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Date:         Thu, 8 Feb 2007 11:01:50 -0700
Reply-To:     Keith Hughes <keithahughes@QWEST.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Keith Hughes <keithahughes@QWEST.NET>
Subject:      Re: Poptop Raise Assists (Fryeday content)
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

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)

>Date: Thu, 8 Feb 2007 00:09:37 -0500 >From: Joy Hecht <hecht.joy@GMAIL.COM> >Subject: Re: Poptop Raise Assists (Fryeday content) > >I don't get it - why should it be any easier to push a pole than to directly >push the poptop? You're not getting leverage here. > > > >Joy > >:::-----Original Message----- >:::From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf >:::Of David Etter >:::Sent: Wednesday, February 07, 2007 9:55 PM >:::To: vanagon@GERRY.VANAGON.COM >:::Subject: Re: Poptop Raise Assists (Fryeday content) >::: >:::Just a quick thought. >::: >:::How about a low tech approach. >:::An 8 ft. rod or pole (approximately) hinged in the middle. (work with >:::me here now - use your mind) >::: >:::One end is placed on the now unlatched mechanism up top and the other >:::end is placed on the floor, directly underneath the latch. >::: Of course, with the top down, and it being 8 feet long, the >:::'bent arm' is going to sticking out toward the rear seat. >:::Grab the hinge area and pull or push toward the front of the van >:::Bingo! up it goes. >::: Essentially you are creating a second arm like the one >:::already installed only this one is already almost open, giving better >:::mechanical leverage. >:::Your leverage is going to be better working on the horizontal where >:::you can put your weight behind the effort, than it is pushing upward >:::and carrying the entire load on your back and arm muscles. >::: The pole collapses/folds to 4 foot long and stores up above on >:::the bed. >::: >:::It's just a start but I'll do better after my 4 cups of coffee >:::tomorrow morning. ;-) > > > >


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