Developer

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A couple months ago I was testing ArduPlane and some of the different modes. I was not getting on very well in FBW-B* mode. If you look at the image below. You will see the purple track. I was loosing altitude and I couldn't understand why. You can see just before the path goes red, I'd lost a lot of altitude and was heading for some pesky trees. I switched to FBW-A and pulled up out of this 'death dive'. :-o

The problem was that FBWB_ELEV_REV was set to default of 0. This means 'up elevator' (pulling back in the elev stick) means 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.

see http://code.google.com/p/ardupilot-mega/wiki/FlightModesFlyByWire (And I will update the doc ;-) )

*I'd stopped using the airspeed sensor and FBW-B requires you have one, so haven't been using this mode since.

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Comments

  • Thanks for the heads up. One more quirk to add to the pre-flight checklist.

  • Developer
    The APM 2.5 was in a case, with a opaque canopy. The plane held altitude while flying into the wind, then started loosing when running with the wind. Maybe more throttle would have helped, but with it flying away from me loosing altitude, I pulled back on the stick and it got worse. Yikes. It was doing what it was told, I just didn't know that I was telling the plane to do the opposite!
  • It seems holding altitude nice until you changed direction and then you got the decent.

    I had the same: barometers are light sensitive, read this The mysterious AltHold problem .... solved

     

    After I stopped the light reaching the baro through the window in the box, I still got soft descends, because the dim light could still reach the baro form the other side. Now I covert the baro on the board with a tiny black plastic cover, and now I have no problems at all.

    Hope this helps...

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