Hi Bob,

This is is far from blindingly obvious! I hope i didn't make a mistake
though...

the parameterized path function should be:

f(t)=[x(t),y(t),z(t)]=[H*t,(r+(R-r)*t)*sin(2*pi*n*t),(r+(R-r)*t)*cos(2*pi*n*t)]

where t goes from 0 (bottom y=0, r) to 1 (top y=H, R).

if you continue from here the results are getting pretty ugly (tbh i'm
surprised they are getting *that* ugly) but anyway: the total length of the
path is:

a) L = (H^2 + (r - R)^2)*LN((sqrt(H^2 + (2*pi*n*r)^2 + (r - R)^2) -
2*pi*n*r)/(sqrt(H^2 + (2*pi*n*R)^2 + (r - R)^2) - 2*pi*n*R))/(4*pi*n*(R -
r)) + r*sqrt(H^2 + (2*pi*n*r)^2 + (r - R)^2)/(2*(r - R)) + R*sqrt(H^2 +
(2*pi*n*R)^2 + (r - R)^2)/(2*(R - r))

where x^2 is pow(x,2) (and no i didn't calculate this by hand ;-))

I couldn't solve b) and i doubt it would be any nicer than a)

Does this help? :-)

Regards Roman

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