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.

video

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.

video

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.

video

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.

Sunday, August 26, 2007

Trebuchet Part III: Saturday in the Park

On Saturday some friends and I went to the park for the first full day of trebuchet baseball flinging. For most of the morning it was Brain, Jackie, Jackie's dog, and I working out the kinks. Trevor, Sarah, Colin, Adriana, Lisa, and Brett all showed up at some point during the day too.

A good deal of the morning was spent taking video of the trebuchet from the side as it was firing and playing it back in slow motion to see exactly what was going on. When we started, the balls were mostly going line drive, 75 feet out. After watching some slow-motion video it was pretty apparent that the sling was releasing way to late. So we bent the nail way back until we got it just right. This actually accounted for about a 100-foot increase in distance.

Another really nice improvement we made was make a new sling. We cut a big square out of some stiff denim pants, also bound for Good Will. We attached the sling at four points to the rope, rather than just two. This turned out to be a lot more consistent than the design we found on the original trebuchet plans.

After all the mechanics where tweaked we added a giant rock that Brian went hunting for around the park. The rock added quite a bit of weight to the bucket. So much so that the bucket started scraping the ground whenever it came down, and eventually bent the rod so much that it broke off. Next time we'll have to reinforce the hanger better.

video

Trebuchet Part II: The Thursday Test Run

Thursday night I packed up my car full of trebuchet parts and projectiles only to find that the two A-frames are too big to fit in my little VW Golf. So I did what any reasonable person would do in that situation; I gave one to Colin, one to Trevor, and explained to them, in less detail than they would have liked, how to get to the park.

The rest of us got to the park early and scouted out a spot to test our brand-new, medieval siege toy. We decide on a quiet little spot next to a volleyball game at the corner of the park. We figured here we would be out of the way of the big soccer crowds who might get a little suspicious and call the park authorities. As it turns out, we were being a little more paranoid than was necessary. The volleyball crowd showed a lot of interest in our test runs and later, the park ranger walked right by us as we were setting up our ten-foot, projectile weapon of plasticness.

After the first few throws went backwards, sideways, straight into the ground, and nowhere at all we finally got the hang of it. We adjusted the string lengths, made a new sling, and added weight. We got the baseballs going 75 feet or so--a far cry from our goal yet enough to get us all really excited about the following Saturday. We'll spend next Saturday in the same place, tweaking, test, and seeing just how far we can get this thing to go.

After it got dark we all went out for dinner at Jose's. This was pretty lucky because just as it was getting dark, it began to rain pretty hard. We walked over to Jose's, parked our giant A-frames just outside the restaurant, and went in to wait out the pouring and thundering. As luck would have it, it ended just before our dinner, making for a much more comfortable trip home for Colin and Trevor.

video

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.