Action dynamic model (was Re: Key Leads and Inertia)

[Bill Ballard]

At 8:00 AM -0700 5/3/03, Keith Roberts wrote:
>Theinput to the dynamic models would have to be real pianists until you could
>refine a mechanical finger to duplicate the results from real fingers. What
>came first, the chicken or the egg?

I don't think so. I agree that among pianists there is an infinite 
variety of ways in which the pianist can move the key. And a great 
many of them could be simulated (for academic purposes) using 
calculus. However whatever maneuvering the key may be put to on the 
way down, at a certainly point the jack escapes and at that point the 
only thing which is important is hammer speed. The pianist's motion 
is summarized in the instantaneous velocity at the point of 
escapement.

What is important to the music is that the pianist feels that as 
though he can getthe action to do what he wants: compliance(?). 
That's where we as piano technicians can help by making sure that 
three separate forces of friction, gravity and inertia are 
individually enough to provide a "back-pressue" for the pianist, but 
not so great as to over-power. And then balancing them.

So, no. The product of mass and acceleration is always calculable. 
What makes the discussion easier is to standardize the descriptions. 
That means with a standard "keystroke".

At 9:54 PM -0400 5/4/03, Classic Touch Ent wrote:
>So what is the purpose of a dynamic action model? to study the 
>action? to study pianists? both? Can we start by studying action 
>dynamics first?

To study the action. And to keep it simple, with simplified schemes 
of motion. Studying the pianist is actually a far more dynamic 
endeavor than studying the action. How the action behaves under force 
can be modeled theoretically. Studying pianists has to be recorded in 
the field, with say, optical motion sensors. If we want to know how 
pianists move, we have to measure them multiple times per second.

I gather that for the most part, the behavior is predictable. Any 
being predictable, in a way, static. The only thing dynamic about it 
is the number of ways a pianist will move it. But regardless of how 
the pianist moves the key, its motion will still be predicted by 
plugging the real values into the mathematical model.

We have to decide what we want to study, the base-line motion of the 
action according to a model, or the actual motion, whipped up bay a 
real pianist.

Bill Ballard RPT
NH Chapter, P.T.G.

".......true more in general than specifically"
     ...........Lenny Bruce, spoofing a radio discussion of the Hebrew 
roots of Calypso music
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