It creates more stable frame allowing putting one or more filament spools above.
This mod does not require any changes in Firmware.
Bottom parts connecting motor to the frame are actually a remix of the Original Parts: https://www.prusa3d.com/prusa-i3-printable-parts/
Does not require any additional changes Hardware or Software
@ +0mm with reinforcement : https://www.thingiverse.com/thing:3337357/
Does require small Software change
@ + 18mm with reinforcement : https://www.thingiverse.com/thing:3334944/
Does require extensive Software and Hardware changes :
@ +30/33mm with reinforcement :
What You need :
2 pcs - 608zz bearing
2 pcs - m8x400mm threaded rod
2 pcs - m8x450mm threaded rod
+8 pcs - m8 nut for the above
*8 pcs - m8 washer ( note that the outer diameter should not be more than 18mm)
8 pcs - m3x20mm
8 pcs - m3ns nylon lock nut din 985
185g PET-G (21% infill, 2 perimeters)
2 pcs - m4x40mm
2 pcs - m4x20mm
4 pcs - m4 nut
Does not matter
At least 2 perimeter walls. Layer height 0.2mm or 0.27mm recommended. PET-g is better than PLA since the latter makes it too stiff.