How to Build a Boy Scout Catapult

Written by bob white
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How to Build a Boy Scout Catapult
Building a catapult is a fun Boy Scout project. (Medieval Catapult image by Dario Corno from

The word catapult is derived from the Greek words, "kata pultos," meaning "shield piercer." The catapult was used for thousands of years as a military weapon. It enabled early warriors to launch projectiles over castle walls and other armaments. Recently, catapults have been used in local pumpkin throwing contests and by the Boy Scouts to learn teamwork. You can build a catapult in a day with the right materials and some simple instruction.

Skill level:

Things you need

  • 3 8-foot spars
  • 3 15-foot spars
  • 1 15-foot thin spar
  • 1 3.5-foot spar
  • 50-foot piece of 1/4-inch rope
  • 7 12-foot long pieces of 1/4-inch rope
  • Double pully
  • Large tin can
  • One 20-inch long, 1/4-inch rope

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  1. 1

    Build the front face triangle with the three 8-foot spars. Lay the spars out in a triangle and lash each connection together with the 12-foot rope sections.

  2. 2

    Raise the triangle to stand vertically. Lash two of the 15-foot spars two-thirds of the way up each side. Lash the third 15-foot spar on the bottom of the triangle.

  3. 3

    Build the throwing arm with the thin 15-foot spar and the 3.5-foot spar. Lash these two together in a cross. Attach the smaller spar about 3 feet from the thicker end of the 15-foot spar. Attach the tin can to the thinnest end of the 15-foot spar with the rope.

  4. 4

    Attach the throwing arm to the catapult's body. Rest the shorter sides of the throwing arm on top of the 15-foot support arms and lash them on lightly so they can still rotate.

  5. 5

    Fasten the pulley to the centre/bottom of the triangle with one of the 20-inch ropes.

  6. 6

    Fasten the centre of the 50-foot rope to the thickest end of the throwing arm and then run the two ropes into the double pulley out either side of the catapult.

Tips and warnings

  • Be careful not to release the ropes once you have launched a projectile. This will cause the throwing arm to return to the ground at a speed that could hurt someone. Assign someone to monitor the safety of the launch and control the individuals around the catapult for safe execution.

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