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PixHawk Altitude Issues

Posted by Brian Christal on March 14, 2014 at 2:02pm

Hi,

I have a flying wing with PixHawk "mostly" working. Sometimes it seems to have a problem with altitude when in auto mode and flying a waypoint mission. Here's what it does:

Fly RTL mode OK

Fly manual mode OK

Switch to Auto with preprogramed waypoint mission loaded. Plane accelerates and descends while heading for waypoint 1. Can't react fast enough to switch back to manual and climb. Plane hits dirt.

It's done this behavior a couple of times. One of the times I changed all my waypoint altitudes to 200M. Then the plane flew fine, way up there. Log attached. Any ideas?

Thanks!

Brian

2014-03-14 13-40-41.tlog

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Replies

  • Andersson Beccari February 4, 2017 at 4:32am

    My friend, forget Pixhawk for everything. Try in your jet model, Navio2+raspberry pi. Did work Very well for my jet. 

    Se e flying on YouTube.

    https://m.youtube.com/watch?v=sIpNPc9Y8Ig

    https://m.youtube.com/watch?v=C6jPAKi1SHo

    Havre a good fly.


    Brian Christal said:

    In my case above it was a poorly trimmed airplane. As an old RC guy who learned on sailplanes I always trim so the nose slightly falls. I fly with back pressure on  the stick. Not a good idea with a Pixhawk. Trim your plane in Manual mode so it flies perfectly level. Then you must recalibrate the radio using Mission Planner. Your plane should now stay level as it transitions between flight modes.

  • John Major November 21, 2015 at 3:42am
    Just checked mission plans etc in text mode and grabbed the mission out of the pixhawk using apmplanner (which is quite clear about abs vs rel in the 'on board' waypoints section)
    Text files show reasonable home heights around 704 meters.
    The mission we used was overwritten by our next attempt at that area.
    Alt in logs at launch looked to be in that vicinity.
    Alt of home in plane ...
    592m!
    I'm now pretty sure that the home alt was not adjusted as it was pushed around the map in missionplanner, and used a value from about 9 hours drive away when pre-creating the missions the night before.
    Now adding a step to my checklist to update home location from drone and recheck mission altitudes. Not sure how much I'll be able to see, but at least I'll have the comfort factor of something to check.
    • Brian Christal > John Major November 21, 2015 at 5:06am

      In my case above it was a poorly trimmed airplane. As an old RC guy who learned on sailplanes I always trim so the nose slightly falls. I fly with back pressure on  the stick. Not a good idea with a Pixhawk. Trim your plane in Manual mode so it flies perfectly level. Then you must recalibrate the radio using Mission Planner. Your plane should now stay level as it transitions between flight modes.

  • John Major November 21, 2015 at 2:19am
    I've just run into this today. Still chasing through logs to see what happened. My initial feeling is that there is an abs/rel conversion going on behind the scenes that has a bug (or I'm misusing it). I suspect that I may have created the mission in one place and dragged the home marker to a better vantage point with higher alt which failed to adjust the height of home. Fortunately we were trying to fly with good ground clearance and that combined with terrain avoidance meant the rtl was successful. Will add more when I've looked through it.
    I'll check back if I find anything more helpful.
  • Dennis Megarry July 22, 2014 at 11:17am

    I'm thinking the Pixhawk only reads altitude in ABS mode..  I ran into the same issues..  My APM is always fine, I set 100 meters in the flight plan and it flys 100 meters up from where I turned it on..   The pixhawk gets altitude from the GPS which says I'm at 295 meters already before it leaves the ground..   Few times I've tried it, it wanted to fly to the earth's core,, Lucky for me I was able to get into manual and save the plane..  Pretty much given up on the Pixhawk now cuz not enough out there for people to comment yet on the threads asking questions..  Maybe in the future we can get questions answered..  for now, APM is my pilot!  :)

    I did try it on my RVJet which flew great till I tried Auto... Then nose dived straight to the ground destroying the plane..  Now I don't trust the Pixhawk at all.. too scared to fly it again..

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