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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.