Your helix has radius 200 and the tubing as radius 30. Correct?. This conflicts with R which says they're both 200.
In this event R+r=230. That's what I'll use.
Assume you're wrapping a tube of radius 30 around a helix of radius 200,
This forms a helix. A helix can be represented by
a in this case is R+r=230. The radius of the helix + radius of tubing.
Since you want two revolutions when z=500 units, you have
You have the helix:
It's length in making two revs in a distance of 500 units is given by
Now, this is a cylinder of radius 30 with height 1466.6
Check my calculations out.