The Medieval Trebuchet

What is a Medieval Trebuchet?

The medieval trebuchet was one of the most powerful and iconic siege engines of the Middle Ages. It was primarily used to break down walls and fortifications during castle or city sieges.

What is a trebuchet?

The trebuchet (also known as a trabuchet) is a type of gravity-powered catapult. Unlike earlier catapults that used tension or torsion (like the Roman onager), the trebuchet used gravity via a heavy counterweight to launch projectiles over long distances.

Main parts of a trebuchet:

1. Swinging arm: a large beam mounted on a central axle.
2. Counterweight: a heavy mass at one end of the arm (stone, lead, or a box filled with sand/rocks).
3. Sling: a rope with a pouch at the long end of the arm that held the projectile.
4. Base or frame: a sturdy wooden structure that kept the whole system stable.
5. Trigger mechanism: a device that allowed controlled release of the arm and counterweight.

How did it work?

1. The arm was pulled down, lifting the counterweight.
2. A projectile (stone, incendiary balls, even dead animals) was placed in the sling.
3. The trigger was released.
4. The counterweight dropped, causing the arm to swing and the sling to release the projectile at high speed and distance.

Advantages of the trebuchet:

1. It could launch heavy projectiles (up to 100 kg or more) over 200 meters.
2. It was relatively accurate compared to other siege engines of its time.
3. It allowed prolonged sieges without needing to get too close to enemy walls.

1. Hammer
2. Ruler
3. Pencil
4. Sheets of paper
5. Quick-drying glue
6. Wood
7. Plastic soda bottle
8. Twine
9. Link chain

Everything started with a freehand sketch, this to be able to understand both the functioning and the fundamental parts of the concept.

Let’s get to work! The next step was to carry out the conceptualization of the sketch by designing the 'blueprints,' since it was necessary to make the parts out of wood.

Requirements:

Counterweight - Box

1. 4 pieces of 10 x 5 cm
2. 1 piece of 5 x 5 cm

Base

1. 2 pieces of 34 x 2 cm
2. 2 pieces of 30 x 2 cm
3. 2 pieces of 20 x 2 cm
4. 4 pieces of 35 x 2 cm

Swinging arm

1. 1 piece of 50 x 2 cm

I divided the assembly into 3 parts to allow time for the glue to dry.

Part 1 is the counterweight box; for this, I also used tape to hold the pieces together and then fastened them with quick-drying glue.

Part 2 corresponds to the assembly of the base. Since the triangle is the most stable geometric shape, I built two triangles of equal size, using a ruler in the middle to support the weight. Then, I joined the two bases together.

Part 3, I focused on the pivoting arm, attaching the leftover ruler pieces from the middle of the triangle to create the rotating base. To determine where to attach the base of the pivoting arm, I simulated the arm’s rotation while considering the counterweight.

For this part, I needed the pivot arm to be able to rotate freely, so I found a tube which I later cut to the width I had already defined for the trebuchet.

For the final assembly:

1. I attached the chain to the counterweight box
2. I cut the wick thread to the length of the pivot arm
3. Additionally, I freehand designed the brake device for the rotating arm (although it didn’t work, due to lack of time I couldn’t perform tests or create a replacement)
4. Testing!!

During testing, I identified that the brake device did NOT work because the material was too thin, and that I needed to place a "stop" on the pivot arm so it wouldn’t keep swinging after the launch.