Prusa Mini upgrade to dual Z and direct drive

This Prusa Mini mod adds dual-z frame with direct extruder. It reuses most of the original frame parts.

Extra parts required:

• Two 3030 square profiles, 289mm with M8 thread tapped in the center on both ends. 289mm is the same length as the original Z extrusion, but you could use slightely longer (e.g. 300mm) would work as well.
• Z motor with a threaded rod, connected in series with the original one.
• E3D V6 heatsinks and heatbreak (or a complete v6-compatible heatsink)
• x4 M8 bolts,
• ~x20 M5 16mm bolts and T-nuts .

The included X axis parts are compatible with the BearEXXA X carriage, so it can be used with any Prusa Mini Bear toolhead, but you could also use mirrored MK3S toolhead with this X-carriage: https://www.printables.com/model/1196669-bearexxa-compatible-mk3s-carriage .

Please note that the included files are not adjusted to account for plastic shrinkge (unlike the original parts provided by Prusa). It is important to account for it when printing front and back panels for the Y axis.  For example, when printing them from plain PETG shrink compensation XY to 0.5% should work well (see advanced filament settings in the slicer). The distance between Y-axis  steel rods should be as close to 120mm as possible (error of +-0.2 mm is probably fine).

X axis is based on the BearEXXA design.