An Inertially-actuated Passive Dynamic Step Climbing Wheeled Robot

For their inherent stability and simplicity, wheeled robots are very common in robotics applications – but a major drawback of wheeled robots is their inability to navigate over large obstacles or steps without assistance. Active systems that have been designed for use on wheeled robots to lift the robot over a step – such as USU‟s T3 and Virginia Tech‟s IMPASS – are effective, but are limited due to the size, cost, and power required for the additional actuators. A novel, inertially actuated, passive dynamic system, excited by the motion of the robot, is introduced to allow a wheeled robot to “pop a wheelie” on each axle and hop over a step. The system investigated here is a sliding mass-spring that shifts forward and backward based on the acceleration of the base robot. By coordinating the acceleration and deceleration of the robot, the front wheels can lift over a step and the rear wheels can be pulled up afterward – both actions being a product of inertial actuation. Key advantages of this system are that the design is simple, costeffective, and can be adjusted and retrofit to a different wheeled robot in the future with little effort. This paper presents the development of a novel inertially actuated, passive dynamic step climbing wheeled robot. Derivations of the dynamic model of the inertially actuated system are given and a computer simulation and experiments of an implementation of this sliding mass system are presented, followed by conclusions with possibilities for future work. INTRODUCTION Wheeled robots are common in robotics applications, likely due to their simplicity and inherent stability when at least three wheels are present. Unlike robots that rely on a coordinated effort of legs to move, robots on wheels require very little design effort in order to maintain stability. Many wheeled robots have the need to climb a step: wheeled airport security robots that patrol the facility [1] are limited to moving along flat and slightly inclined surfaces. However, if the security robot needs to climb a curb and a ramp is not nearby, a possible security risk could go undetected. For situations like this where a robot needs the ability to climb a step immediately, some type of design is required to allow this maneuver. While other robotic platforms, such as legged robots and some snake-like robots, are able to surmount large steps by manipulating themselves to rise up, wheeled robots are limited to flat surfaces and small steps. A wheeled robot can naturally climb steps that are lower than the radius of the robot‟s tires [2], but larger steps are insurmountable by basic friction contact of the wheels on the step. Robotic platforms have been designed to allow wheeled robots to climb steps [3-12], but these platforms rely on additional actuators, such as motors or hydraulic systems. For these options, extra power and added processing for control and coordination of these actuators are needed for the extra degrees of freedom. We present a novel approach to climbing large steps with a wheeled robot utilizing a passive dynamic, inertially actuated sliding mass. This technique involves attaching a passive system that is inertially actuated to allow the robot to climb a step without directly controlling the mass. Before discussing the dynamics involved in this system, a proper introduction to the concept of passive dynamics and what this term generally applies to is required. Passive dynamics were first realized [13] as a more efficient walking pattern that takes advantage of gravity and the natural swing of legs instead of spending effort to actively manipulate legs for walking. In contrast to this original idea of passive dynamics, this research presents an idea Proceedings of the ASME 2009 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC/CIE 2009 August 30 September 2, 2009, San Diego, California, USA