Catapults were machines of war used to tear down medieval castle walls, or at least put a few holes in them. They are also a wonderful demonstration of mathematics and physics, and so make popular school projects. Full-sized catapults require some know-how to build, but a tabletop catapult is a good substitute. They are safe, easy and give you a feel for the skills involved, as well as letting you decide whether or not you're interested in pursuing a larger project.
- Skill level:
Things you need
- Square piece of cardboard, 4 inch
- Long metal barm 6 inch
- 14 small screws
- 2 eye hooks
- 3 strips of wood,12x1 inch
- 8 strips of wood, 6x1 inch
- Large rubber band
- Wood glue
- Marshmallow projectiles
Cut two of your six inch strips of wood at either end. Cut a 45 degree angle and make sure that you cut inward on both sides of each strip. This means that both the longer, pointed ends are on the same edge of the strip. We'll now call this an "angled strip."
Lay out the 12 inch strip horizontally. This will be our "base strip." On the right side end of the base strip, align an angled strip with the bottom, horizontal edge of the 12 inch strip. Because you're aligning the edge that you cut with the bottom edge of the base strip, the angled strip should be at a 45 degree angle. Make sure it angles back toward the base, rather than away from it. Use wood glue and a screw to secure the cut strip in place.
Take a six inch strip and align it vertically with the first two pieces, this will be our "vertical support." One end should meet the base strip and line up with the bottom edge. The vertical support should line up with the unattached cut edge of the angled strip, but the vertical support will protrude a bit beyond the angled strip. Use wood glue and screws to attach the vertical support to the base strip, and the angled strip.
Repeat steps 1-3, but begin on the left side end of the 12 inch horizontal base strip. This will make this part of the frame a mirror image of the first, so that the pieces screw in on the correct sides. Stand these two pieces up, so that the screws face each other. The angled strips should be on the same end.
Connect the two sides using the remaining six inch strips of wood, our "horizontal supports." Connect the base strips with one support at the end with the angled strips. Place the screws in the top of the base strips. The second support is secured at the end opposite the angled strips, connecting the base strips together. The vertical supports are connected by another horizontal support, on the side opposite the angled strips. The last horizontal support connects the two angled strips about one inch to 1 ½ inches down from the vertical strips. Use both wood glue and screws to make the structure stronger.
Make the catapult arm from the remaining 12 inch strip of wood. Drill a hole in the strip about a ½ inch from one end. Your metal bar will need to slip through there, so the hole should be a little larger than your bar. Attach an eye hook about three inches from the other end of the catapult arm, making sure it faces away from the hole you drilled. Make your ammunition basket by folding the four inch square piece of cardboard. Glue it onto the catapult arm, up against the open side of the eye hook.
Attach the catapult arm to the base. With the catapult arm laying "box up," run the metal bar through the first vertical support, then through the hold in the catapult arm, and then through the second support. Dab some glue around it, at each of the vertical supports.
Create the firing mechanism by attaching the second eye hook to the horizontal support connecting the base strips on the side with the angled strips. It should face downward. A rubber band strung between the two eyehooks creates the tension necessary to fire the catapult. Just push the catapult arm down until the rubber band is stretched taut and let go to fire.
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