A couple months ago I was testing ArduPlane and some of the different flight modes. I was not getting on very well in FBW-B* mode. If you look at the image above you will see the purple track that represent FBW-B (Red is FBW-A and Yellow Manual).
While I was flying I was losing altitude and I couldn’t understand why. You can see just before the path goes red to FBW-A, I’d lost a lot of altitude (50m down to 25m) and was heading for some pesky trees. I switched to FBW-A and pulled up out of this ‘death dive’. 😮
The problem was that FBWB_ELEV_REV was set to default of 0. This means ‘up elevator’ (pulling back in the elev stick) means the plane will go to a lower altitude. Setting this to 1, means that pulling back on the stick will put the plane at a higher elevation. This just makes much more sense to me when you are using pull-back to go up in manual that FBW-B does the same.
see http://code.google.com/p/ardupilot-mega/wiki/FlightModesFlyByWire (And I will update the doc 😉 )
*I stopped using the airspeed sensor as I thought it was faulty, now looks it was just my interpretation of the the controls
If you need to dial down the reactiveness of your quadcopter throttle when you are flying in stabilize mode you can add some Expo to it. Expo makes throttle movements less aggressive at 50% throttle, but as you move further away from centre the rate increases still leaving you with full range of power.
Here’s a short video I shot on how program the Expo feature for your throttle channel on an Open9x programmed Turnigy 9x