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Ball Density and Roundness


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#1 Lord Odin

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Posted 29 December 2008 - 05:09 PM

I was extremely bored today, so I did a very boring and lengthy test to see what the density of my Reballs were. I busted out the scale and calipers and started taking measurements. Then I wanted to know how paintballs compared to them. I had to figure out the volume of all balls and as we all know, they are not perfectly round. So I took the highest and lowest measurement of each ball and recorded them. I tried crunching the data and ended up with a roundness test that takes a look at how much each type deviates from being spherical. This doesn't measure shell thickness or fill viscosity; the mass is just measured as a whole ball.

I did find it interesting that most of the time the largest measurements were just off the seam where they bulge out the most. Also, the smallest measurements were usually near the poles of the balls.

Data: http://www.mediafire.com/?jnjfgyzezqm

Edited by Lord Odin, 29 June 2009 - 09:07 PM.


#2 brycelarson

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Posted 29 December 2008 - 05:17 PM

Good stuff man. Nice work.

#3 Lord Odin

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Posted 29 December 2008 - 05:53 PM

Oh, forgot to mention a few things.

The data shows that Reballs are more perfectly spherical than most paintballs. They will deviate less from round than paintballs and would serve as a good testing medium.

Even though they are solid rubber, they are still less dense and lighter than paintballs. It also seems that Reballs fluctuate very little in their weight. On the other end, Polar Ice and Marbs fluctuate quite a bit. Since their mass varies more, that would mean that they could fluctuate in your gun's velocity as well (F=ma). That would affect your accuracy vertically and it would also vary the amount of pain a person would feel.

#4 brycelarson

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Posted 29 December 2008 - 06:07 PM

That would affect your accuracy vertically and it would also vary the amount of pain a person would feel.


and, if mass is changing - your maximum potential range

#5 Lucas

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Posted 29 December 2008 - 06:14 PM

That would affect your accuracy vertically and it would also vary the amount of pain a person would feel.


and, if mass is changing - your maximum potential range


Yup,
That was all else that needs to be said. :)
Good work Man... Nice data table and judging
By it your measurements were acurate and
Precise

#6 kert.

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Posted 30 December 2008 - 08:23 AM

Awesom job! Thanks.

Manufacturers should add numbers like that on the box instead of field, tournament etc.. B)

#7 Merc4Hire

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Posted 03 January 2009 - 05:45 AM

Just another thanks.

I need to come up with something useful to contribute.


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#8 sunshaker

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Posted 04 January 2009 - 04:36 PM

I had to figure out the volume of all balls and as we all know, they are not perfectly round. So I took the highest and lowest measurement of each ball and recorded them.


The water displacement trick wouldn't work here because the water would wreck the paintball (changing the volume), but you can do the fine powder displacement trick. Basically you get some fine sand, carefully measure a given volume of it, place one or more paintballs in a marked container and pour in the given volume of sand. Any difference between the two volumes is the volume of the paintball(s). The paintballs might be a bit dirty afterwards so you might not want to fire them...

#9 Lord Odin

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Posted 04 January 2009 - 05:36 PM

I had to figure out the volume of all balls and as we all know, they are not perfectly round. So I took the highest and lowest measurement of each ball and recorded them.


The water displacement trick wouldn't work here because the water would wreck the paintball (changing the volume), but you can do the fine powder displacement trick. Basically you get some fine sand, carefully measure a given volume of it, place one or more paintballs in a marked container and pour in the given volume of sand. Any difference between the two volumes is the volume of the paintball(s). The paintballs might be a bit dirty afterwards so you might not want to fire them...

That's not a bad idea. How would you know the sand is perfectly level, though? It wouldn't self-level and using something to level it off might introduce human error.

#10 sunshaker

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Posted 04 January 2009 - 07:47 PM

That's not a bad idea. How would you know the sand is perfectly level, though? It wouldn't self-level and using something to level it off might introduce human error.


I can't take credit for that idea, an astronomer (who is also a priest) working for the Vatican Observatory came up with that method for measuring meteorite fragments (yes I tend to remember weird obscure information). He had to come up with a method that did not damage/corrode the meteorite fragment, but that could get into all the small places on the uneven surface. I don't know the exact powder he used nor do I know how he leveled it (maybe vibration or shaking, but that is me guessing). I suspect that the powder in question would have to be fairly heavy and not compactable (so no flour) which is making me thing sand of some kind.

You might have to average the volume of several paintballs.

#11 betasniper

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Posted 04 January 2009 - 08:02 PM

an other way to make it level is center it on a quick spining table. just make sure to not have it spin to fast. another thought of mine is to use a centrifuge.
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#12 Leftystrikesback

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Posted 05 January 2009 - 03:09 AM

The measurements and observations about maximum and minimum diameters agree with what I've measured as well. It may also be interesting to note that the wall is much thicker at the seam and gradually thins out towards the poles as well, so that the poles are thinnest and seam is thickest. But it's a gradual change, from what I've seen the seam is not just a bulge around the equator of the ball. (using Elixir)


The water displacement trick wouldn't work here because the water would wreck the paintball (changing the volume), but you can do the fine powder displacement trick. Basically you get some fine sand, carefully measure a given volume of it, place one or more paintballs in a marked container and pour in the given volume of sand. Any difference between the two volumes is the volume of the paintball(s). The paintballs might be a bit dirty afterwards so you might not want to fire them...


What's wrong with putting the paintball in water? The volume of the paintball that went into the water is conserved, and as long as you weigh it before you put it in, who cares if it's unusable when it comes out. Water, olive oil, alcohol, any liquid will work to measure volume, just make sure the ball sinks.
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#13 Troy

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Posted 05 January 2009 - 09:57 AM

I don't know the exact powder he used nor do I know how he leveled it (maybe vibration or shaking, but that is me guessing). I suspect that the powder in question would have to be fairly heavy and not compactable (so no flour) which is making me thing sand of some kind.


I have to admit, the first thing that I thought of also was vibration also, but I think you are over thinking it. Put the paintball+sand into a cup and heap the sand on top (so it is piled up over the brim) then use a ruler to scrape off the excess. As long as the cup's rim is flat and the ruler is able to touch both sides it would be pretty damn hard to screw up and add human error.
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