Virtual Capstan

[Richard Brekne]

Ron Nossaman wrote:

> >Actually, the distance between the magnets is so stable that I dont think you
> >can notice this with conventional UW/DW measurements. Tho there is a slight
> >difference in the amount of vertical rise in the whippen at this point
> >compared
> >to the key at this point to be sure. In anycase...it doesnt affect the motion
> >characteristics of either measurement noticebly.
>
> No, the distance between the magnets can't be constant ("stable") during
> the keystroke. It's going to be about 3mm wider at the bottom of the stroke
> than it is at the beginning.

Hmm...  I have the action right in front of me and from the beggining of key
stroke to the letoff point there is 10 mm space between them, and at letoff there
is just  under 11.5 mm, through let off and key bottomed out there is perhaps 12
mm. Starting at 5 mm spacing (which I had to hold the whippen down to accomplish)
I got to 6.5 at letoff and perhaps 7mm at key bottomed out.

So I am seeing about a 1.5 mm change in spread through the part of the key stroke
I am most interested in. Still, 1.5 mm is something and I see your point.

> As magnetic field strength lessens in inverse
> proportion to the square of the distance between them as they diverge, the
> lift they supply will lessen. As I said, the pressure on the back of the
> key will also lessen, which will counteract this some - but not entirely as
> the leverages will tell you. The difference may not be enough to get in the
> way, but it is there.

Yes, admittedly it is there. Doesnt seem to affect how BW meaurements behave tho.
How would you suggest gauging the significance of the change beyond our usual way
of measuring UW / DW ?

>
> > > First class lever in the key, second
> > > class lever from the magnet lift of the wippen.
> >
> >Not sure I follow you here. A second class lever is one in which the
> >fulcrum is
> >at one end, the load in the middle, and the input at the opposite end.
>
> That's right. The wippen magnet is the input for auxiliary lift, taking
> some load off the capstan. When the key is played, the magnet on the wippen
> becomes the inertial load on a third class lever with the capstan as input
> as well as still being input on the second class lever taking some load off
> the capstan.

Hmmm... I see the inertial load bit... tho 1.5 or so grams is not much... perhaps
not even enough to consider. But I am still unclear about this second class lever
perspective.  Where is the fulcrum, load and input points exactly ? Strikes me
more like its just entially a second capstan / heel relationship. Especially since
it behaves predictably so if its placed behind the standard capstan.

> >Still unclear what you mean... but I will think on it. In the meantime...
> >total
> >weight involved (now that I'm down to three magnets) is about 4 grams.
> >With 65%
> >on the key and the rest on the whippen.
>
> It may not prove to be a problem, but I still think it should be considered.

Agreed, and again thanks for bringing it up. I still need a bit of clarification
as to this 2nd class lever you envision in here.

Thanks

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