Date:         Thu, 8 Feb 2007 12:15:28 -0700
Reply-To:     David Etter <detter@MAIL.AURACOM.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Etter <detter@MAIL.AURACOM.COM>
Subject:      Re: Poptop Raise Assists (Fryeday content)
In-Reply-To:  <45CB658E.7030807@qwest.net>
Content-type: text/plain; charset=us-ascii; format=flowed

The top could have been raised with a fraction of the energy involved
in that last reply. ;-)

                                        David

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>The idea has both sound and not so sound components.  While use of the
>hinged pole that David is discussing would provide for  a bio-mechanical
>advantage (i.e. pushing/pulling laterally is more biomechanically
>efficient than pushing up vertically), it has some rather distinct
>disadvantages that would lose far more efficiency than that gained
>biomechanically.  As David noticed when he says the arm "is already
>almost open, giving better mechanical leverage", it does get easier as
>the 'scissor' opens, due to a couple of factors.  Primarily, the
>vertical rise for each unit of horizontal travel decreases dramatically
>as the 'scissor' is 'opened', but secondly, because of the decreasing
>translational losses  (force vector addition) as the pivot points
>approach the same plane (not to mention loss of frictional forces).
>
>So...the biggest problem with the idea is that you are additing another
>translational system into the mix.  The rod will not be pushing the top
>mechanism just horizontally, it will push upwards as well.  However,
>since only the horizontal component of that energy will be translated
>into movement of the top mechanism, a great deal of energy is wasted -
>in the identical manner that it's wasted now, without the rod.  Adding
>the rod simply compounds the problem (you "lose" the vertical force
>components of both the rod and the mechanism).  And that doesn't even
>address the issues with lateral stability of the rod.  Now, if you put
>the rod to use pushing *directly* on the top, not the lift mechanism,
>you could create a dual stage process that would raise the top partway
>with the rod, followed by final raising using the normal mechanism.  Now
>*that* would gain actual mechanical advantage, by increasing the overall
>horizontal travel per unit of vertical travel, and minimizing the
>translational losses in both stages.  Worth it?  Doubtful...
>
>Keith Hughes
>'86 Westy Tiico (Marvin)