This is a why to create a simple and fun wood catapult just by using a CNC machine and SketchUp.
Heres what you would need:
-4'x4' sheet .75in thick plywood
-Shop Bot CNC
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Step 1: Sketch Up
First step is to design the layout of the catapult in a 3D model and flatten 2D model. make sure the 2D model is on a 4'x4' bored with a .75in width.
Once you're finished export to DXF, should have been a .Pdf, Remove any extra geometry and run CNC.
Step 2: Building
Once you have all your wooden parts grab one of the large pieces. Lay it flat on the table and stand up the 6 smaller pieces on top as shown in the first photo. Glue those 6 pieces onto the large piece and drill 1 nail through the large piece into each smaller piece as shown in the last photo. Next, add glue to the top of each smaller piece then add the 2nd large piece on top. Then drill one screw through the 2nd larger piece into each smaller piece again. Now you should have the catapult's base as well as the two walls, it should be able to stand like the first photo. Next, You should have a smaller piece left over, and that is going to be your stopper as shown in the 2nd to last photo. Insert that piece the same way you did with the other smaller pieces , but on top. Then, drill a medium size hole through the two big pieces, and drill two small holes through the long medium size piece, use the 3rd photo for help. Now, grab a piece of rope weave it through the first big hole through the first small hole and out through the 2nd big hole. Grab a little pice of extra wood and wrap the rope around it and go back through the same big hole through the 2nd small hole and out the 1st big hole and wrap another piece of wood around the rope. Tie knots were needed to support the rope.(3rd Photo). Finally, twist the 2 wood pieces in the same direction to make the rope real tight. This should make the long medium piece able to bend back and fling forward. Cut the bottom of a plastic cup and screw it into the top of the long medium piece. Have Fun.