RWD-DOF: a dual-degree-of-freedom reconfigurable wheel design for improved robotic mobility

Wheeled mobile robots are efficient on flat surfaces but face limitations in overcoming obstacles like steps due to their fixed wheel radius. This paper presents a novel modular reconfigurable wheel with a dual-degree-of-freedom active reconfigurable mechanism, designed to adapt dynamically to varying step sizes. The wheel's structure includes three curved segments, whose synchronized motion is driven by five-bar linkages and two planetary gear systems. By analyzing the kinematic constraints and both forward and inverse kinematics of the reconfigurable wheel, we established the range of dimensions it can surmount over steps, specifically focusing on height and depth, as well as the relationship with the output angles <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>q</mml:mi> <mml:mn>1</mml:mn></mml:msub> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>q</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:math> of the two motors driving the reconfiguration. Simulations using ADAMS software demonstrates the wheel's capability to maintain smooth, continuous center-of-mass movement over steps and stairs. Moreover, physical prototype testing further confirms the feasibility and advantages of the proposed wheel structure. This adaptive design significantly enhances the performance of wheeled robots in navigating complex environments, offering promising potential for applications in challenging terrain.