Tabletop Trebuchet

I was walking through Home Depot with my six year old son. As we walked around the store looking for a toilet seat I had the thought, "I bet my boys would have fun with a little trebuchet." I know, strange isn't it. Anyway, I had an idea of how I would build it so I bought some pieces of wood and we headed home to make it. After a quick Google search and some sketching on my white board my boys and I headed to the workshop.

Here's what we came up with for less than $10 in materials:

  • Arm Length: 16"
  • Counterweight: 3 lbs
  • Projectiles: anything between .50 and .85 ounces (we use superballs and balls made from duct tape)
  • Effective Range: 5 to 15 feet

Helpful rules of thumb for building a counterweighted trebuchet:

  • Make the counterweight between 100 and 133 times heavier than the projectile.
  • Make the length of the sling (from fixed end to pouch) about the same length as the long end of the throwing arm (i.e., the distance between the fulcrum and the sling prong/hook).
  • Design your rig so that the throwing arm is at a 45 degree angle, relative to the ground, when the trebuchet is locked and loaded.
  • The throwing arm should point straight up (90 degrees, relative to the ground) when the mechanism has come to rest after releasing a projectile.
  • Sling prong/hook angle, sling cord length, and weight of projectile all influence the throwing trajectory.
    •     prong perpendicular to throwing arm: earlier release, higher trajectory
    •     prong angled forward (toward target): later release, lower trajectory
    •     shorter sling cords: earlier release, higher trajectory
    •     longer sling cords: later release, lower trajectory
    •     heavier projectile: earlier release, higher trajectory
    •     lighter projectile: later release, lower trajectory
  • When you want to adjust the release timing start by adjusting the angle of the sling prong/hook (i.e., the pin that holds the "free" end of the sling).