PSN-L Email List Message

Subject: Re: The revised and corrected "zero force" hinge
From: Brett Nordgren bnordgren@..............
Date: Sat, 20 May 2000 23:22:57 -0400

At 10:23 PM 5/20/2000 -0400, you wrote:

>     The slight 'catch' about this 'zero force' design is that unless the 
> belt
>is 'completely flexible', bending the belt over the pulleys involves a force
>which tends to pull the pulleys together - the natural shape of the 'straight
>bit' forming the hinge is actually 'S' shaped.
>     Regards,
>     Chris Chapman

Thanks for the nice explanation.  It is a weird configuration to visualize.

I think because of symetry, there should actually be zero residual 
moment.  If you didn't mark the ends of the cylinders, you wouldn't be able 
to tell how much it had rotated.  The flexures would all continue to have 
the same shape, whatever it was.  In effect, as one flexure winds up, 
another is unwinding in exactly the opposite way.  Think everything cancels 

Although, thinking about it, it's probable that the effect you're 
describing might well allow the axis of rotation to shift very slightly 
depending on the direction of the force on the hinge.  That may be the 
problem.  I'm hoping it's a pretty small effect.



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Larry Cochrane <cochrane@..............>