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Old 10-07-2019, 06:59 AM   #1
Andersp90
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linking rubbers together for more speed?

Muscle physiology has put a question into my mind: why not link rubbers?

If you have a 1m long rubber, and stretch it 1 m (making it 2m long in total), it will have to travel 1m to contract. But if you take the same rubber, split in two (50cm each), and bind it back together, each section only has to travel 50 cm to contract fully.
The power will be the same, but the band should contract twice as fast.

What do you guys think? Does it make sense?

Last edited by Andersp90; 10-07-2019 at 07:19 AM.
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Old 10-07-2019, 09:05 AM   #2
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Re: linking rubbers together for more speed?

What you're proposing is the same thing as doubling the mass of the rubbers your using. You end up with a jerky shooting gun. A long smooth pull makes shots more accurate and is a more efficient use of the potential energy of the band pull due to the physics involved.
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Old 10-07-2019, 09:22 AM   #3
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Re: linking rubbers together for more speed?

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What you're proposing is the same thing as doubling the diameter of the rubbers your using. You end up with a jerky shooting gun. A long smooth pull makes shots more accurate and is a more efficient use of the potential energy of the band pull due to the physics involved.
Its not the same at all. In your example, you have 4 times the rubber mass = more recoil. Here, there is no change in mass, only the speed.

In an inverted roller, the spear moves 2 cm for every 1 cm of band. Linking rubbers should give the same effect (in terms of speed).
If an inverted roller can shoot straight, so can a gun with linked rubbers.
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Old 10-07-2019, 09:48 AM   #4
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Re: linking rubbers together for more speed?

*doubling the mass

Fixed my statement.
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Old 10-07-2019, 09:53 AM   #5
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Re: linking rubbers together for more speed?

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*doubling the mass

Fixed my statement.
I dont think thicker rubbers contract faster. That is the very problem linking rubbers might solve.
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Old 10-07-2019, 10:31 AM   #6
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Re: linking rubbers together for more speed?

You keep saying "linking rubbers together", which is confusing. Unless I'm misinterpreting your original explanation, "increasing rubber size" is a less confusing description and easier to do.

https://www.wired.com/2012/08/do-rub...-like-springs/
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Elastic potential energy (measured in the unit joules) is equal to ˝ multiplied by the stretch length ("x") squared, multiplied by the spring constant "k." The spring constant is different for every rubber band, but can be figured out (see "Welcome to the Guide to Shooting Rubber Bands" below). When the rubber band is released, the potential energy is quickly converted to kinetic (motion) energy. This is equal to one half the mass (of the rubber band) multiplied by its velocity (in meters per second) squared.

Using these equations, you can calculate the velocity of the rubber band right when it is released, and find that the velocity has a linear relationship with the stretch length. (Because the amount of time that the rubber band spends in the air is dependent on its initial height and force of gravity, and these factors should not change between your trials, then how far the rubber band flies depends on its initial velocity.) Consequently, after you graph your data, you should see a roughly linear relationship between the stretch length and the launch distance.
Increasing rubber size increases the k constant. Here's a link which shows the stretch/force plot.
https://www.wired.com/2012/08/do-rub...-like-springs/
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Old 10-07-2019, 10:45 AM   #7
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Re: linking rubbers together for more speed?

We are not talking rubber diameter.

Here is an illustration.

You take a rubber band (1m total in my example), cut it into 4 equally large pieces, and then rejoin them.

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Old 10-07-2019, 10:54 AM   #8
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Re: linking rubbers together for more speed?

Whew...I guess I'm not picking up what you're throwing down. Rejoin them how?? In parallel? Series?

Also, further clarification. Instead of 'doubling the mass', what is really meant is 'increasing the diameter of the cross section' which would increase the k constant, which creates more recoil and when overdone, causes spear whip. If my understanding you correctly, total mass will be unchanged.
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Old 10-07-2019, 11:34 AM   #9
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Re: linking rubbers together for more speed?

Yeah, I read that OP a bunch of times, didn't get it at all. And even now, with the sketch, I am still not getting it

Anders, I think you need to put a gun in that sketch and try again.
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Old 10-07-2019, 11:38 AM   #10
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Re: linking rubbers together for more speed?

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In parallel? Series?
Series.

Lets say that a rubberband can contract at a maximal speed of 25 m/s.

If we stretched a 1m rubber to 3,6m, it would be able to fully contract in 144 ms. If you cut the band in two, each piece would be able to fully contract in 72 ms (because they only have to cover half the distance of the 1m band). Now, if you glue them back together, you still have two pieces, that can fully contract in 72 ms.

So, the "new" band will be able to contract from 3,6m to 1m in 72ms. Twice as fast as the original band.

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If my understanding you correctly, total mass will be unchanged.
Yes, no change in mass.

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Yeah, I read that OP a bunch of times, didn't get it at all. And even now, with the sketch, I am still not getting it

Anders, I think you need to put a gun in that sketch and try again.
The red half circles were ment to illustrate a circular band. I hope it makes more sense with the explanation above.
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Old 10-07-2019, 11:43 AM   #11
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Re: linking rubbers together for more speed?

Your explanation sounds like you want to take a piece of rubber, cut it in half, glue it back together and expect to get twice the retraction speed...?
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Old 10-07-2019, 11:49 AM   #12
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Re: linking rubbers together for more speed?

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Your explanation sounds like you want to take a piece of rubber, cut it in half, glue it back together and expect to get twice the retraction speed...?
In theory, yes.

Its the same principle in your muscles (and where I got the idea from). Sarcomeres are joined in series. The longer the series, the faster the muscle can contract (but with no gain in strength).
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Old 10-07-2019, 11:59 AM   #13
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Re: linking rubbers together for more speed?

You can see it illustrated in this video (sort of).

By linking 5 rubberbands together, you can create a supersonic whip.

https://www.youtube.com/watch?v=2QdEvOLyXZI

Last edited by Andersp90; 10-07-2019 at 12:20 PM.
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Old 10-07-2019, 12:25 PM   #14
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Re: linking rubbers together for more speed?

Cutting it apart and rejoining it won't have any significant affect on k spring constant.
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Old 10-07-2019, 12:33 PM   #15
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Re: linking rubbers together for more speed?

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Cutting it apart and rejoining it won't have any significant affect on k spring constant.
It wont increase the power of the rubber, but it will increase the speed of which it can contract.

You can illustrate it by tying together some rubber bands - the kind you have in your kitchen drawer.

If I was not right, it would take 5 linked rubberbands 5 times as long to contract, compared to just a single rubberband - but the times are almost identical. But the 5 rubberbands will have travled 5 times the distance. So they must be moving 5 times as fast.

Last edited by Andersp90; 10-07-2019 at 12:49 PM.
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