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strongest gun on the site?

A place to ask general spud cannon related questions.
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Unread postAuthor: elitesniper » Mon Mar 17, 2008 10:36 pm

haha, com on bigbob you can do it, think*HYBRID*think*SOUNDBARRIER*think*CARNAGE!* :)
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Unread postAuthor: bigbob12345 » Mon Mar 17, 2008 10:39 pm

:lol:
Im going to have to wait for next quarter though.
my grades are too bad to have any possible way to raise them.
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Unread postAuthor: benstern » Tue Mar 18, 2008 9:56 am

SWAT cannon for sure
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Unread postAuthor: rcman50166 » Tue Mar 18, 2008 11:06 am

DYI wrote:Firstly, I would like to state that rcman's claim about his "General" is a load of genuine, grade A [bovine excrement]. It's a rather small gasoline powered combustion, for those of you who didn't know, and would be lucky to hit 3 000 joules of muzzle energy, much less 20k. Rcman, if EVBEC told you that "General" gets 20k joules, it is broken, and should be euthanised.


Hmm... DYI I'm questioning your lack of faith in my equation. I was too until I looked into it myself. My cannon can shoot a 700mL Poland Spring Bottle 300 fps. That is fact. Now assuming the density of water is 1000kg/m^3, which it has been since the beggining of the universe, the mass of the bottle, or at least the water in it, would be .7kg. Now that I have the mass and the velocity, it is possible to find the energy of the ammunition as it leaves the barrel using Ek=1/2mv^2. So the equation is set up like this: Ek= 1/2(.7kg)(91.44m/s)^2. (oh i found the mistake, forgot to convert fps to m/s) The end solution would be 3762.57312J. Applying the law of conservation of energy, it can be assumed the energy of the cannon itself would ideally be the same. With real world energy losses the energy could very well reach 5000J. Well it appears my cannon isn't average seeing as it "would be lucky to hit 3000 joules of muzzle energy." The calculated energy of the round is with air resistance neglegable in the muzzle velocity calculation using video-aided kinematics. Also the mass of the round is with the mass of the container being neglegable. Even with these accounted for the ending kinetic energy of the round would only increase as a result. If you want me too, just to be a little more valid I could estimate the chemical potential energy of the combustion. I could aslo bring heat into the equation and calculate the blast bypass coefficient. Psh who needs a program to calculate energy when you've got physics on your side? Now that I have a more refined number and a nearly full scientific analysis, do you believe me?
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Unread postAuthor: elitesniper » Tue Mar 18, 2008 11:35 am

stiII penu beats combustion :D
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Unread postAuthor: Fnord » Tue Mar 18, 2008 12:17 pm

Rcman:
You should note that the largest combustion I have comes out to around 3500 joules when modeled with extremely ideal conditions in ggdt. This gun is approximately double the size of the General in terms of barrel length and has a more efficient CB.

While it is theoretically possible for your gun to achieve that kind of figure, I believe you will be limited by heat losses more than anything. You have quite a large amount of surface area on that gun that will be sucking energy from combustion through the entire process.
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Unread postAuthor: SpudFarm » Tue Mar 18, 2008 12:22 pm

_Fnord is right... you don't stand a chance rcman..
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Unread postAuthor: rcman50166 » Tue Mar 18, 2008 12:55 pm

I put the analysis on the thread to show my work. If you see an error in the math let me know. One of us is wrong and if I am the analysis should be all you need to prove it. Otherwise the program is miscalculating a variable. All of my equations are correct. I guarentee it.
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Unread postAuthor: elitesniper » Tue Mar 18, 2008 12:59 pm

what if I unscrew my original chamber and add a 15ft chamber and 25barrel? :roll:
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Unread postAuthor: Fnord » Tue Mar 18, 2008 1:00 pm

Your math is fine.

You estimated the velocity based on a camcorder video. That is the most likely cause of such an error.
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Unread postAuthor: rcman50166 » Tue Mar 18, 2008 1:10 pm

The camera runs at 15 frames per second. Using the same reference point from the video I calculated the distance to be 20ft per frame. 20x15=300. The visual aided kinematic teqnique I used is repeatable. Which I've done. By the way, 300fps is the middle ground. It's not like I was able to calculate an exact number. The number varies 15fps in either direction. But I agree that using a camera isn't necessarily the best technique to use.
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Unread postAuthor: SpudFarm » Tue Mar 18, 2008 1:19 pm

your camera may have 10frames one seond and 20 another... i don't think that is right...
sorry rcman :)

if you get a chrony i will belive you
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Unread postAuthor: SpudBlaster15 » Tue Mar 18, 2008 1:35 pm

Rcman: Your "scientific" analysis is very crude and inaccurate, considering you used a camcorder running on 15 fps to measure the displacement of the projectile during particular time intervals. You have also made a number of (incorrect and not backed by actual physics) assumptions in your analysis, not exactly what I would call "scientific".

EVBEC, which uses data obtained from the pressure curve of a launcher that was actually tested with multiple barrel lengths and a chronograph; puts your "General" at ~240fps when firing a 700 gram projectile, which gives a muzzle energy of ~1900J.

The program that I am working on, which uses a physics based approach and somewhat over simplifies the launcher; puts your "General" at around 2100J.

These results are probably very close to the actual figures, because the damage shown in your videos is unimpressive given such a massive round. The General is just a relatively small, low pressure cannon, and deserves no place amongst true powerhouses like the SCTBDC, the SWAT gun, and FEAR.

Also, you are not Newton, contrary to what your ego portrays.
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Unread postAuthor: rcman50166 » Tue Mar 18, 2008 2:42 pm

Oh I never wanted a spot with FEAR, SWAT, or SCTBDC. The strongest guns on the site are clearly hybrids. I would never make such a foolish assumption.

The analysis does not have a single assumption in it until after the kinetic energy of the round was calculated. And even when I make assumptions, they are entirely educated. The 5000J number was a dirivative of the typical efficiency of a heat engine. Which is usually around 50%. I didn't make it 50% because there is a smaller loss in heat energy (no compression phase other that combustion) Also total energy has to be increased to compensate for blowby and air resistance. (pertaining to the calculation of muzzle velocity)

I looked at the program. It seems there could be two problems with it.

The first is with the graph. The first is that it doesn't account fuel type. It assumes that you use metered propane. Also it doesn't account for 6 spark gaps. (which is what the "General" now has) It also assumes you have one chamber. It also assumes you have one fan. (the "General" has two) It also assumes that the chamber remains a constant diameter.

The second problem (maybe not, I can't make sense of the derivation) is the final energy calculation. How would E=.0005v^2m be derived?

@spudfarm The camera is a consistent 15fps, I've already checked that.

SpudBlaster15 wrote:Also, you are not Newton, contrary to what your ego portrays.


I find that statement completely unnecessary and offensive and appreciate it if you wouldn't post those kind of things in the future.
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Unread postAuthor: SpudBlaster15 » Tue Mar 18, 2008 3:23 pm

I looked at the program. It seems there could be two problems with it.

The first is with the graph. The first is that it doesn't account fuel type. It assumes that you use metered propane. Also it doesn't account for 6 spark gaps. (which is what the "General" now has) It also assumes you have one chamber. It also assumes you have one fan. (the "General" has two) It also assumes that the chamber remains a constant diameter.


1. Gasoline and propane have very similar amounts of potential energy given a fixed volume and stoichiometry.

2. 6 spark gaps in a chamber (or 2) with such a high length to diameter ratio will likely be roughly equal to Latke's chamber, which had 2 evenly spaced spark gaps in a 4" x 12" chamber.

3. Adding another chamber will not make much of a difference in the performance of a launcher if the volume remains the same. You will probably decrease performance, due to the additional flow restrictions required to combine 2 chambers to a single smaller diameter barrel.

4. 2 fans in two chambers will behave in the same manner as one fan in a single chamber.

The analysis does not have a single assumption in it until after the kinetic energy of the round was calculated. And even when I make assumptions, they are entirely educated. The 5000J number was a dirivative of the typical efficiency of a heat engine. Which is usually around 50%. I didn't make it 50% because there is a smaller loss in heat energy (no compression phase other that combustion) Also total energy has to be increased to compensate for blowby and air resistance. (pertaining to the calculation of muzzle velocity)


First of all, I'm not even sure why you are trying to use muzzle energy to obtain a total chamber energy value. If you want that, find the molar enthalpy change of formation for the main components of gasoline, multiply the values by the molar fraction of each component in the chamber, and then add them.

Second, typical combustion spudguns are nowhere near 50% efficient. A few months ago I calculated the efficiency of Latke's L1 at its ideal C:B ratio, and IIRC, it was around 15%. So yes, most of your ramblings are just uneducated assumptions.

I find that statement completely unnecessary and offensive and appreciate it if you wouldn't post those kind of things in the future.


I don't intend to offend you, but that is just how you come across to me.
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