Just a heads up -
We have found that with the latest v3.20 firmware of the RFD900 you cannot set the PPM failsafe behavior to “output nothing” as PX4 expects. The radio requires a valid PPM stream to record the failsafe PPM.
The only option with the upgraded firmware is use the RC_FAILS_THR parameter and you’ll need to record a PPM stream with an invalid throttle value ( < 800us for example).
Not configuring the failsafe PPM could result in a flyaway or crash if the radio link is disconnected.