Jörg Sprave of the Slingshot Channel makes some interesting contraptions. Mostly they are wooden mechanical devices that are usually rubber band powered. He has launched machetes, marbles, arrows and anything else dangerous and potentially deadly.
Well Jörg has made a fully automatic 6 arrow launcher using pressurized plastic coke bottles. His contraption is revolver based and has valves on each coke bottle. There is some sort of barrel which looks like the arrows sleeve over. Sort of like a giant Nerf blaster on steroids. He utilizes a battery powered screwdriver to spin the wheel of arrows. As each valve reaches the 12 o’clock position, the valve is released and the air rushes out pushing the arrow off the barrel.
It is rather impressive and simple.