Virtual Capstan

[Richard Brekne]

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Bill Ballard wrote:

> At 12:35 AM +0200 6/20/03, Richard Brekne wrote:
> >The whippen assist spring simply makes the whippen lighter by
> >pulling up against it from the whippen rail. This really does
> >something quite different. It provides a secondary support for the
> >weight of the action very much in the same sense that the
> >capstan supports the action weight.

Bill writes:

> Under Newton's Third Law (Action and Reaction), the support for the
> force opposing the lifting of the spring is the action frame. Under
> your scheme, the support for the force opposing the magnets is the
> pianist's finger and hand. It doesn't sound as though the forces
> encountered in playing this action have been reduced by transferring
> them to something outside of the system of parts in motion (pianist
> included).

And  Mark writes

     This was my initial reaction.  You do less work at the front
     of the key but the same amount at the back of the key.  How's
     that possible?
     Yet he's got the experimental data to show it works.

Well, first and formost, what is happening is that Im essentially
increasing leverage with respect to weight only. The position of this <<
invisible capstan >> is important. Putting the magnets behind the
capstan would make the action heavier at the key front.. The force
pushes up as much as it pushes down. (again your Newtons Third). Thats
why I call it the an invisible or <<virtual capstan >>. Thats what it
functions like (a bit springy.. but thats not important because we
havent removed the real capstan.) It very well splits the leverage
components (distance and weight) into two independantly adjustable
quantities. This works by changing weight leverage without changing
distance leverage, to put it that way.

5 grams of balance weight  equates to 10 grams of front weight, or 10
grams of DW, or 20 grams of lead centered between the balance rail and
the key front.  This is actually quite a decent range and and allows for
a good deal of varying configurations. You can decide to take out 10
grams of FW from the key, or you can decide to move the standard capstan
back for other touch considerations, or you can use it as a purely
adjustble BW regulator... or some combination of the three for that
matter.

Its funny to watch really.. Take an action model and set it up as in the
photo I sent. Configure it for 50 grams DW with the magnets as far apart
as you can adjust them (13-14 mm or so). Then put a 45 gram weight on
the front of the key and begin to screw down the whippen magnet so that
it gets closer and closer to the key. At some point the key will just
start to move on its own.


> But if you don't intend to counterbalance more than 5g of
> BW, this could be negligible.

> Bill Ballard RPT
> NH Chapter, P.T.G.
>
> "I gotta go ta woik...."
>      ...........Ian Shoales, Duck's Breath Mystery Theater
> +++++++++++++++++++++
> _______________________________________________
> pianotech list info: https://www.moypiano.com/resources/#archives

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html
http://www.hf.uib.no/grieg/personer/cv_RB.html


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