Battle Practicality Factor

Build a homemade water gun or water balloon launcher and tell us about it.
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Silence
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Post by Silence » Sun Feb 25, 2007 4:49 am

EDIT: Just split this thread from WaterWolf's Silver Bullet homemade thread.[/EDIT]

I would like to see a thread discussing the definition of battle practicality. Perhaps a formula...

Code: Select all

BPF = D * log(t) / m
BPF = battle practicality factor for a given gun and nozzle
D = distance in meters
t = shot time in seconds
m = mass in kilograms [u]when full[/u]
Frankly, that is the simplest formula I can think of. Any major or minor suggestions? Also, I don't think any gun can be excellent in all those qualities.

Volume doesn't matter--it's accounted for by the shot time.
Output doesn't matter--this is designed for soakfests, and you'll likely need a large nozzle for range anyway.
Dropoff is assumed to be near zero--I would expect a silver bullet homemade to be CPS.
The number of pumps really doesn't matter. Somebody trying to make a huge gun to get shot time to take advantage of the formula (not that anybody would care) is gonna sacrifice on mass.

Pump force has to be less than 15 pounds, or 67 Newtons. I might revise this limit.

But back on topic. My priorities are...
Size--12-18" max length
Range--50-60 ft
Reservoir capacity--Should be fairly high. No backpack.
PC capacity--Not too important if you tap/pump

Dropoff--Can't have any. Only CPS will work.
Price--Come on, it's a silver bullet homemade...
Last edited by Silence on Wed Feb 28, 2007 10:57 pm, edited 1 time in total.

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Silence
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Post by Silence » Sun Feb 25, 2007 6:13 am

Double-post, but I need to avoid confusion...

The first formula I suggested has some problems.

First: low shot times (think <1 second) aren't well represented. Logs of numbers less than 0 are negative, unless the base is less than 1. And you can have decent battle practicality with low shot times. According to Duxburian, the CPS 2500 is good, with only .8 seconds of shot time. The formula would give it negative battle practicality. I can either change the log to a square root, or change the log's base from the default of 10 to the smallest normal tap shot time allowed by the gun's trigger.

Second: mass values aren't well represented. Using this formula, a pistol is pretty much always better than even a light rifle. We know that's not true, partly because of problems three and four.

Third: range distances aren't well represented. A soaker with a 60-foot range should have far more battle practicality advantage than 20% when compared to a similar soaker with a 50-foot range.

Fourth: reservoir capacities were ignored. I thought the mass would take care of that, but it really doesn't. A rifle should have a bonus of greater capacity as well as the problem of greater weight. Pump time still shouldn't be much of an issue. The pump force limit still stands.

Fifth: something else...

So anyway, I've changed the formula to reflect the problems and their solutions.

Code: Select all

BPF = (D^2 * sqrt(t)) * (V / m)
BPF = battle practicality factor for a given gun and nozzle
D = distance in meters
t = shot time in seconds
V = volume of the reservoir only, in liters
m = mass in kilograms [u]when full[/u]
I also grouped the terms together according to the differences that they counteract.

EDIT: I remembered the fifth one.

Since I'm going so keenly on the BPF, it can't be just for the silver bullet homemade. It has to be able to judge all guns for soakfests. Which means it has to include air pressure guns...

So I've got a calculus problem, as I probably can't handle it for a few more months. Let's say the shot time is left out of the BPF formula. The other variables are also constants, so we have BPF = D^2 * k.

In CPS guns, D is constant, so if we plot BPF vs. D, the BPF doesn't change and it's just a horizontal line. The area below the line is the cumulative BPF.

For air pressure guns, the D would change. If we plot BPF as D increases (going backwards here), then would it be possible to find the total are below the line?

In other words, given a parabola (BPF = D^2 * k) with domain restrictions at zero and at another point (because of shot time), what is the area below the parabola?

I'm going to be so happy once we get into calculus...this is killing me.
Last edited by Silence on Sun Feb 25, 2007 6:22 am, edited 1 time in total.

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SSCBen
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Post by SSCBen » Sun Feb 25, 2007 1:53 pm

For air pressure guns, the D would change. If we plot BPF as D increases (going backwards here), then would it be possible to find the total are below the line?

In other words, given a parabola (BPF = D^2 * k) with domain restrictions at zero and at another point (because of shot time), what is the area below the parabola?
Basic fundamental theorem of calculus stuff. This problem is actually pretty simple (calculus is not hard because of the calculus, it's hard because of all the algebra and rules you have to memorize). I could go into the details for quite some time, but essentially, the area under the curve of D^2 is (D^3)/3. If you have a graphing calculator, there almost always is a function to approximate the area under a curve by using lots of little rectangles.

For this formula however, I don't really know why you would need the area below the curve to calculate anything. It is difficult to make a curve of distance versus time into the shot, which is what matters here. Maximum range would matter, or perhaps average range over the entire duration of the shot.

But if you wanted to use this formula, I suppose the most accurate version would have the integral in it. Personally, I think this formula might not be completely necessary. Battle practicality is subjective and measuring subjective values numerically is difficult.

Now, I think I have a few things that are pretty close to the "silver bullet" homemade water gun.

There is little I would change on my CPS homemade water gun given the choice. The PC can hold as much as you want, which is a very big advantage. The power is unmatched, and soon to be greater. In it's older self, it could get about 60 feet of range to the puddle (I do not measure to the last drop any longer because it's simply inaccurate). To the last drop would be like 63 feet. It's current state only has two layers on it's PC and is sadly only about as powerful as a CPS 2000, with only about 52 - 53 feet of range (this is a problem?). I intend to upgrade the PC, valve, and nozzle system this year. The PC and valve will be of a larger diameter to allow for greater flow and greater force. The PC also will be very heavily layered with bike tubes over top it's already thick CPS tubes. The nozzle area will be upgraded with a rotating nozzle selector of my own design (based mainly upon older homemade Nerf barrel rotation systems). I consider this water gun to the best one I have ever made, and it is soon to be even better. This I seriously consider to be my own "silver bullet" homemade water gun.

Of course, some may not prefer this design because it does not have an included reservoir. I prefer and for the most part use only backpack reservoirs.

Lately I also have been working on an improved SuperCAP type design. With this design I intend to correct several failings of the original SuperCAP design, namely, the enormous size, tubing even being able to come off, the lack of ability to read the gauges on the back, riot-blasts so large that you spin when shooting, etc. The gun actually was far too powerful and for the new gun I bought a regulator with half the flow (and you must consider that I never used the other regulator at more than maybe 50% of it's ability). I never measured range, but I know for a fact that SuperCAP easily shot over 65 feet. This new gun will be a much more compact and better designed SuperCAP. I don't have it made yet (I just ordered a few parts 4 days ago!), but when it is made it will replace my CPS water gun.

The advantages of this design are numerous. Once the air chamber is full, you will get many full tanks of shots out before needing to refill, especially on a low pressure such as 30 PSI, which still would have have over 350 pounds of force (which is a lot when compared against other water guns). The tank pressure will be visible on the gun in this design, to make it easy to know when to refill with air. The power will be unmatched by anyone else. The reservoir should hold a smaller, but definitely not unsubstantial 6.1 liters. The air volume, power, and water capacity are the biggest advantages of this design. The biggest disadvantage would be size for most people, because this will be about as big as a frame backpack. Weight will not be a problem however because the water will only weight 13.5 pounds and the frame backpack puts the weight on the hips, which makes carrying weight much easier.

For people who lack a frame backpack, building may be expensive. The frame backpack may be over half the cost, unless you get a used one or get only the frame part. I own two frame backpacks myself, so this isn't a problem for me.

The new CAP design actually would score extremely high on SilentGuy's BPF. The range is unmatched, the weight is comparable to most water guns (and balanced better), and the shot time is unmatched as well. The largest problem in my opinion is the size. Perhaps any BF formula should factor in size along with weight?

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Silence
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Post by Silence » Sun Feb 25, 2007 4:37 pm

Ben wrote:This problem is actually pretty simple (calculus is not hard because of the calculus, it's hard because of all the algebra and rules you have to memorize).
I had guessed as much, but I unfortunately do not know the differentiation rules just yet. Thanks for telling me the value, I'll at least see if I can do something with it. ;)
Ben wrote:For this formula however, I don't really know why you would need the area below the curve to calculate anything. It is difficult to make a curve of distance versus time into the shot, which is what matters here. Maximum range would matter, or perhaps average range over the entire duration of the shot.
The idea is to be able to see the BPF for a certain part of a shot. Say, if you take the BPF for the first ten seconds only, you'd have limited shot time (10 seconds :p ) but better overall range. The calculus part would probably be able to tell you how long to shoot to get the best BPF. But as you say, it probably would be easiest to use the integral.

That said, it makes it sound like the BPF formula is the be-all and end-all of determining water gun practicality. I agree with you--it isn't. BPF is very subjective and hard to quantify. But at least we can try.

I did not consider physical size in the formula, mainly because the weight is the most noticeable difference between a rifle and a pistol and because I didn't expect such huge gun. Granted, SuperCAP probably is one of the best guns out there.

Thanks for the input, as there are still loads of changes to be made.

Code: Select all

BPF = D^2 * sqrt(t) * V / (2*m1 + m2)
BPF = battle practicality factor for a given gun and nozzle
D = distance in meters
t = shot time in seconds
V = volume of the reservoir and pressure chamber, in liters
m1 = gun mass in kilograms when full
m2 = backpack mass in kilograms when full
This version also differentiates (no pun intended) between backpack guns and guns without backpacks. I'll try to make a more reliable and less leaky backpack and see how it goes.

EDIT: Before I can try doing a version that attempts to get the BPF for an air pressure gun, I need to get some stats regarding shot time, pressure, and volume shot. Ouch. Perhaps an average would be easiest for now.

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DX
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Post by DX » Sun Feb 25, 2007 7:03 pm

Twice. Lost the original long-ass post and then the replacement. If this goes through, it will be a miracle. If this doesn't go through, then there's something seriously wrong with my account.

EDIT: Oh sure, now you want to work. When I'm not posting a novel-length response, now you don't give me any denied access screens. Great.

4 hours of totally wasted time consolidated into one sentence: A mathematical formula for BPF is not going to work unless it takes into account battlefield type, game type family, and progression level in some way that accounts for all them.
Mess With the Best, Get Soaked Like the Rest!

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2007 Red Sox - World Series Champions!

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Silence
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Post by Silence » Sun Feb 25, 2007 7:59 pm

Ugh--I've lost two long posts in a row before, but not 4 hours' worth. Sorry to hear that. And it's usually because of Internet problems for me, not denied access. Anyway, can you return to the previous page and see the post still there? Perhaps it's an extension or something, but I *usually* see the text there.

It's true that this won't work for everything, if at all. This specific formula is definitely for 1HK on an outdoor battlefield. Progression level is definitely more complex.

But creating a formula for a different scenario should be just as easy.
  1. Identify the most important factors--weight, range, etc.
  2. Put the positive factors in the numerator and the negative factors in the denominator.
  3. Use the squares of the most important factors and the square root of the least important factors.

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DX
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Post by DX » Sun Feb 25, 2007 8:17 pm

When there's an error, only WWc holds my text. Everywhere else wipes it clean.

The current formula actually would work best for an OSF and wouldn't work at all for one hit games. The way it weighs shot time is different than the way shot time works in a good OHK/OHS. Ig2g, see you at like one in the morning.
Mess With the Best, Get Soaked Like the Rest!

2004 Red Sox - World Series Champions
2007 Red Sox - World Series Champions!

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Silence
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Post by Silence » Wed Feb 28, 2007 10:57 pm

Just split the thread, as WaterWolf thought the Silver Bullet homemade thread was getting too off-topic.

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joannaardway
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Post by joannaardway » Thu Mar 01, 2007 10:19 am

Looking at this, BPF has the 6th wierdiest units ever:

m^5*s^(1/2)*kg^-1

Beaten only by electrical capacitance (A^2*s^4*kg^-1*m^-2), Electrical potential (kg*m^2*s^-3*A^-2), Resistance (kg*m^2*s^-3*A^-1), Magnetic Flux (kg*m^2*s^-2*A^-1) and inductance (kg*m^2*s^-2*A^-2)

But aside from that, you've created a good measure of the practicality - of course, mass and capacity have to be traded off against each other - as in real life.
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