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Autopilot - second test, plane flies in wrong direction

Posted by Harapan on March 20, 2014 at 3:40am

Two successful flights with drone (plane) today, but the second flight (with the exact same waypoints/set up as the first flight) was a little strange...

Almost as soon as the drone was launched it banked right and started trying to fly in the wrong direction. We hit RTL almost straight away and it circled perfectly for us. We then restarted the mission from ground control station, and it then happily followed the WPs and landed perfectly.

I have attached the Tlog here. Does anybody have any idea what made it decide to fly in the wrong direction at first, especially after an earlier perfect execution of the same mission?

Many thanks!

2014-03-20 09-28-51.tlog

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Replies

  • James Parkes March 20, 2014 at 4:53am

    Hi Harapan, 

    You lost GPS lock, the number of satellites dropped to zero twice while flying. Check the GPS and cable. 

    James

    3701688801?profile=original

    • Harapan > James Parkes March 20, 2014 at 7:38pm

      Hi James

      Thanks for pointing this out - we hadn't noticed. A bit worrying, but actually at the points that it lost GPS (around WP 4) it still travelled in the correct direction and we had no problems.

      The part of the mission that we were worried about was straight after launch when it suddenly banked right, just before we hit RTL. A possible idea of ours is that it was trying to swing out right in order to make the tight left hand turn that we programmed at WP 2. However, this theory still doesn't explain why this didn't happen in the same mission the time before. Is this a plausible explanation or not?

      Re GPS dropping out, we will check GPS cable etc. What is the risk of GPS dropping out like this? If GPS lock was lost for a long time would we lose the drone or could we still hit RTL to bring it back?! 

      Many thanks! :)

      • James Parkes > Harapan March 23, 2014 at 2:45pm

        Harapan,

        GPS is a critical part of any autopilot, without it RLT and AUTO will not function correctly. Find the source of the error and fix it ASAP.

        You plane is poorly tuned. Take a look at the first graph below for a section of flight where the plane was circling in RLT.  Your roll overshoots the nav_roll by large amounts and pitch is equally bad with pitch never quite achieving demanded nav_pitch. Follow the tuning guides found here http://plane.ardupilot.com/wiki/flying/tuning/

        3702643900?profile=original

        In terms of what went wrong with your second flight, my interpretation is the following. See the graph below.

        • The Auto take-off begins at A with what I assume is a running hand launch. Between A and B the plane is tilted to the left by 15 degrees while still being hand launched.
        • At B the plane the plane is launched and demands a positive roll correction which is overshot, resulting in the right turn you saw after launch.
        • At C the plane had already stated to correct and was nearly back to level banking only 5 degrees, however shortly after you activated RTL at D, where the plane banked hard right overshooting the demanded 30 degree bank by 10 degrees.

        Another issue I noticed is immediately after launching at B, your altitude goes down to -5m which is unlikely unless you launching off a cliff. Is you barometer adequately protected from wind and turbulence?

        3702643600?profile=original

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