1.    Collect materials.

2.    Build a base and two side supports.

3.    Build a launch arm.

4.     Drills a hole through one of the supports at the top and in the middle do the same on the other side.

5.     Drill  three hole in the launch arm  about four inches apart

6.     Drill a hole four inches from the top end of the launch arm.

7.     Take a piece of ready rod and put it through one of the supports then in the launch arm then the other support.

8.     Put a bolt through the hole at the top end of the launch arm and hook a chain to it then put on a nut.

9.    Take a plastic coffee can and cut off the top three quarters of it then drill it on the end of the launch arm.

10.     Put boards across at each end of the catapult and drill them on so it braces it

11.     On the back end of the catapult, on the brace, bolt on two short pieces of wood then on that wood screw on a piece of wood straight up and down

12.     Then drill a hole straight through them so you can put a bolt through it

13.     Weld a washer on a bolt so that you can tie a rope to it then you put the bolt through the two hole on the board going up and down. Now you have a trigger