The Arbalist Guild

Would you like to react to this message? Create an account in a few clicks or log in to continue.

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

Latest topics

» Ball shooting Crossbows worth the bother
by topfmine Wed Sep 15, 2021 3:24 pm

» Chu Ko Nu - repeating chinese crossbow
by Dark Factor Mon Sep 06, 2021 10:36 am

» Skew of tiller
by drawknife Fri Aug 27, 2021 9:18 am

» tiller desgin
by crusader Wed Aug 18, 2021 10:37 am

» Want to build modern target crossbow
by ora8i Fri Aug 13, 2021 1:20 pm

» starting a 1400's replica
by tghsmith Wed Aug 11, 2021 10:25 am

» New Medieval just about finished
by Dark Factor Mon Aug 02, 2021 6:41 am

» How do I tune this
by stuckinthemud1 Sun Jul 25, 2021 3:14 am

» Plans and materials for my first build
by c sitas Sat Jul 03, 2021 7:39 am

» Bolt rest
by stuckinthemud1 Mon Jun 14, 2021 3:24 pm

» Collotiere a Charavines crossbow
by stuckinthemud1 Sun Jun 06, 2021 2:25 pm

» ash lath and pin-lock crossbow
by stuckinthemud1 Wed Jun 02, 2021 7:56 am

» Late medieval tournament distances?
by stuckinthemud1 Thu Apr 15, 2021 8:20 am

» Cutting delrin straight by hand?
by kenh Thu Apr 01, 2021 8:24 pm

» Other forums like this one?
by stuckinthemud1 Tue Mar 30, 2021 9:23 am

» new find in china, terra cotta warrior site
by tghsmith Thu Mar 25, 2021 4:42 am

» Crossbow Books
by Andy. Sun Mar 14, 2021 3:46 pm

» 95lb ancient crossbow shot faster than 960lb medieval
by Fangbows Fri Mar 12, 2021 11:36 pm

» best type of horn to use..
by kenh Tue Mar 09, 2021 3:16 pm

» re-introduction
by tghsmith Sun Mar 07, 2021 3:15 pm

» 4 fletch question
by 8fingers Fri Feb 05, 2021 3:14 am

» fix bolts
by MPDVM Tue Feb 02, 2021 7:40 pm

» Reverse draw compound bow build
by c sitas Tue Feb 02, 2021 7:20 pm

» New Build for 2020
by Gnome Wed Jan 27, 2021 6:19 am

» Spanning bench ideas
by stuckinthemud1 Fri Jan 08, 2021 1:07 pm


3 posters

    Can we use mechanical pulleys to increase load tension?

    whiteraven
    whiteraven
    Tinkerer

    If there is a will, there is a way.


    TinkererIf there is a will, there  is a way.

    Posts : 89
    Join date : 2012-05-19
    Age : 42
    Location : Mesa, Arizona, USA

    Can we use mechanical pulleys to increase load tension? Empty Can we use mechanical pulleys to increase load tension?

    Post by whiteraven Thu May 31, 2012 4:43 pm




    I've been doing a little research on pulley systems and how to use one to increase the power of a mechanical crossbow. I found this little clip below and it got me wondering, but my mind just can't fully fathom the pulley systems without having a handleful of pulleys and some rope to try them all out.
    Could this work to improve the power of a crossbow?


    Fig. 5. Spanish burton.
    Can we use mechanical pulleys to increase load tension? Span-com
    So now try your skills on this pulley system, Fig. 5, called the
    "Spanish burton". It is shown in Leonardo da Vinci's notebooks. What's
    the number of rope segments 'supporting' the load? That's hard to count,
    for only two forces from one rope act directly on the load. That "count
    the ropes" rule is useless for anything other than block and tackle
    systems. But the analysis of this system (or any pulley system) is easy.
    First assume the system is in equilibrium (either at rest, or with
    everything moving at constant speeds). Start at the right, calling the
    tension in the right rope F. This rope passes over the pulley second
    from the right, exerting an upward force 2F on that pulley. So, to
    maintain equilibrium, the rope acting downward on that pulley must have
    tension 2F. At the next pulley the downward force is 4F, and at the next
    it is 8F, and by the time we get to the last pulley, the downward force
    must be 32F = L. So the mechanical advantage is 32, and there are
    nowhere near that many ropes or even rope segments in the system. (There
    are 5 ropes and 10 segments.)
    DARIVS ARCHITECTVS
    DARIVS ARCHITECTVS
    Siege Engineer
    Siege Engineer

    Posts : 36
    Join date : 2010-08-11
    Age : 56
    Location : Ramsey, MN

    Can we use mechanical pulleys to increase load tension? Empty Re: Can we use mechanical pulleys to increase load tension?

    Post by DARIVS ARCHITECTVS Thu May 31, 2012 5:27 pm

    Pulleys trade distance of motion for tension. They increase distance while decreasing the force of tension. Not usually a thing you want to do in a crossbow. You want to increase tension AND increase distance (draw length). Modern crossbows use cams (NOT PULLEYS) to alter the bow string tension at different points along the throwing distance as the bolt is thrown in order to make the transfer of pressure driving the bolt more efficient than a simple leaf spring prod is capable of. The pressure curve behind the bolt is thus modified for maximum transfer of energy to the bolt.
    Basilisk120
    Basilisk120
    Moderator
    Moderator

    Posts : 548
    Join date : 2010-03-01
    Age : 42
    Location : Arizona

    Can we use mechanical pulleys to increase load tension? Empty Re: Can we use mechanical pulleys to increase load tension?

    Post by Basilisk120 Thu May 31, 2012 5:42 pm

    Might work but would be complicated and have lots of pulleys hanging out in mid air.

    Some randomw thoughts on this pulley system in a crossbow



    This would make for a long draw lenght. The distance F travels is 32 x the distance L is lifted.



    At least with the way it is setup in the picture the prod would be reversed from the a normale crossbow. This may be easily fixed with one more pulley or a slight layout change.



    What is likely to be a big issue is that each pully adds friction and inertia to the system. For a fast moving dynamic system like a crossbow during release this could be an issue.



    I would say that this system would be most useful if you have really strong prod that has a really short throw.



    Something Something Dark Side
    whiteraven
    whiteraven
    Tinkerer

    If there is a will, there is a way.


    TinkererIf there is a will, there  is a way.

    Posts : 89
    Join date : 2012-05-19
    Age : 42
    Location : Mesa, Arizona, USA

    Can we use mechanical pulleys to increase load tension? Empty Re: Can we use mechanical pulleys to increase load tension?

    Post by whiteraven Thu May 31, 2012 5:43 pm

    But could employing the use of pulleys in the loading device allow one to draw a heavier tensioned string than your standard cranking loader?
    DARIVS ARCHITECTVS
    DARIVS ARCHITECTVS
    Siege Engineer
    Siege Engineer

    Posts : 36
    Join date : 2010-08-11
    Age : 56
    Location : Ramsey, MN

    Can we use mechanical pulleys to increase load tension? Empty Re: Can we use mechanical pulleys to increase load tension?

    Post by DARIVS ARCHITECTVS Thu May 31, 2012 8:29 pm

    whiteraven wrote:But could employing the use of pulleys in the loading device allow one to draw a heavier tensioned string than your standard cranking loader?

    Yes, and such a system has been used extensively for large siege crossbows. However, the time it takes to draw the cord in the pulleys in order to span the bow makes the reloading time rather long. As such, it was used primarily for crossbows used in defense. A single pulley for loading was often used for lighter crossbows in the field.

    Sponsored content

    Can we use mechanical pulleys to increase load tension? Empty Re: Can we use mechanical pulleys to increase load tension?

    Post by Sponsored content


      Current date/time is Mon Sep 20, 2021 3:00 pm