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    improving the chu ko nu and medeival crossbow

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    aldorath
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    improving the chu ko nu and medeival crossbow

    Post by aldorath on Thu Apr 17, 2014 10:03 pm

    I have become quite fascinated with crossbow designs from the middle ages and the repeating design from china.
    The chu ko no has a fast ROF but a poor damage and range. Is it possible to have the bow and lever be made of metal? This would decrease the ROF but increase the power and distance.
    For the standard medeival crossbo of 250-300lbs, is it possible to include a spanning lever in the crossbow itself? similar to the one found on the chu ko no or from the game skyrim.
    Lastly, and probably least practical, would a stirrup/hand spanned bow be able to include a bolt magazine? Basicaly after spanning the magazine would be pushed forward to drop bolt in the groove?
    I am not an engineer or boyer so I wanted to posit these ideas to people experiened with cross bows and see if any of these designs would be feasible
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    kenh
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    Re: improving the chu ko nu and medeival crossbow

    Post by kenh on Fri Apr 18, 2014 6:11 am

    First of all, forget skrim or other fantasy designs -- they are FANTASY, not physics and mechanics in the real world.

    The limiting factor in the power/rate of fire of the Chu ko nu is not the material the bow is made from, but the human strength it takes to operate the cocking lever.

    There are a number of true medieval designs which incorporate some sort of cocking mechanism, but not very similar to the Chu ko nu lever -- gafa, whippe, or cranequin. 

    The closest to what you're thinking of is probably the Scottish Borderer's Latchet:
    http://www.todsstuff.co.uk/crossbows/latchet-crossbows.htm

    Here's another discussion of Latchet locks:
    http://thearbalistguild.forumotion.com/t207-latchet-mechanism?highlight=latch

    I'd love any sort of latchet lock myself to build a bow around, but I'm not a machinist or particularly mechanically inclined.  Anybody got a milling machine??


    Last edited by kenh on Fri Apr 18, 2014 6:24 am; edited 3 times in total (Reason for editing : link added)

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    Re: improving the chu ko nu and medeival crossbow

    Post by aldorath on Fri Apr 18, 2014 7:24 am

    telling me to dismiss fantasy designs does not explain WHY they would not work. 
    the skyrim crossbow is the only fantasy design I mentioned since it was an example that has an integrated lever, i now regret even mentioning it in the post since I expected it would get a reaction such as that .

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    Re: improving the chu ko nu and medeival crossbow

    Post by phuphuphnik on Fri Apr 18, 2014 2:25 pm

    Eh you never know unless you ask. Ken's link to the Scottish bow is pretty close to what you use in Skyrim. It would be fun to try to copy it within the limits of real world physics.
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    Re: improving the chu ko nu and medeival crossbow

    Post by kenh on Fri Apr 18, 2014 2:49 pm

    Sorry to be so short with you.  Here and in other archery forums we get a lot of people wanting to build fantasy inspired weapons.  Most fantasy weapons look impressive but the artists and designers who create them don't give any thought to the mechanics of how something is supposed to work and what happens when things move together.  They are not longbow or horsebow or crossbow shooters, or axe wielders or two-handed broadsword fighters or rapier duellists in the real world, and have unrealistic expectations of weapons usage.  I say this as someone who has been involved with real, live edge medieval combat, archery and other skills for nearly 50 years. 

    Looking at the Skyrim "lever action" crossbow illustrations in the Elder Scrolls Wiki:

    The compound prod string with cams, as far as I can tell, gives no advantage in power; which is what a compound setup is supposed to do.  The power stroke is too short for it to be mechanically useful.  Compound crossbows do work, but not with that short of powerstroke.

    The cocking lever system on the skyrim bow has very little, if any, mechanical advantage - the lever arm is so short it would probably be harder to pull back in one stroke with a 25# draw prod than a Cho ku nu.  Even if there are internal gears and ratchets (which does not appear to be the case), such a mechanism would slow down the cocking procedure, making you use a series of short sharp ratcheted pulls to cock the thing rather than the one long pull of a Cho ku nu.  Too much time cocking a crossbow has been the bane (and death) of crossbowmen throughout history.

    The illustration shows the linkage arms having the bowstring threaded through them, which means the linkage and the lever arm both fly forward when the trigger releases the string, and nearly all the released energy goes into moving that mechanism rather than the arrow; thus flight characteristics are even worse than a Cho ku nu.

    Crossbows have a higher draw weight, but that doesn't mean they shoot harder.  We generally compare a given draw weight of crossbow to a (nominally) long bow drawing 1/3 to 1/4 of that weight -- that is a 300# crossbow is functionally similar to a 75# to 100# long bow.
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    Re: improving the chu ko nu and medeival crossbow

    Post by Todd the archer on Fri Apr 18, 2014 6:14 pm

    You should check out the now defunct Twinbow. Uses a built in lever to cock it and features I believe a short 8" power stroke.

    http://www.youtube.com/watch?v=XTHazFZil1A

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    Re: improving the chu ko nu and medeival crossbow

    Post by hullutiedemies on Sat Apr 19, 2014 8:13 am

    A German colleague has built 200# chuko.
    See:
    http://www.fletchers-corner.de/viewtopic.php?f=34&t=24769&sid=5011e86b2dcfc46cb0db4bd1c5822517

    And he seems to be updating to 220 lbs.

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    Re: improving the chu ko nu and medeival crossbow

    Post by aldorath on Sat Apr 19, 2014 10:57 am

    wow that crossbow looks pretty damn cool, i'd love to see how it fires when he completes it. 
    I think its cool to look at older weapon designs and see how they can tinkered with, finding out if something can improved an if no then why. sometimes something cool can result.
    Though from what I've gathered speculating on this forum would have me put in front of a firing squad.

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    Re: improving the chu ko nu and medeival crossbow

    Post by Hermit on Tue Apr 22, 2014 12:15 pm

    First point,'modern fantasy weapons' are not 'old'.Point number two,speculation does'nt merit a firing squad,although exaggeration and petulance might.
                                                                      Hermit.

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    Re: improving the chu ko nu and medeival crossbow

    Post by aldorath on Tue Apr 22, 2014 12:49 pm

    by "modern fantasy weapons" what do you refer to?
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    Re: improving the chu ko nu and medeival crossbow

    Post by Gnome on Tue Apr 22, 2014 6:24 pm

    Aldorath,
    welcome to the forum. It's interesting to me how crossbows and other weapons are presented in video games, fiction, and movies. A lot of times it seems like the fantasy writers and game designers want to give their characters an assault rifle, but since that doesn't fit in with the setting they make a crossbow that is magazine fed and automatic. While such features may be possible to impelement, in practice the more complicated the weapon becomes the less effective it is. Kinda like the same reason we don't have flying cars. While you can make a vehicle that drives down the road and flies through the air, it wouldn't be as good at either of those activities as a single purpose machine.

    I think the reason writers and artists want to present crossbows this way is, well, crossbows are admittedly cool, but drawing them and loading them isn't. I played a lot of Mount and Blade Warband, which is the closest thing to a medieval combat simulator that I've come across, and let me tell you, bending over and fiddling with you your weapon for even 5 seconds while enemies are charging and shooting at you is definitely not cool! Even in a "realistic" show like Walking Dead, I noticed that they don't show the dude actually spanning and loading his crossbow hardly at all, he just seems to always have it cocked and loaded and ready to go.

    So, are such features as auto loading and a clever built in spanning device possible, in weapon powerful enough not to rely on poison darts and completely unarmored opponents? Probably, with enough ingenuity and effort. Would it be worth it? Perhaps as a work of art or a monument of engineering, but hardly practical. I mean, you saw how cool that twinbow is, and I don't think that company is still in business. Cool at it is, it can't compete with simpler, less expensive, more powerful crossbows, not to mention firearms.

    That being said, one "fantasy weapon" I have been toying with for a while, and probably will build a version off inside a year or so, is the "double-barreled" crossbow from the movie "Ladyhawke." Not a fanboy replica, but a functional weapon based on that concept. I know it will be heavy, and complicated, but at least you can shoot it twice before reloading!

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    Re: improving the chu ko nu and medeival crossbow

    Post by jeep on Wed Apr 23, 2014 1:10 am

    Hello Gnome
    Here is my double barrel version. Well I should say that is "twice" more complicate then a normal crossbow.... But "twice" more fun. The first version was a bit like a "fashion design model" I liked it but the hand shooting position was quite odd wile working well. (Trigger are two classic Chines trigger work well) Other it was not very discrete, in the sun it was very hot and the hand were sweating. The wood version was very functional and powerful (two 150# bow). It was a great fun to shoot mobile or flighting target. But at last a lot of work was to be done : difficult with convergence, design of the upper trigger where the mane . A day or other I'll come back to this model. I would be happy to see somebody else attempt. 

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    Re: improving the chu ko nu and medeival crossbow

    Post by jeep on Wed Apr 23, 2014 1:12 am

    Home made coking rope

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    Re: improving the chu ko nu and medeival crossbow

    Post by jeep on Wed Apr 23, 2014 1:14 am

    Shooting

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    Re: improving the chu ko nu and medeival crossbow

    Post by jeep on Wed Apr 23, 2014 1:17 am

    Woody !!

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    Re: improving the chu ko nu and medeival crossbow

    Post by jeep on Wed Apr 23, 2014 1:19 am

    Shooting.
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    Re: improving the chu ko nu and medeival crossbow

    Post by Gnome on Wed Apr 23, 2014 6:19 am

    Ha! I should have figured that if anyone on the forum had already taken a stab or two at a double crossbow, it would be Jeep! They both look awesome. I think mine will be more medieval looking, though. Probably use the same fiberglass prods due to their light weight, but cover them in leather. How many crossbows have you built, anyway?
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    Re: improving the chu ko nu and medeival crossbow

    Post by jeep on Thu Apr 24, 2014 2:33 pm

    I don't really know, something like 16 or 17 . Some of them have been destroyed since or recycled for new one.
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    Re: improving the chu ko nu and medeival crossbow

    Post by hullutiedemies on Mon Apr 28, 2014 10:28 am

    aldorath wrote:wow that crossbow looks pretty damn cool, i'd love to see how it fires when he completes it. 

    There
    http://www.youtube.com/watch?v=vJE55HaQ4ec&feature=youtu.be
    He claims it is 235 lbs with the new bamboo prod.
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    Re: improving the chu ko nu and medeival crossbow

    Post by actionbow on Tue Apr 29, 2014 2:48 pm

    One of the biggest hurdles to a high power chu ko nu is the string friction on the tiller as you cock. It will basically saw your string in half as well as pull your limb tips up at an angle that will weaken most bows. I have overcome this by adding a an articulation to the lever so that the shuttle/magazine assembly slides horizontally with no see saw action. Search my modernized mini chu ko nu post here for an example. It requires a few subtle modifications which I will be happy to explain further if needed.

    I think with a longer lever you could easily make one that shoots in the 150# range without too low of a ROF.

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    Re: improving the chu ko nu and medeival crossbow

    Post by HeroSK on Wed Apr 30, 2014 12:00 pm

    @actionbow, if that is the case with magazine, I am curious about trigger system of your improved cho-ko-nu since downward movement of magazine helps string get out of gash over magazine. There could be some problems about release if magazine slides horizontally. Could you please give more detail about your design?

    Thanks in advance.
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    Re: improving the chu ko nu and medeival crossbow

    Post by hullutiedemies on Wed Apr 30, 2014 12:38 pm

    How low is too low of a ROF ?
    That German dude above got 8 shots in first 15 seconds.

    of course lighter ones shoot faster
    I can empty 7 bolt magazine of this finger operated miniature chuko

    in 2 seconds. But there is a trade off in "stopping power" Wink

    Btw - the classic of modern lever actions has not yet been mentioned
    http://www.youtube.com/watch?v=2-DzbMQytsg
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    Re: improving the chu ko nu and medeival crossbow

    Post by actionbow on Wed Apr 30, 2014 1:38 pm

    I use spring steel under a pin in the lock that slides into a fixed pin on the body. It slides under the spring steel and pushes the second pin upward. I can make a drawing to show the concept. It's not hard to make and works flawlessly after thousands of shots.

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