Why doesn't more rubber give more speed?

Discussion in 'General Slingshot Discussions' started by Adrinalino, Jul 29, 2013.

  1. Adrinalino

    Adrinalino New Member

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    I would appreciate your views on the following issue.

    Yesterday I spend some time doing impact studies with my slingshot rifle.

    I shot 12 and 16 mm steel balls on cardboard layers using different rubbers.

    Using the band calculator the results are nice but making wider or more bands did not give deeper penetration.

    Can anyone come up with an explanation for this?

    Cheers,

    Adrian.
     
  2. MaddyMax

    MaddyMax New Member

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    to get the full speed out of the bands they have to be short enough to be pulled to full stretch to the anchor point just before they would rip.

    high tapering also increases speed.

    the band calculator is just for the tbg bands (i have older ones, there might be a difference to the newer ones).

    for other brands you have to measure, how many times they can be stretched.

    you only have to make the bands wider (or take more layers) when the ammo weight increases.
     

  3. MaddyMax

    MaddyMax New Member

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    sorry, forgot to mention that the longer you wait to release the bands the faster they cool down and loose power.

    means, as soon as you got to full stretch you immediately have to release the pouch.

    edit: sorry again. for slingshot rifles/x-bows more layers of rubber should compensate a bit the cooling down of the bands.
     
    Last edited: Jul 29, 2013
  4. Adrinalino

    Adrinalino New Member

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    The band calculator takes 0,6 kg force per gram ammo weight. What is the idea behind this? Why not more or less?

    Thanks for your help,

    Adrian.
     
  5. MaddyMax

    MaddyMax New Member

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    you might wait for a physics professor or when jörg is back to get this question answered.

    only thing i know is, if the bands deliver more energy than needed it will result in nasty handslaps because of the rest energy. the balls just can be accelerated to the maximum speed the bands retract.
     
  6. Brazilviking

    Brazilviking Thread Hijacker

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    if you want to incease penetration you need more kinectic energy. if the bands reached a limti, maybe you must increase the weigth of your projectile.
     
  7. Peteyspine

    Peteyspine New Member

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    In my Opinion the Bands have a maximum speed whenn you simply pull a Band an release it. Without Pouch and anything.
    I think this speed will be at about 150 m/s when tapered. Would be nice if Jörg could test it with high speed camera.
    When you add a pouch, rubber for tying and ammo to the bands, all of this stuff has to be accelerated.
    That acceleration work needs potential energy from the bands and convert it to kinetic energy and you will have speeds at around 100 m/s.
    That difference of speedd is because of friction (air and rubber) loss of heat in bands and inertia.


    The only way to get higher speeds is to reduce the inner friction of the material. Means thinnner but more Bands.
    And/Or reduce the weight of pouch and tying.

    For more penetration you can use heavier ammo like lead. This means slower traveling ammo, but more momentum (p=m*v) when hitting the target. Kinetic energy should be the same using lead or steel. E=0.5*m*v^2

    Momentum increases linear with mass and speed. But energy increases exponetially with higher speed.

    As you always convert the same amount of potential energy to kinetic energy you will easier achieve more momentum then more kinetic energy.

    I hope you guys understand what i mean.
    It´s hard to explain stuff like that in not your mothers language
     
  8. Adrinalino

    Adrinalino New Member

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    Thank you all for the above. All this I understand (I'm not a professor but a master of physics :) ). The question I raised was : "Why does more rubber not give more speed?"
    With my simple experiments I noticed that giving the sling rifle twice the rubber only gives about 15 % more penetration.

    Any Ideas?

    Thanks,

    Adrian.
     
  9. MaddyMax

    MaddyMax New Member

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    another layer of bands means more of it's own weight.

    so twice the power is not twice the power. :D
     
  10. MaddyMax

    MaddyMax New Member

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    if you go for just penetration, round ammo will not be the best choice. heavy pointy edgy things is what you want.
     
  11. Peteyspine

    Peteyspine New Member

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    Maybe lead filled anti balls B-)
     
  12. Arturo Borquez

    Arturo Borquez Administrator

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    The "unloaded" maximum retraction speed at a certain temperature is fixed, when loaded with a pouch, ammo and air friction the retraction speed will always be slower than the "maximum retraction speed", so there is a limit where adding more rubber (bands layers) and force will not add more speed, on the contrary maybe it will add more friction and big recoil slaps, rubber takes it's time to transfer the stored energy to ammo, that's why long draws (more "acceleration" time) transfer better stored energy into kinetic energy resulting in more speed ...
    Cheers
    Arturo
     
  13. studer1972

    studer1972 scooter trash

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    :eek:<screams like a frighted child/>AIIIE! MATH!:eek:

    Excellent explanations Maddy & Pete.

    Your explanation was clear to me Pete, what is your native language?
     
  14. studer1972

    studer1972 scooter trash

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    You too, Arturo, I should have read the full thread before commenting. Thanks for the good info, folks.
     
  15. Peteyspine

    Peteyspine New Member

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    Natively i speak german.