Maximum effenincy

[FordPrefect]

I just think that it would be a good idea to explore how much energy it would take to propel a paintball to 300 fps, under ideal conditions. That way, we can compare that number to how efficency of a real marker, minus some, because it is not an ideal condition (barrel matches, ect).

[Kevmaster]

in theory, work = force * distance. so if you got a 200' barrel and used a small force (say 10-20 newtons) you could get the ball to 300fps....meaning 5000 shots per 68/3000 tank....lol!!!

[bjjb99]

You would have to apply that 10-20 newtons to the ball throughout its entire trip down the barrel. To supply that force, you would need to continually add gas into the breech of the gun. How many moles of gas are contained in a 200 foot long barrel such that its pressure is sufficient to exert a 10-20 newton force on the back side of a paintball? How does this compare to the number of moles of gas contained in a 68/3K tank?

BJJB - too lazy today to run the numbers himself.

[J_Hoyt]

I get 9.3 moles of Nitrogen in a 68/3k. I'm not gonna post exactly what I did to get that cause it was kind of messy with all the metric conversions and the crappy conversion tables I had.

Joel Hoyt

hey are you the BJJB that posts to RSP quite a bit?

[bjjb99]

For some reason I always seem to be following up one of Jeff G's posts in that newsgroup. I think it's a conspiracy. But to answer your question, yes, I'm the same BJJB. I was originally BJJB here but at the time I did not frequent automags.org and in the intervening months of inactivity I lost my password. So I'm BJJB99 instead.

Last night I got off my butt and did the calculations that I was to lazy to do earlier. My mole calculation agrees with yours reasonably well, though I think you may have used a higher temperature than I did. I get 9.45 moles at 20 degrees C, 3000 psi (204.1 atmospheres), and 68 ci (0.00111 cubic meters). I hope I remembered my ideal gas constant correctly.

For the remainder of the calculation, I get around 0.6 moles per shot in a 200 foot barrel for an exit velocity of 300 fps, assuming constant acceleration and no forces other than the gas behind the ball. So we end up with around 16 shots per 68/3K tank for a barrel that long.

Reminds me of the good old days of 12 grams.

To answer the original question in this thread -- "how much energy does it take to propel a paintball to 300 fps under ideal conditions", just take a paintball moving at 300 fps and compute its kinetic energy. That's how much energy one must impart to the paintball under perfect (the frictionless perfect physics world kind of perfect) conditions. It's arond 0.27 joules of energy, assuming a 3 gram paintball.

BJJB

[pbjosh]

Here are two paths we went down on this before:

https://www.automags.org/forums/showt...threadid=18939

https://www.automags.org/forums/showt...threadid=33441

Josh

[J_Hoyt]

I did my calculations at 25 degrees C. What did you use for the R value in the PV = NRT equation? I used 8.31. I'm not really sure what that value is supposed to represent but my chem teacher last year just said it was 8.31

Joel Hoyt

[bjjb99]

I remember those threads, Josh. I think the first thread you mentioned had my first order calculation spreadsheet link in it. One of these days I'm going to have to get back to working on that thing, but priorities have pushed it to the back burner... gotta get a house built, then move in, then set up my lab and test area, and then I might have some spare time again.

Anyone know where I can get an inexpensive, high quality (inexpensive _and_ high quality? Yeah, right!) laboratory strobe? I want some microsecond pulses of white or near white light for a future test.

Joel, I used 20 degrees C and a value for R of 8.314. I assumed atmospheric pressure to be 14.7 psi, so 3000 psi equals 204.1 atmospheres. I used 101325 pascals per atmosphere to get the pressure value into the right units for the ideal gas equation. Volume was a straight conversion from cubic inches to cubic meters.

BJJB, waiting for a place to put his Newport optics table.

[Redkey]

white light?
optics table?

what are you working on?

[bjjb99]

I could tell you, but then they'd shoot you and fire me.

Ah, what the heck... I'm planning on setting up a Schlieren Optics system to capture and analyze the post-barrel airflow during the firing of a paintball. I think it would be interesting to actually see what happens to the gas after the ball exits the barrel. I have a sneaking suspicion that there may be more going on once the ball leaves the barrel than folks might realize.

Regardless of the outcome, it will be a fun experiment to perform.

Current experiment status: Awaiting house design and construction.
Projected experiment completion: 2004-ish if things go as planned.

BJJB

[pbjosh]

Really quick interuption-

We are planning our house with the Concrete/Foam Block setup with an inital small prow design and later adding out riggers-

How are you doing yours?

Josh

[Redkey]

Josh... where are you building?

I've taken a class on foam block/concrete building. It was pretty cool but I decided not to use it for my house. Having exposed foam in the basement is a no-no as far as the county is concerned. If I were to cover it with sheetrock the basement would be considered finished and therefor taxed as living space.

bjjb... how much light do you need? Would a bank of white leds do the trick?

[pbjosh]

Redkey,

Up above you a couple miles south of the border. I am in Bellingham. I was planning on a possible Brick Basement with Foam/Concrete top end, or building it on a slab. I might do a daylight, I will have to see what chunk of land I can pickup.

Why not a concrete brick bottom? And what was the pricing you figured for the house?

Josh

[bjjb99]

pbjosh - I am not currently at the point where construction materials are an issue. I am still working on the floorplan; there's a nasty bit of wasted space between my family room and my kitchen/"breakfast nook" that I can't seem to get rid of without resorting to 45 degree angle walls. I'm planning on taking my ideas to an architect in the not too distant future to see if he can help (and probably make me poor in the process).

Redkey - a bank of white LEDs won't do it. I need a really short, REALLY bright pulse of noncoherent light. Bright enough to properly expose 35mm film (ASA400) with a single microsecond-or-two flash. I plan on using as much of the flash emission as possible so I don't have stray photons going in useless directions.

Currently I'm thinking about a photography studio flash unit, but I'm not sure what the flash duration is on something like that. The overall plan is still very fluid, so it may well turn out that I don't need microsecond flashes, but rather a couple of orders of magnitude longer in duration. Basically I need to freeze the paintball in mid flight and minimize blurring of the imaged airflow pattern.

BJJB

[steveg]

Hey Redkey have you considered doing without a basement.
my wife and I are about 1 month from moving into our new
house. because of the geology rock,rock,rock and more rock
a basement wasn't feasible, so we did a slab on grade
with the added bonus of in-floor radiant heat.

the first floor 23x26(with 9 1/2'ceiling) work shop compensates for the lack
of basement