Development of wireless control system for a spherical robot

Abstract: The purpose of this thesis was to develop a control method which can reduce
oscillation of lateral motion for a pendulum driven spherical robot operating
on flat surface. The spherical robot provides a unique mobility and has
several applications in surveillance and entertainment.

Controlling a spherical robot is a challenging problem till today due to its
nature of kinematics and dynamics. Firstly, its nonholonomic nature prohibits
the use of conventional state feedback control laws. Secondly, kinematics of
a spherical robot cannot be expressed as a chained-form system to utilize
nonholonomic control algorithms. However, various types of nonlinear control
algorithms were proposed to settle the problem though none of them provided
satisfactory result.

The kinematics and dynamics of the pendulum driven spherical robot was
investigated followed by linearization for longitudinal and lateral motions
through frequency and state space transformation. Moreover, the
controllability of the states of the system was maintained during
linearization. A robust self-tuning sliding mode controller which suspends
oscillation, maintains desired speed and compensates for unmodeled parameters
was developed. The implemented control system consists of control station,
prototype robot equipped with on-board microcontroller and sensors, and
wireless communication link.

Simulation and experimentation were conducted to test peformance of the
control laws in suppressing oscillation and maintaining desired speed of the
robot. The robot traveled to the commanded trajectory containing straight
line and curve with relatively minimum oscillation at desired speed. Thus,
the sliding mode control is an effective controller.