Introduction: Torsion Catapult

Our group is creating a ballista catapult. When researching the catapult's past, we found that the catapult was invented around 400 BC in the Greek town of Syracuse. The very first catapult invented resembled a crossbow. It was called the Gastraphete. The Greeks, impressed by the destructive power of this new weapon, created another version called a Ballista, which they used as a defense weapon against raiding armies. Originally, the Ballista was best described as a giant crossbow that fired spears instead of arrows. Many types of Ballistas were popular between the Greeks and Romans, but the one thing they had in common is that they were all powered by twisted sinew ropes. The Ballista was accurate and could fire spears a great distance, but they were difficult to build and were limited to hitting what they could see.


3— 2” x 4” x 8’ long Stud (Common); 1.5” x 3.5” x 8’ (Actual)

1— ½” diameter x 10’ long PVC Pipe

50’ length— ¼” diameter Braided Polypropylene Rope

Electrical Tape

Assorted nuts



Wood screws

¾” x 3 ½” Lag Screws

Step 1: Making the Base

Cut your 8ft wood stud in half

And place them across each other

Then cut two 15in pieces of wood

Lay the 15´in pieces on both ends of the 4ft studs

And then screw them together

It should make a box with

Step 2: Making the Frame

cut 2 9in pieces of wood

then cut one 18in a piece of wood

now lay the 18in a piece on top and set one 9 in the pieces on each end

It should look like the picture above

then you are going to cut 2 12 in of wood

After you are going to attach the 12 at a 35-degree angle

Step 3: Attaching the Frame to the Base

take your frame and place it on top of the base

you will need to angle the 12 in the wood so the can easily connect to the base

After the screw the frame where the end of the 12in the touching the end of the 4ft pieces

should look like the picture above

Step 4: Adding the Rope

Take some rope and tie it to one of the handles at the side. Then run it through one side of the catapult and through the middle of the arm, ending it by running through the other side and wrapping it around the other handle and going back through the holes, wrapping around the first side handle again, and repeating until 3 passes are done.Then, you go over the handle which makes you go under/behind the catapult throw arm after you go through the side pieces. (over, through, under, through, over). Then when going through again, you go over/in front of the center throwing arm. Through the side piece hole again and under/behind the handle. Then wrapping the rope around that side handle and going on top of the side pieces now, going over and under the center arm as many times as possible, in a figure 8 position. If any rope is left over, such as scraps, you can wrap the ends by the throwing arm together with it, and you will be good to go.

Step 5: Making the Sling/cup

place cup on top of catapult arm on the front side

use metal flatheads to pin it in

Step 6: