rickhemmings
Apr 11 2008, 11:25 PM
Has anyone measured or come up with a way to measure the RPMs of a disc as it leaves the hand? (during a drive). I'm also interested in at what rate the spin deteriorates over time. any thoughts?

stack
Apr 12 2008, 12:44 PM
i would guess its almost a bell curve of speed... seems that for a lot the disc starts out fast out of the hand and actually increases at one point during flight. Evidence of this is watching a wobbly disc straighten up or the phenomenon we call high speed fade?

how to do it... I would think if someone had a high speed camera and taped a drive (w/ a big mark on one part of the rim on a disc)... you could count the revolutions that way.

rickhemmings
Apr 12 2008, 01:37 PM
Yes, a high speed camera with mark/marks could get the speed on release (unfortunately expensive!). I'm quite certain that the spin will decrease over time due to parasitic drag. If the air speed of the disc increases after release due to head wind or gravity when thrown down hill the disc will go into/ increase it's high speed turn mode.

Birdie
Apr 12 2008, 11:09 PM
I am no authority by an means, but I have had some physics in high school...

...and surely a disc does not speed up at any time post release.

cgkdisc
Apr 13 2008, 01:14 AM
Actually, a putt being vertically dropped in is likely going slightly faster upon striking the bottom of the basket than upon release. You must understand the gravity of this situation. ;)

rickhemmings
Apr 13 2008, 01:24 AM
Chuck, I know you're smart, look at all those computers next to you. So help me figure out how to measure disc spin.

cgkdisc
Apr 13 2008, 01:42 AM
I think the reason this hasn't been solved with a simple method is that I'm not sure there's much useful benefit for knowing how fast a disc spins. What would be your reason?

cgkdisc
Apr 13 2008, 02:04 AM
I think one way that might be easy to execute would be measuring the speed of a roller shortly after release or even at several points along the route. Measure the elapsed time the roller takes with sensors (people with stop watches?) spaced every 50 feet. For purposes of discussion, let's assume the disc is touching the ground throughout the measurement and there's no slippage. 50 feet = 1524cm. A 21cm disc has a circumference of 66cm. That means the disc rotates 23 times over 50 feet. If that takes 1 second then that's 1380 RPM, worst case.

citysmasher
Apr 13 2008, 12:40 PM
Take a disc out at night and attach an LED to the rim. Then video tape the throw and count the rotations over a certain number of frames.

Frankly, this "vision" technology (what it is called in industrial applications) is how the ball golf analyzers work. They take a ball with a stripe marked on it. The camera takes tow pics, one at impact (it is triggered by the sound) and one shortly thereafter. The computer analyzes the position of the line on the ball and extrapolates the data.

davei
Apr 13 2008, 10:03 PM
I think the reason this hasn't been solved with a simple method is that I'm not sure there's much useful benefit for knowing how fast a disc spins. What would be your reason?



Scientists I worked with at Aerovironment reasoned that a disc essentially rolls out of your grip and therefore has a spin rate proportional to its forward speed. In other words, you calculate how fast a disc needs to spin to roll whatever forward velocity. We measured the highest air velocities at around 70 MPH and calculated spin from that. We were throwing 21.7 cm discs.

rickhemmings
Apr 13 2008, 10:10 PM
Thanks to all for your intelligent responses, now I can crunch the #s and calculate some spin rates

cgkdisc
Apr 14 2008, 10:41 AM
We measured the highest air velocities at around 70 MPH and calculated spin from that. We were throwing 21.7 cm discs.



That works out to 2300RPM.

rickhemmings
Apr 14 2008, 01:17 PM
Yes, good math! It's hard to say at what rate the spin slows down though. If you throw a disc off a cliff or mountain and angle it downwards at the correct angle, and throw it with the correct amount of speed, so it will not accelerate because of gravity or decelerate due too much nose up, it will not turn over or fade during it's flight. I remember doing this and watching it happen, and the perfect throws would go into glide mode for it seemed like 30 seconds to a minute before they would begin to wobble and fall out of the sky. (it's easier to do with neutrally stable discs, like some putters or a comet etc)
I think when this happens the spin may have dropped very low, I'm thinking of a bike still remaining gyroscopically stable even at very low speeds. I guess some disc sacrifices and a stop watch are the next step

circle_2
Apr 14 2008, 01:42 PM
I remember an old post made long ago...that as a spotter in a snowy tourney...he noticed that the beginners' drives would spin (under the snow's surface) for a while upon landing...but that the pros' discs would spin much longer.

I don't think one can overspin a disc...but one CAN throw too hard/fast and coupled with inadequate spin will induce turnover.

Seems to me that a marked disc filmed from above would best illustrate spin rates.

crusher
Apr 20 2008, 11:17 PM
A marked disc will tell you how many RPM's it has. It needs a camera mounted directly over the immediate flight path and shooting at 500 frames per second. I've done this before but can't recall RPM's, but we did hit speeds of 70 MPH.

atxdiscgolfer
Apr 21 2008, 12:26 AM
:Dyour joking, right?

mikeP
Apr 21 2008, 08:52 AM
I think the reason this hasn't been solved with a simple method is that I'm not sure there's much useful benefit for knowing how fast a disc spins. What would be your reason?



Scientists I worked with at Aerovironment reasoned that a disc essentially rolls out of your grip and therefore has a spin rate proportional to its forward speed. In other words, you calculate how fast a disc needs to spin to roll whatever forward velocity. We measured the highest air velocities at around 70 MPH and calculated spin from that. We were throwing 21.7 cm discs.



From this I gather that your grip (with which you roll the disc out of your hand) along with your armspeed determine the amount of spin you impart on a disc. A solid grip with a clean release results in the most spin and all the benefits that go along with that.

crusher
Apr 21 2008, 11:37 AM
No I'm not joking! Note that this was done almost 10 years ago, discs fly faster now than they did then!

davei
Apr 21 2008, 04:14 PM
No I'm not joking! Note that this was done almost 10 years ago, discs fly faster now than they did then!



Discs are still launched at around 70 mph for the big boys. The decay rate is much slower, which means the discs maintain more speed for a longer period of time. The initial speed is the same.

davei
Apr 21 2008, 04:19 PM
I think the reason this hasn't been solved with a simple method is that I'm not sure there's much useful benefit for knowing how fast a disc spins. What would be your reason?



Scientists I worked with at Aerovironment reasoned that a disc essentially rolls out of your grip and therefore has a spin rate proportional to its forward speed. In other words, you calculate how fast a disc needs to spin to roll whatever forward velocity. We measured the highest air velocities at around 70 MPH and calculated spin from that. We were throwing 21.7 cm discs.



From this I gather that your grip (with which you roll the disc out of your hand) along with your armspeed determine the amount of spin you impart on a disc. A solid grip with a clean release results in the most spin and all the benefits that go along with that.



Yes, if by "clean" you mean sharp/quick/strong and off axis torqueless.

Lyle O Ross
Apr 21 2008, 07:01 PM
I think the reason this hasn't been solved with a simple method is that I'm not sure there's much useful benefit for knowing how fast a disc spins. What would be your reason?



Scientists I worked with at Aerovironment reasoned that a disc essentially rolls out of your grip and therefore has a spin rate proportional to its forward speed. In other words, you calculate how fast a disc needs to spin to roll whatever forward velocity. We measured the highest air velocities at around 70 MPH and calculated spin from that. We were throwing 21.7 cm discs.



From this I gather that your grip (with which you roll the disc out of your hand) along with your armspeed determine the amount of spin you impart on a disc. A solid grip with a clean release results in the most spin and all the benefits that go along with that.



Yes, if by "clean" you mean sharp/quick/strong and off axis torqueless.



I'm not sure I agree with this.

If for no other reason than it assumes a very static relationship between speed of release and spin rate on what is a very dynamic process. I know for sure that I can take some off of my throw and work on putting a whole lot more torque on the disc, that is, I can vary the rate of spin on my disc and rate of forward motion consciously.

Now, it might be that the difference is spin rate between trying to put torque on the disc and not trying to put spin on it is not statistically significant. I would argue that is weak at best, given that the effects on disc flight between each type of throw is significant, at least for me.

More importantly, this seems contraindicative of your own definitions on tendon bounce and it's effect on disc flight. Perhaps what you are saying is that under ideal conditions, the best you can do is to have the disc roll off your hand at the maximum forward speed thus achieving the maximum torque. I'd still argue this in incorrect but will wait for your answer.

davei
Apr 21 2008, 08:05 PM
[
I'm not sure I agree with this.

If for no other reason than it assumes a very static relationship between speed of release and spin rate on what is a very dynamic process. I know for sure that I can take some off of my throw and work on putting a whole lot more torque on the disc, that is, I can vary the rate of spin on my disc and rate of forward motion consciously.

Now, it might be that the difference is spin rate between trying to put torque on the disc and not trying to put spin on it is not statistically significant. I would argue that is weak at best, given that the effects on disc flight between each type of throw is significant, at least for me.

More importantly, this seems contraindicative of your own definitions on tendon bounce and it's effect on disc flight. Perhaps what you are saying is that under ideal conditions, the best you can do is to have the disc roll off your hand at the maximum forward speed thus achieving the maximum torque. I'd still argue this in incorrect but will wait for your answer.



As I said previously, this is the PHDs at Aerovironment, who said that maximum forward velocity is directly related to maximum speed as if it is rolling out of your grip. These are some pretty smart guys, who have done some world record breaking things in aerodynamics. Your arguement would be with them, not me.

mikeP
Apr 22 2008, 08:43 AM
[
I'm not sure I agree with this.

If for no other reason than it assumes a very static relationship between speed of release and spin rate on what is a very dynamic process. I know for sure that I can take some off of my throw and work on putting a whole lot more torque on the disc, that is, I can vary the rate of spin on my disc and rate of forward motion consciously.

Now, it might be that the difference is spin rate between trying to put torque on the disc and not trying to put spin on it is not statistically significant. I would argue that is weak at best, given that the effects on disc flight between each type of throw is significant, at least for me.

More importantly, this seems contraindicative of your own definitions on tendon bounce and it's effect on disc flight. Perhaps what you are saying is that under ideal conditions, the best you can do is to have the disc roll off your hand at the maximum forward speed thus achieving the maximum torque. I'd still argue this in incorrect but will wait for your answer.



As I said previously, this is the PHDs at Aerovironment, who said that maximum forward velocity is directly related to maximum speed as if it is rolling out of your grip. These are some pretty smart guys, who have done some world record breaking things in aerodynamics. Your arguement would be with them, not me.



So is it possible to throw slow, but put a lot of spin on a disc? I definetely notice a difference in flight when I switch up a couple of things related to my release. With newer, wide rimmed drivers I do a full run-up and reach back. With slower discs (compared to the wider rims), I often do a very slow walk/run up, barely reach back at all, and simply concentrate on a quick clean pop. This results in my most controlled flights. The slower the disc is, the closer I can max it out with this release compared to the reach back. However, with the fastest discs there is a noticible difference in favor of the reach back. If I don't go 100% with the wider rimmed discs, they don't "work" for me.

I bring this up because I always thought that the second release I described, was as Lyle said, throwing with less speed and more spin. Perhaps this is not the case and other factors are at work.

davei
Apr 22 2008, 09:52 AM
[
I'm not sure I agree with this.

If for no other reason than it assumes a very static relationship between speed of release and spin rate on what is a very dynamic process. I know for sure that I can take some off of my throw and work on putting a whole lot more torque on the disc, that is, I can vary the rate of spin on my disc and rate of forward motion consciously.

Now, it might be that the difference is spin rate between trying to put torque on the disc and not trying to put spin on it is not statistically significant. I would argue that is weak at best, given that the effects on disc flight between each type of throw is significant, at least for me.

More importantly, this seems contraindicative of your own definitions on tendon bounce and it's effect on disc flight. Perhaps what you are saying is that under ideal conditions, the best you can do is to have the disc roll off your hand at the maximum forward speed thus achieving the maximum torque. I'd still argue this in incorrect but will wait for your answer.



As I said previously, this is the PHDs at Aerovironment, who said that maximum forward velocity is directly related to maximum speed as if it is rolling out of your grip. These are some pretty smart guys, who have done some world record breaking things in aerodynamics. Your arguement would be with them, not me.



So is it possible to throw slow, but put a lot of spin on a disc? I definetely notice a difference in flight when I switch up a couple of things related to my release. With newer, wide rimmed drivers I do a full run-up and reach back. With slower discs (compared to the wider rims), I often do a very slow walk/run up, barely reach back at all, and simply concentrate on a quick clean pop. This results in my most controlled flights. The slower the disc is, the closer I can max it out with this release compared to the reach back. However, with the fastest discs there is a noticible difference in favor of the reach back. If I don't go 100% with the wider rimmed discs, they don't "work" for me.

I bring this up because I always thought that the second release I described, was as Lyle said, throwing with less speed and more spin. Perhaps this is not the case and other factors are at work.



You can definitely throw slower with more spin, and you can throw fairly fast with insufficient spin too, (especially sidearm), but when you're talking 70 mph, everything needs to be happening together. No slip. No holding the arm speed back.

Lyle O Ross
Apr 22 2008, 11:25 AM
[
I'm not sure I agree with this.

If for no other reason than it assumes a very static relationship between speed of release and spin rate on what is a very dynamic process. I know for sure that I can take some off of my throw and work on putting a whole lot more torque on the disc, that is, I can vary the rate of spin on my disc and rate of forward motion consciously.

Now, it might be that the difference is spin rate between trying to put torque on the disc and not trying to put spin on it is not statistically significant. I would argue that is weak at best, given that the effects on disc flight between each type of throw is significant, at least for me.

More importantly, this seems contraindicative of your own definitions on tendon bounce and it's effect on disc flight. Perhaps what you are saying is that under ideal conditions, the best you can do is to have the disc roll off your hand at the maximum forward speed thus achieving the maximum torque. I'd still argue this in incorrect but will wait for your answer.



As I said previously, this is the PHDs at Aerovironment, who said that maximum forward velocity is directly related to maximum speed as if it is rolling out of your grip. These are some pretty smart guys, who have done some world record breaking things in aerodynamics. Your arguement would be with them, not me.



Sorry Dave,

Didn't mean to sound too argumentative...

What this reminds me of is Theo Pozzy's throw analysis where he showed that a player throwing at 45 miles an hour could have as much distance as a player throwing at 70 miles an hour. What was the difference between the throws? I would assume, maybe incorrectly, torque or spin.

I've always viewed the throw as having two components, forward speed and spin. I also had thought that varying the combination of those two results in significantly different flight mechanics and distance.

It might be that at 70 miles an hour that you reduce the throw to a strict linear relationship between forward motion and spin off the hand but I'd say that is incorrect simply based on what baseball players can do at significantly higher speeds. We know for example that one type of release can result in a ball with virtually no spin and another can impart enough spin to make the ball curve significantly even at speeds greater than 90 miles per hour.

I don't know what Aero did (i.e. what they actually measured), but I might point out that aerodynamics are not the same as muscle physiology and nerve reaction. I suspect that even at 70 miles an hour that some players have a lot of room to change the mechanics of their throw thus optimizing spin on the disc.

I'd dearly love to know what they measured and what means and numbers they drew their conclusions from.

Lyle O Ross
Apr 22 2008, 11:28 AM
BTW - I fully admit, this could be simply semanitics. However, the way your post read seemed to indicate that at 70 miles per hour, you can assume that the spin is determined strictly by the speed of forward motion, i.e. that 70 miles per hour. If that is the premise, than I disagree.

circle_2
Apr 25 2008, 10:58 AM
Quit bein' soooo scientific, Lyle!?!! :p :D

Given a person's potential, I believe the more important overall component is simply 'timing'.
From the set up beginning with footwork to beginning winding the bio-spring, to the plant, to ending the reachback (straight arm) or shoulder turn (bent arm) and then beginning to prime the pump with a smooth transition toward forward motion...THEN unwind the wound-up spring......SNAP.....followed by a healthy follow through to dissipate all that energy in favor of joint-life-extension!

How did that read? :)

Lyle O Ross
Apr 25 2008, 01:35 PM
Quit bein' soooo scientific, Lyle!?!! :p :D

Given a person's potential, I believe the more important overall component is simply 'timing'.
From the set up beginning with footwork to beginning winding the bio-spring, to the plant, to ending the reachback (straight arm) or shoulder turn (bent arm) and then beginning to prime the pump with a smooth transition toward forward motion...THEN unwind the wound-up spring......SNAP.....followed by a healthy follow through to dissipate all that energy in favor of joint-life-extension!

How did that read? :)



Arrrrgggghhhhh!

That was the sound of my soul being ripped out! :D

Science is everything my man. While I likes your description, it doesn't answer the beginning question. Essentially, what's the best way to measure spin. If you argue that the best way to measure spin is to measure forward velocity, then you should be able to defend that position. I admit, the caveats that I'm raising are anecdotal, but they are based on real world, dare I say it, scientific measurements and concepts.

I'm betting some smart slob could come up with an electronic sensor on a patch that every time the disc rotated would send a signal or count up to give you real rotations per time interval. For example, you'd have a receiver in your pocket, each time the disc rotated around, a directed radio signal from the patch would hit the receiver and add a bit. Then you simply ask how many bits per time interval and shazam.

circle_2
Apr 26 2008, 10:12 PM
HAHA!! I say all this cuz I've seen guys who look like they can throw far...and there's some that throw far and there's some who can't. Then there's the little scrawny guys that flat out BOMB! (Lyle, you've seen all this, I know...)

Is it ALL spin? Is it ALL speed? Is it ALL nose angle? Oh-oh...we're at 3 possible variables now...and science needs to throw in the hat. :eek: :D

stevenpwest
Apr 26 2008, 11:28 PM
I'm betting some smart slob could come up with an electronic sensor on a patch that every time the disc rotated would send a signal or count up to give you real rotations per time interval. For example, you'd have a receiver in your pocket, each time the disc rotated around, a directed radio signal from the patch would hit the receiver and add a bit. Then you simply ask how many bits per time interval and shazam.



Several people have, though I wouldn't call them slobs. If all you want to do is count rotations, you slap a sun sensor on there. It just records the variation in the amount of light. Once per revolution, it will get brighter. That's how NASA does it.

On page 187 of "Spinning Flight - Dynamics of Frisbees, Boomerangs, Samaras, and Skipping Stones" Ralph D. Lorenz shows a picture of a Frisbee he had all wired up for all sorts of measurements.

To quote "Among the interesting phenomena identified in these studies is the existence of nutation in the early part of the throw. A good throw will avoid exciting nutation, which seems to subtantially increase drag."

Guess I'll go take a stack of discs out to the field and work on my nutation boredom.

rickhemmings
Apr 27 2008, 01:30 AM
Interesting, Had to look up nutation though: "A wobble in a spinning gyroscope or other rotating body".
Also of note, someone will be posting measured spin rates at different release speeds on this thread sometime this week. stay tuned... :cool:

stack
Apr 30 2008, 02:56 PM
thats very interesting to me because earlier i guessed that somehow the disc spinning almost speeds up after the initial fling by observing the flutter (nutation).

i still think there may be some merit to this... thinking of a football thrown wobbly yet really hard will wobble and then can turn into a spiral shortly after release... i would think the rpms has to increase from the wobble to the tight spiral.

Lyle O Ross
Apr 30 2008, 07:08 PM
thats very interesting to me because earlier i guessed that somehow the disc spinning almost speeds up after the initial fling by observing the flutter (nutation).

i still think there may be some merit to this... thinking of a football thrown wobbly yet really hard will wobble and then can turn into a spiral shortly after release... i would think the rpms has to increase from the wobble to the tight spiral.



I'm not sure I understand this logic. My understanding has always been that a certain level of spin in necessary to keep the disc from wobbling at a given forward velocity. For example, if the disc is traveling at X and that requires a spin rate of 70 rpm for there to be no nutition, then if you are a disc, and spin at 60 rpms at a speed of X, you wobble. The wobble stops when the nutation increased wind resistance causes enough drag to slow the speed of the disc to X - 1, a speed which only requires 60 rpms to eliminate nutation. That is, it isn't that spin has increased, rather that forward speed has decreased.

I don't know if this is correct, but it seems much more likely than the other model. Increasing spin would require the addition of a force at a vector to the disc. Where that force would come from escapes me.

stack
May 01 2008, 12:15 AM
thats very interesting to me because earlier i guessed that somehow the disc spinning almost speeds up after the initial fling by observing the flutter (nutation).

i still think there may be some merit to this... thinking of a football thrown wobbly yet really hard will wobble and then can turn into a spiral shortly after release... i would think the rpms has to increase from the wobble to the tight spiral.



I'm not sure I understand this logic. My understanding has always been that a certain level of spin in necessary to keep the disc from wobbling at a given forward velocity. For example, if the disc is traveling at X and that requires a spin rate of 70 rpm for there to be no nutition, then if you are a disc, and spin at 60 rpms at a speed of X, you wobble. The wobble stops when the nutation increased wind resistance causes enough drag to slow the speed of the disc to X - 1, a speed which only requires 60 rpms to eliminate nutation. That is, it isn't that spin has increased, rather that forward speed has decreased.

I don't know if this is correct, but it seems much more likely than the other model. Increasing spin would require the addition of a force at a vector to the disc. Where that force would come from escapes me.



to help with where my thoughts are coming from... think of speed of object traveling and number of revolutions as being somewhat arbitrary.

think of a figure skater... they go into a spin (arms and non supporting leg spread out wide)... they dont add any extra force yet when they tighten up (pull arms & leg close) they greatly increase the RPMs or spin... if you hit a DG mini with a golf club it will start out kind of wobbly (not spinning much) and will eventually 'flatten out' and start spinning (possibly faster?)

here's a link to a girl breaking the world record for skating RPMs (~1:30 in)... this illustrates how they speed up w/o adding any extra force and could help illustrate how it may be possible for a disc to actually increase in RPMs after the initial propulsion
(not saying this is the most ideal type of throw... wobble obviously isnt good off the tee ;)

ice skater spinning (at about 1:30 into the video) (http://www.youtube.com/watch?v=VYV5jq1oMm0)

rickhemmings
May 01 2008, 01:19 AM
There is a correlation between wobble and spin. The more a disc wobbles the faster the spin will decrease. During the wobble, the angle of attack will constantly change, in addition to which, the disc's surfaces will present them selfs to the oncoming air at steeper angles. More drag will equal less spin. The disc does not have any appendages to pull in, the "skater effect" can not happen.

stack
May 01 2008, 01:56 AM
i hear ya on the arms but to me observing a wobbly football throw turn into a tight spiral mid flight or a dg disc ripped off the teepad starting off wobbly and flattening out soon after is what I was trying to compare it to.

it makes sense (and may not be scientific) that the football or disc could be launched with tons of power but not efficiently for the shape of the object and have it travelling at a speed of X w/ a certain amount of rpms... only to have the object find its proper flight path and fly as intended and actually spin which I would imagine would be an increase in rpms.

another example is hitting a DG mini with a golf club... tons of power go from the club to the mini and it gets blasted into the air... the first initial flight is extremely wobbly and the rpms really can't be that high... shortly after the mini finds the proper flight path and flattens out and it 'appears' that the rpms would have increased.

i know observations and fact/science dont always add up... just helping explain where my observations are coming from.

rickhemmings
May 01 2008, 02:26 PM
To test your theory, you could insert a hot needle through the center of an old disc using a vicegrip and open up the hole slightly. Then hold the vicegrip, needle, (with a round bead slid halfway down) and disc assembly out your (passenger side!) window at 40 mph or so and start it wobbling. If the disc starts to spin you win!

IMO, since the air will hit the wobbling disc evenly on both sides, there will be no asymmetric force to create, or continue the spin, but please, try to prove me wrong. :cool:

stack
May 01 2008, 03:08 PM
want to make sure i'm clear that i'm not about proving anyone wrong just trying to talk thru things to help figure them out.

and as fun as this test sounds all it would prove is that a disc can flatten out from a wobble... i've played with numerous players that the disc starts wobbly off the tee and flattens out along the way to know that its possible... i wouldnt think that part is in question. the only thing im curious about is if the disc actually spins faster once it gets 'flat' than when its wobbling. (unless you are saying to try and somehow measure the rpms while hanging it out of the window)

stevenpwest
May 02 2008, 12:28 AM
There is a correlation between wobble and spin. The more a disc wobbles the faster the spin will decrease.



True, but it would happen in a vacuum without any drag from the air.

Although a disc doesn't have anything to pull in or out, it can change its moment of inertia. The moment of inertia of a disc is bigger when it is in a flat spin than when it is flipping end over end. A wobble is somewhere between these two.

So, when the disc goes from wobbling to flat spin, the moment of intertia gets bigger, and to conserve angualr momentum, the angular velocity must get smaller. It is the same as the figure skater putting her arms OUT. Thus, the RPM's actually decrease when the disc stops wobbling.

The reason the disc stops wobbling is another story. But we all know that it does.

rickhemmings
May 02 2008, 12:48 PM
Very interesting info! Do you think if the disc flies flat, or it wobbles, the rpms will decrease from the moment of release until it hits the ground? I wish there was an easy way to measure this. As far as measuring rpms when the disc is released, this has recently been done and the data is being compiled. Here is a picture of the disc that was modified by Erin Hemmings to record each revolution magnetically. It works like a charm and the results are quite interesting. I'll leave it to him to explain how it works. He will post soon. [url=http://img236.imageshack.us/my.php?image=img8214ko2.jpg][img=http://img236.imageshack.us/img236/5663/img8214ko2.

rickhemmings
May 02 2008, 01:18 PM
http://picasion.com/pic2/378518767c13b77f32611a6c01ee9696.gif

Lyle O Ross
May 07 2008, 06:09 PM
thats very interesting to me because earlier i guessed that somehow the disc spinning almost speeds up after the initial fling by observing the flutter (nutation).

i still think there may be some merit to this... thinking of a football thrown wobbly yet really hard will wobble and then can turn into a spiral shortly after release... i would think the rpms has to increase from the wobble to the tight spiral.



I'm not sure I understand this logic. My understanding has always been that a certain level of spin in necessary to keep the disc from wobbling at a given forward velocity. For example, if the disc is traveling at X and that requires a spin rate of 70 rpm for there to be no nutition, then if you are a disc, and spin at 60 rpms at a speed of X, you wobble. The wobble stops when the nutation increased wind resistance causes enough drag to slow the speed of the disc to X - 1, a speed which only requires 60 rpms to eliminate nutation. That is, it isn't that spin has increased, rather that forward speed has decreased.

I don't know if this is correct, but it seems much more likely than the other model. Increasing spin would require the addition of a force at a vector to the disc. Where that force would come from escapes me.



to help with where my thoughts are coming from... think of speed of object traveling and number of revolutions as being somewhat arbitrary.

think of a figure skater... they go into a spin (arms and non supporting leg spread out wide)... they dont add any extra force yet when they tighten up (pull arms & leg close) they greatly increase the RPMs or spin... if you hit a DG mini with a golf club it will start out kind of wobbly (not spinning much) and will eventually 'flatten out' and start spinning (possibly faster?)

here's a link to a girl breaking the world record for skating RPMs (~1:30 in)... this illustrates how they speed up w/o adding any extra force and could help illustrate how it may be possible for a disc to actually increase in RPMs after the initial propulsion
(not saying this is the most ideal type of throw... wobble obviously isnt good off the tee ;)

ice skater spinning (at about 1:30 into the video) (http://www.youtube.com/watch?v=VYV5jq1oMm0)



I'm sorry I didn't see this earlier but better late than never. That said, I disagree with your comparison. Indeed, the ice skater has added a force or energy to the equation. The skater moves their arms from an extended position to a less extended position while they are spinning. That movement adds energy to the equation. It takes energy to pull your arms in against the centrifugal force, i.e. you are working at a 90 degree angle to that force in a vectored manner, such that the energy gets redistributed into a faster spin. Think about it like this, your arms are out and you pull them in, you pull them in 2 inches. The force appears to be directly in towards your body but it's not. The reason it's not is that you've spun as you pulled them in, so the vector that the force is on is actually circular. That is the force of pulling your arms in plays out in a circle around your body causing you to spin faster. (if you read up on precession you will see that this is remarkably familiar to that concept).

More importantly, you're comparing a disc to a spinning body, the first case being a static flying body, no arms to pull in, and the second being a dynamic flying body (sort of) where there are moving parts, the arms. Such comparisons always fail the smell test. Your models should have more in common with a flying disc than a spinning body does.

Even more importantly, while I'm not a physics major, I'm pretty confident that you don't ever get something from nothing. Otherwise we'd have a perpetual motion machine. If the disc picks up rpms, it's getting energy from somewhere. It might be that the energy comes from forward motion, but the disc would slow down as the energy from the forward motion translates into rpms. Such things might be possible but what causes the transfer of forward motion energy to spin energy? There is nothing in this equation that could accomplish that task.

Other points: even in the mini case you wrote about, I'd still go with the model I've proposed, that you impart some spin on the disc on contact, but it isn't enough to compensate for the forward motion so the mini wobbles.

BTW - part of the reason that I support this position is that the stuff written by Blake T. and Dave Dunipace also supports this view. You might go to Discgolfreview and read what's posted there.

Lyle O Ross
May 07 2008, 06:52 PM
There is a correlation between wobble and spin. The more a disc wobbles the faster the spin will decrease.



True, but it would happen in a vacuum without any drag from the air.

Although a disc doesn't have anything to pull in or out, it can change its moment of inertia. The moment of inertia of a disc is bigger when it is in a flat spin than when it is flipping end over end. A wobble is somewhere between these two.

So, when the disc goes from wobbling to flat spin, the moment of intertia gets bigger, and to conserve angualr momentum, the angular velocity must get smaller. It is the same as the figure skater putting her arms OUT. Thus, the RPM's actually decrease when the disc stops wobbling.

The reason the disc stops wobbling is another story. But we all know that it does.



While this possibility seems more likely than the first, I still see at least one problem with it. Essentially, the model is that the wobble is imparted by some unspecified vector and that slowing the spin down stops the wobble.

Let me begin by pointing out that in almost every case, it is not top pros who have mastered the art of putting lots of spin on their discs that have wobble, indeed, it is usually the rookie who does not know how to put spin on their disc who gets a wobble. You might argue that the rookie is doing something else wrong to introduce wobble but I'd still say that most of the wobble I've seen was when there was almost no spin on the disc.

http://www.afda.com/skills/physics.htm

This link gives a description of the introduction of wobble onto a disc and argues that poor technique introduces insufficient spin and hence wobble. The argument isn't clear but nonetheless supports the concept that wobble is due to low spin. I'll continue to look for more examples since the evidence so far isn't clear.

stevenpwest
May 07 2008, 10:16 PM
[/QUOTE]

While this possibility seems more likely than the first, I still see at least one problem with it. Essentially, the model is that the wobble is imparted by some unspecified vector and that slowing the spin down stops the wobble.

Let me begin by pointing out that in almost every case, it is not top pros who have mastered the art of putting lots of spin on their discs that have wobble, indeed, it is usually the rookie who does not know how to put spin on their disc who gets a wobble. You might argue that the rookie is doing something else wrong to introduce wobble but I'd still say that most of the wobble I've seen was when there was almost no spin on the disc.

http://www.afda.com/skills/physics.htm

This link gives a description of the introduction of wobble onto a disc and argues that poor technique introduces insufficient spin and hence wobble. The argument isn't clear but nonetheless supports the concept that wobble is due to low spin. I'll continue to look for more examples since the evidence so far isn't clear.

[/QUOTE]

First, it would be more correct to say that stopping the wobble slows the spin down. Now, let's talk about what causes the wobble. It is not merely lack of spin. A disc with no spin at all would not wobble at all.

The article actually says "If the thrower puts spin on the disc at an angle to the flat plane of the disc, it will wobble and lack control." So, yes, the wobble is imparted by your unspecified vector the player is just pushing or pulling in an imperfect direction.

The article doesn't say that a lack of spin causes wobble. However, a lack of spin will make the wobble last longer and be more noticeable (thus, your reference to most of the wobble you've SEEN). So, wobble is not caused by slow spin, but revealed by slow spin.

More spin will translate to a faster reversion to the stable state, perhaps so fast that the wobble is not observed. And, of course, the more highly skilled player who can put a lot of spin on a disc is probably better at avoiding wobble, too.

On another subject: I have a theory as to why disc APPEARS to spin faster when wobble goes away.

When a disc is wobbling, your eye tracks the wobble. The high side of the disc is on the right, then the left, then the right...

After the disc stops wobbling, your eye tracks the spin. The yellow side is on the right, then the left, then the right....

According to Dr. Lorenz, the rate of wobble is half that of the rate of spin.

Since spin is twice as fast as wobble, the disc appears to start "going around" twice as fast at the moment your eye shifts from tracking wobble to tracking spin. This appears to be a sudden speeding up of the spin when the wobble goes away.

rickhemmings
May 08 2008, 01:46 AM
My head is spinning, and or wobbling :confused:

Lyle O Ross
May 12 2008, 06:10 PM
O.K. Steve, here's the fault. It took me a while to find it, I went to the God of disc golf throwing, Dave Dunipace. BTW - there have been many times when I've questioned Dave's logic, in almost all of them I found that Dave was right. He's spent a lot of time thinking about this and is one of the best resources this sport has.

Go out on a windy day. Take a disc and throw hard into the wind and down wind. What you're going to find is that when you throw into the wind, you will get more throws with off axis torque, wobble, than when you throw down wind. Now, why would that be?

If we take what you've written, either, the rookie makes the mistake that creates wobble more often when throwing into the wind than when throwing with the wind, or, the player puts less spin on discs thrown down wind than discs thrown into the wind. Either of these possibilities seems unlikely.

The reason you see the difference is because the wind speed actually changes the "relative" speed of the disc. If I throw a disc at 40 miles an hour in no wind, the disc is traveling 40 miles per hour relative to the air around it. If I throw the disc into a 20 mile per hour head wind, the disc, thrown at 40 miles per hour, is traveling at 60 miles per hour relative to the air around it. If I throw it down wind it is traveling 20 miles an hour. The "apparent" speed of the disc varies in each situation, but the spin should be relatively unaffected. In the high speed situation, where the speed is faster than the spin can compensate for (my position), you get wobble. When the speed is slower, you get less wobble.

This is consistent with the notion that it is the reduction of speed that removes the wobble and not the reduction of spin and that indeed, you need adequate spin to prevent wobble at high speeds.

stevenpwest
May 13 2008, 12:03 AM
The fault with what, exactly?

With this, I take it: My guess is that wobble is caused by a force which is applied at an angle other than perfectly tangent to the edge of the disc (or perfectly aligned with propelling the disc forward). To get wobble, something has to push the disc in a way that does something other than make it spin or go forward.

In your windy day scenario, the third possibility you didn't mention is that wind pushes the nose up or down, providing a source for wobble. Throwing upwind would apply more of this force, and downwind less. Thus, more wobble (more precisely, a greater "rotation angle") for upwind throws.

I agree that it would take more spin to overcome the greater "error" introduced by the stronger relative wind affecting the disc. But not in the way I think you think.

I don't think greater spin prevents wobble entirely. I think that for any given "error" force, greater spin (more "good" force more momentum where you want it) will cause the wobble to be flatter (the rotation angle to be smaller). Also, the disc will stabilize to a flat spin faster.

But I can't see how wobble can be solely the result of insufficient spin. That is your position, isn't it?

Lyle O Ross
May 13 2008, 06:55 PM
The fault with what, exactly?

With this, I take it: My guess is that wobble is caused by a force which is applied at an angle other than perfectly tangent to the edge of the disc (or perfectly aligned with propelling the disc forward). To get wobble, something has to push the disc in a way that does something other than make it spin or go forward.

In your windy day scenario, the third possibility you didn't mention is that wind pushes the nose up or down, providing a source for wobble. Throwing upwind would apply more of this force, and downwind less. Thus, more wobble (more precisely, a greater "rotation angle") for upwind throws.

I agree that it would take more spin to overcome the greater "error" introduced by the stronger relative wind affecting the disc. But not in the way I think you think.

I don't think greater spin prevents wobble entirely. I think that for any given "error" force, greater spin (more "good" force more momentum where you want it) will cause the wobble to be flatter (the rotation angle to be smaller). Also, the disc will stabilize to a flat spin faster.

But I can't see how wobble can be solely the result of insufficient spin. That is your position, isn't it?



That's exactly my position. The reason that is my position is because that is the position taken in a number of documents I've read about the stability of disc flight. If you remove all spin from a disc, you can have stable flight under a very limited set of circumstances. To get stable flight, you have one speed where the forces acting on the disc counteract. If you move away from that area, the disc tumbles. To get stable flight, you put spin on the disc and thus gain more stable flight over a wider range of speeds.

The fault I'm pointing out is simply that spin being equal upwind or downwind [remember that you have put spin on the disc at the point of release and your snap should not be wind dependent] you get different frequencies of wobble. The only thing that has changed at the point of release is relative speed, not spin. If the spin is the same, the speed different and the wobble varies with the speed, well it is not spin rate that effects wobble it is speed. BTW - the concept that movement through the air will scrub off spin should be compared to the concept that it will scrub off speed. The profile of the disc as it goes forward, while flat, is still substantial relative to the profile of the surface of the disc as it spins. There is little aerodynamic drag on the surface of the disc that would cause a slowing, even with the wobble. There is significantly more in the forward motion of the disc traveling through the air. That is, you will scrub off speed much more quickly than spin in any event, thus reducing speed relative to spin at a much faster rate.

stevenpwest
May 13 2008, 11:59 PM
If you remove all spin from a disc, you can have stable flight under a very limited set of circumstances.



True, and I think those circumstances are only when there is no force acting to induce wobble. No wind pushing the nose of the disc up or down, and no error in the throw.


To get stable flight, you have one speed where the forces acting on the disc counteract.



I don't think there is a magic speed where all of a sudden the flight is stable, and below that speed the disc tumbles. (Whether you are refering to the forward speed of the disc OR the RPM's.) I think your next sentence says it better:


To get stable flight, you put spin on the disc and thus gain more stable flight over a wider range of speeds.



The key word being "more". I think any non-zero amount of spin would, eventually, result in the disc transitioning into a stable, flat spin. Of course, it might take a lot longer than the flight time of a normal throw. A whole lot of spin will eliminate the wobble fast, and a little spin will eliminate it slowly.


The fault I'm pointing out is simply that spin being equal upwind or downwind you get different frequencies of wobble.



I don't disagree with that. I think that the reason for the differences is that there is a greater wobble-inducing force from throwing upwind.

Also, I don't think it is actually the frequency of the wobble that varies, rather it is magnitude of the wobble. Maybe that's what you meant. According to Dr. Lorenz, the frequency of the wobble (how often one side of the disc goes up and down) is pretty much locked in at half the spin rate. The magnitude of the wobble (the rotation angle, or how far the sides of the disc go up and down out of plane) is what I think gets bigger with "more" wobble.


The only thing that has changed at the point of release is relative speed, not spin. If the spin is the same, the speed different and the wobble varies with the speed, well it is not spin rate that effects wobble it is speed.



I think greater speed creates a stronger relative headwind to push the disc out of alignment, causing wobble. So, for any given rate of spin, greater speed will induce more wobble (for an equally imperfect throw).

But, just because speed affects wobble does not mean than spin can't affect it, too.

Anyway, if it is not spin rate that affects wobble, what happens to your position that wobble is solely the result of insufficient spin?

Lyle O Ross
May 20 2008, 12:07 PM
If you remove all spin from a disc, you can have stable flight under a very limited set of circumstances.



True, and I think those circumstances are only when there is no force acting to induce wobble. No wind pushing the nose of the disc up or down, and no error in the throw.



To get stable flight, you have one speed where the forces acting on the disc counteract.



I don't think there is a magic speed where all of a sudden the flight is stable, and below that speed the disc tumbles. (Whether you are refering to the forward speed of the disc OR the RPM's.) I think your next sentence says it better:

<font color="red"> While in a real world setting, you'd have external factors affecting disc flight, for this example it is better to assume a neutral environment where you can look only at disc flight mechanics, i.e. no wind, no grip lock, no errors in the throw, you'd do this test in a wind tunnel. When a disc is flying with no spin in such an environment there are two forces acting on the disc. The first is a nose up tendency caused by the lift on the wing. It is nose up because the center of gravity is behind the wing where the lift occurs (this by the way is why Aerobie invented the flying ring, instead of one wing in front of the center of gravity, you have two wings with lift eliminating the nose up tendency. The second is a down push caused by the camber of the disc. When the disc rotates these two forces act differently than when the disc is not rotating; however when the disc is not spinning, there is exactly one, as you called it, magic speed where the two forces counter and the disc flies straight. I didn't make this up, I read an article by a NASA aerodynamics engineer.</font>


To get stable flight, you put spin on the disc and thus gain more stable flight over a wider range of speeds.



The key word being "more". I think any non-zero amount of spin would, eventually, result in the disc transitioning into a stable, flat spin. Of course, it might take a lot longer than the flight time of a normal throw. A whole lot of spin will eliminate the wobble fast, and a little spin will eliminate it slowly.

<font color="red"> Given what I just wrote above, your zero spin model has a problem. If again, you are flying in a neutral environment, no spin, and at a speed that allows the disc to fly with out tumbling, how do you introduce spin? What vector introduces spin? Where does the energy come from? As I wrote to Twisted, you could argue that the energy comes from a reduction in the forward motion, i.e. you use the energy from the forward motion to impart spin, but I don't see how? There is no mechanical force that takes the forward motion and translates it into torque in a neutral environment. Physics 101 teaches us that movement doesn't just happen, it requires a force. To increase spin, you need to introduce a force. </font>


The fault I'm pointing out is simply that spin being equal upwind or downwind you get different frequencies of wobble.



I don't disagree with that. I think that the reason for the differences is that there is a greater wobble-inducing force from throwing upwind.

Also, I don't think it is actually the frequency of the wobble that varies, rather it is magnitude of the wobble. Maybe that's what you meant. According to Dr. Lorenz, the frequency of the wobble (how often one side of the disc goes up and down) is pretty much locked in at half the spin rate. The magnitude of the wobble (the rotation angle, or how far the sides of the disc go up and down out of plane) is what I think gets bigger with "more" wobble.


The only thing that has changed at the point of release is relative speed, not spin. If the spin is the same, the speed different and the wobble varies with the speed, well it is not spin rate that effects wobble it is speed.



I think greater speed creates a stronger relative headwind to push the disc out of alignment, causing wobble. So, for any given rate of spin, greater speed will induce more wobble (for an equally imperfect throw).

But, just because speed affects wobble does not mean than spin can't affect it, too.

Anyway, if it is not spin rate that affects wobble, what happens to your position that wobble is solely the result of insufficient spin?



<font color="red">I don't think you understand my position, my position is that it is the relationship between speed and spin that controls wobble. Excess speed with insufficient spin results in wobble. You can do one of two things to solve the problem.

First, you can remove speed while keeping the spin the same. As you'll recall, this is what I'm arguing has to happen based on the aerodynamics of the flight plate as it turns and of the forward motion of the disc through the air, that is, the greater resistance of the disc as a whole means that speed will decrease faster than spin.

Second, you can increase spin to compensate for the speed. This is what Twisted argues is happening. I've countered this above, by asking where the energy to impart more spin would come from? No model for that possibility has been put forward.

BTW - one other thing, I've read numerous articles by both lay and professional people, all that argue more spin is good and that you can't get too much spin. More spin makes a flying disc fly more neutral (my wording), whether it is under stable or over stable, the disc comes to a stable position and flies flatter with more spin. Never, in ten years of reading articles, have I ever read one expert that said reducing spin makes a disc fly better. All of them state clearly that more spin results in better flight.

In terms of the frequency of the wobble, I don't know, and I don't think the point is relative to the argument as a whole. The question is, what imparts wobble, and how do you make it go away? Secondarily, why is it that the wobble disappears about half way through the flight when it does occur?

Last point, your notion that a rookie throws a disc differently to impart wobble seems unlikely to me. Look at the power grip, the bonapane (sp?) the flip the bird and the fan grip. The reality is that any one of these grips is rigid enough to impart a great deal of wobble on the disc and yet Pros do not. The reality is that good disc flight mechanics, spin and speed, overcome whatever wobble will be imparted. Here's an experiment for you. Go out and throw. Mess with the grip, angle, what ever you want. When you find something that regularly imparts wobble on the disc no matter how much spin you put on it come back and tell us about it. Good Luck! </font>

gnduke
May 20 2008, 04:13 PM
I have a simple theory as to what happens to wobble in flight.

I see it in much the same light as a spinning top or gyroscope. As long as the object has sufficient rotational speed, it will fight to a stable rotational plane. The immediate side effect of off-axis torque wobble is that it burns energy to correct the wobble and bring the forces into plane. The energy that is bled off is rotational speed. An experiment is readily available using a suspended bicycle wheel. If you have a method of reaching a verified speed (a drill and a handheld tachometer) measure the degrade time of a tire from speed x to y, then spin it up again and introduce some off axis torque by tilting the axle, verify whether the wobble cancels itself out and measure the degrade time from x to y.

As far as why wobble is more evident at higher air speeds than it is at lower air speeds (same ground speed throws into the wind versus with the wind), it is because there are greater aerodynamic forces at work on the disc moving at a higher airspeed.

Let me put my idea forward this way, With a perfect release, the gyroscopic forces are in balance with the flight plane of the disc and there is no wobble in the disc. The maximum amount of energy is preserved at launch and the minimum amount of energy is consumed during flight.

In a release that includes off axis torque in a vacuum, the gyroscopic forces almost instantly cancel the wobble and the flight is smooth almost from the start.

As we add aerodynamic force, the fun starts. Changes to the attack angle of the disc add greater aerodynamic off axis forces to the disc at higher air speeds. Thus it takes more time and energy to stabilize a wobbly release into a head wind than it does into a tailwind.

Of course that is just my understanding of what would cause the observed actions. I am sure someone will point out the shortcomings of my theory.