This is a project I made for my high school physics class. I originally was going to make a Trebuchet but found myself scrambling for time due to my busy schedule and settled down on a Catapult instead. I made it out of various materials, wood, foam, rubber bands, and even a bit of plastic. Enjoy.

Supplies

Wooden polls 10 (max height of 70cm)

Wooden plank (Styrofoam works too, however, you will need to tone down power)

Hot glue/nails (10 nails)

2 screws

Rubber bands (lots)

Resistant band (better for heavy resistance)

Bottle, one that is sturdy

two pencils

A plastic container or something the ammo can sit in.

PVC pipe 1 foot

Step 1: The Base

I started out with a 40cm by 60cm base and then two 60cm long pieces to go on the edges. Then cut the polls into pieces that are also 40cm long. use 3 nails (in line with where the polls are, see picture) on both sides to make a barrier on each side. The polls will also follow this same pattern. Next, cut out square pieces of styrofoam. These pieces will help keep the next pieces at an arc, for the masts of the project (nail those in as well). Cut out 4 pieces of the pole into 70cm long and then tie them together with a little left on the top, make two of these (see photo for reference). Once you have both pieces, set them up in the appropriate area and hot glue them in. Then on top of the y shape, you have created tie/glue a longer piece across.

Step 2: The Power

For this part, I'd cut out a nice big piece of styrofoam, probably around 25 cm long and 10 cm wide. Put the two pieces together and stab a nice big hole through both of them. Next, you are going to glue them on the outside of the mast as shown in the picture. Then, poke a hole on both sides with the pencil and leave it halfway stuck through as shown in the picture. Finally, you are going to take your resistance band and tie it together, unless it is already in a loop. Cut the PVC pipe in half and then take the opposite ends of the band and push them through the holes. You will then slide the pipes through the holes. (make sure the band is tight or else you may need to tighten the band).

Stick two remaining poles or something thick in the middle of the band and begin twisting. When you believe it is tight enough, stick the main pole through by using the two little ones and opening them (you will need a second hand).

Step 3: The Launcher

Take the plastic container and cut the top part off so you have a shallow bowl. Next, you will want to screw it in on the top so that it 100% stays on. With the remaining rubber bands create two chains.

IMPORTANT:

If you decided to make the base out of wood then stick with a 4 rubber band chain

however, if you decided to stick with styrofoam then go with 5 or 6 long chains, or else it will break.

Take the chains and connect both ends to the end of the top of the pole and the opposite ends on the opposites sides of the masts as seen in the introduction photo.

Step 4: The Range Adjustor (optional But Highly Recommend)

Tape the bottle to the mast right across where the poll will be stopped, make sure you tape it a lot, or else it might break. Depending on the angle of the bottle, it will change the range. When the bottle is facing up towards the pole, it will be in its long-range mode, but when it is facing down it will be in its short-range mode. Next, take a small piece of the pole, about 10cm, and tie it strongly right above the cap of the bottle. this will help keep the bottle a little more stable.

Finally, take two 6 pound weights and put them on both ends of the base. Then you are ready to fire.