Virtual Capstan

[Richard Brekne]

Bill Ballard wrote:

> At 7:15 PM -0500 6/22/03, Ron Nossaman wrote:
> >>20 grams x (WC,WMag / WC,Cap) yeilds the net lift on the casptan by
> >>the magnet
> >>force upwards at the whippen magnet. This is a negative number because we are
> >>lightening the load on the capstan.
> >
> >Unless I missed something, yes.
> >>A very neat way of viewing all net effects of this extra <<virtual capstan>>
> >>through the eyes of the real capstan and corresponding key ratio.
> >
> >It's the simplest approach I came up with.
>
> It also makes the decision that the leverage doesn't change. By
> translating the uplift at the magnets to their actual force applied
> at the capstan, we simplify things considerably. Nothing like making
> measuring points a constant instead of a variable. But we have to
> uphold the correlary of this situation, which is that the leverage is
> not changed by the installation and operation of the magnets.

I think you missed something somewhere Bill. Rons description bear out quite
clearly what my BW measurements show. The leverage does change.... in terms of
weight. As it must.

You could accomplish much the same thing by orienting the magnets so that they
attract and put them behind the capstan... though how the distance between the two
magnets throughout the key stroke would change. Be a bit more difficult to access
for adjustment... but you could still use your metal capstan regulating tool :)
Probably would also amplify the apparent difference between beginning leverage and
end leverage through the stroke. Getting over that initial resistance with magnets
could maybe be done by moving them farther out on the whippen (closer to the
balance rail pin). But I hadn't really thought that as necessarily a big thing to
want to accomplish.

But I digress

>

I dont see any real significant reduction in friction going on here. I mean the
only place it could possibly reduce friction is at the capstan... and that doesn't
account for much of the total action friction to begin with. Nor do repeated DW/UW
measurements show any real big gain here. Perhaps a grams difference.

>
>
> This thread on "Virtual Capstans" might seem like an off-shoot of its
> immediate predecessor, "Key Leads and Inertia", in a search for an
> action which is easier to play (whatever that means). So far we've
> concentrated on how it lightens the DW (BW, really). That's a matter
> of the static balance of the force of gravity on either side of the
> key. Ric, you had said that the ability to adjust BW was far less
> important than being able to measure the action's moment of inertia,
> and from that, begin to find empirically a proper level of inertia
> for a piano action.

Bill, this little apparatus is handy in that it provides an inexpensive and very
easy to adjust and install alternative to other schemes that deal with being able
to regulate touchweight (BW). It does so in a unique fashion, actually I think its
quite cute. And anyone has the right to design and install it, as all this
discussion here and in other places functions well as part of the Public Disclosure
I initiated a few days back.

Being able to adjust BW visa vi being able to measure the actions moment of inertia
and the rest of that remain different issues with different priorities. I might be
clever enough at all this to chase Rons or Stephen's reasoning and calcs down
(grin... given enough time), but being able to find a way of measuring the moment
of inertia for a given key, and develop a method for designing predictably inertia
levels into an action (integrated into a Stanwood like static balance precept) is a
bit more daunting a task for someone like myself and will take more time, and
certainly more heads then just mine. Actually our friend Mark has some pretty good
ideas in this connexion.


Cheers
RicB

--
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