The Darwin design seems to be based on a cube of 500 mm rods. This works fine when your local hardware store has rods/studding in 1 meter lengths. Unfortunately for those of us in the USA, rods here tend to come in yards (914.4 mm). You just can't get two 500 mm rods out of a yard so there was significant material waste.
The Mendel only has two pieces (the X bars) 1/2 yard long or longer. Taking each from a yard long length of rod leaves plenty for one of the shorter bars (Y or Z). You can get all the parts from 8 yards of studding and three yards of bar. This should make it much easier/cheaper to buy mechanical parts for a RepRap in the USA, particularly if using 5/16" in place of 8mm.
