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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3D Robotics
Comment by Chris Anderson on March 29, 2012 at 4:32pm

Nice one! Now added to the manual here

Comment by EllisSu on March 30, 2012 at 6:55am

My TX is DX7s and that's work too, tks. 

Comment by Tom in NOVA on March 31, 2012 at 1:13pm

Would this work for the Turnigy 9x?  I upgraded to the ER9x firmware.  It's reading a 972 pulse on THR/CH3 with the stick down at zero, the motor starts at 1050, but when I turn off the radio the last pulse settings remain.  

I read that you can program the ER9x to send alternating signals every few microseconds that APM2 can detect, but the APM2 code needs to be modified to read it.

Any way to set the 9x for failsafe with APM2?

Comment by Crispin on March 31, 2012 at 1:55pm

I should have added something else to the blog.

The above will should work for most receivers which have some sort of fail safe mode. You need to find where you set the travel limits for your throttle (In the Spekrum it is Settings > Servo Settings > Throttle)

Your TX and RX then see this as the zero throttle. You need to then see how to tell your RX "in time of panic, go to zero throttle" As this new zero throttle is enough to trigger the APM fail safe, it'll do it just fine.

Once you've done that, you need to change your throttle limits back to normal.

You do not want your normal throttle zero to be able to trigger the APM fail safe!

Comment by Jay on April 25, 2012 at 3:38pm

FYI to do this on the Turnigy with ER9X firmware, just goto Setup on model 2/10 page and turn E. Limits to ON. Then goto Limits on model 6/10 page and change CH3 0.0-110 instead of 0.0-100. This should drop you down to 940uS or so in MP. Bind with RX. Go back to Setup on model 2/10 page and turn E. Limits to OFF. Test by turning off your TX while connected in MP.

Comment by james sowell on May 3, 2012 at 6:15pm

should it be about the same for futaba 8fg

Comment by Dave on May 3, 2012 at 8:07pm

Jay, what Rx are you using with the Turnigy 9x? 

I'm using the matching Turnigy 9X 8C v2 and the outputs freeze at their current settings if signal is lost.  Nothing changes, so it seems it's not possible to detect loss of signal.

Comment by Jay on May 3, 2012 at 8:14pm

I am using the FrSky DIY module with a FrSky VF8R receiver that has a failsafe. I do not think the stock Turnigy receiver will let you set a failsafe.

Comment by Mike Waltz on May 17, 2012 at 7:11pm

"Turn off radio and throttle should not drop to around 920uS (or whatever it was beforehand)"

You meant "should NOW drop" right?

Comment by Crispin on May 18, 2012 at 12:54am

Thanks Mike. I'll get it updated.

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