• Gonna hurl?

    Enterprising seventh-grader builds a full-size, working catapult
  • If we ever need to storm a castle, we'll know where to turn: to 13-year-old Trevor Cluff of Madrone Trail Public Charter School.
    • email print
    The seventh-grader just built a catapult that acts like a giant sling-shot and will hurl a volleyball 50 yards down the field using only the power of gravity.
    With nary a sound and no electricity or gunpowder, his 12-foot-tall catapult — sometimes called a ballista or trebuchet — transfers the energy of a falling, 140-pound bucket of concrete suspended from a seesaw length of wood. The plunging bucket delivers force to the other end of the throwing arm, which moves skyward while pulling a sling on long ropes. The projectile in the sling, given tremendous and sudden acceleration, sails about 50 feet up in the air.
    A clearly delighted Cluff grins and explains that when his class was studying Roman warfare last year, the teacher said she'd like to see someone build a desktop model of a catapult to show the kids how warriors derived power for siege engines in the ages before artillery, guns, steam engines, or anything but horsepower and human-drawn bows.
    Not satisfied with a model, Cluff thought, why not build a real one that you can actually fire?
    "I love to build stuff out of wood," he gleamed. "Mom and Dad were really surprised, and the kids in class were very impressed."
    Catapults are first found in 400 B.C. in battles of the Greeks. They were used for a couple thousand years to hurl rocks, fireballs and pointed projectiles over or through fortified walls. With modern, mechanized war, they faded from use but still must be admired as one of the most energy-efficient tools of war.
    "This guy Trevor is one creative student," said Joe Frodsham, director of the public charter school on Ross Lane. "He's very good with his hands and very persistent. He keeps experimenting till he knows the machine inside and out."
    Cluff found no definitive plans for a catapult on the Internet, so he had to study the Roman machines — "they were pretty smart" — and invent a lot of the devices to make it all work, he notes.
    Creating the sling "took a lot of thinking," but he finally found ways to lift the dead weight with pully and rope, secure it to the flying end of the seesaw, lock it in place with a peg, release the energy by pulling the peg, then — the most complex part of the machine — rig the lines so they let go of the lower half of the sling at exactly the 12 o'clock position so the projectile could sail free with all the power behind it.
    Having the power and potential of an authentic military weapon, the catapult could be dangerous, but the school allows Cluff to fire only a soccer ball — nothing from the pile of pumpkins nearby.
    The motivated seventh-grade inventor notes that he didn't receive a grade or credit for the project. He did it just for the pleasure of reverse engineering an ancient machine and watching it work.
Reader Reaction

    Events Calendar