How to adjust spin vs. speed

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Re: How to adjust spin vs. speed

Postby Wyno » Tue Sep 22, 2009 5:52 pm

Bradley wrote:Wide rimmed drivers have much more plastic toward the rim. So, in my explanation of leveraging the disc pivot, the head of the hammer is heavier.

It is obvious that wide rimmed drivers have the vast majority of the plastic in the rim, but it's not obvious that this translates to more MOI?
A wider rim negates some of the effect of moving plastic from the plate to the rim, and since the grip is further in towards the center the net result - I think - is less MOI. Since weight is evenly distributed around the disc it's not like changing just the head of the hammer, might be like giving the hammer a slightly heavier head but at the same time shortening and fattening the handle :-)
Bradley wrote:the head will not "reach a higher speed" because it is heavier

Ok, that might be muscle memory from a lot of hammer work intruding on my thinking :-)
Anyway, there's two things happening at once here; You think the MOI is heavier in drivers and this is bad, I think the MOI is heavier in putters/mids and It's good (contributes to that higher speed you were talking about). Mafa seems (much) more able than I am to do the maths on MOI, i'll go to sleep now and hope he or someone else comes up with a better look at this before I get into deeper shit than I am already... HopeI'll think straighter tomorrow :-)
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Re: How to adjust spin vs. speed

Postby JHern » Tue Sep 22, 2009 6:49 pm

mafa wrote:First thought: the wide rimmed discs should have _lower_ moment of inertia than putters and Rocs. The wide-rimmed types have more mass near _center_ of mass/disc as opposed to mids/putters which are higher and have mass near the rim.


This is true if the flight plate has the same thickness and density in both cases, and both drivers have the same outer radius. I was just comparing a Boss and Cyclone by eye, and it does seem as if the Cyclone has more plastic mass at a larger radius than the boss. But some discs seem to have a thicker flight plate (e.g., putters like the Magnet), so that a lot of plastic mass is still near the center, and the rim mass is much greater on the Boss (enough to make a big difference).

That being said, the differences should be slight if you think about it carefully, and it probably isn't worth making a big deal about MOI. I would imagine that total disc radius and mass are the biggest factors in changing MOI (e.g., the ultra-star is a massive and huge radius lid).

The bigger picture has to do with angular momentum, the product of spin rate and moment of inertia. If the molds only vary in MOI by 20 or so percent (normalized by mass), then varying the spin rate by a factor of 2 will be far more important in determining the rotational stability of the flying disc.

But for now, I'm going to go to the field and practice snap.Bradley Walker's video has gotten me really anxious to go and try out his concepts.
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Re: How to adjust spin vs. speed

Postby JR » Tue Sep 22, 2009 11:36 pm

mafa wrote:I think this is also an excellent discussion on disc stability. I think JHern did a great job explaining how pitch moment (nose up/down) will turn the disc (or angular momentum of the disc). Reading this morning Bradley's comment on how easy or hard is it to torque different types of discs I started to think how the shape of disc affects the moment of inertia.

NERD ALERT!

First thought: the wide rimmed discs should have _lower_ moment of inertia than putters and Rocs. The wide-rimmed types have more mass near _center_ of mass/disc as opposed to mids/putters which are higher and have mass near the rim.

I decided to try to empirically determine MoI's of different types of discs. Simplest approach I could find is to form a pendulum which each test disc. Set each subject vertically onto a horizontal knife blade bearing (in a way that the inside of the rim touches the knife blade) and determined the period of oscillation of the formed pendulum. With a little bit of math and physics could determine the MoIs to some accuracy. As a sanity-check for my method compared Hummel's and my result for 175g Ultra-star. Sane. Here's the results for couple of discs.

http://www.kolumbus.fi/mfranssila/DG/MOI.pdf

-No big differences across the subjects (apart from Ultra-star)
-Rocs and putters have bigger MOIs than wide-rimmed discs as expected
-Lighter discs have smaller MOIs (duh)
-Monarch's groove does not make it dynamically less stable as I thought. Compare Starfire and Monarch.
-stability comes mostly from the aerodynamic properties than the MoI. Compare Sinus AP and Aviar P&A

Matti


D[m] is the same number for a Roc and Aviar. Are you sure of that and what changes in conclusions come from the difference? I'd think an Aviar had a smaller diameter and rim width close to equal without comparing side by side and checking PDGA approved discs list.

Wyno obviously speaks much better Norwegian than me. He got that Finnish sentence correct.

Measuring videos can be done on you monitor with a tape measure and knowing the frame rate and the recording speed of 300 pictures per second. I don't know what frame rate there is in the top down video after the editing by mafa. Original video plays at 29.97 pictures per second so the duration of one picture is 1/300*29.97=0.0999 seconds. The disc with a color bar Avery threw was an Xcaliber so you get it's diameter from there. There can be perspective errors etc. so the figures are only ballparks. Measuring how much the disc moves from one picture to other in relation to disc diameter and the duration in time of one picture tells you the speed of the disc. Do several pictures and you can see the acceleration changes. You can eyeball or use devices to measure angles as well but I haven't gotten there.

If the disc is 21.2 centimeters in diameter and looks on the monitor to be 1.2 cm in diameter and it moves 2 centimeters on the screen the disc moves at 21.2/1.2*2/0.0999*3600/100000~12.7 kilometers per hour.
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Re: How to adjust spin vs. speed

Postby JHern » Wed Sep 23, 2009 12:09 am

In planetary science we usually give the moment of inertia of a celestial body relative to a sphere of constant density with the same (average) radius. This ratio is always smaller than one for a body of any significant size, where self-gravity is enough to make the heavy stuff fall into, and be compressed within, the middle. An uncompacted, undifferentiated asteroid, on the other hand, would have a value near 1. (Earth is somewhere around 0.2)

For a disc, it would be most interesting to cite the moment of inertia relative to a cylinder of constant density and the same radius as the disc (m*r*r/2, where m is mass and r is radius). This ratio would always be less than 2, which would be the value for a thin cylindrical shell with all mass distributed at radius r (i.e., all rim, no flight plate, like the aerobie ring). Because all legal throwing discs have some sort of rim for gripping, this ratio would also be greater than 1. And, best of all, it is non-dimensional!
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Re: How to adjust spin vs. speed

Postby mafa » Wed Sep 23, 2009 12:32 am

D[m] is the same number for a Roc and Aviar. Are you sure of that and what changes in conclusions come from the difference? I'd think an Aviar had a smaller diameter and rim width close to equal without comparing side by side and checking PDGA approved discs list.



To clarify: D is the distance from inside of the rim to the center of the disc. It's not diameter of the disc which I did not need in my calculations. Just measured from the inside of the rim to the center of the disc.

mafa wrote:
First thought: the wide rimmed discs should have _lower_ moment of inertia than putters and Rocs. The wide-rimmed types have more mass near _center_ of mass/disc as opposed to mids/putters which are higher and have mass near the rim.


This is true if the flight plate has the same thickness and density in both cases, and both drivers have the same outer radius. I was just comparing a Boss and Cyclone by eye, and it does seem as if the Cyclone has more plastic mass at a larger radius than the boss. But some discs seem to have a thicker flight plate (e.g., putters like the Magnet), so that a lot of plastic mass is still near the center, and the rim mass is much greater on the Boss (enough to make a big difference).


To JHern and Bradley. Putters having thicker flight plates explains why their MoIs aren't even higher compared to drivers. In any case, discs weighing over 170 g have quite small differences.

Bradley. What's different between Rocs and drivers are the distances from the inside of the rim to the center of disc. It's the D in my experiment. Could this differing lever explain the differences in launch speed? When the disc pivots around thumb and index finger, this the effective length of the "club" formed by the disc radius to the center of the mass.

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Re: How to adjust spin vs. speed

Postby TheTyrant » Wed Sep 23, 2009 5:43 am

Consciously trying to do this seems like a technique that could disrupt muscle memory, especially if you're in the process of developing clean form. The only time I think newish players should be considering this is for any type of roller aside from long distance open ones.
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Re: How to adjust spin vs. speed

Postby mafa » Wed Sep 23, 2009 2:51 pm

It is obvious that wide rimmed drivers have the vast majority of the plastic in the rim. The flight plates are paper thin compared to say, a putter, and many of the blunt nosed wide rimmed drivers can barely make weight. A Max can only be found on max weight for example because of the all the plastic in the nose.


Did part of my homework and quickly measured flight plate thicknesses of the discs in my previous study. I had to measure quite close to the rim since the micrometer I was using does not allow over 30 mm distance from the edge of the disc.

From Star Destroyer to Dx Aviar, flight plates went from 1.75 mm to 2.2 mm in thickness, latter being the Aviar. Latitude 64 discs (Spike and Sinus) were in the 3 mm ballpark. The differences are surprisingly small.

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Re: How to adjust spin vs. speed

Postby JHern » Wed Sep 23, 2009 5:09 pm

TheTyrant wrote:Consciously trying to do this seems like a technique that could disrupt muscle memory, especially if you're in the process of developing clean form. The only time I think newish players should be considering this is for any type of roller aside from long distance open ones.


I think this seems to be a good summary of the technique part of this thread, after all has been said and done. It is better to have clean form and just change up discs to get any significantly different flight pattern.
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Re: How to adjust spin vs. speed

Postby Bradley Walker » Thu Sep 24, 2009 8:23 am

Blake is going to kill me...

Actually, adjusting spin is quite easy, and no longer difficult for me to do now that I use the Snap and disc pivot technique outlined in my last video.

For the least spin and greatest forward velocity, the disc must be pivoted using the weight furthest from the center (the head of the hammer). The arc of the pivot will be wide and the spin rate will be lower.

On the other hand, of you pivot the CENTER of the disc the forward velocity will be lower but the spin will be higher. You are effectively throwing the hammer about halfway up the handle. Which makes it easy to spin it faster. Although you might lose some velocity out the hand...

Basically, do not use a wide pivot for putters, I use a narrower pivot around the center for most shots, as a wide arcing pivot can cause wobble.

I will cover this in my next video... the Phil Drill is based on a an "around the nose snap" spinning around the center of the disc. I never put 2 and 2 together about the "throwing the far side of the disc" until recently. I always threw around the center of the disc. That is why my drivers never had the relative distance of my putters and mids.
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Re: How to adjust spin vs. speed

Postby Bradley Walker » Thu Sep 24, 2009 12:29 pm

PS: The more you lever around the center of the disc, the more spin you will get, and you will also never get true nose down.

Center disc spin snap=slightly nose up (which is not a bad thing necessarily)=slightly closed wrist at launch

Full leverage/length disc pivot=nose down= big wrist extension

Why?

Momentum.

Once you start the head of the hammer swinging you can't stop it.
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Re: How to adjust spin vs. speed

Postby JHern » Thu Sep 24, 2009 5:12 pm

Bradley Walker wrote:Blake is going to kill me...

:lol:

Bradley Walker wrote:Actually, adjusting spin is quite easy...For the least spin and greatest forward velocity, the disc must be pivoted using the weight furthest from the center (the head of the hammer)...if you pivot the CENTER of the disc the forward velocity will be lower but the spin will be higher...I will cover this in my next video...


I think we're definitely going to need more video on this Bradley. While I now understand how you're generating snap and I like the basic explanation, I still don't quite understand from this description how you can purposefully pivot the disc from the "head of the hammer" vs. the "center of the disc." It seems to me like pivoting one means pivoting the other. And it is hard to imagine this making a big difference. Please explain.

One thing that could make a difference is changing the grip from the 9-o-clock position you seem to advocate to something more like 12-o-clock. Of course, its hard to imagine that you wouldn't lose forward velocity and spin as well by moving from 9-o-clock to 12-o-clock, so all you get in effect is a weaker throw, and that is definitely not what we're interested in obtaining. OK, never mind.
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Re: How to adjust spin vs. speed

Postby Blake_T » Thu Sep 24, 2009 9:41 pm

On the other hand, of you pivot the CENTER of the disc the forward velocity will be lower but the spin will be higher. You are effectively throwing the hammer about halfway up the handle. Which makes it easy to spin it faster. Although you might lose some velocity out the hand...

Basically, do not use a wide pivot for putters, I use a narrower pivot around the center for most shots, as a wide arcing pivot can cause wobble.


i consider these to be two different throwing techniques. you cannot easily duplicate the same launch trajectories along with speed/nose down by changing these up but yes, spin will change. imo, using this change just to manipulate spin isn't the reason to do it, but if you want to change your flight line, yes, it is a viable option.

with that in mind, if you look at the launch position of the disc in terms of relative body height, you'll get two different spin rates depending upon where on the frontal axis you are.
if the frontal axis of rotation goes through vertically through the front knee and thus intersects the upper body somewhere along the chest and through the back.

if the disc is launched from above the intersection point of the frontal axis and the back and a wide pivot from my experiences yields the greatest amount of spin (without having to try for spin). a narrow pivot when launched above the front axis intersection makes it nearly impossible to get nose down unless you are throwing an anhyzer.

launches from below the front axis intersection allows for a much greater variety of positions, grip tendon flexibility, and elbow extension etc.
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Re: How to adjust spin vs. speed

Postby JHern » Sun Sep 27, 2009 2:28 pm

Blake_T wrote:...yes, spin will change. imo, using this change just to manipulate spin isn't the reason to do it, but if you want to change your flight line, yes, it is a viable option...


But again, the whole premise is that changing spin changes the flight line.

I'm thinking about writing a code to do some flight simulations of discs to try and be more quantitative about all this, and show more explicitly how this all works. I can't simulate the throwing mechanics itself without a lot of effort, but probably can do the flight without too much trouble.
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Re: How to adjust spin vs. speed

Postby Blake_T » Sun Sep 27, 2009 3:27 pm

But again, the whole premise is that changing spin changes the flight line.


but people don't manipulate spin to the same degree that they manipulate other factors.

an example: a "proper" sky roller requires a release point that is above the front axis intersection. the wide extension arc is a natural part of the mechanics of this throw and it inherently generate more spin than a narrow extension arc. it is not possible to throw this in a mechanically sound manner from below the front axis intersection. the focus is not the spin, but the mechanics. the spin caused by the mechanics in this case is incidental.
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Re: How to adjust spin vs. speed

Postby JHern » Sun Sep 27, 2009 4:30 pm

Blake_T wrote:
But again, the whole premise is that changing spin changes the flight line.


but people don't manipulate spin to the same degree that they manipulate other factors.

an example: a "proper" sky roller requires a release point that is above the front axis intersection. the wide extension arc is a natural part of the mechanics of this throw and it inherently generate more spin than a narrow extension arc. it is not possible to throw this in a mechanically sound manner from below the front axis intersection. the focus is not the spin, but the mechanics. the spin caused by the mechanics in this case is incidental.


The point is, these are flip sides of the same coin. There is no point in denying that certain throwing motions generate certain speeds, spins, and angles, all of which affect the flight of the disc, which is the whole point of making the given throw.
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