Curves from equasions

This should get your hats smokin.
I can do this with a sine wave, but now I need to wrap a helix around
a rod and I can't come up with an equasion that works.
Can anyone suggest an equasion for a curve that results in a helix
wrapped around a rod?
This would be a cylindrical csys type and the helix would be like
wrapping a short spring around a round rod.
Not like pushing a tube through a spring. The spring is 90 degrees to
the rod and wrapped around it.
The imaginary rod can be considered a circle in the XY plane and the
length runs in the Z axis.
The spring would be perpendicular to the rod so that its diameter is
along the Z axis. Then the spring would be wrapped around the rod. It
can be one wrap or more.
Appreciate any suggestions (except indecent ones).
Thanks Peter

 

Thank you very much. The equasion was exactly what I needed.
Peter

 

Super deal. ;^)

And a big attaboy to you for the quick and accurate response. It would have taken me a day of digging to come up with it. Except, by the time I logged on again to this NG, question asked AND answered. You can go to a lot of the "better", "more popular" Pro/e sites and NOT get responses this quick or at all. 41 minutes to a response; over night, EARLY A.M. (doing equations in noBadCAD's sleep) with the actual, detailed solution. Hat's off, this effort was in the true spirit and best practice of this NG!!

David Janes

 

A very prompt reply indeed and thanks again.
As a point of interest, this equasion will produce the required curve
in both WF3 and WF4 (the only two versions that I have access to).
However when I try a variable section sweep using this curve as the
trajectory, in WF4 it works perfectly, but in WF3, it won't work. Even
when the sweep shape is a simple circle, it fails. I have noticed this
with a few other equasion curves when using them as a trajectory for a
sweep in WF3.
When it fails a right click over the error box shows a greyed out
"Trajectory error". They must have fixed this in WF4.
Peter