Projectile

 Projectile toc

 Pictures of the trebuchet, while building.


These were the original arms but they were garbage. They made it difficult to put the axle in and it was hard to put different stop bars on it because there wasn't really anything to put them on to. The arms might have been strong enough by themselves, but probably not.



Jesse and his dad worked on the arm and axle and bearings and made the arm it out of aircraft aluminum. It has two ball bearings on the sides so the whole axle moves freely. The two sets of bearings lets the arm work with even less friction then one bearing in the middle, that would be attached to the arm. This made the catapult even more efficient. Yeah..pretty cool.



See...the axle wasn't working out too good with these arms.The problem was was that there was no lace to put it on top of. The original idea consisted of putting them on top of two pieces on 3/4" x 3/4"and then bracing that to the ground. However, a different idea seemed better.






Instead of using just the 3/4" x 3/4" we put wood plywood under the arms because it made it much easier to put the axle on (as you can see the little whole in the top corner) and it also made it easier to put a stop bar in (the three little wholes under the whole on the top). Since little wholes could be drilled into the plywood easily, it made it possible to put different stop bars in so we could change the angle of the arm upon release. This also made sure the force of the stop bar, the force of the axle, and everything else could stand the pressure.However with all of this the original arm still broke off due to the force of axle going forward when it his the stop bar. To reinforce this we put another peice in front of the arm and braced that to the top and screwed it straight through to the plywood.




For the tension we use surgical tubing. This is very common on sling shots so we figured it would have encough tension to meet our requirements. We severely underestimated the force of the tubing. Just using one band (wraped in a loop so it was really two bands) we flung far past the requirements. And when we but and extra band on for fun we broke the axle and bent the arm.



When the catapult was loaded it was held down by a simple pin that was pulled out with a string.

media type="file" key="Movie 5.mov"first attempt. pretty successful. media type="file" key="Movie 6.mov"that's how far it went. media type="file" key="Movie 7.mov"then we doubled the bands to make it go further

Since using two bands bent the arm we reinforced it with more aluminum and then put steel down the sides. Even with all this, the arm still bent a little but not enough to matter./ When the axle broke it split the wood in front of it. So to prevent this problem we put a piece of steel in between the axle and the wood hoping to disperse some of the impact. We also replaced the arms in the front.

Things tried so far, while shooting...
When shooting we made sure to keep the cup (the thing the ball sits in) from bending. If the cups angle is changed then the entire trajectory of the object is changed. Also we are changing the distances shot by changing the angle, not the tension. Here's a graph of Distance s. Angle. The graph is very close, in theory the farthest distance should have been 45 degrees.

Instructions for Use
First, hook one or two surgical tube rubber bands onto the hook on the base and the other one at the short end of the arm.For optimal firing distance, make sure the tension bar is in the hole toward the front of the trebuchet. For less distance, put in the hole that is farther from the front. Turn the adjustable hook near the center of the arm and/or move the stop bar to adjust the angle from which the object will be fired. Next, pull the arm back and carefully lock it into place by placing the pin into the metal loops at the end of the base while the arm is all the way down. Fire the trubuchet by pulling the string attached to the pin straight out. Adjust the angle for the distance of the target (smaller angles go closer, larger angles go farther), and repeat the firing process until the target is annihilated.

Suggestions for future building
I suggest stronger, thicker wood (or just use metal) wood is very weak and it easily breaks. Also instead of building the catapult idea, which has a stop bar, make yours into a trebuchet, where the object releases itself. In doing so there is no need for a stop bar. This means your trebuchet will not withstand as much force as a catapult. Also make sure your face is not over the way of the arm. I personally have got hit on the head and it hurts, if it was loaded, I might have died (at least a concussion).