# Equivalence between steel tension springs and latex tubes



## AndrewF (11 mo ago)

I'm wondering if is there someone that has a way to calculate the spring size needed to replace latex tubes using tension springs that can produce equivalent elastic force. 
This would be very useful to design a slingshot that can rely on more reliable and less prone to fault and worn out tension system based on springs rather than rubber.


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## Valery (Jan 2, 2020)

Unfortunately, replacing rubber with springs is a dead-end development for the slingshot, take my word for it. Just as useless are various blocks, pulleys, and the like. A qualitative leap will happen when there is a new polymer, stronger and faster than latex.


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## MraK111 (Nov 19, 2021)

Один мастер делает блочные луки и арбалеты на основе газовой пружины, если вы действительно крутите, то я думаю, что вы можете сделать что-то похожее на рогатку на основе газовой вакуумной пружины =)


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## Crac (Mar 3, 2013)

Well you could try, some machine design calculations:


Load = PI() * Wire_diameter^3 * Safe_stress / ( 16 * Radius_of_coil * Geometry_factor )

Geometry_ratio = 2 * Radius_of_coil / Wire_diameter

Resilience = Safe_stress^2 * Volume_of_spring / ( 4 * Modulus_of_rigidity * Geometry_factor^2 )

Deflection = ( 4 * PI() * Number_of_coils * Radius_of_coil^2 * Safe-stress ) / ( Wire_diameter * Modulus_of_rigidity * Geometry_factor)

Geometry_factor = ( 4 * Geometry_ratio – 1 ) / ( 4 * Geometry_ratio – 4 ) + ( 0.615e-3 / Geometry_ratio )



Cool beans!!! Now _you_ have a way!



If you where going to get some springs made… You find someone really good at making them, tell them what you’re looking for and pay them a lot of money.

Swapping our rubber for steel would be a terrible idea. Our rubber retracts much much faster.


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## AndrewF (11 mo ago)

Valery said:


> Unfortunately, replacing rubber with springs is a dead-end development for the slingshot, take my word for it. Just as useless are various blocks, pulleys, and the like. A qualitative leap will happen when there is a new polymer, stronger and faster than latex.


Why? Could you explain the reason?


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## AndrewF (11 mo ago)

Crac said:


> Well you could try, some machine design calculations:
> 
> 
> Load = PI() * Wire_diameter^3 * Safe_stress / ( 16 * Radius_of_coil * Geometry_factor )
> ...


thanks for the hint, but the retraction speed should depend on the kind of spring e.g. harder carbon steel springs are way faster than inox steel springs, are you sure that they are slower than rubber? I'm interested to deepen this topic.


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## Hoss (Jun 3, 2014)

Can't even imagine using springs on a slingshot. 

Sent from my MAX_10 using Tapatalk


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## S.S. sLinGeR (Oct 17, 2013)

It’s a gimmick. Use latex. It’s all you need. I hit my targets all day with plain old cheep latex. Keep shooting no matter springs or rubber 😀


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## AndrewF (11 mo ago)

Hoss said:


> Can't even imagine using springs on a slingshot.
> 
> Sent from my MAX_10 using Tapatalk


probably because you consider the simple "classic design", not those more complex with a magazine and a leverage system to reduce the force needed for loading with powerful tension


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## High Desert Flipper (Aug 29, 2020)

Just thinking out loud, but a slingshot that used leaf springs for propulsion would seem to be a bow... A design that seems to have stood the test of time, although the steel ones from years gone by proved to be slower than good wooden ones. And now, for better or worse, fiberglass laminates moving onto carbon. Also a design where pulleys and levers have made a difference (again, for better or worse).

Now a slingshot that uses coil springs like tubes seems like it must have been tried. I would be skeptical and curious. Skeptical yes, for sure. And curious to see if anyone could make it work. I enjoy playing a lot on my own and it would be neat to see if somebody could play around and make this work very efficiently. Either way it seems like something might be learned, or some fun had, or maybe just some curiosity satisfied.


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## Valery (Jan 2, 2020)

AndrewF said:


> Why? Could you explain the reason?


Today, rubber is the leader in the amount of energy stored per kilogram of weight. The springs will be very heavy and cannot be stretched "all the way" because of residual deformation. In the end, moving down the path of replacing rubber with springs, we will get a very bulky and heavy design, while being completely ineffective. In an attempt to improve the design, we will come to the conclusion that the coil springs are not suitable, and start using flat springs, they work much more efficiently. After a series of modifications and improvements, we will be surprised to find that we have a ... crossbow!  Then we cut the fork off the wood, mount the latex on it, and go hole a tin can.


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## Northerner (Nov 9, 2010)

.... and handslap would be quite painful with steel "bands"


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## AndrewF (11 mo ago)

Valery said:


> Today, rubber is the leader in the amount of energy stored per kilogram of weight. The springs will be very heavy and cannot be stretched "all the way" because of residual deformation. In the end, moving down the path of replacing rubber with springs, we will get a very bulky and heavy design, while being completely ineffective. In an attempt to improve the design, we will come to the conclusion that the coil springs are not suitable, and start using flat springs, they work much more efficiently. After a series of modifications and improvements, we will be surprised to find that we have a ... crossbow!  Then we cut the fork off the wood, mount the latex on it, and go hole a tin can.


not convinced by these arguments,
steel is heavier but springs can have a very strong traction in a small size so "bulkier" is definitely not true, rubber certainly has more stretchiness than steel, but a latex tube isn't more elastic according the physical definition of elasticity and a spring doesn't need to be extended as much to have peak tension... the principle could be somewhat similar to the crossbow with metal limbs that doesn't use rubber and can shot very strong blows with a relatively compact design, but this is a specific weapon with specific characteristics


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## Valery (Jan 2, 2020)

AndrewF said:


> not convinced by these arguments


Well, look at existing examples of weapons that work on the energy of springs, whether flat or cylindrical. These are bows, crossbows, and air rifles/pistols. Everywhere the accumulation of energy is due to pre-compression of the spring. And there is not a single pattern that uses the energy of a pre-stretched spring. Why? Answer this question and you will understand why the spring slingshot has no prospects.
I guess I haven't convinced you even now. Then prove the contrary, assemble a workable sample, comparable in parameters with an ordinary slingshot, and show it in operation. And I will immediately spit on my diploma of mechanical engineer. Or maybe even eat it!


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## Biker_Bob (Mar 26, 2020)

Isn't this a moot argument?
A slingshot that uses steel is a bow or a crossbow, if you want one of those then go and buy or make one.
Have a look at "The Practical Guide to Man Powered Weapons and Ammunition", it's all in there.
In a nutshell though the trade off is that whilst steel has much higher strength it has far less flex. So you're into pulling less hard for longer (latex) or pulling extremely hard for a short time (steel).


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## AndrewF (11 mo ago)

Biker_Bob said:


> Isn't this a moot argument?
> A slingshot that uses steel is a bow or a crossbow, if you want one of those then go and buy or make one.
> Have a look at "The Practical Guide to Man Powered Weapons and Ammunition", it's all in there.
> In a nutshell though the trade off is that whilst steel has much higher strength it has far less flex. So you're into pulling less hard for longer (latex) or pulling extremely hard for a short time (steel).


Saying that everything that has a spring to push something is a bow or a crossbow is utterly wrong. It's a bow if it is a bow, it is a crossbow if it is a crossbow. Those are specific weapons with a specific structure where an arc (bow) or a crossed arc (cross-bow) is used to create the elastic traction on a string attached to the arc limbs to push an arrow.

Even my wood stapler uses a spring to push out pins but definitely it isn't a crossbow and it isn't a bow.


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## S.S. sLinGeR (Oct 17, 2013)

Andrew welcome to the forum to start. You would do well on a debate team. 🤣 quick ? Can you fit this slingshot in a pocket? Plus would the springs loose tension over time? Is this about speed or size of ammo with the spring thing? I still feel with latex you would be way faster and more pocketable then a “spring shooter”. This is a cool idea! I’m curious how you make it work. You have me “tuned in” now sir.


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## AndrewF (11 mo ago)

Valery said:


> Well, look at existing examples of weapons that work on the energy of springs, whether flat or cylindrical. These are bows, crossbows, and air rifles/pistols. Everywhere the accumulation of energy is due to pre-compression of the spring. And there is not a single pattern that uses the energy of a pre-stretched spring. Why? Answer this question and you will understand why the spring slingshot has no prospects.
> I guess I haven't convinced you even now. Then prove the contrary, assemble a workable sample, comparable in parameters with an ordinary slingshot, and show it in operation. And I will immediately spit on my diploma of mechanical engineer. Or maybe even eat it!


Saying look at the design of existing elastic weapon is a non-argument, when the purpose is creating something new. The fact usually is used a compression spring rather than extension spring (a thing that rather could support a spring type over another) it is irrelevant in steel spring vs rubber debate, unless you explain how from a physical stand point this should proof in some way that rubber is better.
In classic simple slingshot design without leverage certainly a spring would be impractical because it requires more strength to accumulate force in less extension while rubber with its stretchiness is smoother and more comfortable and gradual, but in a design with leverage to accumulate tension things are different and stretchiness wastes area of movement to the leverge and having more elasticity in the strict physical sense of the term is helpful.
Maybe my idea is wrong regardless and springs are really that bad in every slingshot designs possible, but till now the arguments seems based on prejudices rather than mechanical physics.


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## AndrewF (11 mo ago)

S.S. sLinGeR said:


> Andrew welcome to the forum to start. You would do well on a debate team. 🤣 quick ? Can you fit this slingshot in a pocket? Plus would the springs loose tension over time? Is this about speed or size of ammo with the spring thing? I still feel with latex you would be way faster and more pocketable then a “spring shooter”. This is a cool idea! I’m curious how you make it work. You have me “tuned in” now sir.


What I'm thinking about isn't huge but it isn't something that would fit in pocket either.


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## High Desert Flipper (Aug 29, 2020)

Valery said:


> Well, look at existing examples of weapons that work on the energy of springs, whether flat or cylindrical. These are bows, crossbows, and air rifles/pistols. Everywhere the accumulation of energy is due to pre-compression of the spring. And there is not a single pattern that uses the energy of a pre-stretched spring. Why? Answer this question and you will understand why the spring slingshot has no prospects.
> I guess I haven't convinced you even now. Then prove the contrary, assemble a workable sample, comparable in parameters with an ordinary slingshot, and show it in operation. And I will immediately spit on my diploma of mechanical engineer. Or maybe even eat it!



I like your analysis of where we are today, but I also like and encourage the thinking outside the box creativity. I am usually the one who shows myself why and how things don't work. Being an experiential learner I have done it over and over and over. And on occasion, I surprise myself.

I have seen "bows", and levered / compound bows powered by elastic that people put together to play and experiment with. I haven't seen any that outperform current bows, but some on youtube look like they do pretty well. And spearguns use elastic. And while I haven't seen an air rifle / pellet gun powered by elastic maybe I just haven't looked around enough. So while it seems compression springs are the way to go there, maybe somebody just hasn't applied elastic correctly. And for slingshots, maybe there is something new waiting to be discovered.

I love working things out by theory but am also always curious to see somebody have an actual go at it. Sometimes I wonder what it was like when the surgical tubing powered wrist rocket gang met the dude who said "I think flat bands might have some advantages. If you'll hear me out this is what I'm thinking..... and if you cut them with one end wide and the other end narrow so you get trapezoidal bands instead of rectangular ones, then.... Well yes, it does sound like it would be complicated to make them, but I think you could set up a system where it wouldn't be that bad if you just got one of them roller cutter things and a matt and....". That must've been interesting since whoever started down that rabbit hole didn't have access to Snipersling /GZK / precise elastics- they probably started out with rubber bands and maybe came upon TBG gold before too long. And here we are today. It would have been fun to be a fly on the wall back then, and really interesting to watch the transition from then to now.

I see this as less of a debate and more of a fun thinking outside the box exercise. And if I had to put money on a winner I would go with your suggestion that the next advance will be a sheet polymer that out elastics elastic. But still fun to toss ideas around and consider all the possibilities IMHO. Only better if a few actually go to the bench and try to put some of the ideas into practice. Sure, many in a row will fail, but once in a while we will end up with tapered flat bands.


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## Jcharmin92 (Aug 28, 2021)

Someone on here posted the sling cat or something like that and it had a spring mechanism. In my opinion it's not worth the time or energy.


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## Valery (Jan 2, 2020)

High Desert Flipper said:


> But still fun to toss ideas around and consider all the possibilities IMHO. Only better if a few actually go to the bench and try to put some of the ideas into practice. Sure, many in a row will fail, but once in a while we will end up with tapered flat bands.


I agree with your opinion. 
But I also do not claim that it is impossible to build some kind of throwing weapon based on cylindrical springs. I am arguing that it makes no sense. 
Let me explain: the spring slingshot will lose to the classical version by all parameters, in weight, dimensions, and speed, too. And it is not even worth mentioning the complexity of manufacturing and price. 
As a result, instead of a simple construction that can be made in half an hour, we get something crossbow-like. But this design will also be an outcast in the crossbow niche, as it will lose in all parameters to the crossbow, except for the overall width. And there the gain will be minimal and unprincipled. 
For example, in the USA they make a wonderful crossbow TenPoint Nitro X, the width of the arms in the cocked state is only 18 cm. 
The problem is that in our universe the laws of physics and mechanics are immutable, there is no way around them. That is why cylindrical springs are not suitable for throwing weapons, they are inferior to flat springs by energy margin. And for the slingshot, there is no better material than latex. In any case, not yet.


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## High Desert Flipper (Aug 29, 2020)

Valery said:


> I agree with your opinion.
> But I also do not claim that it is impossible to build some kind of throwing weapon based on cylindrical springs. I am arguing that it makes no sense.
> Let me explain: the spring slingshot will lose to the classical version by all parameters, in weight, dimensions, and speed, too. And it is not even worth mentioning the complexity of manufacturing and price.
> As a result, instead of a simple construction that can be made in half an hour, we get something crossbow-like. But this design will also be an outcast in the crossbow niche, as it will lose in all parameters to the crossbow, except for the overall width. And there the gain will be minimal and unprincipled.
> ...



I also agree with you and admire your analytical take on this.

I also agree that the laws of physics are immutable and define the space of what is possible. It is fun to watch people explore that space to see if there are any undiscovered corners, especially when they use creativity to apply the laws in ways others haven't thought of. Entertaining to watch even if most who try fail to find any virgin territory. It will be a sad day when that space is fully mapped and there are no more discoveries to be made. Note- in this context "discoveries" applies more to creative working within the bounds of physical laws and not so much discovery of new ones.


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## Valery (Jan 2, 2020)

High Desert Flipper said:


> It will be a sad day when that space is fully mapped and there are no more discoveries to be made.


Let's wait for news from Area 51!


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## Roll Fast (Sep 19, 2021)

High Desert Flipper said:


> I like your analysis of where we are today, but I also like and encourage the thinking outside the box creativity. I am usually the one who shows myself why and how things don't work. Being an experiential learner I have done it over and over and over. And on occasion, I surprise myself.
> 
> I have seen "bows", and levered / compound bows powered by elastic that people put together to play and experiment with. I haven't seen any that outperform current bows, but some on youtube look like they do pretty well. And spearguns use elastic. And while I haven't seen an air rifle / pellet gun powered by elastic maybe I just haven't looked around enough. So while it seems compression springs are the way to go there, maybe somebody just hasn't applied elastic correctly. And for slingshots, maybe there is something new waiting to be discovered.
> 
> ...


Well said.
The discovery from trying stuff yourself is where great ideas come from.
And muddling around out in the shop if nothing else gets me out of the vacuuming!
I have a compound bow (2 actually) and a cross bow and a ...........
The slingshots are so nice and portable and light and pocketable etc.
And I have tried to make a bow. It is not easy. So I really admire and give credit to the bowyers.
Myself, I like making slingshots. Very satisfying.


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## AndrewF (11 mo ago)

Valery said:


> I agree with your opinion.
> But I also do not claim that it is impossible to build some kind of throwing weapon based on cylindrical springs. I am arguing that it makes no sense.
> Let me explain: the spring slingshot will lose to the classical version by all parameters, in weight, dimensions, and speed, too. And it is not even worth mentioning the complexity of manufacturing and price.
> As a result, instead of a simple construction that can be made in half an hour, we get something crossbow-like. But this design will also be an outcast in the crossbow niche, as it will lose in all parameters to the crossbow, except for the overall width. And there the gain will be minimal and unprincipled.
> ...



Still, I haven’t seen any physic explanation or any comparative calculation in your replies. Also, crossbows use a crossed arc and it is a design many centuries old when material and manufacture design were highly constrained by technology and manufacture available, born before coiled spring invention around 1900, various centuries after archery was already replaced by firearms and after becoming niche tools for archery enthusiasts who therefore would not have distorted the original design into something different than an archery tool (designing something without any arc at all that cannot even fall into the definition of the thing supposed to upgrade), they have not been evolved significantly anymore. So the assumption that things are designed that way because it's the best way possible and all the others don't make sense or are certainly worse, it's totally baseless.

Laws of physics and mechanics are immutable but not innovation.


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## High Desert Flipper (Aug 29, 2020)

Roll Fast said:


> Well said.
> The discovery from trying stuff yourself is where great ideas come from.
> And muddling around out in the shop if nothing else gets me out of the vacuuming!
> I have a compound bow (2 actually) and a cross bow and a ...........
> ...



I am with you 100% on the puttering and experiential learning. After keeping at it for a long time I figured out how to turn a board into a passable shooting bow. It took a lot of time and experience to get there. I am finding slingshot frames to be an equal or bigger challenge. No problem to get a Y shape that will hold bands and propel a ball, but I have been trying to make a frame that feels at one with my hand and has fork width and height just where I want them. This has been a months long quest that is progressing but is still far from done. Most new attempts feel like advances and then I find something else I want to tweak. A grand and rewarding obsession.

The progress keeps me motivated to keep going and also gives me a great sense of admiration for some of the really talented frame makers on here.


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## Northerner (Nov 9, 2010)

One of the wonderful attributes of latex bands is that they can be stretched 500% or more. The average person can pull 6 to 12 pound bands and easily break 200fps with appropriate ammo sizes. The lightweight latex bands will fly over or through the forks and then recoil back towards the shooter during their recovery movement. The band's light weight allows them to stay on a fairly true path when accelerating the ball passed the forks. 

I'm not so sure there are springs that will allow the massive stretch of latex. A small diameter coil wouldn't allow the elongation without damage to the spring. A very large diameter coil would be cumbersome. At the completion of the shot the spring coils smash together and might produce some nasty recoil. With an airgun, there is a piston that is cushioned by an air column and pellet resistance. Even then, some airguns have terribly annoying recoil when tuned to powerful levels. They often use spring guides and piston liners to maintain a straight spring movement without canting. With a spring powered slingshot the sudden stop at the forks might not be so comfortable.

The original poster was referring to tension springs for power but we have seen a type of ball shooting device that used a leaf spring idea. I'm lost for the name but it was a short "longbow" with a type of pouch made into the string. The shooter flips the bow when shooting. The YouTube video showed a guy shooting it quite accurately. The problem with leaf springs is the need for limb length to get the required draw length... and it's still a bow. You need a big back pocket to carry one of these. 

With all this said, I'm still looking forward to seeing some designs by the original poster. Possibly there are ideas that have not yet been explored. The frame will need to deal with the sudden stop when the spring completes the shot cycle. The lower stretch of the small diameter tension spring will require a long spring to get to anchor. Care has to be taken to avoid bending the wire sideways. Shooters with beards might be a bit fearful of the closing coils.


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## AndrewF (11 mo ago)

Northerner said:


> One of the wonderful attributes of latex bands is that they can be stretched 500% or more. The average person can pull 6 to 12 pound bands and easily break 200fps with appropriate ammo sizes. The lightweight latex bands will fly over or through the forks and then recoil back towards the shooter during their recovery movement. The band's light weight allows them to stay on a fairly true path when accelerating the ball passed the forks.
> 
> I'm not so sure there are springs that will allow the massive stretch of latex. A small diameter coil wouldn't allow the elongation without damage to the spring. A very large diameter coil would be cumbersome. At the completion of the shot the spring coils smash together and might produce some nasty recoil. With an airgun, there is a piston that is cushioned by an air column and pellet resistance. Even then, some airguns have terribly annoying recoil when tuned to powerful levels. They often use spring guides and piston liners to maintain a straight spring movement without canting. With a spring powered slingshot the sudden stop at the forks might not be so comfortable.
> 
> ...


The springs have way less stretchiness but the problem is that the stretchiness of rubber is a vantage when you use directly tensioning but an issue when you use a leveraged tensioning system.

A thing that to peak elastic force needs to be extended so much would consume the leverage maximum motion range (the leverage basically converts an ample motion to create a narrower but way stronger motion). So, a thing that peak elastic traction force without need too much extension as a strong steel spring is better when you have a leverage, despite it would be too hard to be used directly without Superman strength, and there the rubber is better because it has more span to accumulate the force gradually.


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## Valery (Jan 2, 2020)

AndrewF said:


> Still, I haven’t seen any physic explanation or any comparative calculation in your replies


Please. Let's start with Hooke's law. It is valid for rubber. It is also true for a coil spring, but with one caveat: only for small stretches and compressions. Modern latex can easily be stretched 6-7 times. The steel spring at this elongation will either be permanently deformed (residual elongation) or destroyed. Wager! 
By the way, it would be nice to see a sketch of your design for a substantive discussion. Then I can more accurately point out the weak points.


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## AndrewF (11 mo ago)

Valery said:


> Please. Let's start with Hooke's law. It is valid for rubber. It is also true for a coil spring, but with one caveat: only for small stretches and compressions. Modern latex can easily be stretched 6-7 times. The steel spring at this elongation will either be permanently deformed (residual elongation) or destroyed. Wager!
> By the way, it would be nice to see a sketch of your design for a substantive discussion. Then I can more accurately point out the weak points.


and here you seem ignoring that I need exactly something with high elastic strength but low stretchiness that doesn't need to be extended several times its length to peak its maximum force, because I have to use it with a leverage as explained


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## Valery (Jan 2, 2020)

AndrewF said:


> and here you seem ignoring that I need exactly something with high elastic strength but low stretchiness that doesn't need to be extended several times to peak its maximum force, because I have to use it with a leverage as explained


No ignoring! 
However, it is difficult to discuss a subject without seeing it. It's like the parable of the three blind men who groped the elephant. That is why I ask for a design sketch. But in any case, each intermediate element, be it a lever or a block, takes away a part of useful energy, sometimes a significant one.
Don't consider my question rude, do you have a technical education?


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## AndrewF (11 mo ago)

Valery said:


> No ignoring!
> However, it is difficult to discuss a subject without seeing it. It's like the parable of the three blind men who groped the elephant. That is why I ask for a design sketch. But in any case, each intermediate element, be it a lever or a block, takes away a part of useful energy, sometimes a significant one.
> Don't consider my question rude, do you have a technical education?


I'm an engineer


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## Biker_Bob (Mar 26, 2020)

So am I
..a slightly less argumentative one, who hasn't joined a slingshot community forum to argue about how slingshots are rubbish....


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## Northerner (Nov 9, 2010)

Are we talking about a small handheld shooting device or a massive _spring-sling_ with long limb-like levers with pivots and coiled tension springs at the base? The pic below shows a crossbow with levers and springs. Is this the direction you are thinking?


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## Valery (Jan 2, 2020)

AndrewF said:


> I'm an engineer


Beautiful! At least we can talk as equals. Now we have to wait for the sketch.


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## treefork (Feb 1, 2010)

AndrewF said:


> I'm an engineer


Have you figured out how to hit a target consistently with a slingshot ? Have you done any slingshot builds ?


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## AndrewF (11 mo ago)

Biker_Bob said:


> So am I
> ..a slightly less argumentative one, who hasn't joined a slingshot community forum to argue about how slingshots are rubbish?


I haven't joined here to say that slingshots are rubbish but to get info because as hobby I have intention to design a strong leverage aided slingshot, but I'm facing a lot of prejudices against springs as if I had said who knows what blasphemous nonsense. 

I simply replied to claims which can be summarized in

- no rubber = it is some crossbow... 
or 
- rubber = design less bulky than steel spring
or 
- rubber = more elastic than steel spring, confusing elasticity (that is measured as ratio of stress to strain) with stretchiness
or
- if it isn't as something already done = it's a stupid idea

I would have been a lot less argumentative without certain baseless assumptions which imply I'm going to do something extremely illogical and stupid without even having a clue how I want to implement it.


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## AndrewF (11 mo ago)

Northerner said:


> Are we talking about a small handheld shooting device or a massive _spring-sling_ with long limb-like levers with pivots and coiled tension springs at the base? The pic below shows a crossbow with levers and springs. Is this the direction you are thinking?
> 
> View attachment 362412


Not exactly, it's a two-handed device with long leverage that extend an orthogonal tensioner and basically would need 2 ample movement to fully tensioning the elastic actuator and if I use many very thick but short cut latex tubes similar to speargun rubber, pre-tensioned, they are too bulky and very prone to rupture others needs too much extension to reach adequate peak tension, for this reason I'm looking for steel springs to reach peak force without too much elongation needed, since the leverage system gives a very powerful traction on elastic actuator but also a small movement span.


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## StringSlap (Mar 2, 2019)

I think the OP is referring to something like this. It's been around for a long time. It's huge, heavy and in my opinion a gimmick geared towards the power hungry (same as modern compounds and crossbows). If it was any good and a significant improvement in what we are already using, wouldn't we all have one?


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## AndrewF (11 mo ago)

StringSlap said:


> I think the OP is referring to something like this. It's been around for a long time. It's huge, heavy and in my opinion a gimmick geared towards the power hungry (same as modern compounds and crossbows). If it was any good and a significant improvement in what we are already using, wouldn't we all have one?
> 
> View attachment 362445


the mine it's a very different design with a different way to tensioning springs


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## High Desert Flipper (Aug 29, 2020)

I really do enjoy thinking outside the box. I also love waiting to see what the future brings as people try putting ideas into practice. Hard to beat imagining what the future may bring then seeing what comes.


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## S.S. sLinGeR (Oct 17, 2013)

In the end can it fit I’m my pocket? If it can’t then it’s not for me. Now I have many shooters that won’t fit in the pocket but there just target shooters. But I want it to be pocketable for me. Target shooters are the same as a bow to me. I shoot them often I shoot instinctively just walking around and shooting leaves and grass and such. I want portability. Nice job on becoming an engineer! Again you would do well on a debate team. 😀 But remember we are all “brothers of the bands here”. You have great ideas. But we just want to shoot and relax not debate. I hope the spring thing works out for you. I’ll stay with cheep latex.


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## Roll Fast (Sep 19, 2021)

StringSlap said:


> I think the OP is referring to something like this. It's been around for a long time. It's huge, heavy and in my opinion a gimmick geared towards the power hungry (same as modern compounds and crossbows). If it was any good and a significant improvement in what we are already using, wouldn't we all have one?
> 
> View attachment 362445


Wow!
That is some piece of machinery!
Guess if I wanted something complicated I could go out and shoot my PSE bow. 
That's kind of what I like about slingshots. Can be built very quickly and they are nice and small and compact. And cheap.
That being said, people who want to try cool new ideas or simply crazy ideas they've had, more power to them.
That's probably how we got to where we are now. 
The above does use the lever to make use of steel springs. Pretty easy to make a coil spring on the lathe or even with a threaded rod and a hand held drill. And then try it out and keep making different versions until you got something. Lots of fun and like I said, if you're busy out in the shop, you don't get stuck doing the vacuuming. Seems to work for me anyway......
BTW: many years ago when I was managing the RND shop and new product development for a big construction equipment company, I experimented with a number of different approaches to new product development. That was when 3D solid modeler CAD was just becoming available.
The approach that seemed to work the best was to build mock-ups and experimental models out in RND with very experienced guys and then get the CAD guys to draw up what worked. And make sure they didn't stray very far cause the CAD guys always wanted to make it their own and change it.
Mind you, this was construction equipment, not airplanes. If you were designing airplanes or rockets if would have been different. It would have been pretty hard to get these machines off the ground at 25 tonnes each.
Anyway, lets see the CAD models or the mockups. Or calcs. I would find it all very interesting.
Thanks for posting the idea!


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## DynamicEjecta (Nov 27, 2021)

This is a very interesting thread.

I recently learned about constant force spring (the spring that retracts your tape measure/dog leash) at the local robotics team. I wonder if this works better than the cylindrical/leaf spring proposed so far?


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## DynamicEjecta (Nov 27, 2021)

Prototyping for a minimal viable product is also easy and dirt cheap. Just get one of those retractable badge clip and replace the clip with a pouch.

A new way of frameless slingshot?


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## Crac (Mar 3, 2013)

In post 1, you ask about just replacing tubes for springs in a slingshot… You’ve got the right answer to the wrong question and now we are further and further off topic.

You’ve drip fed a few indications but, I’m not sure what the concept or goal is. I am very interested if you can share and articulate what you are working on.



Previously, you asked about some big tubing… And I estimated the draw force to be 110 Kgf or 250 lbf.


So let’s get serious and bring out the big bold “Q”s.

*Q1.* Is this the same project, using the same draw force?

*Q2.* Does that force or the range of forces I gave you, fit your expectations?





AndrewF said:


> thanks for the hint, but the retraction speed should depend on the kind of spring e.g. harder carbon steel springs are way faster than inox steel springs, are you sure that they are slower than rubber? I'm interested to deepen this topic.


If you want an exact solution not a general solution: I / we need an exact design. You seem to demand nothing less and that’s OK.


You need to get the machine design element sorted out first, and that’s a job for someone who can design / make springs. With your ideal spring, or with ANY workable spring, and a design that can be measured, tested and analyzed either with differential equations or with a tool of your choice.

So moving forwards, let me pose these as ‘Little questions’, or “Lq”. The good news is you don’t need to publically answer these… but you need to have these answers to get the springs designed.

*Lq1.* Spring rate?

If this is the same project, you have load figures vs strain for rubber or simply a bunch of load figures for a constant rate spring. *N.B* spring rate to inertia will be key to performance: w = (K/I)^(1/2)… you will also need to refer inertias, you might want to take a moment with this. It will be an interesting design goal for someone, and an interesting math problem for someone else.


*Lq2.* What free length for the spring? And you might want a little preload to keep it captive.

You know the first part, a little practical engineering will overcome the second part.


*Lq3.* What spring travel?

You know this.


*Lq4.* Package size, like what length and diameter for a coil spring?

You know where it has to fit, plus the design goal of use minimal material.


*Lq5.* End treatment / winding style.

You know this, or quickly figure it out.



OK, Back to the serious questions*:

Q3.* What general physically scale are you thinking for your device, so length, width and depth? 

Hands in the air with a tape measure will be fine.


*Q4.* What general performance are you thinking; In terms of ammo and speed?

A lot of people here will be interested in this.


*Q5.* What general role or application are you thinking; Is this a personal toy or a commercial product for hunting? 

Again, a lot of people here will be interested in this.


*Q6.* Are there any other technical embellishments or stand out features?




Thanks, in advanced.


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## Biker_Bob (Mar 26, 2020)

Aarrgghhh!


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