This is a variation of a catapult, called a trebuchet. This is a step by step tutorial on how to build a successful trebuchet that can launch a projectile from 8 to 12 ft.
Step 1: Find a Substantial Base
Start by finding a base that isn't too thin or too heavy, because the arm needs a balanced base to be able to launch the projectile a long distance.
Step 2: Add Wheels
Wheels can be added by wood glue or already be attached to the base. The wheels will give the trebuchet more momentum, rather than having a non moving base.
Step 3: Add the Sides
The sides must be cut equally to match each other, preferably in triangular shapes and flat on the tops of them. Also no more than 50 cm tall.
Step 4: Cut a Hole in Each Side
The hole or cut must be even on each side. It must be loose enough for the PVC pipe to either sit in or go into to, and be able to turn and twist.
Step 5: Add the 2 PVC Pipes
One PVC pipe must connect from one side to the other, while the other PVC pipe must connect to the horizontal pipe, which is connected to each side.
Step 6: Connecting the PVC Pipes
You can use many methods, but the method used here is the 2 PVC pipes being connected to a 4 hole plastic connector, which turns it all into 1 connected piece. You will have to cut the horizontal pipe in half and connect it into the connector with cement glue.
Step 7: Cut 2 Thin Pieces From a Plank of Wood
This 2 cut pieces of wood must be cut equivalent to each other. You then must drill 2 holes in each piece of wood, one on each end.
Step 8: Making the Sling
The sling can be made of any type of light weight material. You can use cloth or anything like that. Once you have found your material you then cut 4 holes in the square shaped sling, one in each corner. Then string must connect to the 4 drilled holes in the wood, thus allowing your sling to work and function.
Step 9: Connect Your Weight
Connect two 5 pound weights to the other side of your arm. In this trebuchet the PVC pipes goes through the weight and once on is capped at the end using a cement glue.
Step 10: Add Your Trigger Mechanism
Drill a small hole in the base towards the back under the weight. Connect twist ties from the arm all the way to back side of the base, which will allow the weight to stay up in the air. When you cut or move the twist ties forward at the bottom under the weight the sling is launch by the weight dropping and making the arm go forward.
Step 11: Add a Projectile
Your projectile must be a small object, that isn't too heavy or too light, and must fit in the sling. This one used a golf ball.