The break-in effect: New tests

Discussion in 'General Slingshot Discussions' started by JoergS, Nov 28, 2011.

  1. JoergS

    JoergS Administrator

    5,803
    109
    63
    In order to further clarify the advantage of tapered bands, I re-watched the slomos done with Destin's camera. <br><br>I noticed that the elongation of the rubber close to the pouch was a lot higher than the factor 5,5 (which is the way the band was cut). It was more like 7.<br><br>So it seems possible that the extreme overstretching is responsible for the speed advantage, as that does not happen on untapered bands. <br><br>In order to test this, I made a stretching stick. I put on a 2cm wide strip of TB Gold and <br>markered the 10 cm length point. Then I attached a hand grip, with a karabiner in order to draw with the scales. <br><br>The first interesting finding: TB Gold can be stretched to the factor 8! That is right. But the draw weight increases steeply between 7 and 8. <br><br>Second interesting finding: The relaxed length increased. After stretching it out to the 80 cm, the relaxed length was 12 cm instead of 10... <br><br>Of course there is hysteris, means, if you keep the rubber drawn out it looses power swiftly. But it recovers, and fast. After 10 minutes, the relaxed length was 11 cm.<br><br>Third finding: Stretching the rubber that far breaks it in, means, changes it forever. The rubber did not go back to 10 cm. It stayed at 11, even after a few hours. <br><br>Fourth finding. Once broken in (stretched out to 80 cm and held there a bit), the rubber permanently looses draw weight.<br><br>See the attached graph - after the break in, 80 cm draw can be achieved with the draw weight needed for just 70 cm in unbroken in condition. <br><br>What does this mean? Well, the next experiment must be to cut a much shorter and thinner band set than usual, without tapering, that can be stretched to factor 8. The chrony will tell what the effect will be.<br><br><div style="margin:auto;text-align:center;width:100%">
    <a href="http://2.bp.blogspot.com/-OssCCWdVpS8/TtPnFNeA55I/AAAAAAAABJM/AHtbx8qm8kg/s1600/Stick.JPG" class="postlink" target="_blank" rel="nofollow"><img src="http://2.bp.blogspot.com/-OssCCWdVpS8/TtPnFNeA55I/AAAAAAAABJM/AHtbx8qm8kg/s400/Stick.JPG" border="0" alt=""></a><br><br><a href="http://4.bp.blogspot.com/-jm_73swRRJ4/TtPpJvpxKII/AAAAAAAABJg/HKlAZ7sIua0/s1600/Breakin2.JPG" class="postlink" target="_blank" rel="nofollow"><img src="http://4.bp.blogspot.com/-jm_73swRRJ4/TtPpJvpxKII/AAAAAAAABJg/HKlAZ7sIua0/s400/Breakin2.JPG" border="0" alt=""></a>
    </div>
     
  2. CEZ

    CEZ New Member

    934
    0
    0
    Very interesting, looking foreward to the next experiment. What would happen if you would use more than one band?
     

  3. JoergS

    JoergS Administrator

    5,803
    109
    63
    The effect would be linear. Two bands (same dimensions as the single one, each) double the draw weights, in all and any cases.
     
  4. gerzson

    gerzson New Member

    6
    0
    0
    I think this means that the tapered bands will loose power with usage. The thinner part is overstretched with every draw, and that seams to weaken it.<br>It would be intresting to know after how many draws the power is going down a significant ammount or even be surpassed by paralel bands.
     
  5. JoergS

    JoergS Administrator

    5,803
    109
    63
    We don't know that yet. The break-in effect happens as soon as you overstretch a single time. In other words, every tapered band that has been shot just once is broken in at the thin side.<br><br>So it is possible, even likely, that the overstretching makes the bands faster. The overstretching may reduce the inner friction, by tearing the rubber molecules that are too wound up to stretch in full.
     
  6. Ryan Wigglesworth

    Ryan Wigglesworth Senior Member

    1,570
    0
    0
    Very cool, thanks for sharing <img src="http://r28.imgfast.net/users/2815/14/20/70/smiles/4053770264.gif" border="0" alt=""><img src="http://r28.imgfast.net/users/2815/14/20/70/smiles/4053770264.gif" border="0" alt=""><img src="http://illiweb.com/fa/i/smiles/icon_cheers.png" alt="cheers" longdesc="28">
     
  7. Kyl

    Kyl New Member

    247
    0
    0
    I have often considered these effects. My intuition led me to think something like this was going on. Good job hammering out an experiment to bring this to the light of day. <br><br>I had noticed that a new band set was stronger but not faster than a broke in set. <br><br>Thanks Joerg