FBW-A lethargic

I'm new to the ArduPilot, and trying to tune gains for the first time. I've got the plane flying pretty well in stab mode, but when I switch to FBW-A it is extremely lethargic. It flies straight and is stable, but a full stick-deflection in roll only results in a few degrees of bank. The bank limit was set at 35 degrees and I bumped it up to 45 degrees, but can never reach the limit. Is there something simple I'm overlooking? Thanks.

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  • I've had this same issue on all of my X8 wings running apm2.5. Aircraft with nearly default PID's navigates beautifully in auto mode. I wanted to work on the fine tuning so I followed the wiki on tuning PID's. Spent a bunch of time trying to get FBW rolling to 45, the first step after confirming manual flight.

    Came to the conclusion that somewhere in the software the elevon mixing for FBW must be affecting us. I believe that the software was "taking the difference" between the max pitch up angle of 15 degrees and max bank of 45 degrees. I could only get about 25 degrees of roll in FBW despite the fact that I have huge elevon travel. (look at the radio calibration screen while moving your sticks to see what I mean) If you move the stick all the way left, you do not get full travel of the roll channel. You have to move it left and down to get 100% travel. I haven't tried to modify the radio calibration procedure, maybe we should just move the sticks full left-right and up-down during the calib? (not to the corners) 

    Luckily it works great in the important AUTO and RTH modes. Now I just use FBW to test the nav gain.

  • Developer

    Kevin - you have something wrong.  There should be no problem with finding a gain set that is fine for both stabilize and FBW.  Keep looking at it.

    Check that you don't have a unit/scaling issue with your bank angle limit.  I can't remember off the top of my head, but it may be in centi-degrees.  You should be able to have the airframe on the ground and give full stick deflection, then manually bank the aircraft and see the ailerons center as the bank angle approaches the max bank value.

    Next thing to check would be your radio calibration.

    Do you know how to use the tuning graphs in Planner?  You can set them up to see the current and commanded bank angle in real time.  If you have the max bank set to 45 degrees you should see the commanded bank angle go to 45 when you give full stick deflection, and you should see the actual bank angle tracking the airframe attitude.

  • Moderator

    Hey Guys,

    Read the wiki section here on tuning your aircraft. It specifically talks about how to tune your PID settings starting with stabilize then FBW and progressing to RTL and Auto. The wiki really gives a pretty good guide for tuning and lists the parameters you want to tweak.

    Regards,

    Nathaniel ~KD2DEY

  • I aggressively changed the default angles to:

    max pitch 45

    min pitch -45

    max bank angle 50

    With that my Bixler 2 can climb out at 45 degrees after take off and do nice turns in FBW (A).

    A good "dry" test is to put the plane into FBW and tilt it to the side until the ailerons start to decrease deflection (as the bank angle is reached). You will notice that the ailerons start to decrease quite a bit before the max bank angle is reached. Maybe that deflection is not big enough to keep your plane banked?


  •  Are there PID parameters associated with FBW?

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