Spektrum DX8 and AR8000 Failsafe setup

I've been struggling to understand how to get the APM failsafe working properly and have yet to find some clear instructions that a noob like I can follow. It suddenly dawned on me how to get it all setup.

Here is my normal zero throttle output:


Here it is when the radio is off:


The AR8000 can be taught what to do if it looses contact with the mothership. The default is to leave or move the throttle to zero. As you can see, zero is normal and not enough to invoke the APM failsafe. (see here for more info on the APM Failsafe: http://code.google.com/p/arducopter/wiki/AC2_Failsafe)

What you need to do is tell the AR8000 to go below zero when the radio is lost and here's how you do it:

  1. Turn on the radio and go into servo setup.
  2. Find the throttle travel setup (on the DX8 it's the first screen)
  3. Scroll down to negative travel (Left hand 100%). Change that to as high as it'll go. 140% in my case.
  4. Confirm in Mission Planner that throttle input is now around 920uS
  5. Turn off radio and receiver.
  6. Insert Bind plug into RX and turn on.
  7. Remove bind plug from rx. Light should continue blinking.
  8. Ensure throttle stick is down.
  9. Turn on radio while holding down bind button. Radio should rebind.
  10. Turn everything off.
  11. Turn radio back on and change the throttle throw back to 100%
  12. Turn on quad and connection with MP
  13. Confirm that minimum throttle is back to around 1100.
  14. Turn off radio and throttle should now drop to around 920uS (or whatever it was beforehand)
  15. If not, start again.
  16. Now go to parameters in MP
  17. Find THR_FAILSAFE and set it to 1.
  18. Find THR_FS_ACTION and set it to 2 (1 = continue on Auto mission, 2 is RTL)
  19. Click on the write params.
  20. Click on Refresh to ensure it wrote it.

What you have done is told the receiver that when you loose contact, this is the new throttle position. It is of course, way lower than normal range. The low value is enough to trigger the APM failsafe which will RTL and land.

This all works in theory for me and MP seems to agree, I'll be out testing it tomorrow but just wanted to get it all down on paper so to speak.

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  • Good news that it works when turning the tx off. :)  Nervous times. 

    One thing that I was convinced was a problem though - talking from memory here so may be wrong or things have changed since:

    To cancel FS you have to have a mode change. I had a a few crashes when flying auto and on the edge of the Tx range. My thoughts are such:

    Rx loses signal, drops throttle to FS value.

    Rx regains signal and comes out of FS

    Rx loses signal and goes back to FS.

    At some point, the APM thinks it's throttle-down and your quad crashes.

    I had it twice and a friend once - auto flight, about 3/4 of a mile from where I was standing. First two times, while flying auto, radio was dangling by my side, antenna pointing down, against my leg; loads of attenuation. Heli crashed, logs showed nothing interest other than FS triggering.

    Tried again with radio held up above my head and it flew fine.

    I'm scared to test the scenarios....

  • Moderator

    Hi all,

    I can confirm that this works very well. It's freaky being able to turn off your transmitter and still have your copter fly. (;

  • @Sergio

    Yes, that is how it works. Mine is setup like that as well but I have not tested it in real life. Have you tried it?

    A simple way for testing FS is to take the props off.

    Throttle up and put it about 50%. Heli now thinks it's flying.

    Move the quad about 20m and place it at a different height (up on a table or something). 

    Trigger the FS and listen to the motors. They should increase in pitch as they try to climb and then RTL.

  • JTK,

    I don't know if it'll behave like that. I've not used the receiver for a while now since switching to Pixhawk.  Give it a try and let us know how it goes.


  • Going to ask here since its very related to my issue/question. I upgraded to 3.2 and I was testing all the features before going out and putting my X8 in the sky. I was about able to get RTL Failsafe activated. I am using the Spektrum satellite receiver and not the AR8000. I set the lower throttle like it states in the blog but when after binding and going back to normal and powering off the transmitter, Channel 3 does not drop to the lower setting. 

    Correct me if I am wrong but afterwards I did some digging and read that when the satellite is used, the Failsafe is different in that It uses the lost signal for 2 seconds or more to activate the Failsafe.  I need some help on the subject. 

  • I would have really appreciated if that was part of http://copter.ardupilot.com/wiki/throttle-failsafe/

    Took a while + google to find this and figure out why the Tx off never drops lowert than throttle low.  Thanks anyway.

  • The theory will be the same, your settings might be different though and how you get to them...
  • just wonder if same setup will work on my futaba 9c? thanks in advance

  • Yep, field tested. It was between 1-2 meters.

    I'll check it again later today and let you know what happens.

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