as you noted.  The reason it flies backwards in GPS when you get the attitude mode level is the controller now sees stick input via the trim as a request to move in GPS mode.  Sticks are not centered as far as the flight controller sees it.