<div style="background-color: rgb(255, 255, 255); padding-top: 5px; padding-right: 5px; padding-bottom: 5px; padding-left: 5px; margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-family: Arial, Verdana, sans-serif; font-size: 12px; ">Newbie here

I have a Tamiya Pershing, a Futaba 2.4 gHz 4 channel radio, and a question...
</div>How do I change the Main gun fire control to a push button on the radio instead of the default trim/stick combo?

Take the back off of you TX and wire in a push button to the circuit board containing the connections off the trim pots.  You'll wanna wire/solder into the neutral position and the trim up postion wires on the circuit board.  Then you can drill a hole and postion the button on the back or shoulder of the TX.

Hope this helps.

What he said.  Here's how it's been done on Spektrum radios.  Futaba may be similar.  Firebuttons