Aircraft is undershooting waypoint altitude - what am I doing wrong?

Posted by Bret C on February 17, 2013 at 8:15pm

Guys:

Today I was testing a 2.5 APM with MP 1.235.  

The aircraft (Ritewing ZII) flies under stabilized flight as well as manual -OK.  When I switch to auto mode, the aircraft turns toward the first waypoint, but it heads downwards to what looks like a point near ground level.  I tried switching between both absolute elevation as well as normal elevation with a height above ground about 600 feet, but the aircraft still heads toward a point on the ground.

The ground elevation displayed on the MP is accurate.  I am using a Ublox GPS.  The APM is mounted on the top of the plane (in the wind because of a lack of space).

I would appreciate any suggestions, please.

Thank you.

Bret C

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Replies

  • Bret C February 25, 2013 at 5:08am

    Group:

    As of late yesterday we finally had success with the Ardrupilot auto pilot flying way points and also holding attitude.  As time and weather allows, I will conduct followup flight tests and file a more complete document here on the action taken from the contributors of this thread.  But out of curtesy of contributors to this group, I wanted you to be the first to know that I finally got the auto pilot to work and hold altitutde with a short note.

    The two settings that I changed were:

    1. In the "Flight Planner" of the "Mission Planner" I changed the "default altitude" to 600.  I doubt that this actually corrected anything as I am of the understanding that this only sets the default altitude of the way points as they are created. (600 was the same altitude that I had set for the way points manually but did not set the default setting)
    2. In the hardware configuration of the mission planner I had unchecked the "use airspeed sensor" but still had the "use airspeed" box checked.  Since I was previously used the airspeed sensor but recently removed it, I still had this box checked.

    I suspect the culprit was the "use airspeed" box being checked.

    Please look for more details of the resolution in the next few days.

    Thank you to everyone who have helped with this challenge.

    Bret C

  • Chris Card February 20, 2013 at 7:45pm

    In the Mission Planner hardware configuration tab there is a link to get your compass declination.

    3692628148?profile=original

  • Bret C February 20, 2013 at 5:04am

    As a follow up to some of the groups questions and comments, where should the compass offsets be set?  Mine are currently set as follows:

    (COMPASS_OFS_X) -89

    (COMPASS_OFS_Y) 133

    COMPASS_OFS_Z) -105

    (COMPASS-USE) ENABLED

    Most of these settings are from a friends parameters who sent me his files to help me get started.  Not fully understanding this, I would think I should start with all these set to 0?

    Thanks guys.

    Bret C

  • Bret C February 19, 2013 at 7:54pm

    Here are a few logs from today.

    I am still looking for solutions

    Thank you guys!

    Bret

    2013-02-19 17-03-51.tlog

  • Ravi February 18, 2013 at 5:44pm

    try to fly the aircraft under manual mode and leave it hands free if you can. i think aircaraft could have pitch trim problem. also chk the CG. under auto mode aircrafts are very sensitive to CG. if nose heavy they loose height under auot mode. also while leveling through mission planner keep the nose 2 deg up. this should work

  • Simon Howroyd February 18, 2013 at 12:02am

    When you are flying in manual what altitude does the plane think it's at? With APM mounted in wind, this may knacker the static pressure readings for altitude.  In MP there is an option to bias the altitude between GPS & pressure. Swing it more towards the GPS side & see what happens. GPS is traditionally rubbish for height, but may be better than noisy static pressure.

    Look here for more APM static pressure info.

  • Warren Eather February 17, 2013 at 11:46pm

    Hi Bret,

    What does your ElevationProfile graph look like? (Flight Planer/(right click) Map Tool/ Elevation Graph)

    Waz

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