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    Of Bows and Torsion Engines

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    Post by OnlyHuman Mon Jun 12, 2017 8:22 am

    I didn't know where to post this, and this part of the forum seemed the most fitting. I apologise if you think this is unrelated to this particular board.

     After trying to understand how to maximize a crossbows effectiveness I've came to the conclusion that torsion engines are the way to go, assuming you can call whathever it is you made a crossbow after that. 

     A short search had me stumble onto two very impressive desings from very seperate timelines: 

     Talisman's Mantis and the manuballista.

     Seeing both are effectively reliant on torsion engines I've got convinced that I was on the right path. However I questioned the use of the static limbs used on the tradional and handheld ballistas and apperantly on Mantis. My reasoning is that if you can store enough energy in the engine itself it will be very hard to turn due to the stress. Becoming some sort of an anchor -a riser, if you will-  that stores useable energy and allowing the bow limbs to bend and store even more energy. 

     The obvious problem could be the torsion engine breaking apart due to extreme stress. However I think that can be managed with the modern materials. What truly worries me is that the possibility of the forces cancelling eachother out if the force vectors are not aligned, effectively making the mechanism useless and ineffective.

     I realize that this isn't anything traditional, but as I've said: I didn't know where to posts this. Do you think it is possible? Have you seen anything like I've described? Am I overthinking it and it would simply not work due to logical reasons?

     TL;DR: Can you combine torsion engines with bow limbs to shoot faster projectiles?
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    Post by kenh Tue Jun 13, 2017 5:05 am

    The Mantis is not IMHO a torsion engine --- there is no cordage being put under tension (the basic definition of a torsion engine).  It is a crossbow implementation of the common modern compound bow technology, which allows shorter, more rigid limbs and gives relatively high draw weights without as heavy of  full draw/cocked holding tension.  The Mantis has weight minimizing open strut limbs which bend to store energy, not cordage under tension.  There is a separate section here for compound crossbows.

    A Manuballista is the hand-held version of the late-Roman torsion engine called the ballista.  It had short, non-bending arms, and depends solely on the energy stored in twisted cordage for its power.   There is a separate section here for torsion engine crossbows

    I don't believe that, even with modern technology and materials, you would gain any significant amount of energy storage (say 10% or more)  by trying to combine bending limbs and torsion power.
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    Post by OnlyHuman Tue Jun 13, 2017 5:15 am

    I've noticed that Mantis' limbs do not bend. I reckon that it employs thick, tightly coiled springs as torsion engines. That is why I called it that.

     As for your answer, I thought that might be the case. However, I still wonder how insignificant is insignificant? Perhaps it is enough to give it an edge? 

     I guess I'll try and see. Though I am guessing that will take time.

     Thank you for your answer.
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    Post by jocky Tue Jun 13, 2017 2:46 pm

    The Talisman crossbows seem to use compressed gas as a spring (they don't give a lot of detail about it) : http://www.talismancrossbows.net/promise.html

    The limbs are apparently completely rigid.
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    Post by Anatine Duo Tue Jun 13, 2017 5:55 pm

    I agree the Talisman appears to have rigid limbs.  I guess in a loose interpretation of "torsion" one could say that because the limbs rotate around pivot points and the force applied by them is torque then it is a torsion engine, BUT the gas spring providing the force is very linear so that part is definitely not a torsion engine.

    Can a torsion-style launcher benefit from working limbs as the arms?  Maybe... but let me ask another question... can a conventional bow benefit from a stretchy string which might help store energy?  The answer to the latter seems to be "no" which is why strings and cables get made of materials with higher modulus of elasticity (less stretch) ... but I can't really explain why this is so.  Maybe the mass of a working string robs energy from the projectile?  Would the mass of a working-limb-style arm on a scorpio be more than a deep, rigid beam style?  I think so... see 2 by 8 rule of beam theory.

    ...but I'd love to see it work.  Seems like it might require another level of tiller, fun
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    Post by Geezer Tue Jun 13, 2017 8:14 pm

    I am under the impression that a stretchy string reduces the amount of bend you get from the prod... and in most cases, one gets less power from a stretch string than from an equivalent movement of the prod.  This may not be the case in all instances. Given the substantial power and efficiency the slingshot guy gets out of latex bands, there may be cases where a stretchy string and immoble prod is the best way to go.  Geezer
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    Post by 8fingers Tue Jun 13, 2017 11:15 pm

    In 'The Traditional Bowyers Bible' they cover the effects of different tillering, and having a flexible arm in a manuballista is like whip tillering a bow, reduces power, and can lead to premature failure of the limb, would require both to be tillered, and would add another variable in tuning an already complicated mechanism. Stretchy string can also rob power as you loose energy in internal string friction and more bizarre phenomena.
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    Post by OnlyHuman Thu Jun 15, 2017 2:22 am

    Thank you all for your answers. Quite a lot to take into consideration. Especially the strechy string point. 

    I'll continue drawing on possible ideas. In the hopes that I can get a reliable plan.
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    Post by c sitas Fri Jun 16, 2017 2:55 pm

    If you take the time to check , the talisman is not considered a "Crossbow". It shoots an arrow or bolt, but is not accepted as a bow by any organization that I'm currantly aware of.It's fast ,it's very accurate. There is a lot to be said for it but, being a bow is not one of them.
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    Post by JacobL Mon Jul 31, 2017 9:40 pm

    If you google ''Gearhead T15 Pro'' you can see that the company has made a rubber powered bow that can shoot at 200 FPS. They use some simple short bow limbs to add velocity to the rubber, and pulleys to keep it functional. This setup is similar to a tapered bow limb. When you pull the end of the limb far enough, the lower part bends with it. When the top retracts, it goes first and then the lower end comes after. It is not too efficient but it reaches high velocities. Be sure to check out Joergprave's ballista slingshot as well
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    Post by c sitas Tue Aug 01, 2017 8:09 am

    Jacobie; I checked out the Gearhead. In my mind I don't see it passing for a bow. You would have to talk the a national archery ass. to get an opinion.We'd only be talking for hunting and competition.
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    Post by JacobL Tue Aug 01, 2017 6:49 pm

    Agreeable. It's more of an assisted slingbow. Actually who do yout ask about things when it comes to defining a bow? Legally, I mean
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    Post by c sitas Wed Aug 02, 2017 9:04 am

    Well in the US. it would go state by state. Pocession is one thing , using it is another matter. For the most part, if the bow gets it's power from "a bent stick" you'd be legal in all states. Some states have laws more on arrows and weigths than anything else.I would say, to be safe , I would check local laws as to where I'm going. Years ago ,I used to go up to Ontario Canada bear hunting with the bow . Done that for 17 years.The dog hunters screwed the bowhunters up where I live ,so I went north to hunt.Both places have their "tree huggers"and they always make for interesting times.
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    Post by JacobL Wed Aug 02, 2017 10:58 am

    I see. I'll be sure to keep watch of the legal stuff, then. And yes I cn agree with that. The most stupid part is how pistol crossbows are banned but large crossbows aren't. Pistol crossbows are for small game, not very powerful, I doubt they'd seriously damage someone. Meanwhile something like a scorpyd ventilator is fully legal. Very dumb.
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    Post by Phil Abrahams Wed Aug 02, 2017 4:49 pm

    Hello all,i have some new pic's of the updated Mantis Crossforce torsion bow and will get more done plus a vid or two.I have been very ill for the last 6 month's but now back to feeling normal.I call it a torsion bow as the limb's pivot to compress the nitrogen gas spring power plant and work's more or less exactly like the Roman siege engine's but with a high tech spin on it,lol.Of Bows and Torsion Engines 2_313
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    Last edited by Phil Abrahams on Wed Aug 02, 2017 5:05 pm; edited 2 times in total (Reason for editing : Picture's)
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    Post by JacobL Wed Aug 02, 2017 9:15 pm

    Thanks for the reply Phil! In Canada, is the Mantis still considered a crossbow by Canadian Law? Also, what is the lightest projectile it can shoot and at what speed and what draw weight? VERY interested in the Mantis! And good to hear you've gotten out of the sick spot, I know how much those can impede progress. -Jacob
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    Post by Phil Abrahams Thu Aug 03, 2017 10:26 am

    Many thank's Jacob,on projectile's you can go as low as 250 grn's and get 500+ fps on the Mantis and over 550 on the Mantis Elite and also shoot arrow's to over 1,000 grn's at 300+ fps,i would think it would be legal in Canada as long as it's under 500 fps as it is still archery equipment with the bowstring propelling the projectile.Draw weight's are fully adjustable from 200lbs to 350lbs on the Mantis and from 250lbs to 400lbs on the Mantis Elite,i am so very thankful to be back from the living dead,lol and right now these crossforce torsion bow's are available and also in full custom option's.Will be bringing out the optional crossbow bullet bolt rail later as soon as i have ensured that it's completely safe and with this you can shoot very cost effective expendable projectiles,please do not hesitate to ask me anthing else regarding this piece of sporting archery equipment as i am alway's here,Phil Cool. Of Bows and Torsion Engines Crossf10


    Last edited by Phil Abrahams on Thu Aug 03, 2017 10:36 am; edited 3 times in total (Reason for editing : adding pictures)
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    Post by JacobL Thu Aug 03, 2017 12:01 pm

    Thanks Phil! Should I ever invest in a good quality crossbow, I'll hit you up with a deal. What kind of bullet ammo would you be looking at shooting with the Mantis? Marbles would be the cheapest pick, which I would be happy to use. Problem though is that they only weigh about 84 grains. Steel balls in the 11 mm calibre would be a good choice. What kind of speed would you expect to see from the ball ammo? Also how would you go about keeping it in place when the device is cocked?
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    Post by c sitas Thu Aug 03, 2017 3:58 pm

    Jacobie, A German company makes a little sled that works on all setups.
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    Post by Phil Abrahams Thu Aug 03, 2017 5:33 pm

    Hi Jacob if you want a Mantis crossforce compound then i will give you the very best deal i can on one.I do not shoot ball's from the crossforce bow i shoot bullet bolt's with an offset rifled fluting to make them spin and can go down to 100 grn's or up to over 600 grn's,they are around 9" long and are shot safely by using a specially developed over rail (bullet rail) with a sliding breach to load them and push them back against the cocked bowstring just like loading a bolt rifle and they are magnificent to shoot.I used to ricochette them off quarry rock face's at dusk with huge hail's of spark's and shoot wine bottles shattering them,lol,Ill get some pic's of them onto here in the next couple of day's Cool .
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    Post by JacobL Fri Aug 04, 2017 11:27 am

    Oh wow! That sounds very cool. A rifled bullet is much better than a round ball. I would love to see one in action. How is the spin achieved, actually? It would be interesting to make a small sled which shoots a spray of lead shot like that on  the Zubin X340, I'd love to see that, especially at 500 FPS, would be like a high power pellet shotgun Laughing

    And C Sitas, I believe that is the Kostka Lightning. I've googled LOTS about it, but always came up dry. Never could find much info. I wonder how tough it is on the bow limbsa
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    Post by c sitas Fri Aug 04, 2017 11:42 am

    i don't think it's tough on limbs at all cause they short draw the bow .You can purchase the last time I looked. At that time I think it was like 9.95 and postage. That's been a while back though.
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    Post by Phil Abrahams Fri Aug 04, 2017 11:48 am

    Hi Jacob the bullet bolt achieve's the spin with rifled flute's very similar to a reamer bit.And yes we do shot gun type round's with this system too using carbon tubing blanked off at one end then filled with arounf 5-20 6mm steel ball bearing's or  or lead shot or music wire length's that helicopter to the target a wad hold's them in place and there is a choke on the rail that make's the projectile's come flying out at very high speed allowing shooting moving target's it is wicked at over 550 fps,will show all this very soon,i'll upload pic's of the rifled round's and bullet rail tomorrow. Cool
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    Post by Phil Abrahams Fri Aug 04, 2017 11:57 am

    Yes this system can fully withstand shooting very light projectile's it has numerous advantage's over conventional flexing bowlimbs and is very quiet when shot even with very light 100 grn bullet bolt's or scatter round's and above all no splintering or failing limb's and this was the main reason for this system to overcome the problem's associated with flexing limb's.
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    Post by JacobL Fri Aug 04, 2017 9:02 pm

    I'm very interested now. I just gotta start saving up cash Laughing, spend so much of it on projects and such. Since it can reach above 500 FPS, I assume it would fall under the legal classification of a firearm, so I'd need to look into a PAL, right? Also, you mentioned scattershot rounds. Do you have a video of this? Very interested in that!

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