Firing Buttons for the FUTABA Transmitter
by JC

1) This system is for FUTABA only. Airtronics and Ace require a slightly different system

2) The electronic circuit shown will allow one channel to have two firing buttons. When one button is pushed the servo arm will move from center to one side. When the button is released, the servo arm will move back to the center. When the other is pushed. the servo arm will move in the other direction.

3) The template is for four firing buttons i.e., two channels are required.

4) TEMPLATE: Cut out the template (actual size is 2 1/4" by 2 1/4") and glue to a 1/8" thick piece of plastic. Drill the four smaller holes with a #43 bit and tap 4-40. Drill the larger holes with a #I bit (.272"). Now you can cut out the mounting plate. Feel free to sand and paint the BACK side of the plate.

5) Remove the back of the radio and disconnect the battery. Unscrew the four screws on the face of the radio that hold the gimble in place.

6) Note that there are three wires going to each pot on the gimble. The two outside wires are red and black while the center one is either yellow or orange. The yellow and orange wires are the signal wires. Cut the wires and remove the gimble.

7) Mount the firing buttons to the plate to the inside of the radio using 4-40 socket head cap screws.

8) The two pots shown shown in the above circuit are 5K ONE TURN TRIMMER POTS. Mount them to a small circuit board and adjust each to 2.5K and mark this point on each pot.

9) Simply wire per the diagram as shown.

10) The firing buttons are "MOMRNTARY SWITCHES - Normally closed" type.

11) Adjusting the 5K pots will determine how far the servo arm swings.