Trebuchet

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Trebuchet

Post by Earle on Sun Jan 18, 2009 8:03 pm

This does not mean the catapult building team is off the hook. Far from it....however, I've always wanted to build one, so I knocked this one out today. Well, the big Regional competition is just around the corner, and I wanted to make sure we had a catapult of some sort. . I had three neighbors all stop by to see what I was doing, and one hung around to help fire the test shots. We are using oranges as our projectiles at competition, and by the second try (after two tennis balls--too light) I was hurling it about 85 feet down the block. I'm changing the weights tomorrow and adding wheels and generally finishing up, but here's today's progress.







The ideal weight ratio for a treb is 133:1, and with a 5-6oz orange, I'm looking at about 50-60 lbs counterweight. I was using 40-45 today, but tomorrow I will test with 60 lbs.

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Re: Trebuchet

Post by Earle on Mon Jan 19, 2009 6:42 pm

Well, I did some changes today to the weight and structure. I changed the weight from 40 lbs to 70 lbs. I reinforced the aluminum rod that the weights are on, and drilled and secured all the woodwork with 3" drywall screws. I also added 4 castor wheels, b/c as I found out, when the fixed weights fall, they of course want to fall straight down, but get pulled by the fulcrum in the center. As such, you loose energy, and if your weight is too heavy, it could move or even flip the treb. By adding the wheels, the treb moves slightly forward as it swings, releasing about 20-25% more energy into the swing.

As for the release, you secure one rope to the bottom of the arm, and the other rope has a loop on it, which is slipped over a nail that has had the head snipped off. That way, when the arm swings up, the loop comes off and the projectile continues on its arc. Another change was taking the small, screwed in eyehook that was part of the quick release, and replacing it with another eyebolt that goes through the whole 2X4 arm and is bolted on the other side, thereby getting rid of a potential accident.

I did about a 1/2 dozen shots before I took this vid, which is why the fixed rope end came loose and went flying too. However, I now can consistently get the little 'ol orange to go sailing for about 120-130 ft. depending on the wind!!! Yesterday my max was about 80 ft, so the extra weight and wheels really gave it a boost.

On a side note, one does tend to get a ton of neighbors asking what you're doing! LOL I asked some neighbor kids if they wanted to fire it...I barely finished the words and they were piling out of my neighbors car to do it. Hahahahaha Here is the vid (It may be hard to see, but the orange hits the center of the road at the end of the street, just in front of the house--about 8' from the two minivans):





Also, I do plan on giving it a coat of stain and all, but that is for another day. I did, however, make a 20 ft target today as well (a city with two towers, two sections of wall, one gate, and archimedes).

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