In ancient warfare, the ballista was a feared weapon used by Romans and others in sieges, on ships and on battlefields. Similar in design to a crossbow, a ballista could be small enough to use as an anti-personnel weapon and large enough to hurl heavy spears through ship hulls. You can make a mini ballista out of common lumber. The weapon's power comes from ropes employing a principle called torsion.
Lay two 36-by-4-by-1-inch pine boards parallel on your work surface. Nail two 12-by-4-by-1-inch pine boards between the larger boards to form a rectangle that will be the ballista frame.
Place the other two 12-by-4-by-1-inch pine boards inside the ballista frame, butting up against the sides but turned perpendicular to the rest of the frame's boards. Nail them in place to create the bow arm stops.
Stand up the ballista frame and place the remaining 36-by-4-by-1-inch pine board perpendicular to the frame, over the bottom piece of the frame, to create the ballista stock. Let about 8 inches of the stock overhang what will be the front of the ballista, leaving 2 feet for the rear of the ballista.
Cut 45-degree angles at each end of the four 24-by-2-by-1-inch pine boards. Nail two of the boards so they brace and butt against the top edge of the ballista frame and the side edges of the back portion of the ballista stock. Turn the other two braces horizontally and nail them so that they butt up against the bottom edge of the ballista frame and meet underneath the rear of the stock.
Drill or cut four 3/4-inch holes in the ballista frame. Place each hole centered between the front and back edges of the frame, about 1 inch in from the edge of the bow arm stops. Drill two holes on top of the frame and two on the bottom; the top holes should line up with the bottom holes.
Cut the 24-by-1/2-inch wooden dowel into four equal pieces. Drill a 1/4-inch hole near one end of each 6-inch dowel. Cut the 12-by-1/4-inch wooden dowel into six 2-inch pieces. Place four of the 2-inch pieces through the holes in the 6-inch dowels to form the ballista stanchions. The smaller dowels will serve as stops.
Thread rope through the top and bottom holes to create the torsion springs. Place a washer and 6-inch wooden dowel over each hole. As you thread the rope through the holes, loop the rope over the dowels and back through the holes so that the dowels are holding the rope in place. Continue the process until you have a bundle of at least eight ropes on either side of the ballista frame. Pull the rope as tight as you can manually and tie the ends of the rope.
Drill a 1/4-inch hole near one end of each of the 12-by-1-by-1-inch pine boards to form the ballista arms. Place a 2-inch dowel through each hole to form the bowstring stops.
Place the smooth end of one ballista arm through the middle of one set of torsion spring ropes. Set the lower stanchion so that the stanchion stop rests against the ballista frame. Standing toward the rear of the ballista while holding the ballista arm straight toward the front, wind the top stanchion toward the outside of the frame -- clockwise for the right stanchion and counterclockwise for the left stanchion.
Wind the stanchions until they are tight and turn them so the stanchion stops rest against the ballista frame and hold the torsion ropes in place. The ballista arms should be held straight forward by the torsion ropes.
Cut a 6-foot piece of rope. Cut two holes in the top and two holes in the bottom of the 6-by-6-inch piece of leather to form the cup. Tie one end of the rope around the end of one of the ballista arms, thread it through the piece of leather, wind it tightly around the other arm, thread it back through the leather cup and tie it tightly to the other end of the rope. Trim any excess rope and center the cup. The bowstring should be somewhat tight.
Tips & Warnings
- Place any sort of "missile" in the cup -- like a water balloon -- pull it back and see how far your ballista can shoot.