Locomotion of a cylindrical rolling robot with a shape changing outer surface

Abstract

A cylindrical rolling robot is developed that generates torque by changing shape (eccentricity) of its elliptical outer surface. Shape change commences four times per revolution, whenever one of four elliptical axes rotates past an inclination called trigger angle. The robot is equipped with a sensing/control system by which it measures angular position and angular velocity, computes error with respect to a desired step velocity profile, and changes shape of the outer surface at these times accordingly. A series of trial rolls are conducted using various trigger angles, and energy consumed by the robot's singular servo motor is measured and used to calculate energy consumed per unit roll distance. Results show that for each of three desired velocity profiles tested, there exists one or more trigger angle values that result in relatively low energy consumption per unit roll distance. When the robot operates within this optimal trigger angle range, it undergoes minimal actuation burdening and inadvertent braking, both of which are inherent to the robot's control system and act to lower the robot's energy economy during locomotion. Moreover, this optimal range generally shifts towards the vertical as angular velocity of the robot increases. A mathematical model of the robot's motion is developed and applied in a simulation program that is used to predict, analyze and further understand the robot's locomotion.