Design and control of a snake robot for narrow space application

Abstract

In snake robot research, one of the most efficient forms of locomotion is the lateral undulation. However, lateral undulation, also known as serpentine locomotion, is ill-suited for narrow spaces, as the body of the snake must assume a certain amount of culvature to propel forward. Other types of motion such as the concertina or rectilinear may be suitable for narrow spaces, but is highly inefficient if the same type of locomotion is used even in open spaces. Though snakes naturally can interchange between the use of serpentine and concertina movement depending on the environment, snake robots based on lateral undulation to date are unable to function satisfactorily in narrow spaces. In undergoing concertina movement, the snake lifts part of its body off the ground to reduce friction; this cannot be reproduced in planar snake robots. To overcome the inability to adapt to narrow spaces, a novel type of gait is introduced in this research. With slight modifications to the membersof the multi-link snake robot, the robot normally developed for lateral undulation is able to utilize the new gait to negotiate narrow spaces. The modifications include alterations to the snake segments as well as elements that mimic scales on the underside of the snake body. Scales, often overlooked in snake locomotion reseach, play an important role in increasing backward and lateral friction while minimizing it in forward direction. This concept provides the basis for movement in the proposed gait. Through kinematic studies the viability of this gait is illustrated. The appropriate configurations for a five-link snake robot of the proposed design are studied, resulting in the values for the angles between the links at each instance such that the whole body would move forward. The inverse kinematics is derived using geometrifal and trigonometri formulations, while the forward is estimated using a polynomial function. The kinematic study is followed by a dynamic analysis based on Lagrangian mechanics. The same polynomial estimates are used to determine the actuating torque and duration of actuation required to propel the robot forward. To verify the proposed gait, a prototype is developed and tested. The performance of the prototype shows that such a gait is viable for executing motion. The test, however, was conducted on high friction surfaces. Nevertheless, the lateral displacement of the segments is found to be reasonably low compared to traditional serpentine robots, hence demonstrating the efficay of the gait in narrow space application.