Mechanical design of multifunctional quadruped

Abstract

This paper describes the mechanical design of a multifunctional four-legged walking machine that is being developed at the Robotics Research Centre, NTU. The major factors influencing the design requirements include minimisation of the weight of the machine, large workspace of the legs, good energy efficiency and relatively high walking speed. The designed walking machine can adopt a variety of configurations such as insect, mammalian, reptile, or human like. The design is invertable and the machine using the legs as manipulators can even perform basic pick and place functions. Lengths of machine leg segments are: 0.12 m––thigh segment and 0.14 m––shank segment, body has a square shape with the side 0.08 m. Total weight is 1.5–2 kG (depends on the type of feet attached and construction of the body frame). The speed of motion depends on the type of implemented gait (side walking with separated legs motion and body transfer, turning motion, stair climbing etc.), during basic straight line quadruped crawl (only one leg at a time in transfer) on a horizontal surface it is 0.045 m/s. It should be stressed that the speed depends on leg configuration and the step length. For shorter steps the number of leg transfers for a given travelling distance is larger and the walking speed is lower. On the other hand, a shorter step length implies that the leg resultant mass will be transferred over a shorter distance in relation to the body frame and the total displacement of the machine centre of mass will be smaller which increases the vehicle stability compared with the situation when the step is longer. Considering different gaits with diverse configurations we can summarise that the walking speed range of the legged autonomous vehicle machine is between 0.001 and 0.045 m/s.