Print gears, wheels, train body.
There are two bars as a support for engine mount,
to be cut out inside body (no need for support).
Gears and wheels need support or there is version with simple support.
All gears can be clicked in the train
Insert simple DC6V engine with 2mm shaft, size (WxHxL) 20x15x25mm
Simple rubber diameter 15mm may be glued on wheels.
All mounting points of axes should be lubricated with technical petrolatum, also small gears.
It works, runs a little bit too fast and loud,
there is problem with climbing on duplo bridges yet (too long body),
will fix in a next version.
There is a room for 2 AA batteries at a front of the train.
[2017/04/15] added motor gear with more backlash - 0.55mm
[2017/04/16] train.scad with sources
modified involute_gears.scad (correction for circular_pitch)