Catapulta IBERO

Hello, I am a student at Universidad Iberoamericana Puebla. I am currently in my freshman year, and this summer I enrolled in a course called "Engineering Project 1". In this course, I have learned to use 3D design software such as SolidWorks. I have also learned to use machinery for cutting and sanding metal, as well as cutting wood with different types of saws. With all this knowledge, I set out to create my final project for the course: a catapult. In this instructable, I will guide you through my process of making it, along with the skills I have learned.

For this project, we will use MDF wood, strong adhesive of your choice, a rope, hammer, hacksaw or metal saw, wood nails, number 4 C-clamp,a drill and a bit the size of our nails or smaller, to make the holes where the nails will go, this with the objectibe of the nails going in more easily, we will also use measuring tape and 3D filament. Here is the list of materials: 4 wooden boards measuring 50 cm long x 14.5 cm wide and 18 mm thick, 4 additional boards measuring 50 cm long x 12.5 cm wide and 18 mm thick, one board that will serve as the catapult arm measuring 50 cm long x 6 cm wide and 18 mm thick, and finally, we will use a rods with the diameter of your choice, in this case, I will use 2 oak wood rods. We will also use 3D-printed parts that we will design later.

We will start by cutting all the pieces with the machinery or tools we have available, always with caution and using protective gear such as lab coats and safety boots. Once we have all the pieces mentioned before, we need to measure them to ensure there are no errors. The goal is for the catapult to be 50x50x50 cm.

For this project, we were asked to perform a laser cut on the catapult to meet the course's knowledge test requirements. It is not necessary for you to do this if you do not have the machinery available. I engraved the name of my university with a laser to fulfill this requirement. Next, we will continue assembling the base with the wooden boards of 50x14.5x18 using nails and a drill with a bit slightly smaller than the diameter of the nails.

With the help of our drill, we will make the holes for the nails. The images show the position in which the boards will be placed for the wooden base. The position of the holes and the nails will always be vertically aligned with the width of the board as shown in the image. Once we have all the holes drilled in the base pieces, we will align it in the shown position and proceed to place the nails in their respective holes. After that we will use the metal saw to cut off any excess nails protruding from the bottom of the base.

Once the base is finished, we will use the remaining 4 wooden boards to create X-shaped bases that will be nailed to the lower base of the catapult. This X-shaped frame will serve as a support for the pole on which we will place the arm that will launch the desired objects.

First we will place the boards in an X shape without any specific inclination. With the help of our drill, we will make two holes in the center part of the X, these need to go through both boards. The holes will be used to secure this base with the nails. We will repeat this same process until we have two X-shaped bases. The goal is for them to look like shown in the images.

3.5

Now that we have both bases ready, we will proceed to assemble them. The X-shaped bases will be positioned on either side of the bottom base. We've made lower cuts on them to ensure they don't affect the balance and support of the catapult. Using a drill, we'll make two holes on each side of the X-shaped base, ensuring the drill goes through both the X-shaped base and the bottom base of the catapult. Once this step is completed, we will secure the X-shaped base in place by hammering nails, and repeat the same process on the other side. Once assembled, the catapult should look like it does in the images.

Next, we will show images of two 3D-printed pieces we made. These pieces serve different functions, named Piece 1 and Piece 2. Piece 1 supports the ball we will launch, while Piece 2 is a handle that attaches to the catapult arm and the supporting stick. Images of the blueprints for both pieces are provided for your reference in creating them, along with assembly photos showing how the pieces fit together. A brief description includes the most critical measurements.

The support of Piece 1 is adjustable depending on the objects you intend to launch. This piece must also have a slot where the catapult arm will fit, with dimensions of 6 cm in width and 18 mm in thickness. Piece 2 will have a cylinder where the supporting stick for the catapult arm will fit. In our case, the interior diameter of the cylinder is 37.60 mm. Similarly, the piece should have a slot where the catapult arm will fit.

The rest of the measurements are flexible, as well as the type of filament and infill used for the 3D printing.

Once we have the printed parts, as we saw earlier, they need to be glued to the catapult arm using strong adhesive. We will attach these pieces to the catapult arm exactly as shown in the 3D assembly. After the glue has dried, we will add two nails to the underside of the arm. These nails are intended to hold the rubber bands that will power our catapult. Similarly, we will place another nail on the bottom base of the catapult to secure these rubber bands.

For the tension mechanism, we will use the other wooden stick we have and small portions of MDF wood. First, we will make the bases for the tension mechanism using MDF. Plans for the bases of the mechanism are shown, and we can cut them in wood or print them in 3D, The bases will be placed as shown in the photo, behind the arm of the catapult.

Once we have the bases ready and in place, we will proceed to make a hole in the wooden stick. The diameter of the hole depends on the thickness of the rope we will use for the tension mechanism. Once we made the hole, we will pass the rope through it and tie a knot on the other side to secure it. Then, we will tie the other end of the rope around the stick to be able to tension it. The excess rope will be passed over the arm of the catapult, above the handle for the ball as shown in the pictures.

We now have the tension mechanism and the rubber bands in place for the power of the catapult. As final details, we added three different stops to the catapult to solve various problems. The first stop is a wooden board 50 cm long and 12 cm wide, placed transversely at the bottom of the catapult arm, as shown in the image. This stop is intended to prevent the catapult arm from throwing the ball downward due to the tension of the rubber bands.

The other two stops were nailed to the top of the bases in an 'x' shape, using leftover MDF wood that we had. The purpose of these stops is to prevent the catapult arm from moving out of position due to the tension released by the rubber bands when the catapult is activated. All these adaptations are optional and not necessary unless you encounter the same problems as we did when building the catapult.

Finally, we reinforced all the bases of the catapult by adding more nails to give the catapult more stability. The catapult is finished, and it just needs to be tested!