Design and control of a spherical mobile robot

This paper describes a type of mobile robot with a spherical shape designed to act as a platform to carry sensing devices or actuators in an environment where the conditions are harsh and the stability of the mechanical platform is critical. A remotely controlled internal unit drives the spherical robot. The paper focuses on the design and motion control of a robot with a spherical shape. The developed control modules are implemented in digital programmable logic devices, using a hardware description language named VHDL. The digital hardware controls multiple devices: a multichannel analogue-to-digital (A/D) converter, a pair of radio-frequency (RF) modules and four radio-controlled (R/C) servos. The robot motion is modelled by a configuration space function using the path curvature. The motion controller was designed to drive the robot to the desired path using control based on the path curvature. Because of the lack of a special steering mechanism, the robot steers only by controlling the displacement of its centre of gravity.