How to Build a Ballistic Catapult

Make a 6-foot-by-3-foot rectangle out of the 2-inch-by-4-inch lumber. Cut the lumber with a tenon saw. Screw the ends of the lengths of lumber together with two decking screws in each corner. This rectangle forms the base of the catapult. Cut a 6-foot-8-inch length of lumber. Lay it on top of the rectangle, running lengthwise down the center. Fix it in place with a decking screw in each corner.

Cut two 4-foot lengths of lumber. Position them vertically inside the base opposite each other. Position them in the center of the 6-foot-long sides of the rectangle with their 4-inch-wide faces flush with sides of the rectangle. Fix them in place with three decking screws through each.

Cut four 5-foot lengths of lumber. Using four of these lengths, form an upright isosceles triangle on each long side of the base. The length of lumber in the base forms the long, bottom edge of each triangle while the 5-foot lengths form the sloping sides. Cut the ends of the lengths at an angle so they fit flush together. Position the lengths and fix in place with decking screws. The upright in the center of each triangle should divide each into a right angle triangle.

Drill a hole just wider than the metal pipe through the lumber at the top points of the two triangles. Drill another hole of the same size 10 inches from the end of the remaining 5-foot length of lumber. Align this hole between those you drilled in the two triangles. Slide the metal pipe through the holes to form the axle of the catapult. The central piece is the catapult arm.

Drill a hole just wide enough to fit the rope through the short end of the catapult arm. Slide rope through the hole and attach 20 pounds of weight lifting weights. Drill a hole of the same size through the other end.

Tie a foot of rope through the free hole and tie the other end to one corner of a square foot of cloth.Tie another foot of rope to the opposite corner of the cloth and tie the free end of this rope to the metal ring.

Bang a nail to half depth into the firing arm beside the hole where the rope is tied. Saw off the flat head off the nail with a hacksaw. Bend the nail towards the catapult arm but leave a gap of about an inch between the metal and the wood. Twist the nail so that, with the firing arm horizontal and the weights to your left, the nail points towards the top-right-hand-corner of the firing arm.