Nothing to add ...

What exactly is to do with that servo ??? "activated" or NOT.

BTW note the servo ALWAYS is activated ... you just "tell " it the position you want it to reach @ 50 times per second ...

As Archangel wrote, your R/C set very probably can do that without any added Gadget ...

Just ... RTFM ( just Read that ... R/C Manual !!! )

Now, the good question is ...
Does this pushbutton already exist aboard your transmitter ??? ....

this could be an interesting story, then.


Alain