Judging Eagle

Hundreds of years ago, the Chinese developed, and manufactured on a cottage-industry level, a wooden device that could fire 12" crossbow bolts with moderate accuracy, had a pull weight in the 25-30 lb range, and had a fairly short range. This device was the repeating crossbow, or chu-ko-nu.

What the chu-ko-nu had in favour of it, was its rate of fire. A single chu-ko-nu was able to lay down a hail of fire, somewhere in the order of 10-12 shots per minute. Compared with the reload rates of regular bows and crossbows at about 1-3 per minute; it's obvious to see why such a low powered weapon was kept around, and used by peasant households to defend themselves.

Now, here's the fun bit, allowing us to use one for real, and for Nerf launching applications.

Myself, personally, this project has been all about finding a decently accurate (20-30' accuracy I'm fine with; I'd prefer 50'+ though), short range, high rate of fire weapon, that can be built out of the most basic of materials; like wood, and string, nails, and wire.

I'm personally going to modify the original chu-ko-nu plans, since the original machine is entirely too cumbersome and bulky.

Original design:


http://www.atarn.org...e/rept_xbow.htm

Footage of a Chu-ko-nu in action:

there's lots:

Demo:

Demo 2: http://www.youtube.com/watch?v=4DaD_HGBoWw&feature=related

Diagram & Process: http://www.chinahist...ko-nu-zhuge-nu/

A brief tutorial on construction: http://www.youtube.com/watch?v=Vf97Fn11_Lc&NR=1&feature=fvwp

A small bit on their function, design, and creation:

http://military.disc...peating-cr.html


Ok, so, now a person can understand what I'm sort of basing my ideas on. The magazine is really the most phenomenal part. The bow is... a bow, it's an ancient, and revered weapon; but it's not adding anything new here. The handle and stock is... just a complicated double hinged lever system. Again, nothing that even the Egyptians didn't invent thousands of years ago.

What I'm going to leave intact is the magazine. The bow arrangment doesn't really impress me (too low, the force on the bolt should be acting along the curve axis of the bow, not at an angle to the curve axis of the bow). Nor does the very clumsy looking stock and handle-lever arrangement. The firers in all of the videos do not have obvious control and direction over the weapon's postion, or how it aims. That's a recipe for inaccuracy. Even a handle under the stock would improve the control that the wielder has over the weapon.

I am shortening the stock, turning it into a handle that rests under the magazine; the "lever" that slides the magazine forward will also be removed, and replaced with a 'pull' handle that will come out of the back of the magazine.

Right now... the prototype is made out of scrap wood, index cards (to fill gaps between the top of the magazine, and the bottom; there was a gap wide enough for an index card folded 4 times to fit onto either side of the bottom 'rail' of the magazine.

The overall design is going to be a bow at the front; the magazine mounted to the back of said bow; a hole drilled into the bow to allow darts/bolts to pass through (I wanted to straighten the alignment of the bowstring and the path along which the bolts fly; a common design flaw in crossbows is that the bow is usually 'lower' than the quarrel groove).

With no handle, or stock the 'reloading' will be done by wrapping wire along the centre of the bowstring (bungee cord really), and 'pulling' it backwards (there's a channel at the back of the magazine to allow the wire and handle to attach to the bowstring.

Without a stock, the magazine won't have an automatic method to 'fire'; I plan on resolving this by making a very minimal stock for the magazine to rest upon, with a handle that uses a reverse clothespin trigger (I need to push -up-, not pull down, to fire the chu-ko-nu).

Right now, overall dimensions are as follows:

magazine: 23cm long 5.2 cm wide 7 cm tall, 8 cm tall at front stopp block

'bow': a length of maple with the grain almost perfectly aligned (the curves of the grain along the axis are all curved towards one side, and the centre of the grain is very close to one of the long, widest, sides of the wood; are pretty much what I'd use if making it into a bow). .... I might eventually upgrade to metal; like a ground down saw blade; but for now, it's a prototype, and going to be all wood construction.

I've got a BBB that I need to convert into looking like a "bow"; the main reason is one of cosmetics, the other is one of change in function.

The basic idea is that I want to use Zorn Lemma's BBB Overhaul idea.

Except that I want to make the bow more like the old Nerf Bow, in removing the handles; and building a handle on the plunger.

Things that I want to do to this BBB (some straight from from Zorn's Thread)

-I'm removing the back half, so I won't need reinforced parts in the back half; I filled mine with green stuff (a games workshop epoxy putty, it's green and blue... I actually don't know if it's safe compared to expoxy putty. D: Does anyone here know any better? The stuff becomes very hard, and is normally used to fill gaps in metal models; or help bond metal models)

-I'm going for the Method 2 Plunger Head; a series of metal and neoprene washers

-I want a more resilient plunger shaft; so I'm thinking of building the above Plunger Head on a length of threaded rod. (good idea? bad idea?)

-Build a handle to draw back the plunger

-Place a washer at the base of the plunger tube to reinforce the plunger tube

Hopefully, I'll be able to get some threaded rod that's a good length.


click for larger image

Is the bulk of the original interals that I'll probably keep. If I have my way; I'll replace the plunger tube with a threaded pipe, and a screw-on cap that is epoxied or glued to keep it in place. I'm not sure this is possible.

Of course, I'm thinking about replacing the spring; but I might keep it b/c of lower draw weight, and saftey concerns; a real "Bow" cannont have greater than a 20 lb pull when using modified normal arrows for what I'll be using it for. So getting a 100' range isn't necessarily good.

Accuracy is really what I want. Not retarded power/range.

I've got a feeling that I might "over" build some parts if I use a metal tube for the plunger tube, but whatever, the "bow" will last that much longer.

.... actually, now that I think about it, some of the black ABS piping could be used to make a plunger assembly, maybe replace the front piece with an ABS to PVC coupling, and see if I can get something that fits the inner diameter of the ammo type that I'm planning on using (Fome's "Arrows" made from grey pipe insulation specifically)

Anyway, the "remaining" parts that I want to have left will be pretty much this:


click for larger image

The plunger rod is just there because I didn't remove it. In hindsight, the reinforcing of the plunger rod is unnessecary, but w/e.

I'm planning on doing mostly cosmetic work after that. Hopefully it turns out well. I find that it's just a matter of planning and patience when it comes to building purely cosmetic things though, so I'm not too worried.

Edit: for some reason, I can't nest URL (link) and IMG (image) BBcode; Url BBcode around Img BBcode gives me text with a link, and Img around Url seems to do the same. Also, resizing images to make them smaller isn't implemented on these boards. D: Ah well, I'll just post the full images.