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. > >----- >
