"The Rubber-Gonne": Minimalistic Crossbow

Discussion in 'Show off your homemades!' started by JoergS, Sep 22, 2013.

  1. JoergS

    JoergS Administrator

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    Yesterday, I wanted to make another small crossbow, after all these looong weapons I recently presented.

    The challenge: The smallest possible encapsulated (=safe) crossbow for 20" 2219 crossbow arrows. That's right, arrows, not bolts. The difference: Arrows have fletching.

    In Terry Pratchet's "Discworld" novels, there is a weapon he calls the "Spring-Gonne". Basically a length of steel tube with a spring that shoots steel bolts. Highly illegal in that universe! I wanted to make that weapon, but adapt it to rubber of course, and (as mentioned already) for fletched arrows.

    So I designed a crossbow that can "chamber" these arrows.

    [​IMG]
    [​IMG]
    [​IMG]

    As you see it is not much larger than the arrow itself.

    I attached the strongest rubber that allows me to cock the weapon with the butt plate against my chest (very quick reloading that way). Eight bands of TBG, 3cm straight, per side. Total draw is about 150 lb.

    The tip protrudes, which not only allows for broadheads of any kind - but it also makes it possible to safely unload the weapon.

    [​IMG]

    Total weight is 650 gramms (1,5 lb) with the rubber installed (but w/o the arrow).

    The weapon shoots very accurately and is reasonably powerful. It cleanly goes all the way through my 70kg spec'ed archery mat (I used a "virgin" part of course).

    [​IMG]

    I think this is a very legit weapon - ideal as a backup crossbow!
     
  2. xXdoomXx

    xXdoomXx Junior threadjacker ag. J

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    Looks great joerg on question have you already talked with forum tech about a design or even a slingshot forum app I have a thread if you wanna check it (don't have to tho)

    :) J
     

  3. Moin moin,
    ? Balistisches Problem?
    Wenn der Pfeil beschleunigt wird, verformt er sich doch.....
    Dann müsste es an das Holz schlagen, was ein wenig Geschwindigkeit kosten könnte... aber viel wichtiger genauigkeit.....
    Kannst du ein 20m Clip davon machen? und Geschwindigkeit messen?
    -
    Oder ist das ein "nahkampf" mittel?
     
  4. JoergS

    JoergS Administrator

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    Wieso sollte sich der Pfeil verformen? Das ist ja kein Bogen, es gibt kein Archer's Paradox.

    Das Ding schießt sehr genau, aber mangels Visierung sind Tests nicht sinnvoll.
     
  5. Moin moin,

    auch mit einem Versprung im Bogen, kommt es - wohl aufgrund der Trägheit des Pfeiles (oder ist er wie ich faul, und möchte sich eigentlich "nur" nicht bewegen) zu einer Verformung. Der Hintern des Pfeiles (Nock - dah wo die Befiederung ist) wird von der Sehne ganz schön hart, in den Hintern getreten. So das er (der Pfeil) nach vorne ausweichen muss..... Der Kopf (Pfeilspitze) möchte aber nicht so richtig mit..... aufgrund der Länge, und der Durchbiegung verformt er sich ..... (nicht für dich so geschrieben Jörg, du weist um was es geht, nur für anfänger.... bevor ich wieder PM´s von dehnen erhalte, was ich damit meine....)


    Wenn nicht, lege doch mal Durchschlagpapier oder etwas an das Holz, oder Lippenstieft an den Pfeil an, und schaue nach, ob er ihrgendwoh dagegenstößt.
    -
    Eine Visierung dürfte für dich doch kein Problem sein.... oder lieber einen Einschusstisch?
    Einen Stabilen Tisch, mit aussparungen, in die der "Bogen" genau hineinpasst, und immer gleich liegt (Notfalls kontrolle mit Laser, wenn das in D erlaubt ist....?) Den es soll ja der "Bogen" gut hier wohl Rifle getestet werden.... und nicht der Schütze, obwohl das Klohbürsten Ding, verdammt genau wahr!

    [ame]http://www.youtube.com/watch?v=SuHW8InB5tk[/ame]

    [ame]http://www.youtube.com/watch?v=JIeP5Z08Kqs[/ame]

    [ame]http://www.youtube.com/watch?v=jinC7pG1eVg[/ame]

    je nach beschleunigung..... deshalb auch die gewünschte Geschwindigkeits messung.


    Es geht aber (mit dem abgestimmten Pfeil, und Beschleunigung) auch ohne Durchbiegung:
    [ame]http://www.youtube.com/watch?v=ZQHodqZgDNM[/ame]

    [ame]http://www.youtube.com/watch?v=WqJgaZxREf0[/ame]

    Hier mal Spinn:
    [ame]http://www.youtube.com/watch?v=qWsXc-kW5NY[/ame]
     
    Last edited: Sep 22, 2013
  6. JoergS

    JoergS Administrator

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    Bei den kurzen, dicken Aluschäften (2219er, 20") und der kompletten Führung wird der "Tritt in den Hintern" keine Durchbiegung erzeugen.

    Ich habe gerade mal auf 20 Meter getestet, einfach über den Lauf gezielt. Das geht ganz gut. Streukreis ca. 30 cm - nicht übel ohne Visierung.

    Vielleicht baue ich mal ein Red Dot drauf oder so. Aber nicht mehr heute.
     
  7. CEZ

    CEZ New Member

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    Very legitimate looking indeed, I have made the bullpup one some time ago with similar specs of rubber. It would send the arrow through two stacked 18mm particle boards. Wouldn't go through a bunch of rags though:)
     
  8. onnod

    onnod Im from Holland, isnt that weird?

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    great crossbow joerg!!
     
  9. VWscooby

    VWscooby Senior Member

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    Anything inspired by the Discworld novels gets a thumbs up from me!
     
  10. Antraxx

    Antraxx #7

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    Very Nice.
    The moment i saw those huge amounts of rubber on the muzzle i know this thing means buisness.
    What would a normal or compound bow with average drawweight do from that distance to the mat? Will it also fully penetrate?

    I´m also interested in accuracy. But i wouldn´t go too far and add a sight. Why not just clap it to a table and frire it in the same position. That will deliver the best results.
     
  11. FIAAO

    FIAAO Failureisalwaysanoption

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    Cool :cool: Makes me want to re-do my arrow-shooter!
     
  12. Withak

    Withak aka Whitehawk!

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    I like this design very much Joerg! At some point, I hope to build something like this. I think this design is one of my favorites. And, I got to learn about 'Archer's Paradox' - very interesting concept - I've never heard of it before, but then, I'm not an archer.
     
  13. Slagskimmer Mike

    Slagskimmer Mike thinks TBG smells better than roses

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    Some drawings for this one would be sweet frosting for the top of my unfinished projects mountain:p
    (or just some pictures of the insides)

    The broadhead option is sweet.
     
  14. JoergS

    JoergS Administrator

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    The weapon isn't as powerful as a commercial compound crossbow - however it is legit. There is good accuracy and nice penetration. Of course it is MUCH smaller and A LOT lighter than any crossbow on the market!

    Made the video, it is currently uploading. Accuracy and power is of course demonstrated.

    As usual I have no drawings, and can't take pics as I glued the parts together (saves space and weight). But it is SO simple. Very straight forward.
     
  15. HenryDaniels

    HenryDaniels New Member

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    Great job, Jeorge. I am 14 and just getting into the expansive world of slingshots. I've watched many of your videos and i would have to say this is one of my favorite weapons. I am an aspiring engineer and in my opinion all you would need to make that sling bow perfect would be an inline folding stock. The stock would add plenty stability to your shooting while still leaving the crossbow compact.
     
  16. JoergS

    JoergS Administrator

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    [ame]http://www.youtube.com/watch?v=HVb2bsTznD4[/ame]
     
  17. rock slinger

    rock slinger I rarely shoot rocks!

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    Joerg, I am in deep thought on how you made that barel for the arrow. I hope to design and make something similar, but I do not yet understand. I plane on making one that shoots standard size arrows with the blocks cut off of them. My design will include a shoulder stock, and a pistol grip with a different trigger. Could you please explain how you did that. Thank you in advance.
     
  18. JoergS

    JoergS Administrator

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    A shoulder stock really isn't needed for such lightweight, recoil free weapons. Medieval crossbows never had shoulder stocks. When guns came along, the stock was added so the shooters could aim in spite of the heavy kick.

    Nowadays manufacturers add the stock so the weapon resembles a gun, plus the overpowered products are so front heavy that you need the stock for balancing.

    The barrel is simply made from three thin layers of wood, the middle one is cut out for the lowest feather, the others just to fit the shaft. The slots in the side plates are rasped out to match the two upper feathers.