Fork width

Discussion in 'General Slingshot Discussions' started by SpeedyRK, May 17, 2012.

  1. SpeedyRK

    SpeedyRK New Member

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    What effect does the width of the fork have on the shooting of a slingshot or crossbow?<br><br>Thank you,<br>Patrick
     
  2. pelleteer

    pelleteer Middle Aged Delinquent

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    I can't give you a definitive answer, but my own experience has been that in factory slingshots that use tubular rubber, the narrower forked ones, like the Barnett Strike 9/Black Widow and the Marksman Classic, are far more sensitive to fork alignment, while the wider forked models, like those from Trumark, are far more forgiving if your fork alignment is a bit off. In other words, the wider ones are easier to shoot accurately. With boardcut or natural forks that use flatbands I don't notice this phenomenon at all. I actually prefer a narrower fork on these styles. Others may have different experiences, of course.
     

  3. Ryan Wigglesworth

    Ryan Wigglesworth Senior Member

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    <div>
    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>SpeedyRK wrote:</b></span></td></tr>
    <tr><td class="quote">What effect does the width of the fork have on the shooting of a slingshot or crossbow?<br><br>Thank you,<br>Patrick</td></tr>
    </table>
    <span class="postbody"><br><br>fork width makes you loss speed the more width you have , there is a video by gamekeeperjohn on youtube about this... see if you can find it. he uses a very wide fork for the comparison tho</span>
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  4. SpeedyRK

    SpeedyRK New Member

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    Thanks! I'll go check that out. The power, at least, makes a lot of sense. The amount of power being transferred into the motion of the projectile is increased the smaller the angle of the band and the projected, hypothetical "straight" line splitting the slingshot in two.<br><br>As for the accuracy, I still do not quite understand that. (Which could also be because of my amateurism at actually shooting slingshots)<br><br>Thank you,<br>Patrick
     
  5. pelleteer

    pelleteer Middle Aged Delinquent

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    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>SpeedyRK wrote:</b></span></td></tr>
    <tr><td class="quote">
    <br>As for the accuracy, I still do not quite understand that. (Which could also be because of my amateurism at actually shooting slingshots)<br><br>Thank you,<br>Patrick</td></tr>
    </table>
    <span class="postbody"><br><br>I don't understand it either. It's just something I've observed. No idea why it happens, though.<img src="http://illiweb.com/fa/i/smiles/icon_scratch.png" alt="scratch" longdesc="33"></span>
     
  6. JoergS

    JoergS Administrator

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    Well, a wide fork means less power, but it also makes it far easier to pull out. <br><br>I noticed that when I built my latest slingbow - basically a slingshot with 80 cm fork width and pretensed bands. <br><br>Using two lengthes of Thera Tube Black was still very very easy to draw - an impossible task on a normal slingshot. I had to go all the way up to speargun rubber to reach my strength limit. <br><br>In other words, you simply need a bit more rubber if you want to use a wider fork. The draw weight and the power will still have the same ratio.
     
  7. mr_paradox

    mr_paradox New Member

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    It is a simple physics problem.<br>Ideally your forks should have zero distance between them <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2"><br><br>Basically draw a vector diagram with one fork.<br>It should be a right angle triangle<br><br>As the distance of the elastic gets closer to the fork, the angle increases, so therefore the percentage of the force applied behind the projecticle decreases.<br><br>The maximum velocity will decrease also.<br>I think Jorge gave a figure for maximum velocity of elastic.<br>As the fork width increases, this will decrease for the same reason.<br><br>I am too lazy to draw a pic and upload it <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2"><br>But you can get the idea from this pic <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2"><br><a href="http://demonstrations.wolfram.com/EnergyOfASlingshotDavidAndGoliath/" target="_blank" rel="nofollow">http://demonstrations.wolfram.com/EnergyOfASlingshotDavidAndGoliath/</a><br><br>deltaX is the displacement.<br>The force along deltaX will be Force in elastic multipled by cosine (angle deltaX and Force of elastic).<br><br>Same with velocity.
     
  8. Qajaq

    Qajaq New Member

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    Seems to me the wider the fork the more speed you'd get but you would sacrifice power. So, with relatively light ammo you could gain speed and the opposite might be true with relatively heavy ammo? If what I'm saying is true, couldn't we have the best of both worlds by building a "ball shooting crossbow" like Joreg's weapon with very heavy rubber (I'm thinking spear gun rubber or TB silver tubes) and add two rollers narrowly located closer to the release point/trigger mechanism? Wouldn't this add some power and velocity to a relatively heavy projectile in the beginning of the shot where you would effectively have a narrow fork while taking advantage of the wider fork in the latter part of the shot which might better accelerate the ammo?
     

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  9. Arturo Borquez

    Arturo Borquez Administrator

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    I don't think so ... no geometry magic, what comes out is always less of what comes in, I mean energy ... I don't think the rollers would be a good idea as shown, could give a "roller" hit and will slow down retraction = less energy out or efficiency ...
    Arturo
     
  10. Qajaq

    Qajaq New Member

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    Arturo, thanks for the reply and you're right, I am looking for some geometry magic and you're also agree about what you said about roller hits. Joerg has come up with some interesting videos and good ideas and inspirations. What I'm looking to do is build an accurate slingshot to shoot something like 13mm/1/2" lead balls about 50 or 60 feet with a velocity around 225 fps. At this time I'm planning to build a more powerful version of his ball shooting crossbow with medieval features, the one with a peep sight with the two pieces of wood which the ball passes thru and helps aiming the shot. I think I might use Double theraband silver tubes. What do you think?
     
  11. Arturo Borquez

    Arturo Borquez Administrator

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    no rollers and your crossbow will be fine, tune the amount of rubber, 225 FPS is achievable for the 13.5 mm lead ...
    Arturo