Engine is derived from the word used to describe a military machine and the person used to operate it was called an engineer. So I wanted to build an engine. As the trebuchet is my favourite seige engine, I decided to build it. This tutorial will help you build a trebuchet and you can ofcourse make some changes in terms of size, design and even working principle. Just have fun tossing paperballs and whatever you can get your hands on.

Step 1: Gathering the Resources

You are going to need:

Two planks of wood of same dimensions( as shown on the left of the pic )
One broad plank of wood that can act as base ( Choose a bigger one to have a low center of gravity )
One long plank of wood to act as arm
One 5 inch nail
Eight 2 inch nails
One plastic bowl
One plastic bottle
Strong thread
Electric Drill
Safety knife

Step 2: Raising the "engine"

Draw two lines equidistant from the sides depending upon the distance you want between the planks supporting the arm. The points which is going to support the planks should be neccesarily equidistant as to add stability to your model. Now drill the holes.

Drill a hole through the supporting planks(near their top part) and the arm plank( At a point in a 1:4 ratio ). This should be such that a five inch nail can pass straight through them..

Take the supporting planks and rest them on the four holes we drilled in the base plank, then hammer the nails and raise your model...

It is starting to take shape now.

Step 3: Building the Arm

To one end of the arm( longer portion ), nail the plastic bowl as shown in the picture. This is going to throw your projectiles. Hammer a nail through the other end of the plank. This would hold the bottle we are about to use.

Cut the plastic bottle in the middle. The lower half is what you need. Now pluck two holes diametrically opposite to each other near the top end. Pass a thread through it and tie a knot so that you can carry it like a bag. Fill it with stones and sand.

Step 4: Almost Finished

Mount the arm between the supporting planks through the nail. Hang the bottle on the other shorter portion of the arm. Now the setup would look as shown in the picture.

You can also put a nail near the bowl and tie a string to it. Now pull down that string, load the trebuchet with its first paperball and LAUNCH...

Here's my first shot with the trebuchet

This is my first instructable so kindly forgive any mistakes. Also I would love to have your valuable comments on how can I improve my instructables. Thank You !!! Have fun. :)