Variable GraviTrax compatible spacer

This gravitrax spacer has variable height. The 4cm spacer you can see in the picture extends about 2.5cm, so it ranges from 4cm to 6.5cm. The 5cm spacer should extend to about 8cm, and so on.

If you want, you can add some more diameters in the diameters array to get more piles (and therefore more extension). But then every single pile will be very thin and therefore very fragile.

The design uses the very nice thread_profile.scad library which you can download here:
https://github.com/MisterHW/IoP-satellite/tree/master/OpenSCAD%20bottle%20threads
You only need to put the thread_profile.scad file in the "libraries" subfolder of your OpenSCAD installation.
The file thread_profile.scad in turn needs the packages https://github.com/openscad/scad-utils and https://github.com/openscad/list-comprehension-demos which you also put into the libraries subfolder of your OpenSCAD installation (in subfolders scad-utils and list-comprehension-demos, respectively).

I recommend a test print (see print settings in the customizer) to cross-check if the thread will work with your chosen settings.

Please read carefully the notes below on the support overhang angle! Cura tends to add support into the threads which ends up in a scrap/unusable part! When using Cura carefully check the preview for erroneous support inside the threads

After printing carefully remove the support such that the threads become functional.

Note: I intentionally only provide the OpenSCAD source file rahter than STL files. Please follow these easy steps to get the STL file you want:

1. install openSCAD: https://www.openscad.org (it is free of charge
2. install the libraries mentioned in the thing description
3. open the scad file of this thing
4. adjust the parameters as you like (height of the pile, etc.)
5. render the design by pressing F6
6. export to STL by pressing F7

With version 0.02 there comes a slightly different printing concept: I unscrew the inner part by half a turn which makes it easier to remove the support. Also I adapted the wall thicknesses to make the part more robust.
In version 0.03 there are some other options commented out for the diameters variable which would lead to only one expansion or to even three.
In version 0.04 I screw out each of the different parts by half a turn for printing. This makes it much easier to remove the support after printing.