Auto & Loiter Mode always Losing Altitude - Log Attached

Hi All ,


-          Flight controller : PIXHACK

-          GPS Ublox

-          MiniOSD


-          GCS : Mission Planner.

-          Firmware : Arduplane 3.4


After previous tests and posted topics here I solve the problem of pitching up and stall , 

now the plane is very stable and work well in manual and stab modes , even when I off the motor during the flight its very stable and decent with glide ,

But when try loiter mode , and Auto mode , It works good and direct to WP or start loiter ,

previous tests the throttle cut , now the throttle is off and start many time and the plane loss the altitude while trying go to waypoint , until it become near to ground I change to stab and control it to gain altitude and try again always decent ,

I am not using airspeed and my cruise throttle in set to 50% ,

What's the algorithm that control the altitude (GPS , Baro , TECS ) ?

which parameter I should change to keep altitude ?

how dose TECS control altitude ? 

here is the Log file , in .Bin format  Log File

Hope I can solve this problem I want to enjoy the auto modes :(

best regards..

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  • Developer

    Your flying within 1km of an international airport.  I STRONGLY advise you find somewhere else to fly.

    Thanks, Grant.

  • Developer

    If you read this you will see in stablise mode the throttle is controlled by THR_MIN and THR_MAX.  You have THR_MAX set to 60.  I suspect that isn't enough for the plane to maintain speed and altitude and a plane will pitch down if it needs to pickup speed.  Further I see in the log that the throttle never goes above 1600 PWM. 

    You have also greatly reduced your pitch limits.  The values on the left are yours and on the right are the defaults.

    LIM_PITCH_MAX        800.0000    2000.0000
    LIM_PITCH_MIN       -500.0000   -2500.0000
    LIM_ROLL_CD         1700.0000    4500.0000
    Basically you aren't allowing the plane to put in much pitch and with the lower throttle setting it is always going to loose altitude.

    The only other option is you have your elevator reverse setting (RC2_REV) around the wrong way so when its in an auto mode and it applies elevator its applying it in the wrong direction.  You should however notice this on the ground in FBWA mode.  On the ground in that mode if you tip the nose of the plane down does the elevator go up in response?

    Thanks, Grant.

    • Hi Grant,

      Very good information 

      I understood the points you said but I want to ask dose my settings make the throttle off when change to Auto ?

      why throttle off ? and some time work in auto for moment then off ?

      In stab mode the cruise speed 40 is good , ant safe altitude I make it 60 % to avoid high wind speed ,
      when I rise the throttle cruise to above 60 % plane start pitching up to stall point
      Even I am using 6 Cell Lipo 5300 mah

      when I change auto I lose throttle

      I use the (RC2_REV) after I see the wrong direction of elevitor in Stablization mode,

      Dose FBWA movement same as auto ?

      ( I will test (RC2_REV) in ground with FBWA )

      Thankx Again ,

    • Pitch up at high throttle is either balance point, or thrust line
    • Bruce Boxter ,

      you mean C G point ?

      the plane is flying well in stab manual and also glide with out throttle ,

    • Yes, cg point.
      It's possible you have too much longitudinal dihedral and the cg too far forward,
      The thrust line generates pitch up.
    • Yes, It was then solved also the motor angle was wrong ,

      Now the pitch up problem solved ,

      Trying to solve the Auto mode losing altitude and throttle off .

    • Developer

      I've already solved the issue.  Please read in detail my response above.  Your PTCH settings are too low.

      Thanks, Grant.

    • Grant Morphett ,

      why the motor is off befor losing altitude in auto mode ?

      if the motor is ok I think the plane will controle the altitude

  • still facing the same problem in losing altitude in all auto modes :(

    I am really getting disappointed , :(

This reply was deleted.