Failsafe apm 2.5 with frsky and turnigy 9x


I'm not sure i'm doing good..

I 'm flying with an apm 2.5, rx frsky, tx turnigy 9x.

I saw the video of Mark Harrison on youtube ( ) explaining how to setup your failsafe setup on your frsky. I did it too..It workds ! nice !

In the manual of the apm 2.5,, the failsafe is explained of an other way :

Do i have to make the setup of the apm 2.5 like explained in the manual if i already follow the instruction of Mark Harrission (seup on the RX) ?




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  • Umm no answer since 2 months, I hope this post is still alive.

    I got the same problem than BertzillAvionics.

    I configured failsafe on my FrSKY to call a RTL. I didn't configure anything about FailSafe into the APM.

    I tested in MP, when I turn off the TX the flight is going to RTL.

    Well, my setup was there since 1 month but I never had the courage to try it. Yesterday, I was ready for the test. I did a 7 minutes flight, did a mission, got some fun in drift mode and then, it was the moment, I positioned the quad at about 30 feets, near of me, and then, turn off the TX.

    Like a rock, the quad went down. As soon as I turned off the TX, the quad has been disarm and all motors stop.

    No big dammage, the quad itself is ok, all props/arms/motors ok...I just broke my skids.

    Well, for now, I don't understand why my quad disarmed. I did several test this morning in MP in FailSafe section to try reproduce the problem. On about 30 tests, one time I reproduced the problem...but I don't know exactly the sequence.

    I have 2 guess :

    1) Maybe I should configure FailSafe into APM (throttle failsafe) rather than FrSKY failsafe ?

    2) I setted my flight Mode by using the Terminal. I have problem having the new PosHold flight mode. In the GUI, when I choose do not work. So then, I putted throught terminal the Flight Mode(12)...which I think it's the PosHold...but when I take a look in GUI, the dropdown is empty for the Flight Mode(12)...there is no equivalent value in the list...

    I don't know if having a blank value like that can cause a disarm on failsafe ?

    here's a picture of the last minutes of my flight.

    any comments will be very appreciate

    Sans titre.png

    • Hi Martin; I am not sure we had the same problem. Mine was occured a bad apm clone board. The crash I had and you identified it as a simmilar to yours was caused by weird "jumps" to a random flight modes without switching on. Probably one of the jumps was to "stabilize mode" while the TX was in the 3 sec recovering period of 900mv. So the APM disarmed motors and I hit the ground.

      After installing a new FC board - all works ok. 

      Detlef - thanks, your posts helped me a lot


    • Hi Martin, the failsafe stuff is a little confusing but its not to choose either one it always is initiated by the RX and the APM is reacting to it. The APM alone can not tell that the RX lost the signal and start a failsafe action if its not told so. Its always the RX which has to tell the APM that there is a problem. You can choose to use the RX failsafe alone but then you must teach all important channels like flight mode, throttle, and sticks a certain value to keep your copter flying or configure the low throttle failsafe in APM and just output a low throttle with the RX in order to let the APM control throttle and the other things by itself.

      If you don't use the low throttle failsafe configuration then the APM doesn't know that your RX has a problem and still thinks you are flying it with whatever inputs it gets from your RX during the RX failsafe situation.

      What I mean if for example I teach my RX to output a value on the mode channel that represents a certain flight mode and forget to teach the appropriate throttle value to keep it in the air it will come down anyway. While if you use the low throttle (lower than zero throttle) APM failsafe config the APM knows the RX lost its signal with your TX and ignores all other inputs.

      Don't know if that explanation helps you... I haven't done much with my quad lately so I don't know what PosHold and mode 12 does. Is that the new name for Loiter in the new firmware?

      • Detlef, thanks for your fast answer :)

        "You can choose to use the RX failsafe alone but then you must teach all important channels like flight mode, throttle, and sticks a certain value to keep your copter flying"

        If I correctly understand, I need to teach my RX...

        So first, as I never did some "teaching" and as I have nothing configured for low throttle failsafe, do you think that's the cause of why my motors disarmed ?

        Second, I don't really understand what you mean by "teach all important channels" I can do that?

        Third, the PosHold is a new flight mode that was previously named "Hybrid mode"'s a mix of Loiter and AltHold.

        Thanks for your time

        • That failsafe teaching greatly depends on your remote control system and RX. Some brands only are able to teach the throttle channel - like my older Spektrum. My FrSky teaches all channels and I've seen some systems that give you the option to choose failsafe as hold current output value or output a preset value.

          The FrSky RXs I have do teach all channels together, not only a single one. So I have to adjust all channels/sticks/switches to the value I want those to output in the case of a signal loss and push the teach button.

          If I leave for example the throttle at zero during failsafe teaching then that is what the RX will output in the event of a signal loss later and depending on what flightmode you activate that could mean motors off.

          The issue why this thread was originally started was because the FrSky RX outputs 0 throttle and mid position for the rest of the channels for 2-3 sec during startup and ignores in that moment all failsafe teach values. So this has to be considered in your mode assignments if you don't want to have a different flight mode activated with zero throttle during startup.

          All I am saying is that the failsafe config greatly depends on your RX and remote control system. There is no simple config or explanation that works for all. When you configure all this you have to look at all possibilities. A good tool is to check the RC calibration screen where you can see the output values of all your RX channels and verify its really doing what you expect it to do together with the flight mode screen and failsafe screen in Mission Planner when you turn your TX off and on.

          It just happened to me that I swapped RXs in my plane and somehow my RX crashed or the PPM cable broke. What my FrSky config was with RTL at 1500us (mid position) didn't work in that case. The RX output 900uS (low value) or the APM read for the flight mode this value with a disconnected PPM cable which was configured to be CRUISE at 900uS. Cruise with the APM plane is hold altitude, direction and speed... at 8km out I lost video :( 

          • DetLef,

            After read your reply, and also read again the FrSky instruction about setting up the failsafe...I found that I did something very wrong.

            As you wrote, when the FrSky learn button is pressed it saved the value of all channels...and I'm sure that when I did this setup my throttle was completly "off".

            So I didn't have a disarm when I turned off my TX...the APM only stopped the motors because the RX told it to do this.

            I think I am right now ?

            • Sounds possible, that's why I like to look at the radio calibration screen in mission planner in order to verify that all channels do the thing I expect them to do and also double check in the flight mode screen and fail safe screen that it is really getting into the right modes.

              Good luck next time!! :)

              • Just to "close" my discussion, I got the courage to try the failsafe again with a good setup on all channels...worked great !!

                thanks again Detlef for ur time.

                • Great! Congrats :)

  • I feel a bit lost. Yesterday I was testing the failsafe's (APM 2.6; firmware 3.1.4. R9X and Frsky). These were first tests after my previous crash one month ago caused by the lack of gps fix. First I was testing RTL involved by mode-switch - it was working properly howyever I had an unknown issue: mulitple and radom mode changes reported by MP without even touching a switches on my radio (first log). After landing I tried to test failsafe switching off my RX while in the air. I am sure I set the RX failsafe function to go to RTL mode and I tested it before start on MP. But after switching off my TX all mots stopped and I gracefully hit the ground. What am I doing wrong? Can somebody help me to read my logs pls?

    Regards Brt

    2014-06-08 20-00-12.log

    2014-06-08 19-39-55.log

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