Easy Catapult Directions

It does the soul good to take on a project that has no immediate goal other than that it is just plain fun. Like pillow wars and snowball fights, catapulting is an unusually rewarding pastime. This easy catapult is simple to build and uses gravity rather than a cocked spring to hurl the projectiles–which can be anything from soccer balls to gallon slugs of cold water.

  1. Catapult Strategy

    • The easy catapult derives from the historical Trebuchet design that puts a heavy counterweight on the short side of a simple lever arm, and either a bucket or sling on the other end for the projectile. The counterweight is lifted to a position above bottom dead center, where gravity tries to hold it, and it is suddenly released. Gravity pulls the weight back down, the lever arm rotates on its axis, and the projectile is rapidly accelerated to a high exit velocity at a point well before its apogee. The projectile is hurled with an extra snap at the end of its acceleration. This particular catapult design has an offset feature that allows the final trajectory to be tailored both to the projectile and the enemy’s position.

    Detail Strategy

    • The counterweight is a clean five-gallon plastic paint bucket. Its weight can be adjusted anywhere up to 42 pounds. The projectile beam is a pressure-treated 2 by 4 wood stud that should be selected for clear grain and no knots. The distinctive feature of the catapult is the center of the beam, where two 2-foot square pieces of 3/4-inch thick plywood serve as the pivot center. The counterweight is hung from the center at a distance of 1 foot from the pivot axle. Assuming the counterweight is at rest at the bottom of its rotation–say the 6 o’clock position, the projectile beam, at the moment of release will be at the 1:30 position, with the projectile heading towards 12 high, to the left, after its release.

    Construction

    • Use two 5-foot long pieces of pressure-treated 2 by 4 wood stud as the main vertical supports. The base consists of two more 2 by 4 studs, each eight feet long. The verticals should be on top of the latter, 5 feet from the rear of the base.
      They should be sandwiched by two right triangle-shaped supports. Make the supports from a 2-foot square piece of the 3/4-inch thick plywood cut in half diagonally. The beam must be sandwiched between the two 2-foot square pieces of 3/4-inch thick plywood and bonded with construction adhesive and square drive alloy wood screws. It should be bolstered with a 2-foot piece of 2 by 4 stud also integrated into the sandwich.

    Ready, Aim, Shoot

    • Fill the bucket with water. Make sure the downfield range is clear. Place the projectile in a large stainless steel kitchen bowl bolted to the end of the projectile beam. Pull the projectile beam down to the 4:30 position. The counterweight pivot should be at the 9 o’clock position. Again make sure no people or pets are in range and release the beam. Mount a red boxing glove at the end of the beam as a safety warning to emphasize the rapidly moving object. Some users also like to blow a boat whistle before a launch.