9xr radio and throttle failsafe?


I am having trouble getting my signal lost/ throttle failsafe working correctly and hope someone can help me out.

The hardware: Turnigy 9XR radio tx, APM 2.5, Spectrum AR8000 rx, Turnigy dlux 40A SBEC speed controller. 

My understanding of the theory and method to set up throttle failsafe with APM 2.5:

1) Set your tx radio up so that the low throttle PWM is below say 950. On my radio I have to turn on extended servo range and adjust my channel one to -125%. this is a low as it will go.

2) Bind to the rx so it sees the throttle at the new low throttle PWM (950) for ESC failsafe. 

3) Reset your radio so that low throttle PWM is say 1000. Again on my radio I adjust channel one to -100% but leave the extended range servo on.

4) Calibrate the APM using mission planner to the current tx radio servo range.

To verify failsafe is working, using mission planner, on the failsafe page. Watching the throttle PWM, turn off the tx radio and you should see the throttle PWM go to 950.

My problem is I never see the throttle PWM drop when I turn off the tx radio, and the APM never goes to RTL (understandably). In addition it seems that the servo range calibration does not work correctly as it sets the low throttle PWM to a higher value so the motor runs even when I have the throttle stick all the way down. I can fix this by resetting my tx throttle servo range to -105%.

Am I not doing something incorrectly or do you think something may not be correct on my hardware/radio? Any suggestions?

thanks for your help.


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  • Thanks for this explanation. I was still missing one point after reading it. I finally found the solution on the net. To set the 100% and more, it's not on the 9XR menu 5 (mixer menu) but in menu 6 of 11 (Limits menu).

    I just tuned the FS on the D4R-II receiver and did 5 flight tests. All RTL perfectly !!!

    • I have finally worked out what the issue is. It's not the radio at all. Some APM boards have outdated firmware that prevents the radio from dropping PWMs at power off.

      This video outlines the issue and shows how you go about updating the firmware on the APM board!


  • MR60

    Hello Tom,

    This is how I did it (but I have another receiver from FrySky instead of Spectrum but the principle remains the same):

    -The principle is to train your receiver (Spectrum) so that when you turn off the radio (TR9x) this receiver will output on CH3 a PWM signal less than 975. I did that by creating a copy of my model in the T9x. On this copy, configure indeed the -125% for the throttle mix. Then place your throttle stick down (T9X will emit at that moment a ch3 less than 975) and follow the specific procedure with your spectrum receiver to tell it this is the output it must reproduce when loosing contact with the radio.

    -At this stage when the transmitter will be turned off, your receiver will loose contact with it, this will trigger the receiver failsafe : that is reproduce the output you tought to the receiver with the step above, that is a CH3 throttle less than 975.

    -The receiver will thus emit a PWM value on APM input ch3 less than 975; this should trigger the APM failsafe on throttle.

    -Do not forget after configuring the receiver failsafe to re-select the first model profile on your radio (you can delete the model copy that you used to configure the failsafe)


    hopes this help

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