Abstract: In this paper, a rotational leg-type miniature robot with a bioinspired actuated middle joint and a tail is proposed for stable locomotion and improved climbing ability. The robot has four independently actuated rotational legs, giving it advantages of both wheel-type and leg-type locomotion. The design parameters of the rotational legs were determined by 3D simulation within the seven candidates that selected by a newly proposed metric. It also has unique characteristics inspired by biological structures: a middle joint and a tail. An actuated middle joint allows the frontal body to be lifted or lowered, which was inspired by a flexible body joint of animals, to climb higher obstacles. Effectiveness of the middle joint was analytically verified by the geometric analysis of the robot. Additionally, a multi-functional one Degree Of Freedom (1-DOF) tail was added; the tail prevented the body being easily flipped, while allowed the robot to climb higher obstacles. A bristle-inspired micro structure was attached to the tail to enhance straightness of locomotion. Body size of the robot was 158 mm × 80 mm × 85 mm and weighed 581 g including a 7.4 V Li-Polymer battery. The average velocity of the robot was
2.74 m•s−1 (17.67 body lengths per second) and the maximum height of an obstacle that the robot could climb was 106 mm (2.5 times of leg length), which all were verified by experiments.

Key words: rotational leg, actuated tail, locomotion, actuated middle joint, bionic miniature robot