3.5 Pellet bow? - Page 2
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Thread: Pellet bow?

  1. #11
    Quote Originally Posted by Greenfield View Post
    The other invention they explored was a giant crossbow designed to hurl stones. They built and rebuilt this one, and near the end of the show they fired it.

    The machine was huge, by the way, and the stone they threw was about the size of a grapefruit. Maybe a small melon. It went about 60 feet total, and while they called it a success, I saw it as a dismal failure.
    I remember that show or one much like it.

    The design was so obviously doomed that one wonders whether Leonardo did it deliberately - I do recall reading stories that he didn't like to invent weapons and sabotaged some of his designs.

    It's pretty much impossible to build a large tension-powered missile thrower - the mechanical strain of bending the bow to store energy will cause it to snap.

    There's a reason why siege engines have been torsion-powered or counterweight-powered for since the ancient Greeks. Using an elastic block or weight to store the energy means your throwing arm(s) can be thick enough not to bend and break when the machine performs its intended task.

    There is a trick to somewhat exceed the limits of a bow-powered missile thrower - the Multiple Bed Crossbow. Instead of one bow at the limits of the materials available, you have two or three bows with the bowstrings linked to combine their energy:



    I doubt they were any better than a similarly-sized torsion arrow shooter such as a cheiroballista though.

  2. #12
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    I think the big one could have been made to work. The only change needed would be to change the one thick cross arm into several layered cross arms.

    It's essentially the multiple bow you've illustrated, but with the "bow" part made of several layers. Think of closely nested parentheses. )))))

    The bows would be so close that they'd slide on one another. The single bowstring or stone sling would be attached to forward most set of arms, and the others would add their power to that one simply by pressing against it.

    As it was, trying to flex those huge, thick limbs essentially stretched the outermost face beyond the limits of the materials. They cracked.

    Also, as any archer or gunnery officer can tell you, you don't level a siege engine at the target. You aim up, to account for gravity. In their demo the huge crossbow was firing level to the ground, as if it would somehow have a flat trajectory.

  3. #13
    Quote Originally Posted by Greenfield View Post
    I think the big one could have been made to work. The only change needed would be to change the one thick cross arm into several layered cross arms.

    It's essentially the multiple bow you've illustrated, but with the "bow" part made of several layers. Think of closely nested parentheses. )))))

    The bows would be so close that they'd slide on one another. The single bowstring or stone sling would be attached to forward most set of arms, and the others would add their power to that one simply by pressing against it.
    That doesn't seem terribly practical to me. A single bowstave built with Renaissance-era technology won't be able to store that much energy without breaking - I'd guesstimate a few hundred Joules - so you'd need an awful lot of them to hurl a grapefruit-sized shot at ballista level velocity.

    It would seem difficult if not impossible to squeeze enough into a frame without them getting in each other's way or the whole construct being so large its too cumbersome to be useful.

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