Deflection, Endmass and Shaft Design
- Thread starter HittMan
- Start date
Fred Agnir said:
Yes...it is Shepard...I think I read a post earlier from a Sheldon...not sure at this point...lots of background noise.
The transformation I'm talking about is the deformation of the cue (the inertial resistance to sideways motion) that is unaccounted for in this rigid body calculation. Mr. Shepard notes..."The tip of the stick is in contact with the ball during the short contact time ∆, and whatever sideways velocity is attained by that point on the ball is also attained by the cue" and goes on to make an excellent study of CUEBALL squirt. I'm simply trying to be heard on the issue that "the effective mass" is, as best I can ascertain, also a rigid body consideration. Correct me if I am wrong.
I know I sound like I'm harping but until we enlarge the scope of the cuestick calculation to include variables for the resistant to sideways motion, I am unsure whether it would be wise to rely on this "squirt" article that concentrates on (gives detail calculation to) the cueball side of the transaction. Even Mr. Newton gave equal consideration to both sides of the transaction (3rd law...equal and opposite). As impulse is the integral of force over time, I also think it would be prudent to introduce an elasticity factor on the cue side as well. I realize this increases the complexity of the study by at least an order of magnitude...I am not downing Mr. Sheldon's work...only our use of it. I applaud the work and don't want to undertake it myself, but i would like to get it in place in my mind.
I am not a dynamics PhD either...I have forwarded several ideas and hope for confirmation...all in the spirit of cooperation. I will admit (again as I have earlier) that I did not realise the undercurrents at work here. I'm on shakey ground with this stuff and hoped to be met kindly, as you have, for my own gain in decisions concerning my business. I believe that manipulating the structure and the material will give more positive (alignment with experience) results than changing the weight in the end of the shaft as I consider the 4 grams or so an inconsequential amount when compared to the elasticity of the shaft and the combined structure of the bridge and grip...if I am correct.
I guess that's where we differ...I'm straining here. I had to read Mr. Sheldon's article several times before I noticed that the cue side of the study had been generalized to allow for a better (possibly simpler, doable) model of the cueball side. It could be that I simply don't understand the collision dynamics and have missed something BUT I have a gut feeling that I am at least partially correct.
What really gets me is that so many people (cuemaker and marketers) have put so much energy into this. If I am right, it is a study of an infinitely stiff shaft...no pun intended...just like Drivermaker said it would be. (levity insert)
Thanks for your consideration.
Andy Bruce (Hitt Cues)
"Effective mass" is not part of the rigid body analysis. When you calculate the squirt assuming that the entire rigid cue stick must move to the side, you get a value of squirt that is much too large. During tip-ball contact, the joint doesn't move to the side at all -- there is not enough time for the transverse wave to get back to the joint. We know there is not enough time from a separate observation of the transverse wave resonance which gives you the speed of the transverse wave.HittMan said:
What hasn't been measured well is the exact shape of the shaft during the tip-ball collision. There must be a bend in the shaft, and if a high-speed camera could record this (at 10,000 frames per second or so), you would get an independent and hard-to-argue-with estimate of effective mass.
Mungtor said:
Sheesh..lighten' up. People take these forums a "bit" too seriously. You can talk for the rest of your life about this stuff...whatever floats your boat. You are right, I would rather play pool and run out. But I can throw my little two cents in - if only to entertain myself. Fair enough?
There are videos that were posted here that show the tip/shaft moving to the side at/during contact with the CB. It didn't appear that the fingers of the bridge hand moved. It was interesting to see. I guess this is in part why the CB travels rather parallel to the stroke.
F
Fred Agnir
Guest
HittMan said:
I don't think this would be considered a rigid body analysis. Again, we are only interested in the effective endmass, which is only a small portion of the rigid body mass (the cue).
Even with Meucci's concept where he partially decouples the ferrule from the shaft, there still is a portion of shaft mass that is involved in the collision. So that's not a rigid body analysis either. That would be a more difficult analysis.
The sideways wave speed down the shaft (not the speed of sound down the shaft) and the .001" contact time seem to determine how much of the shaft could possibly be effecting the collision (speed * time). I think the question is "what is that velocity and how do factors such as material and shape/taper alter that velocity?"
What cuemakers do you think are putting so much energy into this? You do agree that the result is less squirt, don't you? Whether low squirt is important is a completely different topic. Some people like it. Others don't. It's that simple. It's a good thing we have a choice.
Fred
Last edited:
Not sure if this has been asked, but does the pressure exerted on the cue by the bridge (especially a closed bridge) have an effect on squirt? Intuitively, it seems to me that bridge pressure would at least have an effect on the transverse wave, if the bridge length is short enough. Would this also have an effect on either shaft deflection or squirt? On this, intuition becomes pure conjecture for me. I'm guessing that bridge grip pressure does have an effect on shaft deflection. I'm also guessing that the wave doesn't start until after the CB has left the tip, so therefore, the bridge grip pressure should not affect squirt. However, if I understand the transverse wave properly, it sort of defines the effective end mass. If bridge pressure affects the transverse wave, then the effective end mass is being changed, which in turn should alter squirt. The intuitive conclusion I've reached is that bridge pressure does affect squirt. Is this a valid conclusion? I've made a lot of assumptions, guesses, etc., and I don't have an empirical leg to stand on, but I'm curious, since I play with a fairly short bridge length (usually no more than 6").
-djb
-djb
F
Fred Agnir
Guest
My theory:DoomCue said:
I think that if the tranverse wave reaches the bridge hand while the cue tip and cueball are in contact (during the .001 sec) and the hand is rigid enough, then the effective endmass should increase because the collision "sees" the bridge hand.
That would mean a bridge length of less than 6", and hand rigidity that may or may not be possible. That's the rub. Whether or not a person's hand can be rigid enough.
I think this is the issue with the Myth Destroyer set up. The grip hand is so rigid that it doesn't allow the cuestick to naturally slow down like human flesh would. I think that increases the contact time. That increased contact time increases the amount of shaft mass involved because the tranverse wave gets to continue down the shaft during contact. Then the Myth Destroyer has a solid v-block which again doesn't represent a human hand which adds rigidity and may possibly add more mass in the equation. This results in poor Myth Destroyer squirt for the Predator.
Fred
I think that as Fred pointed out, it might have to be less than 6 inches to have an effect. Another point is that compared to wood, the ball and your tip, the flesh of your hand is pretty soft, and a relatively small amount of it is actually moved during the "active" time. An experiment to try is to take something like a coffee mug or drinking glass and form a bridge with that holding the front of the shaft on one side (the side that the ball pushes the shaft towards), and make it very, very short. Like Fred, I'm not happy with the way the cueing machines form bridges. I've heard -- but not seen -- that the new Predator tester does something more realisic for the bridge than it used to.DoomCue said:
DaveK said:
If I understand Fred and Bob correctly, the bridge MIGHT not matter since we puny humans can only exert so much force, and it DEFINITELY doesn't matter if the bridge length is past the effective end mass. I think the only way you could say open bridges are less prone to deflection is if we could exert enough force on the cue with a closed bridge, and use a bridge length short enough to be in the area affected by the transverse wave. Like I said, that's IF I understand them correctly. I'm sure they'll chime in if my understanding is incomplete.
-djb
F
Fred Agnir
Guest
Don't bother reading it. Simple as that.DDKoop said:
And Dave, any time you want to meet up, let's get together (as well as any other players in the Boston area.)
Fred <~~~ Worcester area
Bob Jewett said:
Agreed...
Agreed...likely due to the lack of values for deflection of the shaft and friction of the cloth (which will be mercurial at best).
Agreed...but we "know" that the joint moves after the contact because we can see it.
Agreed...so in my experience one may choose to postulate/hypothesize in an effort to align observation with result. It isn't difficult to observe the shaft deflection...why not make a stab at quantifying the process in acknowledgement...to avoid the "are you going to believe this analysis or your lying eyes" questioning. People know what they experience and it is, consequently, difficult to dissuade them from their observation.
Since we have reached agreement on these points. The question remains as to the significant factors in the actual resistance to sideways motion. Did the experimental parameters I proposed seem reasonable to you? Did you have an estimate of relevant cuestick deflection? Do you have any suggestions?
Agreed...effective mass is a generally accepted term and independent of the the rigid body analysis used in this paper.Bob Jewett said:
Agreed...likely due to the lack of values for deflection of the shaft and friction of the cloth (which will be mercurial at best). Don't you agree?
Agreed...but we "know" that the joint moves after the contact because we can see it...leaving us with "proof" that the endmass is moving, likely levering against the fulcrum of the bridge.
Agreed...so in my experience one may choose to postulate/hypothesize in an effort to align observation with result. It isn't difficult to observe the shaft deflection...why not make a stab at quantifying the process in acknowledgement...to avoid the "are you going to believe this analysis or your lying eyes" questioning. People know what they experience and it is, consequently, difficult to dissuade them from their observation.
Since we have reached agreement on these points. The question remains as to the significant factors in the actual resistance to sideways motion. Did the experimental parameters I proposed seem reasonable to you? Did you have an estimate of relevant cuestick deflection? Do you have any suggestions?
LAMas said:
Observation...the light at the end of the tunnel.
About the movement (or lack of) of the bridge hand..the speed of the transverse wave may account for this or it could just be considered a fulcrum for us country boys...probably doesn't matter much at the table.
That's kinda the point here...does any of this matter much at the table? My original post paraphrased the Biblical saying "choking on a gnat while swallowing a camel" in an effort to question the significance of any of these factors...much less 2nd order issues. We may have been looking at the wrong things in the wrong way...but such is the way of marketers...anything for a buck.
well...if it looks like a duck and quacks like a duck? If it isn't rigid, where is consideration given for elasticity? What would you call it? and why? It doesn't really matter to me what its' name is if it doesn't use or produce a variable for sideways motion of the cue...how can we know if manipulating a component variable will be significant without first taking into consideration whether that component may be significant to the outcome. Take changing the weight in the end of the last few inches of the cue for example.Fred Agnir said:
Precisely, but why should we be content to only be interested in one aspect of the impulse and assign no value to resistance from a recognized degree of freedom? I'm begining to think the "we" you refer to doesn't include me.
OK...I use the speed of sound as an approximation from which to begin...I think you will find that it is not far off. Further, I agree that there is a limited length directly involved. But do you agree that resistance to sideways motion may include resistance to deformation (bending). Clear your mind...why wouldn't it?
It seems to me the the list of marketers/makers is long...but I question the relevance of the design changes to the point I suspect the effect is largely psychological. I also believe we (this "we" includes you) have some responsibility here to be as honest as possible with an uninformed public...that's the other topic isn't it? I suspect less people would be impressed with the idea if it were not held out as an answer to their problems. As mentioned previously, I'm careful about my endorsements.
Now I think we have begun asking the right question...is this a reasonable basis for a well informed choice? Or possibly a precipitating event for a stampede (to use the herd mentality analogy). I have seen quite a few of your posts and consider your input a voice of reason. You have only recently reverted to your older, reliable shaft design because you say you are more used to it. Could it be that the low squirt shafts don't really help much because their focus is in fact trivial when compared to the fullness of approximations required to play the game well or better? I would think that if you could not make the adjustment having already transcended quite a few adjustments, then a beginning or average player would be wasting his time with one. But maybe I'm wrong...you be the judge.