A Slingshot Crossbow

Discussion in 'Show off your homemades!' started by Alukuchen, Jan 11, 2012.

  1. Alukuchen

    Alukuchen Senior Member

    277
    0
    0
    Hey there! <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2"><br>I made a Slingshot Crossbow...<br>Sadly I could't testfire it yet because I have no ammo that is heavy enough ^^<br>overall length: 135cm<br>drawlength: 93cm<br>draw: 23kg = 51 lbs<br>Hope you like it<br>Here are some pictures:<br><a href="http://www.servimg.com/image_preview.php?i=9&u=17120720" class="postlink" target="_blank" rel="nofollow"><img src="http://i42.servimg.com/u/f42/17/12/07/20/07012010.jpg" border="0" alt=""></a><br><a href="http://www.servimg.com/image_preview.php?i=14&u=17120720" class="postlink" target="_blank" rel="nofollow"><img src="http://i42.servimg.com/u/f42/17/12/07/20/07012015.jpg" border="0" alt=""></a><br><a href="http://www.servimg.com/image_preview.php?i=10&u=17120720" class="postlink" target="_blank" rel="nofollow"><img src="http://i42.servimg.com/u/f42/17/12/07/20/07012011.jpg" border="0" alt=""></a><br><a href="http://www.servimg.com/image_preview.php?i=11&u=17120720" class="postlink" target="_blank" rel="nofollow"><img src="http://i42.servimg.com/u/f42/17/12/07/20/07012012.jpg" border="0" alt=""></a><br><a href="http://www.servimg.com/image_preview.php?i=13&u=17120720" class="postlink" target="_blank" rel="nofollow"><img src="http://i42.servimg.com/u/f42/17/12/07/20/07012014.jpg" border="0" alt=""></a>
     
  2. pasquale

    pasquale Member

    282
    24
    18
    Cooles Teil.Wenn du bessere Munition hast wirst du da ein Testvideo hochladen? Wirst du ein Scope auf die 22 mm Schiene anbbringen und welches?
     

  3. SkauneJohan

    SkauneJohan Member

    144
    0
    16
    very cool <img src="http://illiweb.com/fa/i/smiles/icon_cheers.png" alt="cheers" longdesc="28"> . makes me think again about maybe getting rollers for mine anyway
     
  4. JoergS

    JoergS Administrator

    5,803
    109
    63
    Cool! How long are the tubes, in relaxed condition? They must be pretensed quite a bit.
     
  5. Alukuchen

    Alukuchen Senior Member

    277
    0
    0
    Thanks <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2"> each of them is about 58cm relaxed... the pretention is very low, it just keeps the rubber straight but I have to check if the results will be better if the pretetion is higher... do you think I should set a high pretention?<br>jep testvideo and scope <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2">
     
  6. JoergS

    JoergS Administrator

    5,803
    109
    63
    For this kind of draw extension (the distance between the band attachment and the rollers), you must use extreme pretension, or your bands won't be stretched to more than maybe factor three. In other words, you loose a great deal of potential power. <br><br>If you don't want pretension, then you have to move the attachments forward. In any case you should shorten the bands.
     
  7. Alukuchen

    Alukuchen Senior Member

    277
    0
    0
    Just tried it and you are completely right!<br>it is possible to draw it all the way back and lock it over the rifle stock...<br>I will move the rings the bands are tied to backwards right in front of the trigger group and shorten the bands a little....<br>Thanks for your support!<br>I will do a destruction video soo when i have a mold for 20mm lead balls.<br>Jörg would you recommend even heavier ammo for that kind of bands and drawlength?
     
  8. JoergS

    JoergS Administrator

    5,803
    109
    63
    20mm lead is very fine for these bands. You can even go lighter, 20 mm steel for example. <br><br>My strongest crossbows use more tha 100 kg draw weight. Those can handle the really heavy stuff.<br><br>For the 97 cm draw (plus the extension), use a band length of about 25 cm.
     
  9. Alukuchen

    Alukuchen Senior Member

    277
    0
    0
    Yeah I watched the video, that thing is a beast ^^<br>hmm in the end both tubes have to be 170cm long each, that makes a factor of 6,8 with the 25cm tubes. Can that rubber handle a factor of 6,8?<br>I just stretched a piece of that tube to a factor of 5.5 but it absolutely didn't want to be stretched further but of course it could have been limited by my bodystrenght...<br>I still can't believe how powerful that rubber stuff is. A wonderful material!<br>And you were completely right again, the factor of the bandset how it is right now is 3, even a bit less.
     
  10. Tobias

    Tobias New Member

    390
    0
    0
    Sauber gemacht! die Silbertubes halten lange und lassen sich auch 5fach dehnen.
     
  11. mr_paradox

    mr_paradox New Member

    44
    0
    0
    nice <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2">
     
  12. JoergS

    JoergS Administrator

    5,803
    109
    63
    <table width="90%" cellspacing="1" cellpadding="0" border="0" align="center">
    <tr><td><span class="genmed"><b>Alukuchen1992 wrote:</b></span></td></tr>
    <tr><td class="quote">
    <br>hmm in the end both tubes have to be 170cm long each, that makes a factor of 6,8 with the 25cm tubes. Can that rubber handle a factor of 6,8?</td></tr>
    </table>
    <span class="postbody"><br><br>You have to move the attachment forwards, so that there is little pretension. <br><br>If you want to keep it where it is now, you have to cut them to 34 cm or so. They would pre prestretched to 2,15 then, still OK (they will tire out slightly over time, so I would take them off the rollers when you are not using the rifle).</span>
     
  13. Alukuchen

    Alukuchen Senior Member

    277
    0
    0
    Ok <br>Now the tubes are 40cm each and get stretched to a length of 180cm that makes a factor of 4,5. And my bodystrength set the limit. I'm not the weakest guy but it already is a pain to load... the strings the pouch is tied with already begins to tear. A shot over the chrony with a 21g lead ball showed that it had an energy of 45J what is much less than expected, at least in my opinion. 45J are no problem with a regular slingshot so the crossbow does not make sense. But I will try it with heavier ammo and hope for a better result. Maybe the tubes are simply to slow and energy can be maximized by increasing the weight of the projectile.
     
  14. JoergS

    JoergS Administrator

    5,803
    109
    63
    The tubes ARE pretty slow. 65 m/s is actually a very good speed result for the silver tubes! <br><br>The biggest advantage of crossbows is the consistent accuracy. Because of the hysteresis (= rubber looses power quickly when drawn out) a handheld is nearly always faster.<br><br>You should see slightly more energy when you shoot heavier balls, but don't expect miracles.
     
  15. Tobias

    Tobias New Member

    390
    0
    0
    i think 45 joule are good for this device.<br><br>wolltest du nicht mit 20mm Blei schießen? das müste doch mehr wiegen als 21g.
     
  16. Alukuchen

    Alukuchen Senior Member

    277
    0
    0
    naja ich werds noch ausgiebig testen wenns wärmer wird <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2"><br><br>ja ich wollte 20mm blei schießen hab aber keine kokille dafür deshalb hab ich 15,4mm genommen. Das is das kaliber das ich normalerweise mit der zwille schieße <img src="http://illiweb.com/fa/i/smiles/icon_wink.gif" alt="Wink" longdesc="15">
     
  17. onnod

    onnod Im from Holland, isnt that weird?

    6,001
    18
    38
    nice one.<br>the rollers are a very good idea
     
  18. Droolp1g

    Droolp1g New Member

    103
    0
    0
    Very nice piece I'm not going to state anything bad about this piece until i have seen a video of it shoot.
     
  19. general666

    general666 New Member

    44
    0
    0
    awesome looking bit of kit you have me thinking now <img src="http://illiweb.com/fa/i/smiles/icon_wink.gif" alt="Wink" longdesc="15">
     
  20. jeromebickel

    jeromebickel New Member

    4
    0
    0
    Geiles Teil!!! Aber wieso is das nicht mehr auf YouTube? War schon einmal drinn.. ps mach gerade was ähnliches, nur ist meins dann 70cm lang und hat den Mechanismus von jörgs "sniper rife" (das ich auch schon gebaut hab) und wird Md den schwarzen tubes angetrieben.. hat dann auch Rollen vorne aber die gummis werden länger gespannt.. <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2">