First, about the other two theories I've seen:
(1) Al, you would not be that far off on the deceleration theory -- if there were enough deceleration to significantly change the velocity and thus the centrifugal force. There really isn't, unless the swing is terrible. The decel of the average middle handicapper probably doesn't account for even a 5% decrease in clubhead speed from max in the downswing to impact, not enough for the sort of toe bob we're talking about.
So, while centrifugal force is a major contributor to toe-down deflection at impact, it probably doesn't explain "toe bob" -- which is really a dynamic and usually unpredictable component of the toe deflection that isn't simply explainable by centrifugal force.
(2) Lloyd, it isn't a reaction to the toe-up deflection. Deflections and their reactions occur in a single inertial plane. The toe-heel plane is not an inertial plane; it rotates through the inertial reference during the downswing. The toe-heel plane rotates from the target plane (an inertial plane) at the top of the downswing to a plane roughly perpendicular to the target plane at impact. So any reaction to an initial toe-up deflection (caused by casting, for instance) would have to be in the target plane and would not cause toe bob.
But the argument against #2 does suggest another theory. Toe bob may well be a reaction to deflections induced by the golfer during the downswing as Lloyd suggests, but those deflections would have to be in the plane that is perpendicular to the target plane and through the shaft. Let's remember that the target plane is, ideally, also the swing plane. In other words, any off-plane bobbles the golfer introduces during the downswing might induce a reaction that takes the form of an unpredictable toe-heel deflection at impact.
Actually, that makes fair sense to me. One of the things that marks the better golfer is that the swing is on plane... that from the pull down from the top the shaft stays in the target plane, with no forces from the hands pushing it outside the target plane. So if toe bob is a reaction to outside-the-plane forces in the downswing, one would expect less of it from the pro than the duffer.
OK, I think I understand that. Where did I go wrong?
Cheers!
DaveT
At 01:16 PM 1/2/03 -0500, Al Taylor wrote:
Lloyd,
I hate to argue with an engineer since I am out of my league then, but I believe that the TT shaft lab results do show that higher head speeds have greater toe down. Along this area, the Pros usually are still accelerating into impact and, as a result, have little to nil toe bob. The amateur often starts to decelerate prior to impact and the toe then starts back up, or bobs. The TT graphs show that somehow there is often a series of toe ups and toe downs on the later example.
I know that my irons profile is similar to pro iron profiles (wonder why my shot results aren't the same?) but my driver shows some toe bob.
Al
At 09:40 AM 1/2/2003, you wrote:
Royce and Alan The centrifugal force is certainly part of the Toe down deflection at impact. Since toe down deflection is dependent on club head speed this would make the better players with the high clubhead speeds have greater toe down deflection ( opposite True Temper results ). What I described earlier is the other component of toe down defection at impact. As can be seen in all of the Shaft Lab data there is initially a toe up deflection at the top of the swing. This deflection along with the time from the start of the down swing to impact gives the shaft time to go through 1/3 to 2/3 cycle of its natural frequency resulting in some degree of toe down deflection. This resulting defection is a function of how much the club is loaded at the top of the swing to produce the initial toe up deflection. Herein lies the difference between the good player and the others....
