How to Make a Catapult Without Using Rubber Bands
The simplest way to eliminate the need for rubber bands in building a model catapult is to construct a trebuchet. A trebuchet uses counterweight instead of elastics to create torque. The catapult is held in place while a large weight hangs on the other side of a fulcrum. When the catapult is released, the weight pulls down, launching the projectile from the other end of a long beam.
Instructions
- 1 Take the square 5 by 5 inch piece of wood and cut it diagonally to make two identical triangles.
2 Place one 12 inch piece of wood horizontally. Make a mark 3 inches from one end. Take a 10 inch piece of wood and place it perpendicular to the 12 inch piece at the 3 inch mark. Place one of the triangle pieces from step 1 on top of the T shape, so that the 90 degree corner is on the 3 inch mark and the two edges running from it are flush with the 10 and 12 inch wood pieces. Glue the triangle into place (you can screw or nail it in to make it stronger). Repeat the process with the other triangle and one more 10 inch and one 12 inch wood piece. However, on this one you will have to make the 3 inch mark from the other end of the 12 inch piece, and the triangle will therefore be a mirror image of the first.
3 Place the two pieces you just constructed vertically, parallel to one another and 5 inches apart. Take three 5 inch wood pieces which will be the support cross beams. Place one 5 inch piece at each end of the 12 inch pieces, and place the last 5 inch piece in the corner where the 3 inch mark was made, perpendicular to the plane of the triangles, in the 90 degree angle. Glue and screw or nail the pieces into place.
4 Make a dot on the top of each 10 inch plank (facing vertically now) 1 inch from the top. This will be the joint of the fulcrum. Then drill a a hole where each of the dots are. The hole needs to be large enough to fit the 6 inch metal bar through.
5 Take the 16 inch wood piece and screw in a hoop hook (into the 1 by 1/2 inch face). This will be the swinging arm of the trebuchet. Then make 3 dots at 3, 4 and 5 inches from the end with the hook. Drill these the same size as the metal bar hole from before.
6 At the other end of the 16 inch wood piece, screw the other hoop hook in at a 45 degree angle on the 1/2 by 16 inch face. Hammer in a nail on the 1 by 1/2 inch face, leaving half the nail exposed. Cut or file off the head of the nail.
7 Now run the metal bar through the holes in the support, and one of the holes in the swinging arm. If you choose the hole 3 inches from the end, it will provide more torque than the 4 and 5 inch holes respectively, so you can experiment with this depending on how heavy your counterweight is. The arm should swing freely, so if there is too much friction you should make the holes wider. Now attach the counterweight to the hoop hook on the end of the arm closest to the fulcrum (metal bar) using the twist ties or metal wire.
8 Cut two pieces of string at least 18 inches long. Fold your cloth in half and tie a string to each end, making a pouch (much like on a slingshot). You can use a rock, grape or small ball of clay as the projectile (anything that fits comfortably in the pouch). At the end of one of the strings, attach a metal loop (made of wire, or a key chain loop will work fine). Tie the other end of the string to the unused hoop hook. Hook the metal loop onto the exposed nail.
9 Using the card paper, make a runway on the bottom of the support beams. It should run perpendicular to the three 5 inch wood pieces, covering up all three. Fold up the edges of the card paper, creating a straight runway for the pouch to run on while it is being flung by the arm.
10 To fire the trebuchet, place the projectile in the pouch and place the pouch on the end of the runway, under the counterweight. Pull down the arm while you're doing this, so the string is taught. Let go and the counterweight will pull the arm around, launching the projectile.
