2-1 Pulley system

Discussion in 'New project ideas' started by jonathanfv, Dec 21, 2012.

  1. jonathanfv

    jonathanfv Member

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    Hi everybody. I was wondering, did anybody try to build a 2-1 pulley system to take advantage of strong but slow bands? I was thinking about using such a system with a lot of office bands, in some kind of slingshot crossbow. What do you think about the idea? Cause I think that if the bands are strong enough, the projectile should be launched faster than with just the bands themselves (especially with chained office bands).<br><br><a href="http://www.servimg.com/image_preview.php?i=1&u=18000218" class="postlink" target="_blank" rel="nofollow"><img src="http://i12.servimg.com/u/f12/18/00/02/18/2-1_pu10.jpg" border="0" alt=""></a><br><br>As you can see in my image (which is kind of a first draft, and is not well proportionned), the bands are placed in the "disadvantaged" place of the 2-1 system, so the strings pulling the pounch would be pulled nearly twice faster.
     
  2. You could do one piece rollers for that whole design by mine eye. Epic idea btw.
     

  3. jonathanfv

    jonathanfv Member

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    By one piece roller, do you mean using only the first roller from the strings anchor and shooting the opposite direction? I thought of that, but the thing is, the weapon would need to be longer. If I can pull the pouch in the same direction as the bands are installed, the body of the weapon can be shorter.
     
  4. Sorry, didn't think of that. (you didn't list specs like weapon length and such)
     
  5. jonathanfv

    jonathanfv Member

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    Oh, no worries, I like people throwing ideas around. If we combine the best of everybody's ideas, it can end up making something awesome!<br><br>I was thinking about making some kind of rifle with it, and I want to to be not too hard to carry, so I need to make sure I don't waste space, especially lenght. But a system like that could also be used in many different weapons, as a power source, if we think about building weapons in "modules".
     
  6. Check out Joerg's "Bullpup slingshot x-bow" would be a good place to start maybe.
     
  7. jonathanfv

    jonathanfv Member

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    That's a pretty cool model! I was thinking about making a winch system on mine, maybe. I wanted to have a pretty heavy draw, because I'd like my first model to be able to shoot pretty much anything relatively consistently. Like that, I could carry it around and shoot whatever I find.
     
  8. For sure. Can't wait to see what you come up with <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2">
     
  9. JoergS

    JoergS Administrator

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    The pulley setup has one huge and two minor problems. <br><br>Huge: The downwards setup will hurl the pouch upwards and the ball will fly in odd directions. Rollers, in my not so small experience, must be directed sideways, or else the shot goes wild. <br><br>Minor: The friction of the pulleys will eat much of the energy. This means that any advantage of this vs. a straight, conventional band will only show when you use tiny ammo. <br><br>Also minor: The string will lash out like a whip, very dangerous.<br><br>Of course problems are here to be solved, so don't give up - just be aware of these issues.
     
  10. jonathanfv

    jonathanfv Member

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    I'm glad to have your opinion, thanks! <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2"> I will try to come up with pulleys pulling sideways, then!<br><br>The the advantage of it showing only with small ammo, wouldn't that be also showing with heavier ammo if I use very heavy bands? Cause I was thinking the main advantage of it would be with bands that would be slow anyway (office bands), but I could just put more of them in parallel to have a heavier draw.<br><br>By the way, I like that your answers are always positive, you seem to never say never. It's a good trait of character.
     
  11. MaddyMax

    MaddyMax New Member

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    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>JoergS wrote:</b></span></td></tr>
    <tr><td class="quote">The string will lash out like a whip, very dangerous.</td></tr>
    </table>
    <span class="postbody"><br><br>thats also an advantage if you want to build something that makes as much damage as that "laser whips" at the movies. <img src="http://illiweb.com/fa/i/smiles/icon_twisted.gif" alt="Twisted Evil" longdesc="13"><br><br>pulley sideways:<br><br><a href="http://www.servimg.com/image_preview.php?i=14&u=17552695" class="postlink" target="_blank" rel="nofollow"><img src="http://i17.servimg.com/u/f17/17/55/26/95/pulley10.png" border="0" alt=""></a></span>
     
  12. onnod

    onnod Im from Holland, isnt that weird?

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    that looks a bit like the woodland survival flipper <img src="http://illiweb.com/fa/i/smiles/icon_scratch.png" alt="scratch" longdesc="33">
     
  13. MaddyMax

    MaddyMax New Member

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    problem with this is, the bands also have to pull the weight of the pulleys and the cord.
     
  14. onnod

    onnod Im from Holland, isnt that weird?

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    just wondering, why do you have two pulley's on either side in the center, would't one work fine too and have less pussy friction so you would have more speed?
     
  15. MaddyMax

    MaddyMax New Member

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    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>onnod wrote:</b></span></td></tr>
    <tr><td class="quote">just wondering, why do you have two pulley's on either side in the center, would't one work fine too and have less pussy friction so you would have more speed? </td></tr>
    </table>
    <span class="postbody"><br><br>drawn out rubber length must be aligned with cord length and to the draw length of fork to pouch.</span>
     
  16. onnod

    onnod Im from Holland, isnt that weird?

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    hmm, that's true i think
     
  17. JoergS

    JoergS Administrator

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    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>jonathanfv wrote:</b></span></td></tr>
    <tr><td class="quote">
    <br>The the advantage of it showing only with small ammo, wouldn't that be also showing with heavier ammo if I use very heavy bands?</td></tr>
    </table>
    <span class="postbody"><br><br>The problem is that the energy you can invest is limited by your bodily strength. A pulley system lowers the efficiency of the power conversion (from muscle energy to kinetic energy), because of the friction and - as MaddyMax rightfully pointed out - the extra weight of the cord and pulleys. <br><br>A pulley system has one potential advantage: It may allow the shot to exceed the maximum retraction speed of the rubber bands you use. But because of the energy limit (muscle power) and the loss of efficiency, only very lightweight ammo will work. The stronger you are, the heavier the ammo you can use with advantage. <br><br>Straight rubber bands, made from top quality natural latex, tapered, shot in butterfly mode, are really hard to beat. It has been tried, but even an advanced cam equipped professionally designed and machined 1000 dollar weapon like the Raptor only shines with very light ammo. Hard to beat the laws of physics. <br><br>Again, no reason to give up - lots of people said, once upon a time, that mechanical engines can never beat the performance of a race horse. <br></span>
     
  18. onnod

    onnod Im from Holland, isnt that weird?

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    just went to their site, they claim to be the most powerful slingshot in the world <img src="http://illiweb.com/fa/i/smiles/icon_scratch.png" alt="scratch" longdesc="33"><br>"The dual string arrangement makes each shot smooth and accurate and allows<br> the shooting of lightweight ammo. Raptor is the most powerful slingshot in the world."<br><br>edit, just found out they are
     
  19. jonathanfv

    jonathanfv Member

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    Yeah, I red about the losses. I also mentionned wanting to couple that with a winch, tho, so like that man power doesn't matter as much. I think that fast bands are simpler and more effective compared to the "bazooka" my thing might end up being, but I've been curious about it for a while.