Knex War? Answered
Hey guys! Sharir1701 here and, as most of you guys that knew me back when I was still around probably know, I've lost most of my interest in Knex. I do, however still come on the site ever so often to browse, comment and so on. I've noticed during my past couple of visits that there seems to be a "war", so to speak, raging on between some members of the community, regarding the effect of bulldozing a gun with rubber bands, as well as "how good" is the NAR. In this forum I am assuming you all have basic knowledge in Knex gun technology, are familiar with the stated guns and have a little bit of background in mechanical engineering. Moving on. You might know my opinion about the subject already, but I would like to state it once more as well as explain it better, so perhaps some people that disagree with me could understand my point of view. BUT, before I do that, I can't help but feel guilty for tossing the long burning logs into a small fire. About a month or two ago, in one of my visits, I posted a comment on one of Red's topics (or 'ibles, strike me dead for my memory) about my quite specific opinion about each and every one of the three guns in question in the said topic, the ZKAR, the NAR and the TR8. I said a few things about rubber bands and brute force vs. complexion and efficiency, and I may have started something unintentionally. That argument has been around since, if I recall correctly, 2009, but it hasn't been brought up again in a while. I feel like I made that happen and then I enraged a few more people by saying that "efficiency and good design beats brute force any day" (or something like that...). I'm not taking credit for starting this thing again, but rather I'm apologizing for sparking up an old and possibly pointless argument. Nonetheless, I will now explain my opinion on the subject and hopefully nobody gets mad at me for doing so, but if you have a valid counter argument, please state it below in an understandable and polite way. Thank you.
If so, then, what is this whole thing even about? The "KI Crew", as I like to call them, have been very proud of their NAR and TR-n series guns for a few years now. The TR series I'll admit is very good, but I don't accept the "add as many rubber bands as possible" argument. Now, the NAR, personally, I dislike the gun. I have had nothing but bad range tests with it in the 3 times throughout the past 4 years that I've built it, and I've heard similar results from several people and some close friends. I highly doubt I was doing something wrong all THREE times, so don't bother to bring that up, please. The NAR is a gun designed for nothing else but being capable of withstanding great amounts of force and shooting a single round "the strongest a pin gun can shoot". How? Very simple - make a massively dense and very shock-proof body and then just add as many rubber bands as you can before your hands start bleeding. Now, let me explain, I'm saying 2 points here.
First, the NAR is nothing special, just a strong structure with a simple connector barrel and a reinforced pin. We've seen it before, people. The claim that it's a good gun simply because you can put on as many bands as you want, pretty much, is, in my eyes, invalid. So I can make a bomb and just put as much explosives on it as I can afford, surely it'll be better than an atomic bomb... WRONG. It won't. Theoretically, even if it makes a bigger bang, it takes so much effort and it is so non-elegant that it loses it's point within itself. (Do not take this metaphor out of hand! You know what I mean).
Second, and more importantly, I'm claiming that even if my first claim is wrong, if you look at the technical side of things you'll see that the very premise that adding more and more rubber bands to a gun will make it much stronger, is wrong in it's origins. I'm sure we all know this, but let me remind us all the physics of how a basic pin gun works. When the potential energy stored in the strained rubber bands, and rested on the cocked pin, is released, it accelerates the pin. The pin then proceeds to gain speed and it reaches three main milestones:
The initial strike of the bullet (The pin is already accelerated and is just touching the bullet, but the bullet is still).
The point of equality, as I've dubbed it before (Just a few tiny fractions of a second after the initial strike, at this point the pin is ever so slightly slower than it was in the initial strike, but the bullet is now travelling at an equal speed as the pin, with a tiny gap between the two, meaning they aren't actually touching at this point)
And finally, "the crash" (the bullet has left the barrel, the pin is at it's highest speed and is the most energetic as it pointlessly crashes into the back of the barrel losing and wasting all of it's remaining energy).
In a world where you could use 100% of the acceleration of the pin and transfer it all into the bullet, adding more bands would indeed make a much stronger gun. BUT, that is impossible, in fact, it's no where near that. To put it all into a short sentence, the bullet accelerates and fires with a fraction of the energy released during the shot and to a certain limit, it is almost exactly the same amount of energy after a certain point.
So, let's talk Maths. There is a direct correlation between the number of rubber bands on a gun and the amount of acceleration (and force) in the pin when fired. The pin's acceleration as a function of the number of rubber bands on the gun is in the order of magnitude of y=x. That's true, and that is where the misguided claim in question comes from. However, if we take a look at the graph of a bullet's acceleration as a function of the number of rubber bands on the gun, we can conclude, according to the above explanation, that the function is in the order of magnitude of y=sqrt(x). That means that up to a certain pivot, which I claim is, on average, around the 2-3 rubber band mark, adding more rubber bands does in fact produce a drastically stronger shot, but past that point, adding more rubber bands adds more brute force, yes, but it makes the shot stronger only just slightly, and by an increasingly smaller amount the more bands you put on it. BUT, and this is the big BUUT, the graph of the force required to cock the gun as a function of the number of bands on the gun is, again, in an order of magnitude of y=x.
In conclusion, up to a certain, quite low point, adding more rubber bands will give you a drastically stronger shot without stressing the gun too much and without making the pull incredibly hard. However, past that point, adding more rubber bands adds an insignificant amount of power to the gun while introducing a whole lot more difficulty in operating it, resulting in an overall, worse gun. That is why I claim that a gun built around the sole concept of being capable to handle a lot of rubber bands is a nice concept, but is much worse than a gun built around efficiency (meaning you try to invest as much of the potential energy of the pin into the bullet by making a more efficient layout and a smarter usage of the forces in play).
If you got this far, thank you for reading my article, and I hope this will put an end to this silly argument, but knowing how people's feelings work and how male ego and testosterone works, I bet it's far from it. Happy Knexing everybody ;)