Design and Control of Biologically Inspired Wheel-less Snake-like Robot * Zeki Y. Bayraktaroglu, Atilla Kılıçarslan, and Ahmet Kuzucu Vincent Hugel and Pierre Blazevic Istanbul Technical University University of Versailles Saint Quentin-en-Yvelines Faculty of Mechanical Engineering Versailles Robotics Laboratory Inonu Cad. No:87, Beyoglu 34437 Istanbul, Turkey 10 Avenue de l’Europe, 78140, Vélizy, France zeki.bayraktaroglu@itu.edu.tr hugel@lrv.uvsq.fr * This work is supported by the TUBITAK and French Ministry of Foreign Affairs joint project #PIA-1. Abstract - This paper describes our research project on snake-like locomotion of robotic platforms and the results of the experiments conducted with a wheel-less snake-like robot prototype. Biological inspiration has been at the hardcore of the mechanical design and the control method applied to the robot. With closed-loop control applied to the present wheel- less prototype, it has succeeded in progressing through lateral undulation, the most common limbless locomotion type observed in natural snakes. Main results consist of the robustness of the locomotion with respect to the variations in initial conditions and external perturbations. Index Terms - Limbless locomotion. Lateral undulation. Snake-like robot. Biologically inspired methods. I. INTRODUCTION Limbless locomotion has recently motivated the construction of a number of mobile machines taking advantage of the physical phenomena observed particularly with snakes and inchworms. Original works of Hirose [1-3] has inspired many of the following research on snake-like locomotion throughout the world [4-11]. Most of these locomotors consist of mobile platforms equipped with active or passive wheels. Despite their snake-like mechanical structures, locomotion of machines using active wheels is based on the principles of classical wheeled functioning. Most structures with passive wheels have been designed to exert biologically inspired snake-like locomotion [1-11]. However wheeled snake robots are intended to operate over perfectly smooth substrata, i.e. in artificially structured environments. In addition wheeled motion does not appear in natural world. Among various limbless locomotion types, lateral undulation is the most frequently exerted progression by nearly all snake species [12-14]. Fig. 1(a) illustrates the tracks of a snake progressing through lateral undulation. Fig. 1(b) shows the discrete lateral reaction forces that propel the whole body. Snake locomotion through lateral undulation is based on a continuous interaction of the animal’s entire body with its environment. The animal curves its own body so that it could push against the environment’s irregularities. Reaction forces from the so-called push-points constitute together the total propulsive force required for progression in a given direction [12-17]. Locally, sections of the mobile body slide along the push-points and the resulting global force/torque happens to propel the snake. Fig. 1 (a) Tracks of a snake moving through lateral undulation. (b) Three different cases with various number of simultaneous lateral contacts. The minimal number of simultaneous lateral contacts required between the mobile body and its environment is determined to be 3 in case of lateral undulation [13,16]. Highly articulated snake backbone ensures a kind of adaptation to a variety of substrata. Therefore snake-like locomotion is rather suitable for outdoor applications in uneven environments where wheeled and/or legged platforms could not operate properly. In this work we propose a wheel-less snake-like mobile mechanism, capable of exerting biologically inspired locomotion. The mechanical design and the control approach presented in this work have been motivated by our previous works on the subject [18-20]. The second part describes the mechanical structures of the mobile mechanism and its artificial environment. In the third part, the control algorithm and its implementation are presented. The results of experiments are given in the forth part. In the fifth and last part, a discussion on the actual results as well as the ongoing work is presented. II. EXPERIMENTAL SETUP A. Wheel-less Snake-like Mechanism The experimental environment shown in Fig. 2 consists of a horizontal plane with vertical cylindrical profiles representing the available push-points to be contacted during the locomotion. Disposition of the push-points over the horizontal plane is pre-defined. The mobile mechanism consists of ten identical modules (Fig. 3) interconnected with one DOF joint, i.e. the rotation around the vertical axis to the motion plane. Modules are connected through servo- motors which control the relative angular positions between module orientations.