This catapult is doable in about half an hour to forty-five minutes. It doesn't launch very far due to the elasticity of this bungee cord, but a motorcycle strap would much work better.
Submitted by Powell Middle School for the Instructables Sponsorship Program.
Step 1: Parts
3" hinge (I bought a door hinge from Walmart with the screws)
8' of 2x4
12 decking screws
4 eye bolts
3' 1/4 inch rope
90 degree angle support
Tuna Can or other small 3" diameter can
phillips screw driver bit
3/8 inch drill hole bit
Step 2: Create the base
Cut the 2x4 into one two foot section, 2' 3" foot section and one 5' 9" section.
The 5' 9" section will be the base.
Step 3: Attaching the Arm
Attach the hinge about 1' 9" from the back of the board so that one side of the hinge can lay against both sides of the board.
Screw the two foot section of 2x4 onto the other side to of the hinge.
Step 4: Front Arm
Attach the 2' 3" section to the front of the base useing the 90 degree angle on the back and 2 screws on the front.
Step 5: Attaching the can to throw and the eye bolts
Attach the can with one screw in the center of the can at the top of the throwing arm.
Attach an eye bolt on the bottom of the throwing arm directly below the can, and another one on the direct opposite side of the board.
Attach one more on the back end of the board in the center .
Attach the final eye bolt on the front end at the bottom of the front support arm.
Step 6: Attach the Rope and Bungee Cord
Tie the rope with about two feet of slack between the back eye bolt and the bottom one. Next attach the bungee cord from the front eye bolt over the arm onto the arm eye bolt.
Step 7: Finished product
Enjoy your new catapult that the bungee cord controls how far it will fire.