Crossbows - Everything about Building, Modding, and Using your Crossbow Gear

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    Alphabetical evolution

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    hullutiedemies
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    Alphabetical evolution

    Post by hullutiedemies on Wed Apr 03, 2013 11:22 am

    After the H-bow it was obvious to try the fashionable backwards design.
    This let to K-bow

    , wich works quite satisfactorily, but with 6 limbs and massive riser section it is uneconomical to build.

    I soon found out that split limbs were not necessary, also got rid of the the backwards facing "cross-bow".

    So after X-bow comes the Y-bow:


    This makes a durable and lightweight construction as the limbs are separate bows holding their own tension. So the assembly only takes the final draw-weight.

    Added pulleys to the arms out of tarpaulin buttons with acrylic cased stonewall nails as axis.

    This allows twice as long power stroke

    Accuracy is surprisingly good, arrows are going were they are pointed, despite limbs being badly off-balance.

    Unlike the the usual backwards scorpyrd-daVinci bows, this is a true in-swinger. When triggered all moving parts collapse inwards and forwards. So this can be safely shot while in contact with users body or other obstacles on the flanks.

    And the best part

    F/D-curve is fat like a singing lady. This is a true compound bow.


    Coming up next
    - Limbs steamed to matching curvature
    - Second set of pulleys for 50% longer power-stroke
    - Trigger mechanism
    - Stock & bolt rail
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    kenh
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    Re: Alphabetical evolution

    Post by kenh on Wed Apr 03, 2013 2:27 pm

    Yer startin' ta skeer me now, Nerd..... Fascinating..... keep it up!

    Since my initials are K and H that means I gotta build two paleobows. I need to have a talk with the seagrape tree in my girlfriend's backyard....
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    Re: Alphabetical evolution

    Post by kenh on Sun Apr 07, 2013 6:17 am

    I sort of expected you to create a Y bow that features a single forked branch rather than the two interlaced bows design. Not complaining, mind you... just a thought.
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    hullutiedemies
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    Re: Alphabetical evolution

    Post by hullutiedemies on Mon Apr 08, 2013 3:58 am

    That would require a symmetrical forked branch that has inside suitable for bow back.
    It is easier to make two separate limbs - especially composite material limbs. Plus pulling off that cable-bridge allows the device to be folded vertically for transport. Besides stresses would tear a forked or split log apart unless reinforced with wrappings anyway.


    But of course the limbs could be permanently glued or riveted at lower end. That way a cable-bridge would not be necessary. And if I get to make one out of metal , it probably will be bend from a single bar.
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    Re: Alphabetical evolution

    Post by Oppenheimer on Mon Apr 29, 2013 5:52 am

    You´re amazing Nerd Flintstone! First of all I like your primitive and cheap way to design your bows. Also your ligts highspeed arrows are really fun. Tried them and think they are nice to play with my children this summer. Then we have your frictionless limb resulting in high speed. Even if they were mounted on a normal lever axis, they will reduce friction and get precision. Where do you get all ideas from?

    By the way -whath homemade trigger do you use. Do you have any close upp picture on it?
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    ferdinand
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    Re: Alphabetical evolution

    Post by ferdinand on Mon Apr 29, 2013 9:31 am

    beautifull. Really. Post a movie!!!
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    hullutiedemies
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    Re: Alphabetical evolution

    Post by hullutiedemies on Mon Jun 17, 2013 10:03 am

    Oppenheimer wrote: Where do you get all ideas from?

    As I probably mentioned in my introductory message,
    my hobby interest is not so much building crossbows but more into developing them.
    So I try to consciously think "out of the box". I also actively follow advances in modern military technology and try to think ways applying these to muscle powered homemade devices. And since I do not have a professional level workshop with good tools nor the skills of a pro craftsman, I am forced to figure out easy ways to implement my designs cheaply with simple tools.

    Besides having studied machine construction in polytech and written my masters paper on applied mathematics, one exercise project for my undergraduate class was programming laser sensors for ESA weather satellite - so I guess I technically sort of am what Americans call "rocket scientist".

    Oppenheimer wrote:
    By the way -whath homemade trigger do you use. Do you have any close upp picture on it?

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    Re: Alphabetical evolution

    Post by Oppenheimer on Sat Jun 29, 2013 5:08 am

    Thank for your answer Nerd F. It took a while so I tought you disliked the questions. Your interest seems to be exactly mine too. I think Further development of crossbow-making can be made ​​and by aplying technicues and physics from other branches I believe efficiency can be DOUBLED. Too many thinks in too traditional ways and the companies owning the market dot Newbies want to steal parts of it. The result is no development made ​​and just the same devises in different collours of the Year.
    One area you have just opened up is to get an almost frictionless devise, not needing more power input like stronger limbs, etc. Another thing you point out is simplicity like in your trigger.

    Now I wonder what model of yours has the best eficiency? I miss the discussion about energy efficiency in the forum.
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    hullutiedemies
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    Re: Alphabetical evolution

    Post by hullutiedemies on Tue Jul 02, 2013 2:34 am

    Oppenheimer wrote: It took a while so I tought you disliked the questions.
    No, just time and stress management. I usually do not even read replies to my postings until I know I have time to write a response. Photography, editing and uploading of pictures adds couple weeks extra to response time.

    Oppenheimer wrote:
    Further development of crossbow-making can be made ​​and by aplying technicues and physics from other branches I believe efficiency can be DOUBLED.
    Doubled in what way ?
    Any compound system of half decent quality can achieve decent bolt speed with 90% input/output energy efficiency.
    I usually like to think in terms of dry fire speed , the theoretical upper limit should be dictated by speed of sound in material the acceleration system is made of.

    Oppenheimer wrote:
    Too many thinks in too traditional ways and the companies owning the market dot Newbies want to steal parts of it.
    I have been browsing discussions at crossbownation board, and it seems that the industry is not really interested in "open-source" solutions. They want patentable designs they can license. Thats where the money is.

    Oppenheimer wrote:
    Now I wonder what model of yours has the best eficiency?
    With any style, it boils down to minimizing the speed of energy storing spring and minimizing the inertia momentum of the primary string that is pushing the bolt.

    I have a recent new a idea that has not yet been properly tested- scale model was promising though, but there is potential for tripling the bolt speed. ( And awfully simple one - wonder why nobody has ever tried this before )
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    Re: Alphabetical evolution

    Post by kenh on Tue Jul 02, 2013 5:53 am

    NF -- I really look forward to seeing the results of your new idea.

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