I'm just going over the details of animating a chain or belt wrapped around 2
pulleys.  I understand MY math, and the math posted on Wikipedia.

http://en.wikipedia.org/wiki/Belt_problem
(Scroll down to the second, related "Pulley Problem"

The first step to solving the linear length of belt or chain seems to be to
establish the angle at which the belt is tangent to the pulley, and then from
that, the linear length can be calculated.

What is driving me absolutely crazy, is that I'm actually USING FM's code for
animating a belt, and IT WORKS.  But I look at the known parameters (distance
between pulleys and difference of the radii) and consistent with the Wikipedia
math, I use (ARC)COSINE to solve for the angle.  FM uses the SINE.  This doesn't
seems possible.

Then, when I solve for the linear length, I use the trigonometric relationship
to derive the length of the remaining side, but FM employs the Pythagorean
Theorem.  How is this possible when P, the distance between the two pulleys is
the HYPOTENUSE?!

It seems like it ought to turn out oh-so-woefully wrong, but the render and
animation give one of FM's flawlessly beautiful creations.

Can someone look at this and explain what Dark Magic is at work here?
http://news.povray.org/povray.binaries.misc/thread/<web.53c69f83e73deed5e7df57c0%40news.povray.org>/

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