Geez, aren't we a fun group of guys....you gotta wonder about a bunch of guys spending New Years Eve hurling barbs across the internet at each other (present company included <GRIN>). I think there might be some eggnog left, and hopefully my son hasn't drained the last of the bourbon. Looking on the bright side, having a grown son living with us helps me turn over my booze supply. It'd take me five years to polish off a fifth of Jack Daniels.
Royce -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Al Taylor Sent: Tuesday, December 31, 2002 8:25 PM To: [EMAIL PROTECTED] Subject: Re: ShopTalk: shaft flex v.s. frequency Awwww man, and I try soooo hard too. Al At 09:09 PM 12/31/2002, you wrote: >Damn right. We finally got somebody around here who speaks English. > >Hear, hear. > >At 02:53 PM 12/31/02, you wrote: >>Hi Lloyd, >> >>We're talking about the same phenomena so I suspect our differences are a >>question of semantics. If you clamp the butt of the club and displace >>the head and then release it, the club will return to straight (that's a >>quarter cycle), pass through straight to displaced an equal (nearly) >>amount in the opposite direction (half cycle), return to straight (3/4 >>cycle), and pass through straight to its original position (full cycle) >>and repeat. At the start of the downswing a golf shaft is nearly >>straight, flexes back during the downswing due to the forces applied to >>it by the hands, and returns to straight at impact. I consider that a >>half cycle, although because it is a forced oscillator instead of a free >>oscillator the analogy is certainly not exact. With the shaft as a >>clamped free oscillator it begins displaced with zero velocity, a quarter >>cycle later is has zero displacement but the velocity is a maximum, at >>the half cycle point the displacement is again maximum (but in the >>opposite direction) and the velocity is zero. With a swung golf club it >>starts with zero displacement and zero velocity (in a reference frame >>that rotates with the shaft and positive is towards the ball/target), as >>the shaft is driven forward in the swing plane by the hands the club head >>is driven back by its inertia and acquires both negative displacement and >>velocity, at some point the force on the club head from the shaft (driven >>by the hands) determined by the shaft stiffness and it's displacement >>stops its backwards movement (in our reference frame) and starts it >>moving forward. At impact the shaft is again straight (its gone from >>straight to negative displacement to straight again) and the head has >>velocity in the forward direction (its gone from zero velocity to >>negative velocity to positive velocity, in a reference frame moving with >>the shaft). Is this a quarter cycle or a half cycle? Your choice. >> >>This is a very dynamic problem and I have completely ignored centrifugal >>forces on the club. The rate that the shaft tries to recover from a >>displaced position is that of the free oscillation frequency and is >>independent (nearly) of the magnitude of displacement. This shaft >>stiffness (oscillation frequency) must be tuned so that it recovers from >>the time history of its forced displacement (which is determined by the >>individual golfer and their swing characteristics) and is again straight >>(maximum velocity) at impact. Is this simple description complete? Of >>course not. There are many other things going on during the average >>golfers swing that effect the dynamics of the club, but this is, I >>believe, the fundamental response. You are right, of course, that swing >>characteristics are what you want to match with shaft frequency, not >>final velocity. >> >>As far as 'toe bob' goes I am not sure that I know what you mean by >>this. I think it is probably the toe down deflection of the club head >>caused by the centrifugal force on the offset cg of the club head. This >>force increases very rapidly near impact (it's proportional to the square >>of the head velocity) and is resisted mostly by a relatively short >>section of the shaft near the tip. The oscillation frequency of this >>'sub-system' on the shaft is going to be much higher than of the entire >>shaft so the timing problem here is different. The forcing function is >>of much shorter duration and the response much more rapid. It basically >>effects the lie of the club head at impact and occurs easily in the last >>100-ms before impact (at least it does on my Shaft Lab plots). >> >>Are we getting close to the same page? >> >>Regards, >> >>Alan >> >> >> >>At 12:11 PM 12/31/02 -0800, you wrote: >>>Alan >>> >>> First we need to get the 1/2 cycle thought straightened out. The club flex >>>normal to the club face that affects hitting the ball by adding club head >>>speed, preferably returns to impact though only 1/4 cycle of its natural >>>frequency. The deflection during the loading process is controlled by the >>>swing rates or loading rates of the player not the natural frequency of the >>>club. This club release or natural frequency controlled 1/4 cycle seems to >>>occur in all the data I have seen, including Shaft Lab, in the last 100 >>>milli seconds of the swing. This 1/4 cycle time is the most important timing >>>factor in selecting club stiffness not club head speed. >>> >>>Now toe bob is a different problem. The loading that causes toe bob occurs >>>much earlier in the swing and can go through a 1/2 cycle + or - according to >>>the stiffness of the club. The major cause of toe bob is the failure to >>>pause at the top of the swing or a strong casting from the top of the swing. >>>Because of the toe down position of the club at the top of the swing the >>>loading imparted by casting causes a toe up deflection of the shaft. As the >>>club begins to rotate into the position for impact the loading is now more >>>normal to the club face and the toe up deflection is released and now >>>controlled by the natural frequency in the toe bob plain. If the stiffness >>>of the club is such that the club has returned though the 1/2 cycle the head >>>is in a toe down position at impact. >>> >>>I hope this helps clarify your thoughts about the affect of natural >>>frequency on the golf club as related to the swing. >>> >>>llhack
