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How to Make an Elastic Catapult Out of Wood

Elastic catapults are wooden structures used to launch small objects. People have used the larger version of catapults in war throughout history for throwing rocks, spears and other damaging objects. They have a wooden arm that pivots near its center when a weight, spring or elastic cord pulls one side. You can use elastic catapults for demonstrations in physics, models and hobbies, as they are big enough for use on most tables. Build a simple elastic catapult using yard lumber and hardware, with a bungee for the recoil mechanism.

Things You'll Need

Tape measure
2 plywood sheets, 1/2-by-4-by-16-inches
Drill
Drill bit, 1/4-inch
Screw gun
Pine board, 1-by-4-by-20 inches
Plywood, 1/4-by-20-by-20 inches
Oak board, 1-by-3-by-28 inches
13 wood screws, 1 ¼-inch
Metal pipe, with end caps,1/4-by-6 inches
2 metal sleeves, 1/4-by-1/2 inch
Plastic cup, 1-ounce
2 screw hooks, 1/4-inch
Bungee cord, 1/2-by-6 inches

Instructions

- 1
  Measure 1 inch away from a 4-inch edge and both 16-inch edges on your plywood. Drill a 1/4-inch hole at this measurement.
- 2
  Lay your 20-inch board flat. Set the 16-inch sheets of plywood on their 4-inch edges, opposite the edges close to the holes and against the 20-inch edges of the board. Position them so they are 8 inches away from the edges of the board. Screw three screws through each sheet of plywood and into the board.
- 3
  Set the 20-inch board flat on top of the 20-inch plywood so the board's ends are flush with the edges of the plywood. Each 20-inch edge of the board is 8 inches away from the other pair of edges. Screw six screws through the 20-inch plywood to secure the board in this position. This will give your catapult stability.
- 4
  Drill a 1/4-inch hole through the 1-inch-wide edge of the 28-inch board so it is 14 inches away from each end of the board. Drive a screw hook into the board so it is 1 ½ inches away from the edges of the board and 1 inch away from the end of the board. Turn the board over and use these same measurements at the opposite end to screw your plastic cup to the board. Screw through the center of the cup. This is your catapult arm.
- 5
  Position the catapult arm between the 16-inch plywood sheets so the holes are aligned. Slide the pipe through the wood so there are two metal sleeves on the pipe between the arm and the plywood sheets. Screw the end caps on the pipe.
- 6
  Screw the last screw hook into the 20-inch board so it is directly underneath the arm, with the arm vertical. Hook the bungee cord over the two screw hooks and pull the arm down from the end that has the cup when it is loaded.

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