2 A general classification Locomotion Capabilities of a Locomotion Capabilities of a

1 Introduction

The last few years have witnessed an increasing interest in modular reconfigurable robotic technologies. The applications include industrial inspection[1], urban search and rescue[2], space applications[3] and military reconnaissance.

Modular robots are very interesting for research purposes. New configurations can be built very fast and easily, for the exploration, testing and analysis of new ideas. Therefore, fast robot prototyping is another important characteristic of modular robotics, in addition to versatility, robustness and low cost[4].

A general classification of the different configurations of modular robots is essential for the study of their properties. This is not easy because of the infinite number of prototypes that can be built. It is even worst due to the exponential growths of the number of configurations with the modules. As much modules are used, much more configurations are possible. Therefore, a classification is needed to group the configurations and to analyze the properties of the sub-groups.

Such classification is proposed in this paper, based on the topology of the robots and the type of connection between the modules. It is further developed in section .

The sub-group of pitch-yaw connecting robots are very interesting because they feature snake's structure. Some researchers have studied the locomotion properties of these robots. A deeply analysis was performed by Dowling[5]. He focused on learning techniques to move the snake robots. He simulated different gaits: side-winding and rolling among others. Very interesting conclusions are obtained, but the results are not easy to implement on a real robot.

Mori[6] achieved different kinds of lateral rolling gaits on ACM-R3 robot and Chen[7] studied it deeply and proposed to use it in pitch-yaw connecting robots to cross over obstacles. Stoy et al.[8] tested the side-winding gait in a pitch-yaw configuration composed of Conro Modules[9]. A very interesting simulation of the side-winding gait generated by means of genetic programing was achieved by Tanev[10].

For the control algorithm, the CPG approach has been successfully implemented on some modular robots, like Amphibot II[11], Yamor[12], M-TRAN[13] and also on non-modular robots like Aramies[14].

In this paper we focused on finding the locomotion capabilities of the pith-yaw configurations in general, using a sinusoidal CPG approach that can be implemented easily in an eight-bit microcontroller. A pitch-yaw connecting modular robot with eight modules have been built for testing. Five different gaits have been achieved on the real robot. One of them, the rotating gait, is a new one that has not been previously performed in other similar robots, from the best of our knowledge.

In previous work we have studied the pitch-connecting configurations[15] and the locomotion capabilities of 1D and 2D minimal configurations[16].

2 A general classification Locomotion Capabilities of a Locomotion Capabilities of a