Monday, August 20, 2007

Trebuchet Part I: Buying and Building

A month ago I was down in Pennsylvania with Jeff at our friend Sean's house. The combination of the wide-open corn fields and the access to a scrap metal yard always makes me want to build stuff and launch projectiles. So we were at a BBQ, a little drunk, and I stood up and announce "Let's build something." It wasn't long before the words 'trebuchet' and '16-foot-tall-I-beams' also came out of my mouth. We left the BBQ all excited and scrounged around the metal yard until we found all the perfect parts. It's amazing what you can find in a scrap-metal yard. One-ton counter weights for fork lift, a ten-foot-tall metal platform, and, indeed, 16-foot I-Beams.

Now I know what you're thinking: that introductory paragraph has all the makings of a post that will eventually describe my death. But fear not, dear reader, for there is a twist in this plot. In short time, Sean, Jeff, and I realized that a weekend isn't very much time to put together three tons of metal, assembled twenty feet high, and not one of us knew how to weld. This came as a bit of a downer, but Jeff and I decided that once I got back from my road trip we would we would build a small, PVC-pipe trebuchet up in Boston, modest in size but big enough to fling baseballs hundreds of feet.

A few weekends later Jeff and I went to Home Depot to get all the parts. We stacked up a wheely cart with four ten-foot PVC pipes, about twenty connectors, a PVC saw, a couple of eight-foot 2x2's, a few thick metal bolts, a whole ton of nuts and washers, and one big, orange bucket. We were set, we were psyched, and we rush home to do some math.

We loosely followed a set of plans we found on line for a smaller, wooden, tennis-ball trebuchet. We were able to use the ratio of the axle height to arm length and the counter weight to projectile weight ration as well. We also took inspiration from the base design but needed to make a lot of adjustments. Firstly we were making a much bigger trebuchet and secondly, you can only buy 45° and 90° PVC-pipe joints and Home Depot.

We spent Saturday and Sunday morning measuring, sawing, drilling, putting things together, and solving all the little unforeseen problems. Plenty of people showed up over the course of the two days to help out so I was never lonely or in lack of people to do the drilling.

When all was said and done, we tossed all the tools into the bucket for a counter weight and tossed a roll of tape over my car, just to make sure everything looked good. It was late by this point and everyone had Sunday night plans so we agreed to meet on Thursday out in the park to give the trebuchet its first real test run. Stay tuned for Trebuchet Part II: The Thursday Test Run.


Harpie said...

I think the answer to - Could God build a truss so strong he could not break it - is clearly yes.

Anonymous said...

This trebuchet is WEAK. I am truly dissappointed. I believe I am now dumber for seeing the construction.

Mike Machenry said...

What's weak about it?

Anonymous said...

Well, one thing thats weak about it is that the link that i clicked promised plans for a trebuchet 10 feet high and all i got was pictures of you walking around some kind of flimsy prebuilt wooden THING. If you're going to build something and write about it on the internet, then at least show your plans. And why would you cut off right in the middle of the construction for "part 2"?
Its just stupid.

Mike Machenry said...

I think you need to reread that link. It says "We loosely followed a set of plans we found on line for a smaller, wooden, tennis-ball trebuchet." I don't think that constitutes a "[promising] plans for a trebuchet 10 feet high."