How to adjust spin vs. speed

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Re: How to adjust spin vs. speed

Postby JHern » Mon Sep 21, 2009 12:03 am

Blake_T wrote:
You guys are the experts on disc throwing (I'm relatively just an amateur), but Blake, this raises my hackles a bit as a physicist. 8-15 Hz is a variation by a factor of two. The torques acting on a disc in flight will only depend on the flight speed and orientation (i.e., nose/hyzer angle). (I think wind tunnel tests have put to rest any notion that rotation affects the torques.) A disc flying with 15 Hz spin will turn (or fade) about twice as slowly as a disc flying with 8 Hz spin given the same flight speed and orientation.

This is not conjecture, it is a law of physics.


i'm very interested in the physics equations if you have them handy. i was an engineering major for 2 years and a physics major for 2 years but i'm so far removed from it that i only remember a handful of equations.

keep in mind that the 8-15 RPS is a range that encompasses at least 2/3rds of players, possibly more. someone's ability to manipulate spin while keeping launch angles, launch velocity, etc. the same is likely more along the lines of 2-5 RPS. it's the "being able to keep everything else the same while still manipulating spin" part of things that i don't put a lot of stock in.

this is also very dependent upon speed ranges and the disc's aerodynamic properties. if you ever wonder why pro bags are often so similar in terms of their workhorse discs (and the weights), there's only a handful of discs on the market that seem to whittle their way into nearly every pro bag. these discs are usually those that are extremely HSS.

for a player who has an average launch velocity near 70mph (these guys also generally have tremendous amounts of spin), why is it that nearly every disc flips unless it's an extremely stable model and at max weight? how much spin would it take to make a disc like a sidewinder not turn over with a 70mph launch velocity and 5 degrees of nose down?


The basic law is:

dL/dt=I*(dw/dt)=tau

where L is angular momentum, t is time, I is the moment of inertia (about the spin axis), w is the angular velocity and tau is the torque (or moment of force) acting on the disc. d/dt is the time derivative (rate of change with time).

This is a vector equation (and strictly speaking, I is a second rank tensor), so even if the rotation rate is constant, disc turn/fade amounts to a change in orientation of the angular velocity vector and hence non-zero terms in the vector equation. The magnitude of I increases as the disc mass, disc radius, and amount of disc material distributed outward toward the rim increases (it is easy to calculate). Aerodynamic forces (due to linear velocity, orientation, and disc shape) govern tau. For a disc turning in flight, tau is perpendicular to w, and causes the disc to precess even though the rotation rate doesn't change appreciably. According to the basic equation, the rate of turning is tau/I. This is why heavier discs turn over less than lighter discs for the same throw velocity/orientation/disc mold.

The answer to your question about the Sidewinder is: For a very HSS disc, tau might be nearly zero at a given high velocity and orientation (such as 70 MPH, 5 degrees nose down) owing to aerodynamic factors alone, while for a Sidewinder the aerodynamic factors might be such that tau is not zero for the same aerodynamic factors (i.e., speed, orientation). In this case the Sidewinder will turn no matter how rapidly it spins. The relative rate at which it turns will be inversely proportional to the spin rate,

dlogw/dt=tau/(I*w)

Say tau_sw is the torque on a Sidewinder (with moment of inertia I_sw) at 70 MPH and 5 degrees nose down, while tau_od is the torque on "other disc" (with moment of inertia I_od) at 70 MPH and 5 degrees nose down. The relative rate of turn on the Sidewinder is given by dividing the equation for one by the other,

dw_sw/dt=dw_od/dt*(tau_sw/tau_od)*(I_od/I_sw)

Calculating tau for various speeds and orientations is difficult (it involves solving the turbulent flow problem), and would require a super-computer simulation to do it properly. In a sense, what you do is a natural simulation by just going out and throwing consistently at various speeds/nose angles and judging LSS and HSS. A computer simulation can tell you the same things, but at much greater expense. Of course, your number system is somewhat subjective and works in a relative sense, while the full computer simulation would yield more objective data. It would also give a value for tau at all disc speeds, instead of just two speeds (it would be interesting to see the turning torque plotted as a function of speed for various nose angles...it is probably not linear, and could be curved this way or that way for different molds). This isn't, of course, meant to take anything away from the valuable services you provide...it is the best thing around right now.
Last edited by JHern on Mon Sep 21, 2009 7:05 pm, edited 1 time in total.
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Re: How to adjust spin vs. speed

Postby JHern » Mon Sep 21, 2009 12:12 am

Blake_T wrote:something else i was going to mention but forgot.

when you take a disc like a boss, imo, being able to throw > 55mph is more important than how many RPS you can put on it. if you were to throw it 35 mph you'd need an ungodly amount of spin on it to get it to hold stable for very long at all.

on a similar note it would be interesting to see the relationships between both rim width to spin and diameter to spin.


Here's a fun brain teaser...if the Boss had no spin, then it wouldn't turn/fade at all!
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Re: How to adjust spin vs. speed

Postby Blake_T » Mon Sep 21, 2009 12:44 am

thanks for the nerd-work.

there was a long time when i was looking at it more from mathematical standpoints that i felt spin had a lot more to do with things than i believe now. the jist of what i'm picking up is that it's very model dependent and comes into play within specific speed ranges for each disc.

i think it was mainly due to realizing the impact of OAT on people's throws as well as the near impossibility of consistently manipulating spin while retaining "the other mechanics" of the throw.

another thing i've thought about recently is how flight behaviors change with the contrasting styles (swedish vs. american) in terms of throwing (what will be) the nose of the disc vs. throwing the center of the disc in how the release is focused.

yet another thing i used to think about is the deceleration of spin rates over the course of flight and if players that harness more angular velocity on the launch have the same rate of spin deceleration as players who do not clear the wrist as much (even if their initial launch spin was the same).

overall though, for 99.9% of players, i believe spin is the last thing they should worry about.

the greatest overall effect i have seen from spin is how discs riccochet and skip. for those who generate "hyperspin" (less than 1/3rd of those who can throw 450' do), there is a much more noticeable stable "lock-in" for stable discs than players who cannot. when i used to drive far (2002) i had plenty of 440'+ throws that had 0 turn and 0 fade with broken in dx teebirds but my spin rate was absurd back then.
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Re: How to adjust spin vs. speed

Postby Bradley Walker » Mon Sep 21, 2009 12:57 pm

If you watch the video I made in the Snap 2009 thread, I was cut off right before I came to the discussion of MOI (moment of inertia). There is a moment of inertia around the center of the disc but there is also one around the hand itself.

At the disc pivot, which is THE substantial focus of disc power for nearly everyone of normal ability, the heavier the rim, the more difficult the disc becomes to pivot around the wrist. As the weight in the disc becomes more concentrated in the rim, the weight is increased from the pivot point of the lock fingers at a longer moment (the other side of the disc).

In other words, wide rim discs are much harder to snap, because the MOI of the disc around the lock point is so much greater.

From my tests, the wider the rim, the lower the initial velocity. In other words, a Wizard goes 65 MPH, a Teebird, 60 MPH, and a Boss 55 MPH OUT OF THE HAND. I, at first, believed this was all grip related, but I now believe that the wide rim discs simply have a much much greater weight "in the head of the hammer" that must be swung around the arc of the disc pivot.

It is much more difficult to accelerate a golf club of swingweight e8 than it is a c9... it is the same principle. The more plastic concentrated in the rim, the heaver the head of the hammer.
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Re: How to adjust spin vs. speed

Postby masterbeato » Mon Sep 21, 2009 1:34 pm

my throw derives from focusing on leveraging the disc from the rim but i try to leverage the disc from the center rather than the rim because i have been focusing more on the Sweden style lately because i am curious about it. but i have no idea how to go about trying to focus on the center.

the center is different from what you are describing about rim focus, and being changed due to the width of the rim. since leveraging from the rim is changed due to rim width, does it also change when trying to leverage it from the center? or do i just not understand?

the reason why i am asking is because i want to learn more about it and i am asking how to go about doing this?

or maybe everything in the hit is leveraged from the rim regardless of the style but i know for a fact that the Sweden technique is leveraged with far more power.
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Re: How to adjust spin vs. speed

Postby JR » Mon Sep 21, 2009 1:54 pm

No worries at you noticed the danger in assuming :-) Live and learn.

I don't recall exactly how Öystein described things but my recollection is that a table with correlations had only one statistically meaningful link and that was the elbow reach back distance. Which comes from reaching back with the arm plus what you mentioned about the hips and shoulders turning back. They all result in the elbow being farther back. I see no conflict here.

We have a physicist here and I've got 300 FPS obliquely above footage of Avery Jenkins back handing and doing 360s plus nearly vertically down forehands. Maybe you could do an analysis on that to see what you can see. It's on youtube just search with his name and two view points or I could put up the top down data on some file sharing site for easier frame by frame moving for more accurate measuring.

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Wyno wrote:JR, sorry! I guess I tend to assume too much - wich is not very clever when I kind of accuse you of doing just that :-) My bsic assumption is that we're all in here to figure things out.

JR wrote:The one thing that stuck to my mind about the measurements and their statistical analysis was that there was only one statistically meaningful correlation found at 95 % confidence level in relation of flight distance and details of form. That was a positive correlation between lengthening elbow reach back distance away from the target. Untechnically speaking this means that you'll most likely throw farther when you reach back farther with the elbow.

This is not quite correct but seems to be a commom misconception of his findings; the correlation is between hip/shoulder movement and disc exit speed - Carlsen says (freely translated from a norwegian DG forum): "one should rotate both pelvis and upper body farther away from the direction of the throw". This will happen naturally with a long reach back, but he later comments on bent elbow technique as being in no conflict with his own studies.
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Re: How to adjust spin vs. speed

Postby JR » Mon Sep 21, 2009 2:17 pm

Masterbeato I have some slow motion footage of European styles showing wrist action well. Wait and see for yourself. One of the most important Swedes Tomas Ekström has a very DGR appproved form. Whereas Linus Åström uses the left arm with a distinctively Swedish style. Can't promise about Johannes Högberg because I have to see if there's worthy footage available.

JHern there are so many disc configurations for putters, mids and drivers and so many different variable sets among those discs that it's difficult to generalize what kinds of practical effects one would get with each detail modification because ceteris paribus rarely exists between molds when even different plastics tend to change weight distribution etc. on discs of the same mold. That's why it's difficult to pin down a single definition for spin rate change susceptibility in air for disc classes. And how the flight could be manipulated with spin rate change _alone_. When it's more likely hole in your disc selection or the inability to manipulate the flight with intentional OAT, power generation change or puring the shot. However; some discs are clearly responding to a lack of spin more than others. More often than not overstable discs that you can throw at over cruising speed and understable discs you can just make fly straight with your best effort become more stable on bad throws with a slip/poorly timed or powered pinch and the resulting loss in spin rate.

I'm not sure there's much more practical advice for regular throwing than fulfilling flight differences in bag setup and using discs you can throw to every possible way and learning to throw purely and getting enough muscle power to hold on to the disc long enough. Could you please redo muscle power calculations that mafa did in a hurry about the needed pinch power of a 45 MPH throw with the index finger and thumb at pro style rip point of 2.30 on the disc edge to see if you're in the same ballpark with 175 gram disc. If mafa made no mistakes the discs clearly rip and not even a gorilla can hold on at those forces tearing the disc away from the thumb lock. Which means that there's a benefit of having the finger pinch strength of an Olympic athlete.

Anybody else have practical goals to work toward in training and throwing and disc design relative to spinning the disc in different speed to spin ratios? Too tired now going to sleep so my head ain't probably putting out everything relevant now.
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Re: How to adjust spin vs. speed

Postby JHern » Mon Sep 21, 2009 7:16 pm

Bradley Walker wrote:If you watch the video I made in the Snap 2009 thread, I was cut off right before I came to the discussion of MOI (moment of inertia). There is a moment of inertia around the center of the disc but there is also one around the hand itself.


Aha! So this is what you were getting around to saying...BTW, great video. When are you going to post a better quality version? We're going to keep nagging until you do.

Bradley Walker wrote:At the disc pivot, which is THE substantial focus of disc power for nearly everyone of normal ability, the heavier the rim, the more difficult the disc becomes to pivot around the wrist. As the weight in the disc becomes more concentrated in the rim, the weight is increased from the pivot point of the lock fingers at a longer moment (the other side of the disc)...In other words, wide rim discs are much harder to snap, because the MOI of the disc around the lock point is so much greater...From my tests, the wider the rim, the lower the initial velocity. In other words, a Wizard goes 65 MPH, a Teebird, 60 MPH, and a Boss 55 MPH OUT OF THE HAND. I, at first, believed this was all grip related, but I now believe that the wide rim discs simply have a much much greater weight "in the head of the hammer" that must be swung around the arc of the disc pivot...


Yes, this sounds correct. Note, however, that for the same reasons the Boss need not spin as fast to have the same angular momentum as a more rapidly spinning Wizard. In terms of inertial stability against turning and fading, this is the quantity that really counts.
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Re: How to adjust spin vs. speed

Postby JHern » Mon Sep 21, 2009 7:24 pm

JR wrote:JHern there are so many disc configurations for putters, mids and drivers and so many different variable sets among those discs that it's difficult to generalize what kinds of practical effects one would get with each detail modification because ceteris paribus rarely exists between molds when even different plastics tend to change weight distribution etc. on discs of the same mold.....


Yes, of course variety in molds is important, but so is the physics. Consider a big S-turn throw, like a Valkyrie aired out for max D. The more spin you have, the slower the turn of the disc in flight (and the slower the fade at the end), and hence the S becomes tighter. A slower spin rate enhances the turn (and the fade), so that the curvature of the flight path becomes larger and more accentuated. In other words, more spin=less left->right->left motion. Of course, if you have weaker spin, you could just pick up a more stable mold and get a tighter S. And that would take care of that!
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Re: How to adjust spin vs. speed

Postby JR » Mon Sep 21, 2009 11:13 pm

JHern wrote:
JR wrote:JHern there are so many disc configurations for putters, mids and drivers and so many different variable sets among those discs that it's difficult to generalize what kinds of practical effects one would get with each detail modification because ceteris paribus rarely exists between molds when even different plastics tend to change weight distribution etc. on discs of the same mold.....


Yes, of course variety in molds is important, but so is the physics. Consider a big S-turn throw, like a Valkyrie aired out for max D. The more spin you have, the slower the turn of the disc in flight (and the slower the fade at the end), and hence the S becomes tighter. A slower spin rate enhances the turn (and the fade), so that the curvature of the flight path becomes larger and more accentuated. In other words, more spin=less left->right->left motion. Of course, if you have weaker spin, you could just pick up a more stable mold and get a tighter S. And that would take care of that!


Completely agree but that was not my main motivation to write. I was getting at more often applicable real world differences which are brought about by enhancing grip strength and getting a cleaner rip which increases spin rate anyway and you're not gonna throw 400' easily or without wind assistance with a loose/micro slipping grip. Those improvements are something you can train and achieve IRL and are applicable in any throw.

A cleaner grip and possibly somewhat better gripping power is what eliminated left right play fro my 400' line drive with a new DX 175 Valkyrie so the added spin and later rip point and very likely less finger chafing/sticking induced OAT certainly are plausible explanations to the straightened flight. If I had to guess each played a part.

For a max D S-curve a person that was used to a micro slip and suddenly got a good grip and rip at a proper late time with added disc pivot would most likely get a short anhyzer to the ground with a Valkyrie. When throwing the same otherwise because that disc isn't great at flexing back from anhyzer which makes it ideal for that flight line. In this scenario the added spin forces a lessening of anhyzer angle or addition of height thus making a clear impact in distance and the sideways action of the flight at different points. Therefore it's a combination of adjusting your aim, power, grip strength, keeping the throw clean or intentionally messing with it and the election of the correct disc for the job. You need to adjust everything else when one variable changes and that's for me the most important practical function of messing with spin to speed ratio.

One needs to know the changes of spin to speed ratio has in flight just like one wants to be able to manipulate the flight with intentional OAT to increase the amount of available tricks. The benefit being getting closer to the pin and out of any kind of trouble.
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Re: How to adjust spin vs. speed

Postby JR » Mon Sep 21, 2009 11:15 pm

Here's a taster of European wrist action in slo mo footage partially filmed by me and mafa. Slo mos come in later parts and I highly recommend watching each part of day 3 at European Open 2009 as well as the final day.

http://www.youtube.com/watch?v=qUncGn_v ... re=channel
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Re: How to adjust spin vs. speed

Postby mafa » Tue Sep 22, 2009 1:12 pm

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

Conclusions and thoughts:
-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

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Re: How to adjust spin vs. speed

Postby Wyno » Tue Sep 22, 2009 2:55 pm

Hmm that's really interesting Mafa, and extremely nerdy I have to say :-D

Bradley, I was bothered by the same thing as mafa in your reasoning;
Bradley wrote:wide rim discs are much harder to snap, because the MOI of the disc around the lock point is so much greater...From my tests, the wider the rim, the lower the initial velocity. In other words, a Wizard goes 65 MPH, a Teebird, 60 MPH, and a Boss 55 MPH OUT OF THE HAND. I, at first, believed this was all grip related, but I now believe that the wide rim discs simply have a much much greater weight "in the head of the hammer" that must be swung around the arc of the disc pivot

Two things actually; as mafa showed the MOI should not be greater in wide-rimmed drivers. In addition to most of the mass in the rim being towards the center (the sharper/wider the rim, the more pronounced this would be of course), a smaller diameter would make the "lever" shorter as well - so the net result has to be a smaller MOI.

Then it's the idea of exerting energy to make the disc rotate, "leveraging" MOI. I would think that it's actually the other way around, MOI in a larger diameter putter or midrange would contribute to speed and spin. This might seem counter-intuitive if you think that most of the force in the disc pivot is intentional, but it's consistent with the mechanics of the hit and the motion of the disc as I understand it:
    Disc moves forward without rotation
    Rotation starts when arm extends (no conscious effort needed to start rotation)
    Rotation amplified and partially converted back to more disc speed through wrist extension (very little conscious effort here as well - wrist closes because of disc inertia, extends because of tendon bounce. This might be controversial but I believe that even though some conscious extension is possible, it will mostly be too slow to make a lot of difference.)
This theory is also consistent with your own speed measurements.
Power (especiallys static power) in the hand and wrist makes it possible to transfer more energy to the disc (without slipping, as JR has pointed out) and technique would make it possible to time this use of power to some extent and optimize the effects through proper placement of the disc. But I would think the higher speed of putters and midranges is because of a higher MOI.
It would be very interesting if you have some speed measurements on putters or mids with similar rims but distinctly different diameters, If I'm correct the larger diameter should lead to higher initial speeds, this might of course be cancelled by necessary form/grip/wrist extension changes though...
Bradley wrote:It is much more difficult to accelerate a golf club of swingweight e8 than it is a c9... it is the same principle. The more plastic concentrated in the rim, the heaver the head of the hammer.

Well, it takes more power to accelerate a heavy hammer but it can reach a higher speed... provided you have the strength to hold on. Since it's harder to maintain the grip with a wider rim, and this theory stipulates that grip and technique are the limiting factors here, NOT dynamic wrist strength, this is still consistent I think.
The Finn's got it figured out;
JR wrote:there's a benefit of having the finger pinch strength of an Olympic athlete.


Now, I need a real nerd (that is someone who really understands mechanics/physics) to cut me down at once if any of this is wrong :lol:

PS: JR - jeg er norsk så svensk er ikke noe problem å forstå heller, men en osaa puhua suomea ;-) but enough of the code speak :-) I've seen the Avery vids and they're awesome but I wouldn't know where to begin analyzing them... Now,when you put up the other vids you mentioned as well and we can start comparing, that should be interesting! I really love those top-down vids, that's really made a difference in figuring out what the hit should be like.
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Re: How to adjust spin vs. speed

Postby Bradley Walker » Tue Sep 22, 2009 4:55 pm

mafa wrote: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.


Huh? That is exactly the opposite of reality.

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.

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.
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Re: How to adjust spin vs. speed

Postby Bradley Walker » Tue Sep 22, 2009 4:59 pm

Wyno wrote:
Bradley wrote:It is much more difficult to accelerate a golf club of swingweight e8 than it is a c9... it is the same principle. The more plastic concentrated in the rim, the heaver the head of the hammer.

Well, it takes more power to accelerate a heavy hammer but it can reach a higher speed... provided you have the strength to hold on.


That is wrong. You can generate more momentum and force at the same speed and acceleration, but the head will not "reach a higher speed" because it is heavier.
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