Wednesday, August 29, 2007

Trebuchet Part IV: Next Saturday in the Park

We've been flinging a lot of baseballs over the last couple of weeks so everyone is now well practiced in the art of catching baseballs. Coupling that with an abundant access to baseballs gloves, it's become pretty obvious that flinging baseballs no longer has the high probability of injury that it once did. To fix this we decided to fling some different things from the trebuchet this week. Brett was kind enough to donate some things from around the house: a tennis ball, a street-hockey ball, a golf ball, and a can of tuna fish. As it turns out, cans of tuna fish are nearly indestructible.

Later in the day a man walking through the park with his dog decided to stop off in our little corner of the park to outsource his dog-toy-throwing responsibilities. We placed Trevor next to the trebuchet to making a throwing motion with his arm. After the dog learned to follow Trevor's lead, and not run straight into the trebuchet after it was released, we played fetch for a little while. I'm not sure if the dog realized where the ball was coming from but I think the dog must have had some vague notion of "Gees, these guys throw much further than my master." Nothing tires a dog out like 300-foot fetch. We gave her some of the water that we had left and she and her master headed on their way.

Later on, we sent a bunch of people to the store to get Diet Coke and Mentos because we thought that would be a fun thing to fling up into the air. The idea was to put a ton of Mentos in the bottle, but seal it off before they touched the Coke. As it turns out, cans of tuna are not the only thing on the indestructible list.

You see all those videos on the Interwebs of Diet Coke and Mentos have a little hole cut in the top for the soda to shoot out. The amount of gas produced turns out not to be enough to actually rupture the bottle. Which is probably a good thing since we didn't realize that putting something as heavy as a Coke bottle in the trebuchet requires recalibration of the release nail if you don't want it to fly straight up and come right back down on you.

Discounting all of the failures I feel the day was a pretty big success. You're never a failure if you define success late enough.


teddygrl1012 said...

Hey my group in Physics class is researching Trebuchets and we found your website... Thanks for convincing the rest of my group that PVC will work :)

Mike Machenry said...

Hey, you're welcome. You know the funny thing about it is that I've redesigned a lot of the trebuchet from the original plans. Just about the only thing I have not had to change is the PVC frame. And PVC is just so easy to work with that you can make it all quickly with very few tools. Here's a list of things I've upgraded:

The hanger is now aluminum plate because when it's thick, the hanger/arm axle bends out of shape under a lot of weight.

The counter weight is now a dumbbell because when it is a very big weight, like a bucket, the frames need to be far apart, creating a long main axle (which the arm rotates around.) A long main axle makes it easier to bend.

The arm is now made of maple because it was stronger and not much heavier than the original pipe.

Enjoy your building!