A rotor blade is cut out of stainless steel strip size 1.5 * 125 * 625 mm and 40 blades for 20 rotors can be made out of a standard sheet size 1.25 * 2.5 m. A rotor blade is bolted to the front side of the armature sheet with three stainless steel bolts M6 * 12, three large washers for M6 and three self locking nuts M6. The overlap in between a blade and the armature sheet is 23mm resulting in a rotor diameter of 2 * 625 + 156 –2 * 23 = 1360 mm.