Wobble control of a pendulum actuated spherical robot

TL;DR

This paper presents a model-based control approach for a pendulum-actuated spherical robot that effectively reduces wobble during navigation, improving camera stability for surveillance in complex environments.

Contribution

It introduces a novel feedback linearization controller that manages wobble and heading control in a nonholonomic, underactuated spherical robot using a detailed dynamic model.

Findings

The controller successfully limits wobble amplitude and frequency.

The model accurately predicts wobble characteristics during circular motions.

Enhanced camera stability during robot navigation.

Abstract

Spherical robots can conduct surveillance in hostile, cluttered environments without being damaged, as their protective shell can safely house sensors such as cameras. However, lateral oscillations, also known as wobble, occur when these sphere-shaped robots operate at low speeds, leading to shaky camera feedback. These oscillations in a pendulum-actuated spherical robot are caused by the coupling between the forward and steering motions due to nonholonomic constraints. Designing a controller to limit wobbling in these robots is challenging due to their underactuated nature. We propose a model-based controller to navigate a pendulum-actuated spherical robot using wobble-free turning maneuvers consisting of circular arcs and straight lines. The model is developed using Lagrange-D'Alembert equations and accounts for the coupled forward and steering motions. The model is further analyzed to derive expressions for radius of curvature, precession rate, wobble amplitude, and wobble frequency during circular motions. Finally, we design an input-output feedback linearization-based controller to control the robot's heading direction and wobble. Overall, the proposed controller enables a teleoperator to command a specific forward velocity and pendulum angle as per the desired turning radius while limiting the robot's lateral oscillations to enhance the quality of camera feedback.