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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  • Moderator

    Just to confirm - I tried this properly this morning. At 30m, turned off my TX and the quad just stayed there - didn't flinch at all until it went into RTL mode.


  • Moderator

    Nice work Bill.  This was testing in the field yes?  If so, what height did you try it at?

  • I just tested FS_THR_ENABLE set to 1 and it worked. Spektrum DX7s

  • I couldn't find:

    1. Find THR_FAILSAFE and set it to 1.
    2. Find THR_FS_ACTION and set it to 2 (1 = continue on Auto mission, 2 is RTL)

    Is this the correct parameter:

    Throttle Failsafe Enable (ArduCopter:FS_THR_ENABLE)

    The throttle failsafe allows you to configure a software failsafe activated by a setting on the throttle input channel

    Value Meaning
    0 Disabled
    1 Enabled always RTL
    2 Enabled Continue with Mission in Auto Mode
    3 Enabled always LAND

  • Thanks Crispin for this great tutorial, it works very well. There only one thing I can't get to work. In the failsafe options there is one option called ALWAYS_LAND. I have configured this option because I like this one more than RTL. 

    But when I activate the failsafe it's going to execute RTL instead of ALWAYS_LAND and I don't know what I am doing wrong. 

    I am using a DX8 in combination with a AR8000.

  • Thanks Crispin, just used this to setup my radio, now to test....

  • You won't see the throttle go to cruise in the APM radio calibration section as that is reading the values from the rx. The throttle will stay below normal zero which is how the APM detects the failsafe condition.

    You might see it in the logs and tuning graphs though. Without checking, it will be something like Throttle-Out.

    I've not actually looked for that though.

  • Crispin,

    Many thanks for this post. I did this setup and working ok, when I turn off the radio I can see the MP change flight modes as expected. one thing does not happen the throttle not going to cruise mode. even when I start the failsafe throttle stick to the middle, what happens is that the throttle goes to zero, this is correct? I expected the throttle maintain cruising speed for the plane back home safely? (these tests done on land with the GPS locked)


  • Thanks for your guidance and I have done exactly that. When I switched off my Spektrum DX8 transmitter PWM drops to 925 but Mission planner shows Stabilize mode irrespective of what mode I was in before switching off my TX. How to correct this? Thanks

  • Moderator

    Thanks Crispin.  That's been very handy!  Quick question - what did you set as the throttle failsafe value in the settings?  Did you leave it as default? (I think mine was 917).

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