Airsoft robot fireing system

[DiegoChavez]

I am making an airsoft robot, and I need a way to fire the gun. The gun I got is a cheap crossman because it uses low power and can hold a lot of ammo. It is powered by 4 AA batteries. I am thinking on taking out the batteries and connected to some type of relay boar or something connected to the receiver. But I dot know how to do it. I have a spektrum 5 channel transmitter so I only have the landing gear switch left. I need that to fire the gun. Any ideas???