Catapult Project

Catapults have been used since Greek and Roman times. They were used as siege engines against castles and walled cities. The ammunition loaded into the catapults were meant to break the walls with stones, fire incendiary missiles over the walls, or used for biological warfare, such as launching dead animals over the wall to spread disease. The type of catapult we built is a mangonel catapult. We like to call it RZYAACN (our names combined and it sounds cool). The catapult works through torsion, which is the tension caused when an object is twisted in one direction while the other end is motionless or twisted in the opposite direction, with equal and opposite torques at each end. Now to the construction of the catapult, we first had to decide which type we would build. We decided on the mangonel catapult because of its seemingly simple design, need for not too much materials, and awesomeness. We then went to the store Home Depot to buy our supplies. At Home Depot, we bought two 2×4’s (inches) which were eight feet and 12 feet long, and we had a Home Depot employee cut up for us into smaller lengths.

He cut the wood up into two pieces that were 36 inches long, one piece that was 30 inches long, four piece that were 15 inches long, and one piece that was 18 inches long. We also bought one piece of square plywood that was half an inch thick, and had it cut from its original 24 inches by 24 inches size to 15 inches by 18 inches. We bought a 36 inch cylindrical piece of wood, which we sawed at the store into two pieces, 15 inches long each. Lastly, we bought 21 feet of nylon rope at the store, which was cut by one of the employees. We then drove back to the house, where the real construction began. We set up the base of the catapult with the two 36 inch piece of wood and two of the 15 inch pieces, setting them up in a rectangle. We used power drill, and used a drill bit to start the hole, and then drilled in three inch nails to keep the wood in place. Next, we put the remaining two 15 inch pieces of wood on top of the base vertically, 15 inches from the ends of the base on opposite sides, repeating the same process for the drilling and nails. Then, we sawed the square piece of wood in half diagonally to form two triangles, with the help of Ryan’s dad. We then nailed on both of the triangles, one on each side, to the base and uprights, with the hypotenuse of the triangle rising towards the uprights.

Then, we nailed in the 18 inch piece of wood, connecting the two upright 15 inch pieces of wood on the side opposite of the triangles. Then, we drilled a half inch hole in the 30 inch piece of wood 2 and ½ inches from the end of the wood through the middle of the side. Then, we drilled one inch holes that are 6 inches from the end of the base with the triangles attached and 2 ½ inches from the bottom. Now, it’s time for the wrapping of the rope. First, we tied a knot with the rope onto one of the 15 inch cylindrical rods. Then, we put forced the rope through the holes in each piece of wood, going to the other side, wrapping it around the other piece of cylindrical wood one time, back to the other side, and then back to the other side once more. Then, this is where things change. Instead of going through the holes in the swing arm, the rope is wrapped above and below the arm.

The wrapping is basically in a figure 8 pattern. So when you go above the launch arm, the rope is therefore going to go into the next hole and wrap from under the cylindrical rod, which will cause the next wrap to go under the launch arm, and so forth. Then, as we neared the end of our string, we wrapped the rope near the launch arm together once for better tension, and then knotted at the cylindrical rod. Now, with the string in place, we turned the rods towards us from the side with the string and triangular supports. As we turned more and more, the launch arm rose and created a lot of tension, so much so that we had to get Ryan’s dad to do the last turn because it was so difficult, and then had to place a nail to prevent the rod from slipping. We then attached a spherical object to the end of the launch arm to hold our object that we are launching, which is a softball in this case. We drilling a small hole in the middle of the base and middle of the end of the launch arm, and found a piece of wood in the garage that we attached a string to, so that we could plug the hole with this piece of wood attached to string to remote launch the catapult. And that, is how you build a mangonel catapult.