Step ascent modelling of a two-wheeled robot

Abstract

This paper describes the dynamics and control of a two-wheeled robot (TWR) traversing a step. The TWR is able to navigate obstacles by shifting its centre of mass; however this comes at the cost of higher control requirements for stability. Equations of motion are derived for the system and a controller designed taking into account the initial conditions and possible reference trajectories. The TWR can be driven to any equilibrium position on the step by linearising the plant about that point and using state regulation. Analysis and simulation show that specific initial conditions are required for the TWR to avoid rolling back off the step. Limiting conditions of the developed controller are found, which include wheel slip, motor torque limit, and parameter uncertainty. The distance of the centre of mass of the TWR from the axle is the most sensitive to deviations from nominal. The current controller is able to traverse steps up to 5.7cm in height over any ascent time longer than 4.5s.