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Backspin bolts and such


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#1 rntlee

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Posted 25 December 2011 - 12:34 PM

I know, they don't work...but they also can't work!

Consider the following compiled experimental data on lift coefficients:

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Line 1 pertains to sphere's with a smooth surface. V/U is the ratio of the spin velocity (V) to the linear velocity (U). According to this data, most spin-induced forces in paintball (excluding super-high rpm spins like the Apex causes) occur in the negative lift region of the chart (the portion up to about 0.4 V/U). This means that a lower rpm backspin would actually impart a negative lift force and cause a decrease in range.

You would actually want a "topspin" bolt to increase range.
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Edited by rntlee, 25 December 2011 - 12:35 PM.


#2 brycelarson

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Posted 25 December 2011 - 04:16 PM

huh, interesting find.

#3 Molybdenum

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Posted 25 December 2011 - 06:48 PM

-Jack Rice-


He would probably tell you that the number is above 0.4, and there fore is out of the negative range.

Edited by brycelarson, 26 December 2011 - 09:50 AM.


#4 rntlee

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Posted 25 December 2011 - 07:06 PM

well, with a 280 fps initial velocity, the initial spin would need to be around18000 rpm to result in a net positive lift force. The lift coefficient would begin negative but switch to positive as the ball's velocity decayed.

Edited by brycelarson, 26 December 2011 - 09:51 AM.


#5 Cutterj

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Posted 25 December 2011 - 08:23 PM

Big words make me dislike alien

#6 MrEeske

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Posted 25 December 2011 - 09:22 PM

but they also can't work!

A salesman's priority isn't to make the best functional product, just the best selling one. Sensational fads like cross-drilled brake rotors (obsoleted by modern day ceramic pads) and backspin bolts exist just to make a quick buck. HOWEVER, I'm glad to see someone shining the torch of science to bring illuminance the [potentially false] performance rumor of these bolts.

You would actually want a "topspin" bolt to increase range.

Careful with how you say that; the data tells nothing about what may happen with the opposite spin direction. A spin in the opposite direction may have even worse performance, with respect to lift. By the way... what axis is the ball spinning around? From what is shown, we can only assume that the rotation is backspin. The data doesn't say whether the spin is foreword, backward, or even if it's being spun like a bullet.


#7 drg

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Posted 25 December 2011 - 09:42 PM

So spin-induced lift doesn't exist?
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#8 rntlee

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Posted 25 December 2011 - 11:04 PM

You would actually want a "topspin" bolt to increase range.

Careful with how you say that; the data tells nothing about what may happen with the opposite spin direction. A spin in the opposite direction may have even worse performance, with respect to lift. By the way... what axis is the ball spinning around? From what is shown, we can only assume that the rotation is backspin. The data doesn't say whether the spin is foreword, backward, or even if it's being spun like a bullet.


It actually does if you look into the data. The "Magnus effect" is a well documented force affecting spinning spheres. In the graph I posted above, the area below the "0" line is called the "anti-Magnus" region, the area above is the Magnus region. The axis of spin isn't important as the force is relative to the direction of spin. If the spin is off-axis left or right to the direction of travel, the force will act to move the ball to the left or to the right (an Apex "hook shot" is an example).
In the anti-Magnus region, the direction of the net force is reversed, whereas a backspin will now induced a negative rather than positive lift and a topspin will induce a positive rather than a negative lift.

It's interesting to note that this data is the result of measured experiment, not calculation. It's still not certain why smooth sphere's exhibit "anti-magus" properties at low V/U. I'm not aware of any mathematical models that predict it, though I'm definitely no expert.




#9 rntlee

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Posted 25 December 2011 - 11:09 PM

So spin-induced lift doesn't exist?


No, it definitely exists...but the direction of lift just isn't simply "positive for backspin and negative for topspin". It's dependent on the ratio of the rotational speed of the surface of the ball to the linear velocity of the ball. (for smooth sphere's travelling in a viscous fluid)

Edited by rntlee, 25 December 2011 - 11:38 PM.


#10 Kermit

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Posted 26 December 2011 - 12:22 AM

shit, not this again...


Interesting find though, I'd like to see more without alien being brought into it :)

#11 drg

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Posted 26 December 2011 - 02:43 AM


So spin-induced lift doesn't exist?


No, it definitely exists...but the direction of lift just isn't simply "positive for backspin and negative for topspin". It's dependent on the ratio of the rotational speed of the surface of the ball to the linear velocity of the ball. (for smooth sphere's travelling in a viscous fluid)


So couldn't a backspin bolt potentially work, if it achieved the requisite spin?
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#12 andrewthewookie

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Posted 26 December 2011 - 02:51 AM

Yes, but only if they actually put spin on the paintball. So far, there haven't been any tests that have shown them to do so.

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#13 brycelarson

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Posted 26 December 2011 - 09:48 AM

Please leave alien out of this unless it's in a purely neutral conversation. No insults, no name calling.

drg - yes, spin systems can work. Its based on the spin rate ratio to velocity. It's the reason that an Apex set on the higher settings dip before rising. The spin rate (more than 25k) isn't high enough to produce lift until the velocity of the ball has dropped somewhat.

We have high speed footage of the apex - it consistently produces extremely high rotational speeds and always in the same direction. The low blow bolt systems we've filmed produced rotation at speeds and directions that roughly matched any normal bolt system - in other words <2400 at random speeds in random directions.

#14 MrEeske

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Posted 26 December 2011 - 12:59 PM

The "Magnus effect" is a well documented force affecting spinning spheres.

I am acutely aware of the Magnus Effect and how to apply it to a sphere. As I was once a tournament-participating tennis player of several years, playing with spin on tennis balls was a necessity in winning matches (e.g., top spin, back spin, side spin).

For the record, I am a believer of the Magnus Effect. I am not arguing that spin does not induce lift; from my own experience in tennis and with education of fluid dynamics, spin very much induces lift; however, the direction of that lift is dependent upon the axis of rotation and direction of rotation. The concept of the Magnus Effect is that the rotating sphere is creating pockets of low and high air pressure, just like an airplane wing. The location of those pockets of different pressure depend, again, on the axis and direction of rotation.

With that out of the way, what I was criticizing wasn't so much your conclusions about the data, but the presentation of the data. It's a chart with squiggly lines, but what those lines represent isn't well defined. For example, why are there two lines for each sample? The chart seems to indicate that it displays both coefficient of drag (CD) and coefficient of lift (CL), but which line is which? Also, those numbers are entirely dependent upon the Reynolds number of the sphere... does a paintball have a Reynolds number of 94,000?

By the way, one article that data is from, The Aerodynamics of Golf Balls, is specific to golf balls. The article also assumes perfect spheres, which our paintballs are most definitely not due to their seam.

Again, I'm not criticizing the conclusions, I'm criticizing the presentation of data. Give context to the numbers. I'm not trying to kill this conversation, just making sure of the quality of presented data.

Edited by MrEeske, 26 December 2011 - 01:09 PM.


#15 cockerpunk

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Posted 26 December 2011 - 03:50 PM

interesting find, i like the graph.

can i get a source on that? looks to be from an academic paper.

Edited by cockerpunk, 26 December 2011 - 03:51 PM.

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#16 rntlee

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Posted 27 December 2011 - 07:57 AM

interesting find, i like the graph.

can i get a source on that? looks to be from an academic paper.

I took that graph from Gary Dyrkacz's site... I'm not sure if it's his own compilation or whether it originated somewhere else.

#17 rntlee

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Posted 27 December 2011 - 08:09 AM

... what I was criticizing wasn't so much your conclusions about the data, but the presentation of the data. It's a chart with squiggly lines, but what those lines represent isn't well defined. For example, why are there two lines for each sample? The chart seems to indicate that it displays both coefficient of drag (CD) and coefficient of lift (CL), but which line is which? Also, those numbers are entirely dependent upon the Reynolds number of the sphere... does a paintball have a Reynolds number of 94,000?



The chart does show both the drag coefficient and the lift coefficient, with CD being the top line as it is definitely the larger force. The reynolds number of a paintball @ 280 fps is somewhere around 94 000.

By the way, one article that data is from, The Aerodynamics of Golf Balls, is specific to golf balls. The article also assumes perfect spheres, which our paintballs are most definitely not due to their seam.


That's a good point...should well made paintballs be considered "smooth sphere's" ? I think so, as Maccoll obtained similar anti-Magnus readings using wooden spheres. It would really need to be demonstrated via experiment to be certain though.




#18 drg

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Posted 28 December 2011 - 04:24 PM

drg - yes, spin systems can work. Its based on the spin rate ratio to velocity. It's the reason that an Apex set on the higher settings dip before rising. The spin rate (more than 25k) isn't high enough to produce lift until the velocity of the ball has dropped somewhat.

We have high speed footage of the apex - it consistently produces extremely high rotational speeds and always in the same direction. The low blow bolt systems we've filmed produced rotation at speeds and directions that roughly matched any normal bolt system - in other words <2400 at random speeds in random directions.


Right, of course what I'm getting at is that the OP claimed that backspin bolts "can't" work ... which is a pretty broad claim and is not supported by the evidence he presented.

By the way the spin depression/rise effect is well known to anyone who golfs. It tends to happen on lower-loft, longer clubs.

Edited by drg, 28 December 2011 - 04:26 PM.

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#19 rntlee

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Posted 28 December 2011 - 10:21 PM

... what I'm getting at is that the OP claimed that backspin bolts "can't" work ... which is a pretty broad claim and is not supported by the evidence he presented.


I stand by my statement.
"Backspin" bolts will not increase range as low rpm (>18000) backspin will impart a downward force, not a lifting force. Unless you feel backspin bolts are capable of inducing this quantity of spin.
You're question concerned whether spin effects exist, which they do. Unfortunately, for smooth sphere's the forces are reversed at low V/U, which is right where the spin induced by backspin bolts would reside.

It's all an academic discussion anyway... no "backspin bolt" tested here has ever demonstrated an ability to induce any consistent backspin anyway.




#20 drg

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Posted 28 December 2011 - 10:31 PM


... what I'm getting at is that the OP claimed that backspin bolts "can't" work ... which is a pretty broad claim and is not supported by the evidence he presented.


I stand by my statement.
"Backspin" bolts will not increase range as low rpm (>18000) backspin will impart a downward force, not a lifting force. Unless you feel backspin bolts are capable of inducing this quantity of spin.
You're question concerned whether spin effects exist, which they do. Unfortunately, for smooth sphere's the forces are reversed at low V/U, which is right where the spin induced by backspin bolts would reside.

It's all an academic discussion anyway... no "backspin bolt" tested here has ever demonstrated an ability to induce any consistent backspin anyway.


Current or tested backspin bolt designs in specific barrel setups may not work in this way, but that's not to say another design or combination may not be created that does. Since you did not specify the designs to be current or anything at all, you leave your statement open in perpetuity to being proven wrong, and unable to ever be proven right. Sharpen the thinking and be specific, this is supposed to be an egghead type forum, is it not?
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#21 cockerpunk

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Posted 28 December 2011 - 11:07 PM



... what I'm getting at is that the OP claimed that backspin bolts "can't" work ... which is a pretty broad claim and is not supported by the evidence he presented.


I stand by my statement.
"Backspin" bolts will not increase range as low rpm (>18000) backspin will impart a downward force, not a lifting force. Unless you feel backspin bolts are capable of inducing this quantity of spin.
You're question concerned whether spin effects exist, which they do. Unfortunately, for smooth sphere's the forces are reversed at low V/U, which is right where the spin induced by backspin bolts would reside.

It's all an academic discussion anyway... no "backspin bolt" tested here has ever demonstrated an ability to induce any consistent backspin anyway.


Current or tested backspin bolt designs in specific barrel setups may not work in this way, but that's not to say another design or combination may not be created that does. Since you did not specify the designs to be current or anything at all, you leave your statement open in perpetuity to being proven wrong, and unable to ever be proven right. Sharpen the thinking and be specific, this is supposed to be an egghead type forum, is it not?


any negative claim is always "open to being disproven in perpetuity"

thats simply the logic of a negative claim.
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And yes, Gordon is the sexiest manifestation of "to the front."


#22 drg

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Posted 29 December 2011 - 02:07 PM

Perhaps a worthwhile consideration is whether backspin bolts do anything at all. Do they cause a different application of forces on the ball than a standard bolt? I believe the evidence shows that it may. How would you test that? But it's quite possible that the barrel combinations that have been tested have simply not been able to translate that action into anything useful.
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#23 Troy

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Posted 29 December 2011 - 04:36 PM

Perhaps a worthwhile consideration is whether backspin bolts do anything at all. Do they cause a different application of forces on the ball than a standard bolt? I believe the evidence shows that it may.


What evidence?
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#24 brycelarson

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Posted 29 December 2011 - 05:43 PM

Perhaps a worthwhile consideration is whether backspin bolts do anything at all. Do they cause a different application of forces on the ball than a standard bolt? I believe the evidence shows that it may. How would you test that? But it's quite possible that the barrel combinations that have been tested have simply not been able to translate that action into anything useful.


High speed video doesn't - and that's about as good a test as I can think of. Spin is absolutely apparent in an apex - and random and at a low rate on backspin systems just like out of standard bolt systems. So I would suggest that evidence shows that it doesn't. And again - null hypothesis. You are right to argue that in some magical combination it might do something and I can't tell you that you're wrong. That doesn't mean you're right however. You need to produce evidence countering the null hypothesis.

Here's the deal. I spent a good portion of a year on this in the past. I still have seen ZERO evidence that backspin bolt systems are capable of producing spin. This is a worthless and boring conversation until some new evidence comes to light.

#25 drg

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Posted 29 December 2011 - 05:54 PM


Perhaps a worthwhile consideration is whether backspin bolts do anything at all. Do they cause a different application of forces on the ball than a standard bolt? I believe the evidence shows that it may.


What evidence?


http://www.mcarterbr...est-v2-0-a.html

Yup, been discussing and testing this stuff for years. Oh and look the depression-rise effect was discussed in that thread as well ... all those years ago ...

Edited by drg, 29 December 2011 - 05:55 PM.

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#26 drg

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Posted 29 December 2011 - 06:04 PM


Perhaps a worthwhile consideration is whether backspin bolts do anything at all. Do they cause a different application of forces on the ball than a standard bolt? I believe the evidence shows that it may. How would you test that? But it's quite possible that the barrel combinations that have been tested have simply not been able to translate that action into anything useful.


High speed video doesn't - and that's about as good a test as I can think of. Spin is absolutely apparent in an apex - and random and at a low rate on backspin systems just like out of standard bolt systems. So I would suggest that evidence shows that it doesn't.


High speed video, at least of the type you refer to above, only confirms that the barrel-bolt combination does not produce spin at or near the muzzle. That may or may not give any indication of the forces imparted by different bolt designs. Spin is just one possible explanation for a trajectory difference between barrel-bolt combinations. So again, the narrow claim that you have not been able to create any spin using a backspin bolt is accurate while claiming that a backspin bolt does nothing different from a normal bolt is not.

Edited by drg, 29 December 2011 - 06:05 PM.

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#27 cockerpunk

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Posted 29 December 2011 - 06:23 PM



Perhaps a worthwhile consideration is whether backspin bolts do anything at all. Do they cause a different application of forces on the ball than a standard bolt? I believe the evidence shows that it may. How would you test that? But it's quite possible that the barrel combinations that have been tested have simply not been able to translate that action into anything useful.


High speed video doesn't - and that's about as good a test as I can think of. Spin is absolutely apparent in an apex - and random and at a low rate on backspin systems just like out of standard bolt systems. So I would suggest that evidence shows that it doesn't.


High speed video, at least of the type you refer to above, only confirms that the barrel-bolt combination does not produce spin at or near the muzzle. That may or may not give any indication of the forces imparted by different bolt designs. Spin is just one possible explanation for a trajectory difference between barrel-bolt combinations. So again, the narrow claim that you have not been able to create any spin using a backspin bolt is accurate while claiming that a backspin bolt does nothing different from a normal bolt is not.


wha?

i dont even know how to start.

we have the video showing the backspin bolts, with over, under, and matched barrels doesn't produce spin. we also have the shooting data showing it doesn't make it more accurate, or raise the pattern.

what else do you need? i really hope your not trainwrecking this thread (for a second time) based on a single result 4 years ago, which was extrememly marginal, which has been superseded with much much much better testing. oh, you are.

Edited by cockerpunk, 29 December 2011 - 06:27 PM.

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#28 rntlee

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Posted 29 December 2011 - 06:28 PM

High speed video, at least of the type you refer to above, only confirms that the barrel-bolt combination does not produce spin at or near the muzzle. That may or may not give any indication of the forces imparted by different bolt designs. Spin is just one possible explanation for a trajectory difference between barrel-bolt combinations. So again, the narrow claim that you have not been able to create any spin using a backspin bolt is accurate while claiming that a backspin bolt does nothing different from a normal bolt is not.


Imparted spin is what this thread is about bro.
HS video shows no difference in imparted spin between bolts types. If you want to retreat into some hypothetical unknown force that a backspin bolt may impart, that's fine but please cease calling them "backspin" bolts.




#29 drg

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Posted 29 December 2011 - 06:37 PM

Imparted spin is what this thread is about bro. HS video shows no difference in imparted spin between bolts types. If you want to retreat into some hypothetical unknown force that a backspin bolt may impart, that's fine but please cease calling them "backspin" bolts.


We moved past that at post #21. However Bryce in his response at post #23 tries to state that the lack of spin observed in his tests with a high speed camera show that a backspin bolt (nomenclature is irrelevant, at least in discussions beyond semantics, which ostensibly is what we are trying to have here) produces no different forces. I say that no such conclusion can be drawn of the bolt, only of the bolt-barrel combination which we know is much different from the bolt and only the bolt.
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#30 brycelarson

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Posted 29 December 2011 - 06:48 PM

We moved past that at post #21. However Bryce in his response at post #23 tries to state that the lack of spin observed in his tests with a high speed camera show that a backspin bolt (nomenclature is irrelevant, at least in discussions beyond semantics, which ostensibly is what we are trying to have here) produces no different forces. I say that no such conclusion can be drawn of the bolt, only of the bolt-barrel combination which we know is much different from the bolt and only the bolt.


ok, here's the deal. I'm annoyed with this conversation. Show me some evidence that a backspin or low blow, or any other bolt system changes the trajectory of paint. It's standard practice around here for me to close threads that don't produce a conversation about evidence, actual testing or at least math showing something useful. If you want to talk about magic systems - go do that in the rest of the forums.

As always - show me the data.




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