[CAUT] Digest, Vol 1103, Issue 85 Moving Wippen Rail

[Keith Roberts]

Actually I added up the numbers and the 2mm movement of the rail using only
the change in EA as the factor only changes the DW by 1.5g. So therefore the
jack moving toward the tangent line does increase the output of the jack. I
was wrong. It does give strong evidence to my theory though. It is true that
moving the jack away from the tangent line of the jack center will decrease
the force produced at the top of the jack. This directional move of the jack
is shortening the RA as you measure it. According to your action ratio
then; the force is increasing  as the jack rotates away from the tangent
line of the jack center (towards the wippen center). OOps.

What I see when I look at the pictures is the jack is leaned so the top is
on the circumference line of the jack center and that is why the ratio as
you do it works. The window of movement provided by the rep lever is so
small as to not allow much of a change so the figures do not get so far off
as to make a big difference.

Keith Roberts


On 11/3/07, Richard Brekne <ricb at pianostemmer.no> wrote:
>
>
> A good observation. I think tho if you think about it, the balance scale
> has platforms that swing freely. Not only to they tilt if a weight is
> put in them off senter but they swing in or outwards so that the cables,
> wires, whathave you that suspend them from the balance arm find the
> appropriate angle off vertical so as to compensate.  The vertical
> component of weight stays the same because the effective length of the
> arm has changed.
>
> Actually this is kind of cool you mention as I had this long discussion
> with Mark Davidson a while back... who has a physics degree and knows
> this stuff pretty well. He thinks in terms of torque when dealing with
> levers.  My more limited education points me in the direction of
> thinking of the effective length of arms... i.e. translating everything
> in terms of vertical and horizontal force vectors.  As it turns out you
> can actually describe the ratio of a lever at any point in its motion
> both ways.  But its a bit cumbersome to do it my way for ever mm of a
> levers field of motion.
>
> Still.. your balance scale perfectly shows exactly why I think we have
> to admit your position about the jack angle being important as wrong.
> On the other hand...  You did point out that the jack center position is
> also important.  One can find the vertical component... and there by the
> momentary ratio of the leverage at any point by simply drawing a right
> triangle from the position of load input/output to the point of support
> on the lever with the line opposite of the line between these two being
> vertical. A horizontal line from the flange center out to this line then
> is the distance of the arm with the lever in whatever position its in.
>
> Cheers
> RicB
>
>
>    A question back to you. A balance type scale. It has a platform 4
> inches
>    across. the weight doesn't change due to where you put the load on the
>    platform. It is still transfered back to the point on the lever that
> the
>    platform is attached. According to you if we move the load farther
>    from the
>    fulcrum the weight should change. The design of the intermediary
>    device has
>    a lot to do with it I think.
>
>    Keith
>
>
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