Virtual Capstan

[Richard Brekne]

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Bill Ballard wrote:

> At 12:09 PM -0400 6/21/03, Mark Davidson wrote:
> >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.
>
> The data you refer to is static, and is merely a reading of how the
> gravitational pull on each side of the key is balanced across the
> fulcrum.

Correct.

> >I think the answer lies in that fact that the magnets, like a spring, have
> >stored energy that is released as the wippen and key move apart
> >which does some of the
> >work. This energy is stored again as the parts move back together.
> >It wouldn't
> >work if the distance between the parts were not changing.
>
> I don't know how it works for magnets, but for springs, barely 8% of
> of stored force is relieved at the top of the wippen's swing. The way
> to release 100% of the stored energy is to unhook the spring. With
> magnets, the force doesn't exist (excuse me, it doesn't become strong
> enough to be noticeable) until you bring like poles of two magnetic
> fields close enough. That doesn't sound like a force-storing system
> to me. Stored energy is at work however with inertia and gravity, as
> well as deformation of springs.
>
> As far as the wippen and key moving separately (de-coupling), that
> needs to be studied.
>

Agreed also. Been looking at this all day long and it looks like no matter how you
go about lightening up touch weight.. if the whippen is to always sit on the
capstan, then it (and the hammer) has to be heavy enough for whatever key leverage
there is to accomplish that. Whippen assist springs cause this de-coupling, too
much leverage (key) seems to also cause it (shaky here), key leads exchanged for
key magnets I havent though much about yet.

> >
> >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.
>
> Let's be clear about this, guys. When, Ric, you say that at some
> point the key will start to move on its own, I'm assuming that the
> key is moving downwards, meaning that the magnetic repulsion has
> reduced the load on the "bricks'n'mortar" capstan to the point where
> the FW plus the 45g deadweight can overcome the DW.

Yes

> At that point, with the front half of the key moving downwards, the back half
> with
> its "two" capstans and their load would be moving upwards. This is
> not where I would expect to find the gap between magnets expanding.
> Actually, I would expect to find that until a certain point is
> velocity, gravity and the magnetic repulsion would have no trouble
> finding a stable balance.

That seems to be the case despite a discernable increase in magnet separation on
the order of 1.5 mm for this model.

>
> If, Ron, you're thinking of motion of the key which might occurs as
> the repulsive force grows strong enough to force the key down into
> the backrail cloth (showing an upwards motion which a dial indicator
> could read), that may be true. However, as the increasing repulsion
> tries to relieve itself, at a certian point it will have out-run the
> squash in the backrail felt and balance rail punchings, and at which
> the repulsion will have a far easier time pushing upwards on the
> wippen (instead of downward on the key). That's the point at which
> Ric gets the signal that UW has been overcome.

Is THAT what he meant ?? and... you Did mean DW instead of UW in that last sentence
didnt you ?

>
> Let me know if there's something I have to write on the blackboard 100 times.
>
> Bill Ballard RPT
> NH Chapter, P.T.G.
>
>

--
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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