chambered paint

[kauai_paintball]

ok, I have been reading threads on how making a gun that spins paint cant work because the paint inside slows down the spin, and eventually stops it. well why not make your own brand of paint, that has a thin gelatin wall straight through it. It is correct, that when you take a glass of water, and turn it the water dosent move with the cup. but if you have a cup with a chamber down the center, seperating two halves, the water dose move. so, if you took a paintball, and while making it put a thin gel wall through the center, then it would work. or, if you could, put a large X wall through it, so it will spin no matter what position its in when it enters the barrel.

[bjjb99]

Aside from increased manufacturing costs, the chamber walls would act as reinforcement and make the ball less likely to break on impact.

I'm not convinced of the "spinning raw egg" model for paintball fill. I have a few very, very old (we're talking late 1980's vintage) Nelson paintballs. They're so old that the pigment and carrier have settled out almost completely, and you can see their distributions through the transparent shell.

From time to time I have taken one of these paintballs, placed it between my fingers, and spun it rapidly with a snapping motion. I let it spin for a few seconds and then stop it by picking it up.

In no case have I seen a significant redistribution of the pigment and carrier. There's essentially zero remixing of the materials. This indicates to me that (at least for old Nelson paint) paintball fill acts a lot more like a hard-boiled egg than a raw one when spun. Perhaps I'm not spinning them fast enough, but I'd expect to see _something_ using these simple methods.

BJJB

[kauai_paintball]

Originally posted by bjjb99
Aside from increased manufacturing costs, the chamber walls would act as reinforcement and make the ball less likely to break on impact.

I'm not convinced of the "spinning raw egg" model for paintball fill. I have a few very, very old (we're talking late 1980's vintage) Nelson paintballs. They're so old that the pigment and carrier have settled out almost completely, and you can see their distributions through the transparent shell.

From time to time I have taken one of these paintballs, placed it between my fingers, and spun it rapidly with a snapping motion. I let it spin for a few seconds and then stop it by picking it up.

In no case have I seen a significant redistribution of the pigment and carrier. There's essentially zero remixing of the materials. This indicates to me that (at least for old Nelson paint) paintball fill acts a lot more like a hard-boiled egg than a raw one when spun. Perhaps I'm not spinning them fast enough, but I'd expect to see _something_ using these simple methods.

BJJB

Ok, I took several paintballs and shaped them into an egg shape. and then I took two eggs(one hard one soft center)
and then I spun them. the paint acted exactly like the hardboiled eggs. Of course a glass of water wont spin with the cup, but if you take flour, and mix it into the water enough to make it the viscosity of paint, and then spin the cup, the mixture would spin with the cup. the paint fill in the paintbll is very thick usually, which means that it would spin with the shell. if it was spining fast enough, the shell would spin without the fill,
although we cant just assume because water dosent spin with the cup, that paint dosent too. it has differnt tendencies and physics. because of this, there must be some other reason contributing to why the paint dosent travel further then non spinning paint.

[Joni]

Nobody has ever argued that putting backspin on a paintball doesn't make it go further. It can be seen with a flatline barrel. The reason it goes further is that it's an aerodynamic effect, so it doesn't matter if its only the shell spinning. What this discussion is about is the fact that using rifling or another way to spin the paintball to make it more accurate has no effect. Real guns get better accurasy because of rifling, and I guess thats due to the gyro effect. To get the gyro effect, you have to have rotating mass, and if only the shell rotates, the mass rotating will be negligable. I can't see how you spinning a paintball by hand tells you anything. You wont come close to the RPM required for having an effect on accurasy, and when you get to those RPM's, the shell will spin without the filling.

[kauai_paintball]

yeah, but anyday proper logic says that because the fill is so thick it SHOULD spin with the shell.

[Target Practice]

Break open a ball, get paint on your fingers, and rub them together. The viscosity of the paint, IMO, will not allow for the amount of drag needed to rotate the fill.

[bjjb99]

Find a place you don't mind getting messay, and get a 3x3 inch piece of wax paper. Break open a paintball and empty the fill onto it. Now take your finger and flick the fill without flicking the paper. Does the paper move? If so you've imparted enough force by flicking the fill to move pretty much the entire mass of a paintball. If you can do that with just your finger, why wouldn't a spinning paintball shell do something similar?

Spinning a paintball by hand is a just a quick-n-dirty type of test.

The claim is that at high rotational rates the coupling between the fill and shell rotations is weak to nonexistant. The argument for this claim is that the Flatline barrel and other backspin-producing barrels actually do spin the ball at high rates (so the shell is obviously spinning), but axial spin resulting from rifling does not seem to gyroscopically stabilize the paintball in flight (so the fill must not be spinning).

Let's assume the ball makes perfect rolling contact within the Flatline barrel. Its surface velocity is approximately 300 feet per second upon exit from the barrel. This is right around 100000 RPM. I'll admit that I can't spin a ball by hand that fast :) and I certainly don't have the type of hardware necessary to achieve those spin rates in a controlled environment. Keep in mind, however, that a rifled barrel won't put that amount of spin on the ball; in order to do so, you'd have to have one rifling "twist" every 2.13 inches! I happen to own a very old Armson "rifled" barrel, an it looks like it might have 1/4 of a twist per foot. That's over a factor of twenty less than the 100000 RPM maximum spin rate of a Flatline. We're down in the 4500 RPM range now. I still don't think I can spin my fingers that fast. :)

Since I can't test it directly, let's look at this problem from a basic physics standpoint.

Viscosity is a measurement of how well a material conducts lateral forces as a function of distance from a moving surface. It is used to relate the lateral force per unit area imparted on a stationary surface as a result of a second, moving surface located some distance away. We can use this relationship to examine, at least on a first cut basis, what types of forces are working on the paintball fill.

I took a paintball, cracked open its shell, and rubbed some of the fill between my fingers. I then put a bit of olive oil on my fingers and did the same thing. They felt fairly similar, so I'm going to use viscosity values for olive oil as a surrogate for paintball fill. For this post, the two are "close enough".

The viscosity of olive oil is around 0.2 Pascal-seconds.

Let's ignore acceleration effects and just assume that the shell is spinning at around 4500 RPM with a completely stationary fill inside.

At this spin rate, the surface velocity of the paintball shell at its widest point is around 4.1 meters per second.

Let's see what forces are at work about 1 millimeter (0.001 meters) below the surface of the paintball shell.

The lateral force per unit area (F/A) is computed as follows:

F/A = viscosity * velocity / separation_distance

F/A = 0.2 Pa-s * 4.1 m/s / 0.001 m = 814 N/m^2

The surface area of the fill 1 millimeter below the paintball's surface (a radius of 7.636 millimeters) is found by:

A = 4 * pi * r^2

A = 4 * pi * 0.007636

A = 0.000733 m^2

The force acting on that surface is therefore

F = 814 N/m^2 * 0.000733 m^2

F = 0.596 Newtons

The torque working to rotate the painball fill that is further than 1 millimeter from the surface is just the force F acting at a distance of 7.636 millimeters from the center of the paintball.

T = 0.596 * 0.007636

T = 0.00455 N-m

Yes, I know, I'm using a bit of cylindrical thinking and applying it to a spherical case, but I'm looking for a first-cut solution here and not trying to do a full treatment of the problem. In reality you'd get lesser forces near the poles since the surface velocity is lower, and then you'd have to treat all the interactions of different-velocity fluids and I just don't have the time right now to do all the additional calculus. :)

Now to calculate the angular acceleration of the fill...

The moment of inetria for a sphere is 2/5 * M * R^2, where M is the mass of the sphere and R is the sphere's radius.

The mass of a paintball is around 3 grams (0.003 kilograms). We want the mass of that portion of a paintball that is further than 1 millimeter away from the shell. So we've got to multiply the paintball mass by the ratio of sphere volumes. Lots of the pi's and constants cancel out, leaving us with:

M = m1 * r2^3 / r1^3, where

m1 = 0.003 kg
r1 = 0.008636 (the actual paintball's radius)
r2 = 0.007636 (the radius of the fill that's at least 1 mm from the shell)

M = 0.0021 kg

The radius R is simply 0.007636 meters.

So, the moment of inertia is

I = 2/5 * 0.0021 * 0.007636^2

I = 4.837 x 10^-8 kg-m^2

The angular acceleration is simply the ratio of the torque and the moment of inertia:

a = T / I

a = 0.00455 N-m / 4.837 x 10^-8 kg/m^2

a = 94150 radians/sec^2

That's an absolutely huge angular acceleration. Assuming that angular acceleration remains constant, it would take about 5 milliseconds for the paintball fill to reach the same rotational velocity as the shell.

So, based on this rough treatment, it looks like the fill probably gets up to speed while the ball is still within the paintgun barrel. A more thorough treatment might show that the paintball fill gets up to near-shell speeds in about 10 milliseconds or so, but we're still talking about a ball that's less than a meter from the paintgun at that point.

Thoughts?

BJJB

[trains are bad]

Yeah I don't think the fill would ever reach max shell speed outside of the barrel, siince the rifleing is not driving the shell anymore I think the shell would slow down to the fill speed or a little bit of both.

[kauai_paintball]

Ok, well think about this. take an old record player and put a record on it. then turn it on. (dont put the needle on it) what happens? it spins. The outside is always spinning fastest , and the inside is always spinning slowest. thats true foar all spinning objects, wherether sherical or square or whatever. so saying this, the inside should not have to spin as fast as the outside, and stil make the same effect.

[paintballman_13]

Originally posted by bjjb99
Find a place you don't mind getting messay, and get a 3x3 inch piece of wax paper. Break open a paintball and empty the fill onto it. Now take your finger and flick the fill without flicking the paper. Does the paper move? If so you've imparted enough force by flicking the fill to move pretty much the entire mass of a paintball. If you can do that with just your finger, why wouldn't a spinning paintball shell do something similar?

Spinning a paintball by hand is a just a quick-n-dirty type of test.

The claim is that at high rotational rates the coupling between the fill and shell rotations is weak to nonexistant. The argument for this claim is that the Flatline barrel and other backspin-producing barrels actually do spin the ball at high rates (so the shell is obviously spinning), but axial spin resulting from rifling does not seem to gyroscopically stabilize the paintball in flight (so the fill must not be spinning).

Let's assume the ball makes perfect rolling contact within the Flatline barrel. Its surface velocity is approximately 300 feet per second upon exit from the barrel. This is right around 100000 RPM. I'll admit that I can't spin a ball by hand that fast :) and I certainly don't have the type of hardware necessary to achieve those spin rates in a controlled environment. Keep in mind, however, that a rifled barrel won't put that amount of spin on the ball; in order to do so, you'd have to have one rifling "twist" every 2.13 inches! I happen to own a very old Armson "rifled" barrel, an it looks like it might have 1/4 of a twist per foot. That's over a factor of twenty less than the 100000 RPM maximum spin rate of a Flatline. We're down in the 4500 RPM range now. I still don't think I can spin my fingers that fast. :)

Since I can't test it directly, let's look at this problem from a basic physics standpoint.

Viscosity is a measurement of how well a material conducts lateral forces as a function of distance from a moving surface. It is used to relate the lateral force per unit area imparted on a stationary surface as a result of a second, moving surface located some distance away. We can use this relationship to examine, at least on a first cut basis, what types of forces are working on the paintball fill.

I took a paintball, cracked open its shell, and rubbed some of the fill between my fingers. I then put a bit of olive oil on my fingers and did the same thing. They felt fairly similar, so I'm going to use viscosity values for olive oil as a surrogate for paintball fill. For this post, the two are "close enough".

The viscosity of olive oil is around 0.2 Pascal-seconds.

Let's ignore acceleration effects and just assume that the shell is spinning at around 4500 RPM with a completely stationary fill inside.

At this spin rate, the surface velocity of the paintball shell at its widest point is around 4.1 meters per second.

Let's see what forces are at work about 1 millimeter (0.001 meters) below the surface of the paintball shell.

The lateral force per unit area (F/A) is computed as follows:

F/A = viscosity * velocity / separation_distance

F/A = 0.2 Pa-s * 4.1 m/s / 0.001 m = 814 N/m^2

The surface area of the fill 1 millimeter below the paintball's surface (a radius of 7.636 millimeters) is found by:

A = 4 * pi * r^2

A = 4 * pi * 0.007636

A = 0.000733 m^2

The force acting on that surface is therefore

F = 814 N/m^2 * 0.000733 m^2

F = 0.596 Newtons

The torque working to rotate the painball fill that is further than 1 millimeter from the surface is just the force F acting at a distance of 7.636 millimeters from the center of the paintball.

T = 0.596 * 0.007636

T = 0.00455 N-m

Yes, I know, I'm using a bit of cylindrical thinking and applying it to a spherical case, but I'm looking for a first-cut solution here and not trying to do a full treatment of the problem. In reality you'd get lesser forces near the poles since the surface velocity is lower, and then you'd have to treat all the interactions of different-velocity fluids and I just don't have the time right now to do all the additional calculus. :)

Now to calculate the angular acceleration of the fill...

The moment of inetria for a sphere is 2/5 * M * R^2, where M is the mass of the sphere and R is the sphere's radius.

The mass of a paintball is around 3 grams (0.003 kilograms). We want the mass of that portion of a paintball that is further than 1 millimeter away from the shell. So we've got to multiply the paintball mass by the ratio of sphere volumes. Lots of the pi's and constants cancel out, leaving us with:

M = m1 * r2^3 / r1^3, where

m1 = 0.003 kg
r1 = 0.008636 (the actual paintball's radius)
r2 = 0.007636 (the radius of the fill that's at least 1 mm from the shell)

M = 0.0021 kg

The radius R is simply 0.007636 meters.

So, the moment of inertia is

I = 2/5 * 0.0021 * 0.007636^2

I = 4.837 x 10^-8 kg-m^2

The angular acceleration is simply the ratio of the torque and the moment of inertia:

a = T / I

a = 0.00455 N-m / 4.837 x 10^-8 kg/m^2

a = 94150 radians/sec^2

That's an absolutely huge angular acceleration. Assuming that angular acceleration remains constant, it would take about 5 milliseconds for the paintball fill to reach the same rotational velocity as the shell.

So, based on this rough treatment, it looks like the fill probably gets up to speed while the ball is still within the paintgun barrel. A more thorough treatment might show that the paintball fill gets up to near-shell speeds in about 10 milliseconds or so, but we're still talking about a ball that's less than a meter from the paintgun at that point.

Thoughts?

BJJB

Your insane.

[kauai_paintball]

paintball man, dont do read good? hes obviously being sane and not jumping to conclusions, hes providing physics and algebraic proof.

[bjjb99]

Originally posted by paintballman_13




Your insane.

Well, I can't deny that.

However, I'm just doing what's expected in Deep Blue. I'm posting my thoughts with sufficient supporting information for folks to examine why and how I've come to my conclusions. Simply saying "the fill doesn't spin" or "the fill does spin" doesn't carry the discussion along in this forum.

You think this discussion is a bit nuts, take a look at some of the older threads in Deep Blue, in particular the paintball spin physics thread and its predecessor that (I think... might be wrong) discussed the cyclic rates of autocockers. We started getting into computational fluid dynamics in those threads. :)

BJJB

[temps]

EDIT: I don't know what i was smoking this morning...

[Korrosion]

Originally posted by bjjb99


Well, I can't deny that.

However, I'm just doing what's expected in Deep Blue. I'm posting my thoughts with sufficient supporting information for folks to examine why and how I've come to my conclusions. Simply saying "the fill doesn't spin" or "the fill does spin" doesn't carry the discussion along in this forum.

You think this discussion is a bit nuts, take a look at some of the older threads in Deep Blue, in particular the paintball spin physics thread and its predecessor that (I think... might be wrong) discussed the cyclic rates of autocockers. We started getting into computational fluid dynamics in those threads. :)

BJJB

/threadjack
A long time ago I remember reading the cyclic speed for an autococker thread but I dont ever remember finding an answer... What was the max cyclic speed with or without qev's?
/endthreadjack

[Igotu]

You guys stold my Idea I've allways thought about this since I read an article apg about the glass and ice spinning method. It would be hard to put just a wall of gelatin in the midle because the paint wouldnt be even after filling process, unless they made a better machine. I have a video of making paintballs but I dont know how to post videos So whats the conclusion would a chambered paintball work?