Extended Archimedean Spiral Module

While designing a pancake-primary mounting fixture for a Musical Tesla Coil, I needed to generate an Archimedean Spiral to simulate the location of the primary wire in the fixture. I found the Archimedean Spiral Module here on Thingiverse and it was a great starting point. However, it only starts at an initial radius of 0 and only lets you specify the final radius, which led to wrong spacing and positioning for my application.

Instead, I needed to be able to give a starting radius and a spacing for the spirals, and add an arbitrary start angle to rotate it to the correct angle for the fixture. So I modified the module and created this Extended Archimedean Spiral Module.

This module contains the archimedean_spiral_ex() function with the following parameters:
spirals = how many spirals (positive=CCW, negative=CW), can include partial spirals
thickness = how thick you want the arms to be
startradius = beginning radius position
spacing = spacing between radial points
startangle = angle to begin first sweep
center = 'true' centers the spiral arm thickness (default=true)

It incorporates the following changes from the original design:

• Arbitrary starting radius
• Specifying of the spiral spacing instead of final radius
• Arbitrary start angle
• Rounding of the end-points to the nearest $fa angle to allow for fractional rotations without drawing it weird
• Centering option to center the specified thickness of the spiral arms
• Ability to draw the spiral clockwise or counterclockwise by using a signed number for the number of spirals

UPDATE (9-18-2018) : Changed the polygon start and end position by $fa so polygon always starts on the correct $fa angle boundary.