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PID Tuning Stab vs FBW

Posted by Scott Fitzgerald on November 18, 2012 at 7:05am

 I have read all the guides I can find on this forum on tuning pid to my airframe.  When I tune the P in fbw, the aircraft is wild in stabilize.  If I tune in stabilize, the airplane flies very well but control throws are very restricted in fbw.  The controls are so restricted that I have very little authority in fbw.  Turning up the pitch max/min and roll max give more control authority but the command limit angles are not what I want them to be. 

Why cant I tune in stabilize and have those stability values carry over to fbw? 

If I tune in fbw, stabilize is useless.  Do people just tune in fbw and not use stabilize? 

Is there another parameter that is muting the control authority in fbw that I am not aware of?  Maybe a Nav PID loop or something?

 

Thanks

 

Scott

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Replies

  • Scott Fitzgerald November 18, 2012 at 10:18am
    On the PID config page in mission planner the default angle is in degrees ie 45, 25, -15. The Wiki and the parameter definitions show the value being defined in hundredths of a degree. Which is it? If I want 45 degrees, should the value be 45 or 4500? The value in mp has continuity to the advanced parameter list. With 45 selected, is it trying to limit to 45 degrees or to .45 degrees? If it is the latter, the plane is trying to maintain a max bank of 1/2 degree. What I see as a limit to control authority might be the "nudge" overriding things.

    Thoughts?
  • Moderator
    Graham Dyer November 18, 2012 at 9:03am

    FBW-A is of course like a 'rate'-limited mode where the bank and pitch angles are limited, FBW-A mode will try to not allow those angles to be exceeded. Stabilize has no limits so will allow a roll or loop if required.

    You need to find a balance between the FBW-A angle that allows a reasonable bank angle (using LIM_ROLL_CD) and a bank angle that allows effective navigation. If you use an angle of 15° then your navigation will also only allow a 15° bank angle for navigation. I've been experimenting with between 25° and 40°.

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