01/13/06

ADVANCED MODELING - PAGE 3

How to convert your Futaba Transmitter for independent control of the machine gun and main gun fire.

By Frank "the Z Man" and Ken B.  6-18-2002

Additional information provided by Steve and Roy (Nov 03).  Thanks for the inputs!

Caution:  Read the article completely before attempting the modification.  If you do not understand the modification or know how to use a soldering iron, do not attempt it.  Find someone who understands the modification to help you.  FRAG accepts no liability for any damage caused as a result of this process.

OVERVIEW OF FUTABA SKYSPORT 4 TRANSMITTER MODIFICATION:

Using 2 momentary Normally Open (N.O.) pushbutton switches, you will wire them in parallel with the top and bottom trim pots that are assigned to the main gum and machine gun.    This article was originally written for the Futaba Skysport 4 Transmitter.  However, I have also received modification instructions for a Futaba 7UAP Transmitter.  This article will also cover those specific changes in the Step 3 of the modification procedure.

NOTE:  If you do not fully understand exactly what you just read, STOP and get help!!!!

PARTS REQ’D TO MODIFY THE FUTABA SKYSPORT 4 TRANSMITTER:

Radio Shack P/N 275-1547C - N.O. Momentary pushbutton switches, 2 each.

THE TOOLS:

1)      17/64" (6.8mm) Drill bit

2)      Soldering iron

3)       Four pieces of 26AWG wire.  Each piece about 11” long.  The color does not matter.  For the sake of clarity in describing this modification, I used red and green.

THE PROCESS:

STEP 1:   Remove the 4 screws holding the back of the transmitter.  Unplug the transmitter battery and swing the "transmitter back" out of the way.

Back of transmitter off and trainer jack circuit board in place.

STEP 2:   Lift the Trainer board off its mounting pegs and move it out of the way.

  Close-up of trainer jack circuit board.

STEP 3:   Locate the "trim pot" circuit board.  You will be adding wires to this.  If you assigned the gun function to a different trim pot, add the wires that that one.

 Close-up of trim pot circuit board without the added wires. The transmitter wires going to the circuit board should be yellow, black, and red. 

FUTABA 7UAP NOTE:  For the 7UAP circuit board, the wire colors are brown (common) red and black.  Also, the 7UAP circuit board is not located as shown in the center of the transmitter.  The circuit board is located off to one side is it is much smaller in size.  Steve suggests that you trace the wires from this small board and splice the new switch wires to them as opposed to soldering them to the circuit board.  The small size of the circuit board just makes it too difficult to solder the wires to it.  When splicing the wires, it is recommended that you cut the wires so that you can use heat shrink tubing to cover the solder joint.  It is not recommended that you use wire nuts to splice the wires as they might come loose and damage the transmitter.

STEP 4:   Solder the 4 wires to the trim pot circuit board as follows:  Solder one to the top and one to the bottom.  You will solder 2 wires to the center connection.

  Close-up of trim pot circuit board with the added wires.  The red wires will connect to the machine gun switch and the green wires will go to the main gun switch. 

 STEP 5:   Route the wires as shown in the picture.  Make sure that they do not interfere with any moving parts.  Solder the wires to the momentary switches.  The color of the button does not matter.  Each switch should get one of the wires soldered to the center contact and one of the end wires.  Reference the previous photo.  One switch will get wired to the red wires.  The other switch will get the green wires.

  Transmitter with wires in place.

STEP 6:   Before drilling the case, lets test the modification.  Route the wires so that you have access to the switches outside of the transmitter with the back of the transmitter in place.  Don't forget to plug in the transmitter battery.  Place the trim tab to the center position. With the tank powered on, momentarily press the machine gun switch.......it should fire.  Now press the main gun.......it should fire. 

STEP 7:    If both guns fired, it is time to drill and mount the switches so go to step 9.  If either gun did not fire, go to step 8.

STEP 8:   Troubleshooting:

NOTE:  This modification has successfully been performed on several Futaba Skysport 4’s.  We can not guarantee that another transmitter will work the same.  However, it should.

  STEP 8a:   Check the wiring.

  STEP 8b:   Go back to the Tamiya Instruction book and perform the R/C alignment procedure.  For the Tiger, it is step 23. You remember….push the set button and move the sticks up/down/left/right?

  STEP 8c:    If it still does not work, have someone else look at your work.  They may see something you did not.

  STEP 8d:   If you still can not get it to work, remove the wires and put the transmitter back together.  You are not back to the old way of firing the guns.

STEP 9:    Congratulations, you are almost finished.  Now look at the transmitter back.  Notice the 2 mold marks on the inside top left and top right.  We will be using these as our switch locators.

  Close-up of mold mark.

STEP 10:    Using a 17/64" (6.8mm) drill, drill a hole centered on each mold mark.  Now, mount the switches.  Put the transmitter back together (not forget the transmitter battery connector) and secure the 4 screws.  Test your work once more.

   Close-up of mounted switches.

STEP 11:   Now, go play!!!!!!!!!!!!!!!!