4) Crane: This three-degrees-of-freedom crane [30], shown in Fig. 5, is made of LEGO Mindstorms and can be used for lifting objects and positioning them accurately. The crane was controlled using three knife switches. Each three-position switch could provide a positive, negative, or zero voltage to the LEGO motors. The crane is provided with overcurrent and surge protection circuits. All gear sets were made to suit the output torques and speeds for each crane function. Different gear ratios were used for each motor to perform hoisting and trolley motion at different speeds and torques.