Introduction: Torsion Catapult

In this instructable, we are going to provide detailed step by step instructions on how to build a torsion catapult.

Step 1: ​Gather the Materials

-2 3ft 9in planks
-2 3in wood pieces
-5 1.5ft planks
-4ft 3in plank
-2 1in pieces
-2 2ft planks
-2 6in PVC pipe sections
-28 screws
-20ft piece of rope
-9 oz plastic cup
-6ft piece of rope
-2 8in pieces of rope
-1 washer
-1 tennis ball

Step 2: Build the Arm

-Take the 4ft 3in plank of wood and drill a hole .25 inches wide .5 inches from the top all the way through the plank.
-Attach the 9 oz cup to the 1 inch below the hole to the top of it on the 4ft 3inx3.5” side by pushing a washer over a screw then screwing the screw through the middle of the cup.
-Drill a hole that is 1 inch wide through the 4ft 3inx1.5” side of the plank 1.5 inches from the bottom.
-Set aside.

Step 3: ​Construct the Frame

-Drill a hole 6 inches from the edge of the 3ft 9inx3.5” side and 2 inches from the bottom that is 2.5” in diameter on each 3ft 9inft plank.
-Screw together a 3ft 9in plank and one 1.5 foot plank with 2 screws, going through the edge of the 3ft 9in’x3.5” of the 3ft 9in ft one and 1.5”x3.5” part of the 1.5 ft plank. Make sure the holes in each of the 3ft 9in planks line up with each other
-Then, screw the edge of the 3ft 9inx3.5” side of the 3ft 9in plank to the other 1.5”x3.5” side of the 1.5” plank with 2 screws.
-Take the other 1.5” plank and screw 2 screws through the edges of both 3ft 9inx3.5” sides of the 3ft 9in planks into the 1.5”x3.5” sides of the 1.5’ plank.
-Take the 2 3 in pieces and overlap the first .5 in of the 3in piece and the 1.5ft piece on each side of the frame in the middle and screw both of them in.

Step 4: ​Tie the Rope

-Take the pipe piece and put the edge of the 20-foot rope on top of it and knot the edge.
-Push the end through the hole on one side of the frame, in front of the arm, then out the other hole and around the other pipe piece, then back through the hole and in front of the arm and through the hole and around the pipe. -Keep repeating this process until you have 3 strands in front of the arm, 3 strands through it, and 3 strands behind it, and 9 loops on each pipe piece.
-Knot the other end of the rope on the pipe that you didn’t already knot the start of the rope on.
-Tie the 8-inch pieces of rope around both sides of the arm twice on all 9 strands of rope then knot them.
-Twist the pipe piece on the right side of the frame counterclockwise and the piece on the left side of the frame clockwise as much as possible until it’s really tight.

Step 5: Construct the Middle Bar

-Take the 2ft planks and screw it through the middle of each 3ft 9in planks and into the 2’x1.5” sides with 2 screws on each side that are next to each other. Make sure that the bottom of the 2 ft plank is on the inside face of the 3 ft 9 in plank.
-Take the 1.5’ plank and screw 2 screws next to each other through the top of the 2’x3.5” side of the 2ft plank and into the 1.5”x3.5” side of the plank on both sides of the frame.

Step 6: Install Support Pieces

-Take the 1.5’ planks and screw the top edge of the bottom of its 1.5’x3.5” side into the front of the 3ft 9in planks with 2 screws that are placed next to each other along the bottom edge of the plank. Make sure the bottom is 4 inches away from the hole so that there is enough space to turn the pipe.
-Screw the top of it through the 1 in piece of wood and into the 2ft plank under the screws that connect to the middle beam. These screws should also be placed next to each other along the top edge of the plank.
-Repeat this for both support pieces.

Step 7: Attach the Rope Piece That Will Be Used to Pull the Arm Down

-String the 6ft piece of rope through the hole into the front 3.5”x1.5” side of the arm and knot it. Make sure the knot is big enough not to slip through the hole, if it is then unknot it, pull a little more rope through, and knot it twice.
-Tie a large knot at the bottom of the rope, tie it 3 or 4 times so that it's big enough to be used to pull the arm down easily.
-Screw a screw into the middle of the outside side of the back 1.5ft piece but leave 1.5in sticking out so that the knot can be hooked on to it.