Lego Duplo customizable train tracks

You may need to add normal supports depending on the filament you use and your settings. This could help achieve a smoother bottom side.

Description from original author:

Summary

This is improved version of Customizable train tracks

1. It is customizer now! You don't need to use OpenSCAD to generate tracks!
2. But, if you want you can open the single file lego_duplo.scad in OpenSCAD, you don't need to download any libraries
3. You can generate bricks, plates, tracks and calibration parts
4. Tracks were improved to print without any supports - improved knobs and long bridges (set geo use offset to No)
5. Fixed some code issues, which produced non-manifold stl

Version 2

1. Set default knob and stud diameter to 9.4 (KnobD and StudD)
2. Set default wall thickness to 1.5 (BrickWallT)
3. Added small chamfer on the top of knobs
4. Updated calibration parts: dynamic size (depends on GenerateKnobsX and GenerateKnobsY), second track end
5. Got rid of TrackRadius, use Track Length for straight and curved tracks (in studs)
6. Updated curved rails to Type 3, so length of 4 curved rails (30deg) is equal to 4 straight rails (see more here: Lego Duplo Rail Dimensions article 4.2)

Version 3

1. Added Track Width and Track Wheel Width (distance betweens wheels) parameters