In this page you will learn how to make rapid fire items/defenses.
attempt 1
You need redstone and redstone reapeters. place redstone in a 3x3 box, break a cross shape and add repeaters with no delay depending on how fast you want it.
attempt 2 [final attempt]
Place any block in a 2 high diagonal 3 long placement and place redstone torches at the back and put redstone on the top and make a signal with the reapeters and then add any thing you want.