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

» 12th Century Chinese Crossbow Chronographed
by stuckinthemud1 Fri Nov 24, 2023 3:50 pm

» Crossbow Stock
by kenh Tue Oct 31, 2023 6:19 am

» Colletiere a Charavines continuing experiment
by stuckinthemud1 Sat Oct 07, 2023 5:36 am

» Cocking - how
by stuckinthemud1 Thu Aug 03, 2023 4:24 am

» Questions around heavy crossbow lath buildin
by stuckinthemud1 Wed Apr 26, 2023 1:10 am

» Arab Crossbow
by stuckinthemud1 Tue Apr 25, 2023 7:57 am

» prod angle, and lever trigger for sale anyone?
by stuckinthemud1 Mon Mar 20, 2023 5:54 am

» flexible string
by jasper1978 Mon Mar 20, 2023 1:25 am

» [solved]Skane/Lillohus crossbow thread
by stuckinthemud1 Sun Mar 19, 2023 7:44 am

» jens sensfelder
by jasper1978 Wed Mar 08, 2023 11:58 pm

» 400lb Windlass crossbow bolts weight and accuracy shooting high.
by stuckinthemud1 Sun Mar 05, 2023 2:53 pm

» Codex Löffelholz crossbow
by stuckinthemud1 Tue Jan 24, 2023 4:14 pm

» Digitar prodsc
by stuckinthemud1 Sun Jan 15, 2023 2:42 pm

» Troubleshooting
by Andy. Fri Jan 06, 2023 12:29 pm

» Wood Prods
by stuckinthemud1 Fri Dec 30, 2022 12:47 pm

» Colletiere a Charavines crossbow
by stuckinthemud1 Fri Dec 30, 2022 8:54 am

» Simplified Löffelhotz speedloader
by stuckinthemud1 Fri Dec 09, 2022 4:05 pm

» Fiberglass H-bows
by c sitas Sat Nov 12, 2022 8:44 am

» Bad Antler
by drawknife Sat Nov 12, 2022 3:48 am

» Anyone make their own bolts?
by Juniper Mon Oct 17, 2022 8:20 am

» Josef alm in English
by Juniper Sat Oct 15, 2022 4:22 am

» Qin/Han lock drawings
by kenh Fri Sep 23, 2022 8:16 pm

» stirrup dimensions?
by stuckinthemud1 Thu Sep 01, 2022 1:49 pm

» Skane/Lillohus lockbow information needed
by stuckinthemud1 Sun Aug 14, 2022 6:23 am

» need help contacting le musee Dauphinois Grenoble
by stuckinthemud1 Sat Aug 13, 2022 3:22 pm


4 posters

    Limb end pulleys

    avatar
    Hermit
    Workshop Savvy

    Did you see my tool collection?


    Workshop SavvyDid you see my tool collection?


    Posts : 245
    Join date : 2013-09-10

    Limb end pulleys Empty Limb end pulleys

    Post by Hermit Mon Nov 18, 2013 12:20 pm

    I have noticed that quite a few crossbows I see on here have pulleys at the limb ends Pulleys are not cams,which give mechanical advantage,and make cocking easier,all a single pulley can do,is change direction,no mechanical advantage.constructing a bow limb with a pulley on the end is much more difficult.so what am I missing,why is it done?.I am working on the assumption that nothing is done without good reason,so if any of our knowledgeable members can enlighten me,I would very much appreciate it.
                                               Hermit.
    Gnome
    Gnome
    Crossbow Junkie

    I live here!


    Crossbow JunkieI live here!


    Posts : 451
    Join date : 2011-10-16
    Age : 60
    Location : North Georgia

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Gnome Mon Nov 18, 2013 1:48 pm

    Hermit,
    I don't know much about the math involved, even for such a simple mechanical tool as a pulley, but there is mechanical advantage- there has to be, I figure, otherwise rope cocking aids wouldn't do us any good.
    On my current build I've been posting, I just started experimenting to see what I could learn. The first version had the string mounted to directly to the limb tips, to those little brass pulleys that come in rope cocking devices, in fact. They were just mounted to the pins with the ends looped around them. It was a bear to pull and I couldn't draw it very far with my bare hands. I made a longer string and ran it over those little brass pulleys and attached the ends to the back of the stock, and it was easier, but not by much. I replaced the little brass pulleys with larger plastic ones and it actually became workable.
    I had an intuition that using the pulleys would make it easier to draw, but was more than a little surprised when I upped the size of the pulleys again and it dramatically increased the force applied to the projectile, evident by the speed increase.
    How does it work? I don't really know! But unless there is some other variable that I'm missing, it does work. A true compound system would have the strings terminating at the oposite limb ends, and an even more efficient compound action would use cams instead of pulleys. My limited understanding of cams is that they don't provide more mechanical advantage than a comparably sized pulley, they just distribute the release of energy differently.
    Gnome
    avatar
    Hermit
    Workshop Savvy

    Did you see my tool collection?


    Workshop SavvyDid you see my tool collection?


    Posts : 245
    Join date : 2013-09-10

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Hermit Mon Nov 18, 2013 3:59 pm

    Thanks for your reply Gnome,you have the advantage of me,in that I have no experience whatsoever of limb end pulleys,never having used any kind of bow with them.I have had some experience with pulleys,and know that if the pulley pin is not properly fitted through an appropriate bearing material,it can and will bind.Pulleys are generally the same as gears,you can speed them up.or slow them down with appropriate torque advantages,but you have to have more than one.I don't doubt what you say tho',as I have been around long enough to have seen that what won't work in theory,will often work well in practice.
                          Hermit.
    Gnome
    Gnome
    Crossbow Junkie

    I live here!


    Crossbow JunkieI live here!


    Posts : 451
    Join date : 2011-10-16
    Age : 60
    Location : North Georgia

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Gnome Tue Nov 19, 2013 4:17 am

    I appreciate your inquiry, Hermit. Reminds me that maybe I could spend a little time re-aquainting myself with some of the simple math and science I could have explained to you in Latin when I was in 4th grade, but seems to have been crowded out of my gray matter in recent years by such important data as Star Wars trivia and dirty jokes...
    Gnome
    avatar
    Hermit
    Workshop Savvy

    Did you see my tool collection?


    Workshop SavvyDid you see my tool collection?


    Posts : 245
    Join date : 2013-09-10

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Hermit Tue Nov 19, 2013 7:54 am

    Sadly,latin was always my weak point,Mandarin chinese would have been better..........
        Hermit.
    Gnome
    Gnome
    Crossbow Junkie

    I live here!


    Crossbow JunkieI live here!


    Posts : 451
    Join date : 2011-10-16
    Age : 60
    Location : North Georgia

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Gnome Tue Nov 19, 2013 10:16 am

    My wife has a little Mandarin, maybe she can translate!
    Actually, this pulley thing has been bugging me all day. You are correct that in a simple arrangement, with force on one end of a rope, a pulley hooked to a tree and a weight on the other end, there is no mechanical advantage, just reversal of direction. Then it occured to me- in the case of the rope cocking device, and also in the case of a pulley on a limb end, the pulley is not attached to a stable location, it's attached to the mass you want to move, so you are pulling twice as far, with your hand taking half the weight and the tiller of the crossbow taking the other half. It's more like a single stage block and tackle than a single pulley arrangement.
    Gnome
    avatar
    Rizzar
    Workshop Savvy

    Did you see my tool collection?


    Workshop SavvyDid you see my tool collection?


    Posts : 194
    Join date : 2012-08-11
    Location : Germany

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Rizzar Tue Nov 19, 2013 11:55 am

    Hey guys

    I have some problems to understand what is meant by pulley cause my dictionary gives various meanings.
    either a single fixed roll with a rope around to alternate direction, or more a not fixed one (I think that is meant by block and tackle?) with benefits in work.

    So If you mean the pulley to have a translation of physical work this is exactly what a compound crossbow does with its limb wheels.

    A simple one has a translation of better than 2:1 since it is a normal pulley system with a free roll in addition to a drawback from the string fix on the other limb.

    A congenious addition of a cam instead or in addition to a pulley gives the advantage of alternating leverage adding benefits (work/speed) in certain stages of draw/release.

    Rizzar
    Gnome
    Gnome
    Crossbow Junkie

    I live here!


    Crossbow JunkieI live here!


    Posts : 451
    Join date : 2011-10-16
    Age : 60
    Location : North Georgia

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Gnome Tue Nov 19, 2013 2:43 pm

    Yes, Rizzar, I think that is the conclusion I've been stumbling incoherently towards!
    Gnome
    War Song
    War Song
    Fresh Blood

    Doesn't mean
    I'm new to crossbows


    Fresh Blood Doesn't meanI'm new to crossbows


    Posts : 31
    Join date : 2013-11-20

    Limb end pulleys Empty Re: Limb end pulleys

    Post by War Song Thu Nov 21, 2013 8:04 am

    A pulley wheel is just a lever that spans 360 degrees.
    avatar
    Hermit
    Workshop Savvy

    Did you see my tool collection?


    Workshop SavvyDid you see my tool collection?


    Posts : 245
    Join date : 2013-09-10

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Hermit Thu Nov 21, 2013 9:18 am

    the physics of levers is based on 3 things,the fulcrum,the load,and the effort.The fulcrum being the pivot point,load and effort being self explanatory.The result is dependent on the distance from the fulcrum of both the load and the effort,and it's proportional relationship.For example,if the load is one foot from the fulcrum,and the applied effort is 2 feet from the fulcrum,only half the effort is required to move a fixed load.Knowing these facts prompted my question in the first place,as I could'nt see where the advantage was in doing the extra work fitting pulleys.As I also said,not everything that is theory converts to workable facts.
                                                    Hermit.
    avatar
    Rizzar
    Workshop Savvy

    Did you see my tool collection?


    Workshop SavvyDid you see my tool collection?


    Posts : 194
    Join date : 2012-08-11
    Location : Germany

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Rizzar Thu Nov 21, 2013 10:20 am

    I am sorry if I brought some nomenclature confusion into it!

    The thing we have on a compound crossbow is a simple moveable pulley which gives not just an alternating angle, it gives a translation.

    How it works (3rd picture) is exactly the thing it does on a crossbow
    It is a moveable pulley with a load (limb) and one side fixed to an even beneficial moving point (other limb giving more string when drawn).

    The string center is the point that finally "lifts the load" (limb).

    Rizzar
    War Song
    War Song
    Fresh Blood

    Doesn't mean
    I'm new to crossbows


    Fresh Blood Doesn't meanI'm new to crossbows


    Posts : 31
    Join date : 2013-11-20

    Limb end pulleys Empty Re: Limb end pulleys

    Post by War Song Thu Nov 21, 2013 11:44 am

    So you would need at least two pulleys, but I seen a lot of builds on the forum with just one pulley (per limb)? Are those redundant then?
    avatar
    Rizzar
    Workshop Savvy

    Did you see my tool collection?


    Workshop SavvyDid you see my tool collection?


    Posts : 194
    Join date : 2012-08-11
    Location : Germany

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Rizzar Thu Nov 21, 2013 12:52 pm

    No, one pulley is needed for improved translation:
    Limb end pulleys File:Polea-simple-movil2
    http://en.wikipedia.org/wiki/File:Polea-simple-movil2.jpg


    And I think most of the compound crossbows here work the same way.

    Rizzar
    War Song
    War Song
    Fresh Blood

    Doesn't mean
    I'm new to crossbows


    Fresh Blood Doesn't meanI'm new to crossbows


    Posts : 31
    Join date : 2013-11-20

    Limb end pulleys Empty Re: Limb end pulleys

    Post by War Song Thu Nov 21, 2013 5:39 pm

    Ah I see, it would operate as a secondary lever, with one end of the rope tangent acting as the fulcrum and the load sitting between that and the force applied point.
    avatar
    Hermit
    Workshop Savvy

    Did you see my tool collection?


    Workshop SavvyDid you see my tool collection?


    Posts : 245
    Join date : 2013-09-10

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Hermit Thu Nov 21, 2013 8:31 pm

    Thanks Rizzar,I did'nt think of looking it up on wikipedia,but now that I have,I see where the translation comes from,before that,I could'nt for the life of me see the advantage.I don't know what your language is Rizzar,but I'm sure you do better in English than I would in your language.
                                               The oxford dictionary definition of "Pulley" is as follows:
    Grooved wheel fixed in block enabling weights to be lifted...............and.........Wheel or drum fixed on a shaft and turned by a belt for the application or transmission of power.Hope this helps.
                                                     Hermit.
    avatar
    Hermit
    Workshop Savvy

    Did you see my tool collection?


    Workshop SavvyDid you see my tool collection?


    Posts : 245
    Join date : 2013-09-10

    Limb end pulleys Empty Limb end pulleys

    Post by Hermit Thu Nov 21, 2013 8:37 pm

    You and I had the same problem Gnome,could'nt see the wood for the trees................
                                Hermit.
    avatar
    Rizzar
    Workshop Savvy

    Did you see my tool collection?


    Workshop SavvyDid you see my tool collection?


    Posts : 194
    Join date : 2012-08-11
    Location : Germany

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Rizzar Thu Nov 21, 2013 11:27 pm

    Thank you, german is my native language.

    Usually I do not have these problems concerning english.


    But when it comes to the situation of little words having various meanings turning the sentences whole context, it is getting difficult.


    Fortunately physics and maths theirself are kind of universal over all languages Smile
    avatar
    Rizzar
    Workshop Savvy

    Did you see my tool collection?


    Workshop SavvyDid you see my tool collection?


    Posts : 194
    Join date : 2012-08-11
    Location : Germany

    Limb end pulleys Empty Re: Limb end pulleys

    Post by Rizzar Wed Nov 27, 2013 9:39 am

    Since I was reminded on this topic by incidence, I have to point out that my statements rely on simple limb systems with clearly a single rotating pulley on It.

    The cam systems can/will operate in a different way.
    avatar
    Hermit
    Workshop Savvy

    Did you see my tool collection?


    Workshop SavvyDid you see my tool collection?


    Posts : 245
    Join date : 2013-09-10

    Limb end pulleys Empty Limb end pulleys

    Post by Hermit Wed Nov 27, 2013 5:51 pm

    I speak some german Rizzar,spent 4 yrs. there..........rhineland.
                         Hermit.

    Sponsored content


    Limb end pulleys Empty Re: Limb end pulleys

    Post by Sponsored content


      Current date/time is Thu Mar 28, 2024 4:43 pm