Traumatic flight, question on throttle fail-safe

I am not sure what section this post belongs in, so I am putting it in the Misc section for now.


I have a couple of questions that I will put forth upfront.  If you have any input or are curious you can read on for the details of my flight.


Does the radio throttle fail-safe trigger the usual RTL or is it some different wider radius RTL or tune down the PID values to a default set of values?

Is there anyway to disable the autopilot, such that if the plane is landed the fail-safe will not be triggered by a loss of Tx signal?


So here are the details:

I was flying with a Turnigy 9x Tx with the stock AA battery pack.  My batteries were about 3/4 charged when I started.  I was working on getting my navigation parameters down, flying a basic box pattern.  After the first circuit, my Tx voltage alarm beeped several times and the voltage began jumping around.  Before I could do anything, my Tx restarted.  I thought at that point my batteries were dying, so I decided to switch off the Tx, to trigger the RTL fail-safe while I could think of a solution to get my plane down.


Rather than the typical RTL loops overhead, the plane flew off into the distance.  I though at that point my plane would fly off never to be seen again.  It luckily flew a huge radius circle and returned to view over the trees.  At this point I was rushing to pull my Futaba Tx out to scavenge its battery (of a different connector type naturally).  When I threw down my Tgy radio, it restarted, flashing the switch error message.  When I reset the switches I regained control of the plane in manual mode and brought it around for a hurried landing.  (At this point I thought my batteries were just low, and had recouped some power from sitting.)


After landing, I ran to recover the plane, but before I reached it, it began driving around on the ground (back in RTL fail-safe).  The plane managed to take off, tried to turn and stalled due to its low speed.


After picking up the mess of my plane, I played around with the radio to see what was causing the problem.  It turns out the Tx default battery pack holds the batteries too tightly so that the spring doesn't properly push the batteries into the contacts.  Playing with the battery holder I realized that by jostling the pack the you can cause the batteries to loose contact, or have diminished contact.  This must have been my issue in flight.  Also running to the plane after it touched down must have caused the Tx to go out again.


So, although it saved my plane (and later wrecked it), why did the APM fly my plane in such a huge circle about the launch site.  My RTL had been set to 30m radius, but from the kmz the plane flew a 467m circle, that wasn't centred at home.  After a good chunk of the loop it switched centres to a closer point to home and flew at a reduced radius.


The next question would be, should any similar odd situation occur, once a plane is on the ground is there are safety you can activate to disable the APM?  Can you set a switch to disable the fail-safe?


Thank you for any help you can provide.

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  • Has anyone had a similar experience with the RTL acting differently when it went to fail-safe?  I got my radio battery issues all straightened out so that should never happen again, but I would feel better if I knew why the fail-safe did not act as it should, or at least as I had expected it to.

  • Anyone have any additional ideas now that I posted the log?

  • Here is the log...

    2011-09-25 07-34 4.log

  • Developer

    can you upload your log?

  • 3D Robotics

    My bet is that the radio failure did not trigger the failsafe (different radios need different settings to work with the failsafe; it depends on what the signal they put out at radio loss) and instead your plane was just flying straight (possible stabilized; we'd have to see the logs to be sure) and was slight untrimmed so it went in a circle.


    Are you sure it was in RTL mode in the pink section? What exactly does the log say?

  • Developer

    Did you have GPS lock? I haven't looked at APM code in a while, but it sounds like you lost GPS and the plane was flying a blind loop, usually called Circle mode.


  • Just for reference, here is the usual RTL loop.  This is from another flight, but with the same programmed home point and RTL loiter radius.


    So why would the fail-safe RTL be so much different?

  • Developer

    do you have the log? what will show what mode changes took place

  • Moderator
    I don't know if this helps, but I have two failsafe actions, maybe you do too.

    The primary failsafe for my setup is not from the APM, but rather the rx.
    My futaba rx is setup to change ch 5 low (set to RTL) but some rx/tx have other defaults, like rudder hard right, etc. Maybe it was the receiver failsafe settings that caused the circle?
    Apache2 Ubuntu Default Page: It works
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