Prusa I3 single frame z-axis-bottom modified for raising the motors.

Sometimes NEMA motors are longer than frame can hold without touch the base. So I decided to add some parametric modifications to the height of de piece's holes that allow rise the motors.

Modified from: https://github.com/josefprusa/Prusa3/blob/master/old_single_plate/src/z-axis-bottom.scad