Catapults

I think I cope with stress by designing and building weaponized toys.  The ping pong ball guns and now the catapult.  I can remember the stress I was under when I made the trebuchet and the rubber band Gatling gun. The intent of the catapult design was for science.  The design was to allow to figure out the best angle of trajectory, where the rubber band should be placed, and the length of arm.  

I probably oversized the catapult.  The length of the catapult is 24” and the plans need to be printed on 11x17 paper.  I don’t regret the size; it works well.  I might come back and make a desk top version.

The saw tooth design is so the dowels can be moved to change the angle of trajectory, where the rubber band is placed.  It also allows for the arm to easily be replaced.  Over the process of making it, I realized the location of the rubber band was not important but how many rubber bands. 

My kids assembled most of the catapults.  The oldest choose not to participate.  The younger two glued and screwed most of the pieces and cut the dowels to length.  They installed the hooks and placed the location of the dowel stops.  I actually think that I was able to teach the middle child some tricks. 

Here are the mechanical advantage lessons that I think I taught him.  If he remembers them that is a different story. 

• Wedges to split glued parts that are not supposed to be glued.  We used a chisel to separate a clamping joint that got stuck together with squeeze out
• Lever arms, we used a screwdriver to put in the multiple hooks required for the project
• Blade pinch, he learned what happens as you pinch a blade when trying to cut material. 
• What happens when… The catapult has several different options that can change trajectory and tension.  He was able to figure out that different angles caused the marshmallow to fly differently.  He was also excited when I added a second rubber band and told him I doubled his power. 

Overall, the project went well.  They are a little bigger than I thought they would be. They launch marshmallows and ping pong balls about 40 feet.  The kids had fun.