PPM failsafe problem. - it appears to "hold"

ArduCopter Copter 3.2
1

I have been routinely checking planes after a reciever firmware upgrade.
(PPM is configured to just stop 250ms after signal is lost )

Any Pixhawk plane, when signal is lost - displays raw3.ch3 as 900ns, , pitch/roll,yaw channels are showing centered values, and failsafe is detected.

Pixhawk hexas, however, have no indication about lost PPM , I can disconnect the reciever, and all in-ppm will remain as it was last. everything appears as if the reciever is just outputting the last PPM series, - even with RX disconnected.

Is this by design, and what is proper testing procedure ?

2

let me specify , that it works as expected, the “problem” is that it’s hard to properly verify whatever reciever is corectly configured (there’s no apparent difference between an properly configured rx, that stops outputting PPM, and a dangerously configured one that is configured for “hold”)

3

I thought this was covered on the Failsafe page: copter.ardupilot.com/wiki/throttle-failsafe/

Your test may not be accurate as they say the wire should not fail, but it’s possible for the receiver to burn out and in which case something bad is going to happen.

If the receiver goes dead the output pin may go to ground which is maybe detected and handled.

For Frsky the receiver stops sending PPM so it should be handled.

Mike