I had made a Meccano hand operated windmill using parts from a 1950 No. 2 set for a friend and have now motorised it. I have added a non Meccano motor, a two cell battery holder and an ordinary electrical piano switch to it, to switch it on or off. The motor probably has a shaft of 2 mm. I have put a sleeve of a wire insulation(with the wire removed) and put a half inch plastic pulley over it. I am running the motor with two AA cells that give three volts.