h a l f b a k e r yNot so much a thought experiment as a single neuron misfire.
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It irritates me that pneumatic cannons seem to have an irrevocable lead in the pumpkin chunkin arms race. Who can compete with distances of a mile? But the cannon seems inelegant - and maybe inefficient, as I cannot imagine the pumpkins give a tight fit and air escaping around them is wasted energy.
I was wondering - could there be some way to improve that paragon of medieval engineering, the trebuchet? Could it stand shoulder to shoulder with a pneumatic cannon?
[jmvw] got me thinking about this with his proposition for a tremendous trebuchet. I think the two determinants of how far a treb can hurl are the arm length and the drop weight. [jmvw] did some math (which I cannot claim to understand) to show there is a finite length possible for the arm given available materials.
Whens trebs were in vogue, gravity was the fastest accelerating force available. If one accelerated the drop weight downwards faster than gravity, the treb would fling farther. One could use a shorter arm to minimize flex and breakage risk.
Most punkin chunking contests require compressed air as the force for the non-mechanical flingers. I envision a compressed air-driven piston atop the treb weight, slamming it into the ground. I have not downloaded the treb simulator, and am not sure this is an offered variable. Could an pneumatic treb hurl a pumpkin 1 mile? A robot into space?
Trebuchet Space Mission
Trebuchet_20Space_20Mission
UberTreb musings. [bungston, Dec 03 2006]
[link]
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// a shorter arm to minimize flex // |
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I thought one of the principles of trebuchet's was that the arm bent and then 'sprung' back, with this energy being what gave it such great range. From my (limited) experience with trebuchets, the arm is constructed of many pieces wood or whatever, as if to encourage flexing but not to the point of breakage... |
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I don't think anything is supposed to bend or flex on a treb. It sounds like you are thinking of a catapult, that stores energy in a flexed arm like a bow and arrow. |
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I wouldn't think that the pumpkin went
into the barrel all by itself. It probably fit
into a foam form or something... you
know, like with the chicken on
mythbusters when they were shooting it
out of a pneumatic cannon. I had an idea
about modifying a catapult to gain a lot of
distance. I'll submit it I suppose. |
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At county fairs they do use wadding.
Wadding is prohibited under the punkin
chunkin rules, which I will link up in just
a second. |
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Think for a moment about the mechanics of a sling. You whirl the rock-in-a-pouch around (once only, please! that round & round & round thing is for movies & idiots only) and while it is on the rearmost part of its arc, fling the pivot point forward while the rock's momemtum still is obliging it to take the long path around the circle - it has to gain a lot of speed to make up the distance at the same time. To do the same thing with a trebuchet: put the main arm pivot on a dual A-frame affair, the front legs being pivoted at the bottom, and the rear legs consisting of your pneumatic rams. After the initial motion of the arm, just after your pumpkin passes horizontal, ram the pivot point forward, with maximum extension just prior to release. |
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Hurling a robot into space is unfortunately impossible. Regardless of the length of the arm, the force on the arm is always greater then the ultimate breaking force of the strongest materials. Pneumatics won't help for this. But it seems like it should be perfectly possible to hurl something a mile or more? |
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Your device is clever. It will be much lighter than a trebuchet with an impossibly heavy weight. I hope you're planning to build it. You will need enough weight on the front of the trebuchet to keep that side on the ground rather then hopping up. |
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