*** Response below > [Original Message] > From: Alan Brooks <[EMAIL PROTECTED]> > To: <ShopTalk@mail.msen.com> > Date: 10/27/2006 10:13:53 PM > Subject: Re: ShopTalk: Shaft behaviour > > Sorry, Lloyd, this mechanical engineer doesn't buy it. The hands are far > to soft to produce a cantilevered response. Think of the shaft as clamped > between springs, where the pads of the hands are the springs (they are no > where near 'hard points'). The padding of the hands is too soft a spring > to allow treating the shaft as cantilevered.
***What happens when the soft spring bottoms out, say the flesh of your hand against the bone( plus the flesh is hardly a spring), you are against a hard point. It is also not a 'free' beam > end, but I think a better model would be a 'hinged' connection to the mass > of the hands. ***It would be difficult to justify a hinge since the shaft is held in the hands over 5 to 7 inches of length and the wrists are not flopping around during the down swing. The wrists are generally releasing under muscular control during the down swing. If we were holding the club in one hand the hinge model may be appropriate but in two hand we have more leverage and muscular control. Even though the shaft oscillation does not continue past > impact it is still valid to consider the response oscillatory behavior, > even if you are only concerned with a portion of the first cycle. If you > look at the results I got with the tip weight you will realize that I saw a > half cycle with the soft shaft and 3/4 cycle with the stiff one. *** It dose oscillate past impact but is influenced by the impact its self and has no affect on the ball. Your test with the centered tip weight is a good way to see the affect of the Aft C.G. on shaft deflection. The purpose of the FitChip is to select a shaft that would be straight in your test at impact. As you described the soft shaft results in your test it came through a quarter cycle+, not a half cycle as you stated above. If the stiff shaft performed as you indicate it would be a 3/4 cycle. However, there is another mechanism which speeds up the first quarter of the cycle and shortens the next half of the cycle. This is also part of the FitChip Model. The Centrifugal force, even on the centered weight at the end of the shaft, helps close the shaft back to straight but once the shaft is past straight it will reduce the amplitude and time of the next half cycle. Because of the affect of centrifugal force on the shaft the shafts reaction is no longer a sine wave. This would explain the reaction of the stiff shaft as you described it. How much > of that first cycle is relevant depends on the shaft stiffness and swing > timing. *** When all you are interested in is getting the shaft back to straight at impact the first quarter of a cycle is all you are interested in. Again if the shaft is not back to straight or is some where in the half cycle past straight the clubhead will not be a peak speed or square to the line. The real evidence that the model dose work is that I have club makers using the system that are having great success with shaft selection. One of those individuals even posted a report after 8 months of use and nearly 2000 fittings that his success rate was better then 99%. I have found no other system or model that will come close to that success rate. llhack > > Regards, > > Alan > > At 07:32 PM 10/27/2006 -0400, you wrote: > >Alan > > > >Even I will agree that the model is wrong when you think only of vibrating > >the shaft in a frequency meter because you immediately think of multi pule > >cycles. However our model only con ciders the first Quarter cycle of club > >release. After impact how it reacts is no consequence. If the model was not > >correct during this first quarter cycle you would not be able to load the > >club as a cantilever beam. You can look at any picture of the loading and > >unloading during the first quarter cycle of release and the shaft is > >reacting as a cantilever beam. Held straight in the hands and flexed all > >the way to the head. This is because when the club loads in your hands it > >will load basically hard between two points for a mater of less the .03 > >seconds 1. the heel of one hand and 2. the fore finger of the other hand. > >The grip will maintain that position against the two load points until the > >shaft passes the straight position. Therefore, The frequency of the shaft > >will be the same as in a clamped frequency meter for that first quarter of > >a cycle. At the 2005 PCS show a Professor spoke on "Club Fitting of the > >Future". As part of his talk he made the same argument Dave dose about > >measuring shaft frequencies (he also was advocating fitting shaft timing to > >the player as the FitChip dose). After confronting him with the first > >quarter cycle argument I just made above he changed his mind and agreed > >with me. > > > >llhack > > > > > > > [Original Message] > > > From: Alan Brooks <[EMAIL PROTECTED]> > > > To: <ShopTalk@mail.msen.com> > > > Date: 10/26/2006 10:41:14 PM > > > Subject: Re: ShopTalk: Shaft behaviour > > > > > > I read through Dave Tutelman's comments on the shaft behavior model that > > > FitChip is relying on and I agree with him that their model is wrong. > >You > > > can't treat a golf club swung by the hands the same as a club clamped in > >a > > > vise. The vibration mode is not the same. First, the hands are far too > > > soft to 'clamp' the end of the club (as Dave pointed out). Once the > > > initial bending of the club is established at the top of the downswing > >and > > > the club starts recovering from this bending it is more reasonable to > >look > > > at the club as a shaft vibrating between to massive weights on the end > >(the > > > hands on one end and the clubhead on the other, similar to the way a > >guitar > > > string oscillates when plucked in the middle (fundamental oscillation, I > > > don't what to hear about harmonics)). The mass of the shaft is > > > significantly lower (specially for drivers) than the mass of either the > > > hands or the clubhead. The clubhead appears to lead or lag at impact, > >but > > > in reality the clubhead is very nearly at the same place it would be with > > > an infinitely stiff shaft, but the shaft is bowing so the clubhead > >appears > > > to be leading or lagging. This isn't absolutely correct, but it's much > > > closer than most people think. > > > > > > I did some tests with 200-g tip weights (no offset c.g. effects) on > >driver > > > shafts and monitored the shaft behavior with an InPractice video system > > > (60-frames per second). The data is not good enough to make truly > > > quantitative statements, but good enough for some qualitative > > > statements. Shaft bow at the impact point is a function of shaft > > > stiffness, sometimes the 'head' leads, sometimes lags, depending on the > > > vibration frequency of the shaft and the timing of the swing. It does > > > exactly what you would expect it to do. I used an 'A' flex shaft and an > > > 'S' flex shaft and, with my swing, the 'S' flex shaft had oscillated > > > through straight, bowed forward, and recovered back to straight at the > > > impact point. Remember this is with a 200-g tip weight so there are no > > > offset c.g. effects. With the lower frequency of the 'A' flex shaft it > >had > > > recovered to lead slightly from the initial bend at the impact point. > >With > > > a higher frequency shaft, or a lower frequency shaft there could easily > >be > > > a 'lag' at the impact point. > > > > > > With a real clubhead installed the offset c.g. effects add to the shaft > > > oscillatory motion. With the 'S' flex shaft the shaft was bowed slightly > > > forward at the impact point. With the 'A' flex shaft the lead was > >greater > > > than with the tip weight. The offset c.g. effects are sufficient, I > > > believe, that it is unlikely that you would ever see a 'lag' at impact > >with > > > an actual golf club. > > > > > > Regards, > > > > > > Alan Brooks > > > > > > > > > > > > At 07:28 AM 10/26/2006 -0400, you wrote: > > > >Tom. Please take a look at the following link: > > > >http://www.fitchip.com/fitchip4club.htm > > > >I always believed that the shaft reacted just the opposite from the > >pics > > > >above the graph. Your take please. > > > >André. > > > >----- > > > >
