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  need help archery related
« on: November 28, 2008, 21:31:10 PM » by LCD
I had seen a device that works like a cross bow but it doesn't use limbs. Instead it has two tubes / pipes that run parallel to the main riser. When the trigger is pulled there wouldn't be any movement of the outside geometry of the "weapon". I highly suspect that it uses coil springs housed inside the parallel pipes to propel the dart / arrow / shaft down the main riser. .

I had seen this on old 80's magazines from Britton like Guns Revue (if I remember correctly). Now I canít find anything like that any where. If you know what I'm talking about and have any information please let me know. Or fire of an email to me lawrencedebono@rogers.com.

Thanks.
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  Re: need help archery related
« Reply #1 on: November 29, 2008, 23:52:04 PM » by Vincent
Hmmm, interesting.
I too remember seeing something of that ilk on the front of a US Cavalry catalog; I am not sure but that particular weapon might have been powered by co2 cylinders. I have had an interest in elastic potential energy stuff for years.
About a year ago I had started a long never-ending discussion on Archery Exchange Forum about variations of compound bows etc.
The long and short of it is that coil springs are a bad idea for a projectile because of the inherent inertia due to mass.
If effect you might have a mother-of-all-springs driving a bolt, but you will end up with a massive hernia to cock the piece, but the bolt will have a dismal velocity.
This is why in archery, bow poundage is NOt everything; You will need to store all that potential energy in a machine that releases that energy Quickly !

Coil springs are too slow, leaf springs are faster. The problem with the arrangement you describe is that you cannot use leaf springs without the added bulk (crossbow).
You might however use a gas (nitrogen) spring (as found in hatchback doors).
The other way is to use co2 or a pneumatic push but then of course you will loose all the gas every shot, thereby making the system very inefficient.

Sorry if I cannot recall the precise details of the piece you mention, but maybe these very same limitations caused it to die off.
Stil,l I suppose that academically speaking, I find my interest stirred once more--- Thanks!

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  Re: need help archery related
« Reply #2 on: November 30, 2008, 19:36:00 PM » by LCD
Hi Vince, another appearance of the same weapon was on the movie,"who dares wins". The shooter used it to shoot a victim during a piece demonstration.
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  Re: need help archery related
« Reply #3 on: November 30, 2008, 19:48:09 PM » by Vincent
Never saw that film, but I have heard rumors of crossbow and similar items seriously considered for limited official use.
I am almost sure that the one in the US magazines of yesteryear was powered by CO2 "sparklet" cylinders.
The picture on the magazine I can remember had a diver with item in hand, coming out of the water.

Since that time special ops of different countries have developed some pretty odd hardware for similar intended uses. Most seem to be powered by special powder driven cartridges like ancient shoulder harpoon guns of 70 odd years ago.

While discussing this issue on the mentioned archery forum, it transpired that one of the guys I was chatting with was the patent holder for a single nitrogen cylinder compound bow.
It was funny really; At one point he actually wanted to know if I was "stealing" his patent ! Naturally i was just throwing ideas about and we had a good laugh.

Vincent
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  Re: need help archery related
« Reply #4 on: December 01, 2008, 12:40:17 PM » by RB
Interesting discussion Vince and LCD. Suppose a bow is more effective than using coil springs, apart from the mass issue, because of the "gearing" effect - for a small movement of the bow itself, the relatively very lightweight string, in its middle part, moves a far greater distance. Thus although the bow arms themselves may have a low velocity since they have measurable mass, the velocity is amplified where it matters.

I suspect that this is the reason for compound bows - where the "gearing" is even higher, and also as a side effect the draw may be at a more consistent pull weight throughout - i.e. close to full power all the way.

RB

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The Bright Side: "Sir! We're surrounded!" - "Excellent! We can shoot in any direction!"

  Re: need help archery related
« Reply #5 on: December 01, 2008, 13:22:52 PM » by LCD
Less geometry changes is good when one needs to shoot from trees. I had a bad experience with my old Barnett many years ago. The cross bow limb hit the tree when it shot forward and I was pushed back wards, almost off the tree stand. That's why I want some thing narrow with less external movement. I don't mind pneumatic either.

I saw an interesting Horton model with reverse limbs and cams. The limbs barely move. That wasn't bad and I like the tango down grip on it too. The cocking rail that they sell with the bow kept the sting straight. But  the whole set up weighs a ton. I don't know I would really like to find that old contraption that I originally commented on.
This is it  --




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  Re: need help archery related
« Reply #6 on: December 01, 2008, 13:28:41 PM » by RB
Now that's different! I thought my eyes were playing tricks on me...

What sort of accuracy are these devices capable of? I.e. a decent crossbow and it's bolts?

Seems you had a interesting "equal and opposite reaction" with your Barnett!!  Grin  Grin

RB
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The Bright Side: "Sir! We're surrounded!" - "Excellent! We can shoot in any direction!"

  Re: need help archery related
« Reply #7 on: December 01, 2008, 22:15:41 PM » by Vincent
Hi Rb,
interesting observations. "gearing" comes into play but up to a point: If you gear up too much, you will have to contend with the inertia of the arrow, string and limbs themselves.
Fact is that a bow is a deceptively simple to look at but a devil to optimise and hell to quantify scientifically.

Many parameters that come into play at various stages of release and some are conflicting; The equations become a newtonian labyrinth.

Actually with compound bows the arrangement is for a different purpose: It allows the archer to hold at full draw with what is known as "letoff"; And is is a percentage of the peak draw weight. Normally 60 to 80%.
It allows a steadier hold at full draw.

LCD, if you are looking for as limbless a design as possible, I guess you could start with a pair of nitrogen cylinders, sans the heavy push rod- Dont ask me how you are going to transmit the movement to the arrow shaft however.
Very efficient nitrogen springs are used as clamps in sheetmetal, deep drawing and stamping machines.
Some will clamp hundreds of kilos through a small distance.
If you can devise a way to couple say.....500 kilos x 10 mm spring travel, to a small bolt 10 cm in length weighing 50 grams, you will have the mother of all bows.
The moving parts of such a spring will have relatively little mass; It should be extremely fast.

There you go, get your calculus books out, start drawing and file for a patent.

Vuincent

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  Re: need help archery related
« Reply #8 on: December 01, 2008, 23:42:20 PM » by LCD
Yes the new Recon by Horton is a new design indeed. It's about as fast as my Except 200 by Excalibur, but twice the weight. The Horton is ergonomic and it comes with a sort of Magpull retractable stock and tango down grip and all the fancy AR attachments. It's attractive and yes it is weird at first glance but the limbs hardly move. Accuracy - HOLY Toledo - IT"S ACURATE out to 40 meters and barely any drop with the recommended bolts.

Me and the boys were checking the toys before Christmas for ourselves at the local gun store and this thing was among the other bows.  We asked them to try it at their archery range. Price tag (are you sitting down?) $1380Cnd + 15% tax. I can by a Garand for that.  Undecided

I'm going to replay that movie where I saw that darn bow / weapon/ arrow gun and try to print some pictures off it and post them. I agree with you 100% about the gas and piston principal. It might be a B....h to cock but one those pistons are released I'm certain that they can accelerate to a point that they will propel a carbon shaft out to 40 or 50 meter at a good speed. I can see that with my SUV bonnet / hood shock absorbers. 


 
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  Re: need help archery related
« Reply #9 on: December 02, 2008, 10:24:03 AM » by RB
I think that if you take away the "bow" from a cross"bow" then ultimately it's time to start looking at something else altogether  Wink

Sometimes wishing some item to be modified in this way or that, one comes to a realisation that there is a far better tool for the job... friend of mine wanted to design a "sea bicycle" - told him it's already invented, called "canoe"  Grin  Grin  Grin

So personally I think that speaking of gas powering, etc - you may be looking at a "sea bicycle"  Grin

RB
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The Bright Side: "Sir! We're surrounded!" - "Excellent! We can shoot in any direction!"

  Re: need help archery related
« Reply #10 on: December 02, 2008, 10:58:01 AM » by karbine
I think that if you take away the "bow" from a cross"bow" then ultimately it's time to start looking at something else altogether  Wink

Got Ruger?


Cheesy
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  Re: need help archery related
« Reply #11 on: December 02, 2008, 11:00:20 AM » by RB

Precisely!! Sort of!!

(where's the 30-06  Wink)

RB
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The Bright Side: "Sir! We're surrounded!" - "Excellent! We can shoot in any direction!"

  Re: need help archery related
« Reply #12 on: December 03, 2008, 12:23:11 PM » by LCD
Precisely!! Sort of!!

(where's the 30-06  Wink)

RB

I changed my mind about the garand, spent a bit more and ordered a Swiss Arms - our version of Sig rifle. I'll post the picures when it comes in. hopefuly tomorow Just in time to put it under the tree unless my wife will put me under a tree with a head stone on top of me.  Wink


Regarding that weapon (I'm still dreaming) here is a critical picture showing the bolt, string
and the triger group.


The front clearly shows two pullies guiding the string into the side tubes.
 

This is what I meant by side tubes -


If any one has any info please let me know.
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  Re: need help archery related
« Reply #13 on: December 03, 2008, 21:58:28 PM » by Vincent
Ok LCD. Now your talking. Not excellent pics, but they give us some clue or 2.

Number one is that its very unlikely to be a co2 fill up.

The Second is much more important and it vindicates what we have been saying about limb inertia etc:
Look closely at the second picture, You will notice that the pulleys occupy most of the width; Now look at the third picture; The string should occupy only a small fraction of the total width of the "bow". Hence the ends of the string is going to either the front end of the cylinder, if a tension "spring" is used Or to the rear of each cylinder if a compression "spring" is being used.

Either way there is NO all important heavy metal piston rod;
Furthermore, if a nitrogen cylinder is being used, There is no spring weight.......just the string.

Hey we should sign up for technical intelligence photograph analysts !
Vincent
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  Re: need help archery related
« Reply #14 on: December 04, 2008, 01:09:22 AM » by LCD
Now if we can get some one who actually saw them in GB and can give us a maufacturer we will be on the right track.

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 (Read 5665 times) [1] 2
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