Adapted from Backyard Ballistics

How to Build It

Make the Catapult Frame

1. Drill four 1/16-inch pilot holes through the 10-inch frame pieces, with the holes 1¾ inches from each of the four ends and centered vertically.

2. Drill a pilot hole into the center of each end of the crossmembers.

3. Apply glue to the ends of one crossmember and near the pilot holes on the inside of the 10-inch frame pieces; screw the crossmember into place. Repeat this step on the other end.

4. Drill 3/16- and ¼-inch holes through the sides of the frame, 5 inches and 5½ inches on center, respectively, from the front of the frame.

5. Glue the footings to the bottom of the frame, flush with the sides and 1 inch on center from the ends. Drill pilot holes into the center of the ends of the footings; screw the wheels into place.

Install the Uprights and Upright Supports

6. Using the drill-glue-and-screw process, secure the uprights to the frame. The uprights should be 4¼ inches on center from the end, the screws driven in from beneath the frame.

7. Drill, glue, and screw a crossbeam flush with the tops of the uprights.

8. Drill, glue, and screw the supports into position.

Make the Throwing Arm

9. Drill a 1/8-inch hole through the center of the long dowel about ¾ inch from the end.

10. Use the round face of the hammer to shape the washer into a cup.

11. Attach the washer to the dowel (the cup's rim faces up) using the bolt, lock washer, and nut.

Assemble the Torsion Spring

12. Fold the nylon cord in half twice; tie the loose ends with a square knot.

13. Feed the folded cord through the ¼-inch holes, leaving ½ inch of cord on the outside of the frame. Place a washer over each bundle of cord.

14. Insert the 5/8-inch dowels into the cord loops; position the throwing arm in the middle of the cord.

15. Rotate the dowels toward the front of the frame until the arm presses against the crossbeam. Insert the 1/8-inch dowel into the smaller hole.

16. Lower the throwing arm down to the frame. Mark spots on the frame and arm where the anchor and eyebolt will be screwed in.

17. Increase the cord's tension by turning the dowels forward. Lower the arm, hook it into position, and remove the locks.

18. To fire the catapult, load the bucket with a projectile and carefully push the anchor hook out of the eyebolt.

Parts and Supplies

Manual saw and miter box

Ball-peen hammer

Yellow wood glue

18 No. 6 wood screws, 1½ inches long

Power drill with 1/16-, 1/8-, and ¼-inch bits

1 One No. 10 bolt, ¾ inches, with nut and lock washer

2 One 36-inch length of 18-pound nylon cord

3 Two ¾-inch washers, ¾-inch outside diameter, ¼-inch inside diameter

4 Two 5/8-inch-diameter dowels, 1½ inches long

5 One 1/8-inch-diameter dowel, 1½ inches long

6 One small eyebolt and anchor

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