RE: Servo recoil
the site say it can work with out the battle unit pcb .
Recoil Board
Use to simulate recoil of a cannon. Connect between a servo and the battle circuit. When the battle circuit fires a servo will recreate the action of a gun recoil. Contains a separate regulator for the servo.
This can also be used alone. There are three connections, power, ground and trigger. When the trigger wire is pulsed high the servo will activate.
Jimmy