The radio doesnt activate the solenoid. It activates the gun board. The gun board is set up to interpret the signal from the radio receiver into the solenoid opening. 0 (center stick) to +100 (stick all the way forward) is "one direction". 0 to -100 is the second direction. Most dual gun boards will have two outputs, one for each direction of travel. You would then hook those outputs up to the desired solenoids.