Thursday, October 20, 2011

Update on the Trebuchet

I suppose it's about time I actually threw up a post here.

We're almost there. Seriously. It's so close, I can almost picture having to clean the pumpkins up.

After spending the last few days doing some heavy-duty trigonometry on Mr. Ludwig's whiteboard, I marked up some of the 4x4's we're using for the A-frame and, after some final checks, gave the okay for some cuts to be made. Our schools' shop teacher, the incredible Mr. Grimsley, without whose help our trebuchet would be a pile of broken sticks, used a circular saw to cut my wacky angles (around 79.9514 degrees) to give us the beginnings of the A-frame. We measured once the top was cut to fit and realized that we were within an inch of what I had predicted the width would be.

I want ice cream. Or some compensation for getting that close on a 16' span.

Seriously, though, I'm saying that my math was right and that the extra inch is accounted for by the fact that we have a pencil, a circular saw, and a measuring tape to work with.

Hopefully, we'll have the majority of the construction done within the next few days. Then...test launches!

Here goes nothing.

Monday, September 26, 2011

I Can Throw an Apple!

So, I have to begin by saying that I cannot imagine a more productive hour. I have accomplished more in the approximately forty-five minutes myself and my team have to work on our project--designing a fully functional, full-scale trebuchet.

Here's how our fourth design of our small scale model (which is by far our most successful) looks now.

(That's our unofficial office in the background. It's where we've spent every spare second of the last two weeks, modifying designs, experimenting, and seeing how many lightbulbs we can break.)

However, each time I try and explain the structure of this class--we just go off and work on our pet project, which we've all selected and designed for ourselves--I'm met with the same question: 

"So what have you learned from this?"

The answer I'm always sorely tempted to respond with is: For now, I don't care. Once it's built, I'll analyze it and figure out why it works, and that'll be good enough!

But, of course, that wouldn't be entirely true. While building this, we've had enough mishaps, close calls, and epic fails to NOT think about what went wrong.

For example, at lunch today, we were attempting to launch a weight across the parking lot (away from most of the cars) behind the school. The sling left the kilogram weight behind, which I would have to say was a prime example of inertia. The somewhat massive weight was at rest, and it sure stayed at rest.

A slightly bigger episode occurred on our first dry launch with the full counterweight. The small-scale trebuchet is clamped to a TV-cart we stole (along with most of the materials it currently consists of), and the base is formed by a pair of ring stands. On this launch, the trebuchet actually pulled one of the ring stands out of its base, resulting in the projector mount currently used as the axle swinging around the other ring stand, carrying the boom with it.

After this,  we were presented with a prime opportunity to redesign most of the components (because most of them broke). We could have just thrown something together. But instead, we realized that there was a way that offered a greater chance of success. We started testing each individual component, making one modification at a time, to see what would provide us with the most successful launch. We would change the elevation of the axle from the base, and we went through four (four!) revisions of the sling.

But it paid off. We flung an apple 15 yards at lunch today, after which it fell apart, and then, after a few more revisions after school, launched a ball bearing 25-30 yards. We're almost ready to go full scale.

And we've only broken one ring stand.