Effective Parameters for Helical Pole Climbing of the Wheel-based Modular Snake Robot Pongsakorn Polchankajorn and Thavida Maneewarn Institute of FIeld roBOtics (FIBO) King Mongkut’s University of Technology Thonburi Bangkok, Thailand dome @ fibo.kmutt.ac.th, praew @ fibo.kmutt.ac.th Abstract—This research aims to study the factor that affect pole climbing efficiency of the modular snake robot on the cylindrical pole with constant radius. The wheel-based modular snake is climbing the pole by forming itself into a helical or a spiral shape around the pole and using its driving wheel to propel itself upward along the helical path. The joint configuration of the robot can be found from the relation of helical pitch angle, helical radius, and link length of the robot. Five helical climbing configurations with different helical pitch angles and three spiral climbing configurations with different spiral’s end radius were tested on the 18 degree of freedoms, 7 links modular hyper- redundant robot. The experimental result showed that the climbing velocity depends on the distribution of the grasping force and the helical pitch angle. The grasping force is affected by the helical radius and the helical pitch angle. Keywords-Modular Snake Robot; Helical climbing; Spiral climbing; Pole climbing I. INTRODUCTION Climbing robots have been developed for various applications in the past twenty years. The designs of climbing robot are varied depending on their usages such as pipe inspection, fruit harvesting, wall cleaning etc. The mechanisms for climbing in a robot can be categorized as static and dynamic climbing. In static climbing, grasping and body- extending actions are alternated, for example an inchworm climbing motion suggested in [1, 2]. This type of climbing robot usually has two active grippers and can be used to climb across a branch of pipes or trees. In dynamic climbing, grasping and climbing motions happen simultaneously. This type of climbing results in continuous motion, thus has been applied in pole climbing applications as proposed in [3, 4]. In recent year, the modular and reconfigurable robots have been topic of interest by many groups of robotic researchers [5-9]. With modular design, the robot can adapt itself to perform different tasks in various environments including pole climbing. Choset [7] demonstrated the scenario that a modular robotic snake could successfully grasp and roll up a cylindrical pole. His team also invented the Toroidal Skin Drive (TSD) [8] that could drive the robot up the pole in helical trajectory. Goldman and Hong [9] proposed the cost function analysis for designing and controlling a modular climbing robot. They also applied the helical form for grasping and rolling up the pole. In this paper, we aim to study the parameters that affect the pole climbing ability of a modular robot in helical configuration. We are also interested in the wheel-based modular snake robot due to the fact that the direction of its wheels can be adjusted to provide some frictional support for the gravitational force that acts on the robot. In helical configuration, there are two parameters that significantly affect the climbing ability i.e. helical radius and helical pitch angle. The helical radius directly affects the grasping force between the robot and the pole. On the other hand, the helical pitch angle relates to the climbing velocity. However, when the helical pitch angle is increasing, the grasping force could be decreasing to the point that the robot may lose its climbing ability. In the next section, we will discuss about the design of climbing gait of the modular wheel-based snake robot. The kinematics of the proposed helical and spiral pole climbing gait will be explained. The rest of the paper will be organized as follows. Section II describes how the helical pole climbing works, the frame assignments of the robot and the helical and spiral path equations. Section III describes the inverse kinematics and the dynamics equation of the robot. Section IV describes the robot design and the climbing experiments. Finally, the result of experiments will be discussed and concluded in section V and VI. II. CONCEPT OF POLE CLIMBING A. Designing pole climbing gait for a modular snake robot A modular snake robot is designed to be able to perform various types of locomotion such as crawling, rolling and climbing. In order to climb a pole, the robot must apply sufficient grasping force around the pole while moving its body up the pole against the gravitational pull. The helical configuration can be used for this type of motion, because the helical form can provide grasping action while allowing the robot to move upward. For the non-wheel modular snake robot, the robot can roll its body upward when it wraps itself around the pole in a helical configuration [7-9]. For the wheel-based modular snake robot, its wheel can be adjusted to be perpendicular to the ground plane so that the robot can roll its wheel upward vertically as in the non-wheel robot [9]. However, we are interested in the climbing motion that the This work was supported in part by Junior Science Talent Project, NSTDA. Proceedings of the 5th International Conference on Automation, Robotics and Applications, Dec 6-8, 2011, Wellington, New Zealand 978-1-4577-0330-0/11/$26.00 ©2011 IEEE 232