Software control of an eight wheeled-legged hybrid robot

Abstract

Space robots such as rovers have typically used wheeled mobility systems such as the rocker-bogie suspension system. However, NASA's ATHLETE robot featuring a hybrid wheeled-legged mobility system signifies a shift in direction. Legged and hybrid mobility systems improve on wheeled systems in their enhanced ability to move effectively on rough terrain. One class of legged robots that have been strongly researched for space applications are frame walking systems. These robots typically have legs with sliding prismatic joints to provide a degree of freedom in the vertical direction.

The present thesis work is targeted to a hybrid eight wheeled-legged robot called the Zero-Carrier. The robot is designed for transportation of disabled and elderly people, and has legs with sliding prismatic joints to allow stair-climbing ability. The aim of the thesis was to implement the upper-level control software for the next version of the robot. The role of the software is to detect obstacles using on-board sensors and control actuators to move the robot autonomously to overcome the obstacles. To allow implementation, testing and demonstration of the software a simulation platform was developed using OpenGL for 3D visualisation.

The described control software improves on previous versions by providing intelligent control of individual legs using state machines, while centrally coordinating movements to guarantee stability. This results in a wider range of obstacles that can be overcome. Advanced features including centre of gravity control, smooth movement and level movement on slopes are also addressed to improve passenger comfort and safety. Results for a set of simulation test cases are presented which demonstrate the implemented control software's ability to overcome various obstacle situations.

In the context of space robotics, strong similarities were demonstrated between Zero-Carrier and various -researched space robots. The research work therefore provides a relevant examination of the difficulties encountered iii performing the autonomous control of such a complex machine.