Design and analysis of a rotational leg-type miniature robot with an actuated middle joint and a tail (RoMiRAMT)

In this paper, a rotational leg-type miniature robot with an actuated middle joint and tail, called RoMiRAMT, 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 properly selected candidates. It also has unique characteristics inspired by biological structures: a spine and a tail. An actuated middle joint allows the frontal body to be lifted or lowered, which was inspired by a spine, to climb higher obstacles. Additionally, a multi-functional two degrees of freedom (2-DOF) tail was added; the tail provides instant deceleration, and minimized the likelihood of flipping, while allowing the robot to climb higher obstacles. A microcontroller was embedded in the robot, along with a micro-camera and an inertia measurement unit (IMU) sensor. By controlling the robot using the yaw angle signal measured by the IMU sensor, straight movement was enhanced. The body size of the RoMiRAMT is 155 × 80 mm without the rotational legs, and the weight is 593 g including batteries. The maximum velocity of the robot was 2.58 m/s (16.65 body lengths per second) and the maximum height of an obstacle that the robot can climb was 95 mm, which all were verified by experiments.

I. Introduction

Effective mobility is one of the most challenging research areas in mobile robots [1]–[4]. A small mobile robot can be used in place of humans to explore dangerous places [5], [6] collect information, or perform simple tasks. To achieve this goal, efficient mobility including stable walking (i.e., reduced wobbling, straight and fast movement, etc.) and obstacle climbing ability should be ensured. The locomotion of mobile robots can be categorized into three types: wheeled-type, legged-type and a hybrid of wheel/leg type. A wheeled type robot is the fastest among the three cases, and has a simple structure; however, its mobility is limited. For instance, the wheeled type robot would have difficulty climbing an obstacle whose height is more than about half of the wheel diameter. In contrast, a legged robot can climb many different types of obstacles easily, but its hardware structure is more complex, and requires additional actuators. Also, legged robots are usually slower than wheeled robots.