Triumph of the mind (over hysteris)?

Discussion in 'General Slingshot Discussions' started by JoergS, Jan 19, 2012.

  1. JoergS

    JoergS Administrator

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    Have been thinking a lot about the findings of the thermo cam session. I found out that the hysteris effect (= loss of power when a slingshot band is kept stretched) may be caused by the bands cooling off. The obvious question: What if you heat the bands in stretched condition - wouldn't that bring back the power?<br><br>In order to test this, I made a little device that lets me keep a length of band stretched with the fish scales attached to one end. It has to have a hook for the removal of the scales as they switch off after a while, and have to be recalibrated after that. <br><br><div style="margin:auto;text-align:center;width:100%">
    <a href="http://1.bp.blogspot.com/-BazOb5yQI8s/Txh4BGJQHzI/AAAAAAAABUM/hw8JBCAEI_c/s1600/testboard1.JPG" class="postlink" target="_blank" rel="nofollow"><img src="http://1.bp.blogspot.com/-BazOb5yQI8s/Txh4BGJQHzI/AAAAAAAABUM/hw8JBCAEI_c/s400/testboard1.JPG" border="0" alt=""></a><br><br><br><a href="http://1.bp.blogspot.com/-jQQnwDVmi0k/Txh4CSt14SI/AAAAAAAABUU/qRVSPhXGbME/s1600/testboard2.JPG" class="postlink" target="_blank" rel="nofollow"><img src="http://1.bp.blogspot.com/-jQQnwDVmi0k/Txh4CSt14SI/AAAAAAAABUU/qRVSPhXGbME/s400/testboard2.JPG" border="0" alt=""></a>
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    <br><br><br>It works! Tested this over a few days now. <br><br>- Bands are 30mm x 20mm x 150mm (active length)<br>- Stretched to 770mm (factor 5,1)<br>- Have about 4,35 kg initial draw<br>- Draw goes down quickly to3,25 kg<br>- Draw stays 3,25 kg for days (same room temperature)<br>- When heat is applied (with heat gun), the draw can be increased to 4,35 easily<br>- Bands tear at 4,6 to 5 kg<br><br>So it works, the proof is there. The cooling of the bands is the reason for the hysteris, which can be turned around if the bands are re-heated.<br><br>The goal: To build a slingshot crossbow that can be kept cocked for days without loosing power.<br><br>Bought the heat films today (9 of them for good measure):<br><br><br><div style="margin:auto;text-align:center;width:100%"><a href="http://4.bp.blogspot.com/-Ukm_FWqZYIA/Txh5R1eV_lI/AAAAAAAABUg/dX-Gr2ocXno/s1600/heatfilm.JPG" class="postlink" target="_blank" rel="nofollow"><img src="http://4.bp.blogspot.com/-Ukm_FWqZYIA/Txh5R1eV_lI/AAAAAAAABUg/dX-Gr2ocXno/s400/heatfilm.JPG" border="0" alt=""></a></div>
    <br><br><br>These films work on 12V DC, and are listed at 36 W. I plan on making an encapsulated slingshot crossbow (the top can be folded away for cocking the weapon) with several of these films as a heating. A motorcycle battery will provide the power. The front of the slingshot will be <br>closed with brushes so the heated air can not escape.<br><br>A switch and a thermometer will be installed as well, of course. Gotta know when it gets too hot.<br><br>Interesting tests ahead of us! Stay tuned.
     
  2. mr_paradox

    mr_paradox New Member

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    Cool the bands. so that way it will take less force to stretch <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2"><br>Then heat them up <img src="http://illiweb.com/fa/i/smiles/icon_wink.gif" alt="Wink" longdesc="15">
     

  3. SkauneJohan

    SkauneJohan Member

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    very interesting you're the man Jørg
     
  4. Rayshot

    Rayshot New Member

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    That is what I thought about reheating a cooled stretched band set. I will be interested in finding out;<br><br>If a stretched band that has cooled and reheated will have the same speed of a "freshly"drawn out band. It would appear to rebound to a speed equal or closer to a freshly drawn band.<br><br>
     
  5. JoergS

    JoergS Administrator

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    The scientific information I gathered using the thermal heat camera lead to more experiments: What happens if you heat a stretched band, one that already cooled down to room temperature?<br><br>It regains the power it lost during the cooldown phase. That is right, this video has the proof. <br><br>Now I had to use this critical information in order to build a slingshot crossbow that can heat the stretched rubber with the <br>flick of a switch. The result looks bizarre and very uncenventional, but it does work very well. <br><br>Three heating films heat up the interior of an encapsulated band box. Using a strong 3300 mAh rechargeable battery, the bands can make the bands about 20 centigrade warmer than the environment, adding (or, better, regaining) about 40% <br>energy. <br><br>This weapon can be left cocked for a long time, and then - minutes before action is expected - be brought to top performance. <br><br>Two new slingshots are also presented as a bonus.<br><br><embed pluginspage="http://www.macromedia.com/go/getflashplayer" src="http://www.youtube.com/v/f3t2_AX8HUk" width="425" height="350" type="application/x-shockwave-flash" wmode="transparent" quality="high" scale="exactfit"></embed>
     
  6. brainleak

    brainleak New Member

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    Cool experiment, I see the thermal camera paid off. The trigger mechanism looks like it is a scaled down version of the 'walkback' cannon ball launcher. Just upside down and miniature. I didnt get a great look at it during the video but it appeared that was the case.
     
  7. JoergS

    JoergS Administrator

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    Yes, the lock is pretty similar to the walkback design. Very compact and strong.
     
  8. tokSick

    tokSick Senior Member

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    In the beginning i didn' t understand so much with all the explanations and comments about that" thermo thing" but now, with this video it became clear to my ears; Joërg have so much more IN his head than ON his head.<br>Seriously, now i understand what he was talking about.<br>Thanks.
     
  9. Ryan Wigglesworth

    Ryan Wigglesworth Senior Member

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    This is by far the coolest video in a while! All the slingshots in it are one of a kind and amazing! The silenced heater, the flying buttress and the vice gripper, I can't tell you which one i like more!
     
  10. Bill Hays

    Bill Hays New Member

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    Extremely interesting!<br><br>This basically flies in the face from what I remember of High School Physics from.... OMG over 30 years ago now!?<br><br>The stretching should have created heat due to friction... but introducing heat into a cooled stretched band should not have "recharged" it's energy potential! More experimentation needs to take place now... as this knowledge should be able to result in improved performance somehow.