Key Leads and Inertia

[Richard Brekne]

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Stephen Birkett wrote:

>
> Let's adopt the simpler [just as useful] approach you and Phil
> suggested. Point mass action acting at the capstan, plus distributed
> mass keystick. We need estimates for: (i) action mass at the capstan
> (weight will do), (ii) mass of the key *without* leads]. Perhaps you
> have such data from your key balancing work Richard? Also key
> geometry.
>

Action mass at the capstan in terms of weight modified by the ratio of
the shank and whippen is easy enough, tho thats not strictly Stanwood.
His Strike Weight and Whippen weight are not just the pure mass of the
parts either. But any way you like it, getting a figure on this is easy
enough.  Key mass is not something Stanwood uses at all. But finding an
unleaded key to weigh is a simple matter as well.

Key geometry depends on what you want. Do you mean all the dimensions of
the key, up down sideways, variations in thickness.. etc... or do you
mean length of lever ams etc ?

and from a couple other posts

Richard Brekne from Keylead Experiments


     "That gives if so (r/rb)g =  19.6ms^2 which should then be the
     breakpoint acceleration for this example."

     "Fbr then is (140 * 2.5 + Ik/5 )( 9.8/10), and if Ik can be
     understood to be Mrk^2 then thats 140 * 6.25 = 875 which ends
     up yielding a force of514.5 grams. "

Stephen Birkett in his last Keyleads and Inertia post.

     " A quick calc. puts the breakpoint somewhere in the
     mid-dynamicrange for a mid lever lead position (~20m/s^2)."

     "Sure. A loud blow corresponds roughly to 5 m/s at the
     hammer/string impact. Assume uniform acceleration from rest
     over say a 10mm keydip and you can calculate an estimate of the
     accleration for a moderate blow."


Interesting to see how well these two completely different approaches on
finding breakpoint acceleration compare. You started with 5 M/s keyfront
acceleration which you compare to a moderate blow,  I start with ballpark
action components mass and distances from fulcrum to arrive at the same
breakpoint acceleration which yeilded a input force of 514.5 grams.

I suppose this could mean that a roughly 500 gram force at the front of
the key constitutes a moderate blow ?

> Stephen
> --

RicB

btw I got a bunch of hammers packed up and ready to send as soon as I can
get out of bed an off to the post office. Backproblems....

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


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