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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

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

Tools:
Saw
Drill
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.
How far does it launch? I want to use it in my yard for my dogs
I did this as a kid and used a bike tube. The tube would really fling it. Can also take a frozen juice can and cut it in half to use as a cup on the end of the arm. Works good for throwing fruit or rocks or whatever.
I may try this but using a triangle base for stability.and some bike tube. Please put that Bungy thing in the bin. They are dangerous, People have lost eyes and one killed a trolley boy in Oz.
Nice, simple design. I might add a pulley to the top so the bungee cord doesn't wear as quickly, and maybe a block so the arm will stop at the optimal angle to get the best distance. Also, if you have a quick release mechanism of some sort, instead of a rope that has to be pulled along through a ring behind the arm, that might improve the speed, as well. <br> <br>Good job, though. You've got me wanting to build some sort of siege weapon, now.
Nice one because it's so easy and simple <br> <br>by the way filesizes for the movies seem incorrect (for 2013-05-20 19.25.52.mov it says (516x290) 22 KB but it really is 20.7mb in size) <br>
I just started to wonder if the ball is losing quite some momentum due to the tuna can's design. <br>As the catapult's arm accelerates the ball will in addition accelerate from one end of the tuna can to the other (upper) and then bounce against it. possibly at a very bad time which will work against the momentum gained through the catapult's motion. <br>or, more likey, it will give the ball a detrimental (slice) spin. (which is what seems to happen in your video)
My local tennis ball fiend says &quot;Two Paws Up!&quot;
Nice
Great work

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