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OpenTX RFD900X TxModv2 Failsafe Workaround?

Based on what I’ve read here I know I’m not the only person struggling with the failsafes on the RFD900X. I think I have a work around.

My problem has been that when I set up the failsafe as per the RFD instructions the Pixhawk does not recognize the failsafe condition based on throttle failsafe. During testing (turning off the radio) I could get it to trigger an RTL mode so it was functional but not ideal.

I’m using:
TX16S (2.3.9) and Yaapu Telemetry
RFD TXModV2 and RFD900X (Both on 3.16)
Pixhawk Cube Orange (Arduplane 4.0.6)

Here’s my workaround:

1 - Turn on Extended Limits on the Model Setup page of the radio.
2 - On the Output page I set the throttle channel output min (CH3 in my case) to -110%.
3 - Plug the aircraft’s RFD900X into the computer using the FDTI cable and set up the fail safe as per the radio’s instructions. Using 3.16 on both radios I found the “set failsafe” button the GUI worked for me. I didn’t have to use the AT commands, but that should still work. Make sure you have your throttle stick at the bottom.
4 - After getting everything set, disconnect the radio from the computer and re-connect it to the Pixhawk.
5 - Reset the throttle channel minimum to -100% and disable Extended Limits.
6 - Since I’m still mid-build the pixhawk is on the bench. So I reconnected it to mission planner and verified the radio function. At -100% on the radio channel, Mission Planner is showing 986 on the corresponding channel. -110% was about 935 so I set the throttle failsafe value to 960.

When I turned off the radio (with pixhawk connected by USB to mission planner) the throttle channel now drops to the recorded value of~ 935 and now triggers throttle failsafe.

I have not flown this set up yet. I don’t know what monsters this idea may have unleashed so if someone sees some glaring issue please speak up before crunch some expensive gear. At first glance everything seems to be fine, and radio channel calibrations don’t seem to be affected. (throttle output still goes to normal min value of 1100)

If you need the RFD900X instructions for setting the failsafe the manual can be found on page 13:

I hope this helps somebody.

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I appreciate this as I’ll be using Cube Orange on my endurance build soon, albeit using Copter instead of plane.

I think if you’re always using a GCS then the GCS Failsafe may make this irrelevant. However, if you’re like me and occasionally fly without a GCS (Thank you Yaapu) then I think this may be more important.

Through playing with this I’ve noticed that when the radio powers up again my arming was resetting to low (disarm) because I had a “fancy” double switch safety set up through some logical switches. I’ve had to do some dancing around with OpenTX to get my radio channel to stay armed when the radio powered up after a shut down (but only when the switches are in a certain combination). That would be totally disappointing to recover from a fail safe from a radio failure, only to have the aircraft disarm in flight when you powered up again.

Long story short: When you’re testing this on the bench don’t forget to watch your arm status.

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Servers by jDrones