syamaner

As you know, a remote controlled opto isolated kill switch is a very important security feature when using gasoline engines. But it has a down side. You can accidentally activate the switch during flight which can lead to a dead stick landing and sometimes a crash.
I regularly use self designed and produced smart kill switches. I have to make two successive clicks on the transmitter (usually switch A) for the kill switch stop the engine.
Now I am thinking of other solutions where one doesn't have to use special equipment but a regular kill switch.
One solution might be to use to separate channels and two separate switches and a p-mix. ( I haven't tried it).
Another solution might be some form of programming where the kill switch channel will be active only for a limited throttle range (i. e. idle and a couple of ticks above idle). If the throttle stick is well above idle, the kill switch won't stop the engine even if the corresponding transmitter switch is activated. If the throttle stick is at idle or a couple of ticks above idle, the corresponding switch will shut down the engine. Just like the throttle cut function where you can set the throttle stick position, under which the throttle cut function can be activated.
The rationale is that during most of our flying we do not pull the throttle to idle. Most of the time the throttle is at idle or some ticks above idle when we need to stop the engine. On the other hand, right after take off the throttle is well above idle and this phase of the flight is when the most accidental engine stops occur by accidentally activate the kill switch.

Now what I did:

My throttle channel is 3 and kill switch channel is 8 (AUX1) activated by transmitter switch A.
I used a p-mix. Master: Throttle. Slave: AUX1. Switch: A.
The seven point curve is as follows: Point 1 (idle position) + 100, points 2 thru 7 -100
Additionally the subtrim for the AUX1 has been set to one extreme (in my example to - 100 but I think this will depend on the servo mechanical setup, I am not sure). EPA for the AUX1 has been set to +50 and -140.
I made a test using the servo monitor function. When the kill switch is OFF (i. e. engine is running) the throttle stick movement does not change the AUX1 signal which is all the way up. When the transmitter switch A is activated and the throttle stick is at idle AUX1 channel signal goes down (stopping the engine) but not all the way down. Similarly, if the transmitter switch A is activated but the throttle stick is well above idle the AUX1 signal remains on the upper side but not all the way up.

Now my next step will be to test this setup in real time because I don't know whether a regular opto kill switch would recognise the AUX1 signals apropriately.

If there is a more simple and elegant way to do this, please let me know...

PS: English is not my native language and it is highly possible that I could not express myself in this complex matter. So please feel free to ask me questions about the details.

syamaner

Today I have tested this setup and found out that except "subtrim -100" everything was OK. A little bit modification made the function even better.
The seven point curve is as follows: Point 1 (idle position) + 100, point 2 0, points 3 thru 7 -100
When the subtrim has been reset to zero, the setup worked just as planned. Throttle at idle: You can stop the engine using the kill switch. Throttle well above idle or WOT: The transmitter switch for stopping the engine does not work. That means, you won't be able to accidentally shut down the engine during flight.