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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  • Jose, after years of doing this I recently had a similar problem with setting failsafe that turned out to be operator error on my part so you might try going back to basics. Try this: first, set your transmitter to output throttle 'below idle' (150% low side, should be <975usec) as described at the beginning of this post. Turn off the tx. Disconnect the satellite rx from the PX4 and temporarily plug it into a Spectrum satellite-compatible receiver like the AR8000, AR9020 etc. Insert a bind plug into the receiver and apply power via one of the servo ports. Insure the LEDs on BOTH the rx and the satellite are blinking rapidly. If the receiver LED blimks but the satellite LED does not, you have a bad cable or satellite. With the throttle stick at minimum, hold down the tx bind button, turn the tx on, and release the bind button. When the rx and satellite LEDs stop blinking the bind is complete. If both LEDs do not stop blinking then again, you probably have a bad cable or satellite. Remove the bind plug and then power down the rx, finally turn off the tx. You must remove the bind plug BEFORE you turn the rx & tx power off or the failsafe setting will not stick. Re-connect the satellite to the PX4 and reprogram your transmitter for 100% low end throttle. You should be good to go.
  • Have you found a solution?

  • I have the same problem!

  • Nope I cannot get this to work. My setup is a Spektrum DMX9 tx with AR9020 rx satellite plugged into a PX4 Pixhawk. The satellite just does not remember the low throttle setting when I go back to the 1100 PWM setting. I have also bound the rx with the mode fail safe set to RTL and this does not work either. It does work with my Y6 that I fly with a DX7 transmitter but that has the complete rx plugged into a APM2.3 The rest of the setup works fine and the X8 I'm using flies fine but I'm obviously uneasy without the failsafe setup.

    Yes I have tried both the APM Planner and Mission Planner with the same result. APM on an iMac is not very good for this as when the TX is turned off all the radio settings graphics disappear!

    All ideas gratefully received...

  • Good idea I ll try that also!

  • Ah, that should be fine then. The roads look a bit like the roll-out areas on a runway but not quite which is why I was a bit confused.

    What you can do, I think I wrote about it somewhere, is to set the mixer in your radio to "fake" fail-safe. 

    You can then trigger failsafe by causing the throttle to go way down. The advantage here is that you are not turning the radio off and back on again which goes against everything when your expensive toy is in the air. :)

  • Thank you Grispin for you answers! It's not an airport but an industrial area 60km from the nearest airport. So I guess it's the criteria on your first answer that I don;t meet and that was a great relief for me!

    Thank you again!

  • Also Alex, that location of yours looks like it might be an airport of sorts. Is that so? 

    Not sure of the detail and how much it has been followed but I thought that had implemented the "don't fly near airport" feature so your plane might not work there. 

  • The motors will not start if they're not already running.

    If I remember correctly, the following needs to happen:

    Armed, motors running (as if it was flying)

    It has to be more than 20m from take-off point for FS to trigger RTL

    And 5m above where it was. 

    I may be wrong - cannot remember all the criteria. 

    basically, if it's not flying or near home, it won't RTL by itself 

  • Just followed the procedure at home,Failsafe is activated, first short and then long, but the motor does not start. Any comments on that before I go for field test? 

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