How to Build a Wood Catapult With a Weighted Basket

Trebuchets use the force generated by a falling weight to throw projectiles.

In the era before the use of gunpowder weaponry made them obsolete, castles formed the indispensable heart of warfare in Europe. Their construction was one of the primary expenses of any government, and no warlord could be successful without the skill and technical know-how to be successful at siege warfare. One of the primary goals of siege warfare was to break down the stone walls of the castle. For this purpose, large mechanical devices were constructed to fling stones at the high walls. Among the most successful of these was the trebuchet, a type of catapult, which used the power of a falling weight to swing the throwing arm from which the projectile would be propelled. A small model of a trebuchet will provide a look into the rich history of Medieval Europe.

Things You'll Need

• 2- by 1-inch pine lumber (about 24 feet)
• Miter or table saw
• 1.5-inch finishing nails
• Wood glue
• 2-foot bar clamps
• Spring clamps
• Electric drill
• 3/8-inch dowel (about 2 feet)
• Cardboard/posterboard
• Fabric
• Wire cutters
• String
• Weight

Instructions

1. Cut two 1.5-foot lengths and two 2-foot lengths of 1-by-2 lumber. Lay one of the 2-foot lengths on your work surface with the 1-inch side facing down. Lay another parallel to it so that the outside faces of the two pieces are 1.5 feet apart. Apply glue to their ends and link them together at the ends with the 1.5-foot pieces to form a 2- by 1.5-foot rectangle. This will be the base of the trebuchet model. Hammer a finishing nail into each joint, and attach a pair of bar clamps to hold the parts together as the glue dries. Allow this assembly to dry before removing the clamps and continuing.

2. Cut two 2-foot lengths of 1-by-2. These will be the support columns that hold up the arm of the trebuchet. Use wood glue and nails to fix them to the insides of the 2-foot base sides halfway between the narrow ends of the base. Clamp the support columns in place with spring clamps. Cut two more 1-by-2 segments long enough to connect the 2-foot sides of the base together. Glue or nail the pieces to the inside of the base on either side of the support columns, which helps to hold the support columns upright. Viewed from above, the base should be a rectangle with its long sides connected together by four lengths of wood -- the two at the ends and the two that are helping hold the support columns in place. Use clamps to hold all the pieces in place as the glue dries. Allow the glue to dry before removing the clamps and continuing.

3. Cut four lengths of 1-by-2 long enough to connect the corners of the base with the support columns at a point 1 inch below their tops. These diagonal pieces will help keep the support columns from shifting forward and back when the arm of the trebuchet swings. Each piece should start at a corner, rising to meet the support column on the same side of the base as the corner from which it originated. Cut the ends at a diagonal so they can meet at the tops of the support columns; don't extend below the bottom of the base in the corners. Fix them in place with glue and a single nail at each end, and clamp them until the glue dries.

4. Drill a 3/8-inch hole in the top of each support column centered 1/2 inch from the top. These holes should allow a dowel to connect the two sides of the model together, forming the pivot for the arm of the trebuchet. Cut a 1.5-foot length of 3/8-inch dowel to serve as the pivot.

5. Cut a 3-foot length of 1-by-2. This will be the arm of the trebuchet. Drill one 3/8-inch hole through the 2-inch side of the arm, 1 foot from one end of the arm, and two 1/4-inch holes 1/2 inch in from each end of the arm. The larger hole will be where the pivot goes through, and you will use the smaller ones to attach the weight that pulls the arm and the sling that throws the projectile.

6. Cut out a 3- by 12-inch section of strong cloth (nylon will do well) to make the sling. Cut a 2-inch line in the middle of one of the 3-inch sides to make two "tails" on the sling. Tie these through the hole in the end of the arm that is 2 feet from the pivot. Hammer a nail into this end of the arm so that 3/4 inch of the nail projects from the end surface. Use wire clippers to cut the head off the nail, so that it is a smooth shaft. Cut a small hole in the far end of the sling, which will fit over the nail.

7. Attach the arm by putting the dowel (pivot) through one of the support columns, then the hole in the arm, then the other support column, so that an equal amount of excess dowel projects from each support column.

8. Cut a 1- by 1-foot section of fabric to use as a pouch for the weight. Cut a hole in each of the four corners. Place the weight (a brick or pile of fishing weights works well) on the center of the fabric and gather it up around the weight. Cut a piece of string, and push the end of it through the holes in the corners of the cloth. Put the other end of the string through the hole in the end of the arm that doesn't have the sling attached to it, and tie the two ends together.

9. Cut a 4-inch by 2-foot section of cardboard and position it so that it runs on top of the base components down the center of the long axis of the model. Staple it in place.

10. Fire the trebuchet: first push the end of the sling with the hole in it down over the end of the nail at the end of the arm. Holding the sling-end of the arm down near the ground, place a stone, marble or other projectile in the sling and lay the sling on the cardboard strip running down the middle of the frame. When you let go of the arm, the weight should pull its end down while the other end flings the projectile. If the sling lets go of the projectile too soon (the projectile flies in too high of an arc or even backwards), bend the nail forward slightly. If it releases too late (the projectile flies too low or strikes the ground immediately), bend it back.

Tips & Warnings

• Always be careful not to get hit by the arm of the catapult as it swings. Never aim it towards people, cars, houses or anything else it might injure or damage.

References

• Dan Becker's Trebuchet Page