Hi Dave,
At 06:22 PM 8/15/2006 -0400, you wrote:
At 04:22 PM 8/15/2006, Alan Brooks wrote:
What's difficult to do in the models is to accurately model all of the
possible variations in muscle contraction that are possible. Most of the
force/torque models in the physics models are relatively simple
(constant, triangular, square, sloped, etc.).
Max's program is more sophisticated than this. It allows you to define a
profile over time. The big-muscle forces have a granularity of 50msec, and
the small-muscle forces 20msec.
But what do you define for the input to the model? How do you determine
what the muscle-generated forces are? You suggest a good swing isn't this
complex. I'd argue that it most certainly is. No swing is consistently
perfect. Good golfers subconsciously correct their swing for the minor
imperfections they 'feel' when they swing a club. They do this with subtle
variations in the forces the muscles produce. How do you measure this to
be able to model it? Maybe a good swing model doesn't have to be complex
to get good analytical results.
A plucked guitar string doesn't just vibrate at a single frequency, but it
does produce a fundamental tone. It is the harmonics that produce the
'richness' of sound and a good guitarist can vary this by where and how
they pluck the string. I can model the fundamentals quite easily. With a
good vibration analysis package I can also characterize the
harmonics. Kurzweil spent years (and still is as far as I know) trying to
get this 'synthesis' realistic. Why should we expect a golf swing to be
any less complex?
Whereas we humans can apply a very complex force/torque history to the club.
But a good swing doesn't get this complex. Yes, I do know a few people
with somewhat bizarre swings that would probably exercise this feature to
the limit of what Max built in. (Ever watch Charles Barkley? I'm pretty
sure I couldn't model his swing in SwingPerfect.) But I don't care. I'm
not sure how to fit swings like that anyway.
In a sense this defines 'feel'.
I disagree. "Feel" is not the complex force/torque history, which is the
golfer's OUTPUT. It is the feedback to the golfer from the applied
force/torque, the golfer's INPUT.
Is it 'centrifugal' or 'centripetal'?
I suspect the true answer is somewhere in between. The golfer is applying
forces, to be sure. But those forces are being applied in the service of
accomplishing certain positions. So perhaps the golfer's OUTPUT is the
effort to achieve positions -- at least partially -- and the INPUT is the
force with which the club reacts to the golfer's effort.
But even if that were the case, I think that "feel" has to be more than
that. Think about the wristwatch test I mentioned in my response to Don.
Whether the force/torque profile is input or output, it doesn't explain
why the wristwatch does not affect performance, while backweighting does
for some golfers. The force/torque profile would be essentially the same
for the two cases (wristwatch and backweight) for the same club behavior.
So the feel -- which MUST be causing a swing change for golfers where
backweighting makes a difference -- is a lot more subtle than the
force/torque profile we're discussing here.
Which argues that the minor muscle inputs I suggest above have little
effect on the result, only how the golfer feels about it. You mention that
good swings are simple (of course, if they are so simple, why are they so
hard to master?) and perhaps the minor, subconscious muscle inputs are only
effective with a fundamental (as opposed to simple) swing. With a more
complex swing perhaps the minor inputs are 'lost in the noise'.
Ah, the joys of human testing.
We can certainly agree on that.
But is human testing the only worthwhile testing in golf club research?
If physical models aren't worth anything, then neither is robot testing.
I'd be prepared to bet that backweighting doesn't create any measurable
difference in result if tested by a robot. That's because the robot has
been pre-programmed with a force/torque profile over time, and the
feedback -- the "feel" -- is not going to affect that profile. So robot
testing corresponds to the physical model, and that's all it can test.
It has been argued that physicists perform simple tests on simple systems
and engineers do complex tests on complex systems. Both, of course, are
necessary. The simple tests to understand the system (both testing and
tested) and the complex to understand the operational result. The simple
tests are often used to define and validate the physical models and are,
thus, essential to the analysis of the complex system. I have always
argued that the development process includes simple tests on simple
systems, complex tests on simple systems, simple tests on complex systems,
and, finally, complex tests on complex systems. Unfortunately, the middle
two frequently don't get funded.
Cheers!
DaveT
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Regards,
Alan Brooks
