Plane always flies to right of waypoints

Posted by Mapper905 on May 17, 2014 at 11:44am

3691121799?profile=originalDoes anyone know what might cause the plane (Skywalker 2014 with pixhawk, 3dr gps/compass) to always fly to the right of the waypoints?  This results in my planned flight lines being alternately too close, then too far, apart.  This happens every flight, regardless of wind speed or direction; flying crosswind, or parallel. First flight line starts NE corner.

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Tags: pixhawk, survey, grid, waypoints
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    • Mapper905 > Drone-University.com June 17, 2014 at 7:54am

      Yes -- that's my procedure for trimming. I've even verified that the servo values I see in the MP radio cal dialog (sticks neutral) are being transferred to the RC(1,2,4)_TRIM params.

      When I fly in manual mode and just visibly confirm straight/level flight, then transfer those trim values, my cross-track error to the right is somewhere between the original photo and the most recent one.

      This leads to another question:  Is there a more objective process for trimming the aircraft than just flying in manual and trying to observe straight/level flight?  It would seem there should be a better way, given the available telemetry and autopilot modes...?

    • Drone-University.com > Mapper905 June 25, 2014 at 9:20am

      @mapper

      Sorry to answer here, I fail to see any reply function under your last post

      As per explanation (I fished it for you in the wiki), you should only consider nav_roll and make sure it is a constant zero value so a basic horizontal line at 0. 

      As per CheckFBWADemands, it is a value from the full parameters list. I just cannot guarantee tha it is on your version of MP (I have stopped using the latest MP version), you'll have to check but be cautious about changing the value :-)

      Here is the link :

      http://plane.ardupilot.com/wiki/flying/starting-up-and-calibrating-...

    • Mapper905 > Mapper905 June 25, 2014 at 8:14am

      @Drone-University - Your screenshot didn't post...?  I opened the tuning window and the difference between roll & nav_roll is typically 0.3 units -- not sure what the "units" are -- is that significant, or "in the noise"?

      Could you add a little detail about "CheckFBWADemands"? How exactly to I check this?

    • Drone-University.com > Mapper905 June 17, 2014 at 9:01am

      What about that ?

      • If the plane has a tendency to fly left or right…. With your autopilot powered on the ground and connected to your mission planner, select FBWA on your transmitter, select the FLIGHT DATA tuning window and plot the nav_roll and nav_pitch data. With your transmitter sticks centred, these should both be zero as shown in this screenshot. If they are not, you need to repeat your RC calibration or adjust your transmitter trims and repeat the FBWA flight test.
      • CheckFBWADemands : If they are at zero, then you need to adjust the AHRS_TRIM_X (roll) and AHRS_TRIM_Y (pitch) for the difference in angle between the autopilot board and your planes attitude when flying straight and level. You can change these by going to CONFIG/TUNING>>Full Parameter List and adjusting AdjustRollPitchTrims. Incremement by 0,01. if the plane turns to the left, AHRS_TRIM_X should be increased. If the plane loses height with mid throttle, AHRS_TRIM_Y should be increased.

      So basically last resort is to increase AHRS_TRIM_X by steps of 0,01

  • Mapper905 May 28, 2014 at 8:20am

    I flew this morning, again in manual.  MAYBE a little more left aileron/rudder trim was needed--I added it.  It was subtle.  I switched to FBWA and did lots of passes to and from me, parallel with the wind. It seems to fly fine with hands off the sticks.  I didn't turn TRIM_AUTO back on, so the changes I made in manual weren't transferred.  I will do that, and re-fly the mission.  For now though, all I can say is that if trim was an issue, it was as indicated, pretty subtle.  I'm attaching the tlog that goes with the original flight shown in the posted pic.

  • Ben Howard May 27, 2014 at 3:59pm

    Have you checked whether or not your compass is calibrated correctly? Incorrect yaw input may be causing issues 

    • Mapper905 > Ben Howard May 28, 2014 at 8:09am

      My method of checking was simply comparing the heading in my HUD to a compass reading (adjusted for variation). It seemed right to within the precision that I could read the compass.

  • Mapper905 May 27, 2014 at 7:47am

    a) the HUD shows level to within a degree or so.

    b & c) I flew on a calm day and the plane flies straight and level on manual.  I flew toward and away from me, and I don't see any sign of side-slipping.   I set TRIM_AUTO for a flight and transferred the trim settings by switching manual to auto with no stick inputs.

    I've noticed the cross-track error indicator is between 1/2 & 2/3 of a gradation, to the right, on all flight lines.  I suppose that's just another way of stating the original problem...?

    Note: The wind is from the south. For E->W lines, the plane banks left, and yaws left about 10-15 degrees into the crosswind -- as expected.  BUT For W->E lines, the plane is still banking left!  It compensates by yawing 30 degrees right to maintain the desired heading.  That makes no sense to me.

    Any other ideas??

  • Drone-University.com May 17, 2014 at 1:07pm

    Is the plane really balanced in manual mode (warped wing ?)

    - check rudder trimming ;

    - decrease prop size and check again ;

    - change the sense of rotation and put adequate prop and see what happen ;

  • Ben Howard May 17, 2014 at 11:50am

    I have had the same thing happen to me with a Zephyr on the APM 2.6 running 2.7 something firmware. It doesnt happen every time but looking back at it i would say it happens maybe 10% or 20% of the time - never solved it though :(

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