Development of a robust control software for a ball shaped robot

Abstract

Mars Ball is a spherical robot intended for Mars Exploration whose mechanical part was designed by Tomi Ylikorpi in 2008. It uses two motors to complete the pendulum displacement for locomotion in 2 DOF. The aim of the robot is to collect the data in Mars with low energy cost by utilizing wind power for secondary propulsion. This aim requires control the driving velocity and the roll angle of Mars Bali to make ii be able to turn to the wind.

The mathematical model of Mars Ball and the other disturbances models like slope, wind and friction are built. A robust control algorithm- Sliding Mode Control is investigated to solve the difficulties facing Mars Ball system: The whole system is non-linear and coupled. The system depends strongly on the wind and road surface condition. The simulation with mathematical model is first conducted in Simulink with pseudo-switching to solve the chattering phenomenon, the results show that both driving velocity and the roll angle can he stabilized within a short time. The designed controllers are also proved to have good path following capability.

In hardware, necessary sensors for feedback information are chosen according to control algorithm. In software, basic commands from ground station are designed and explained how they are interfaced with on-board computer inside Mars Ball through WiFi. Finally, the control algorithm that will be implemented in on-board computer is tested in Adams simulator which simulates mechanisms of Mars Ball's prototype, to verify the effectiveness of designed controllers.