A Wheel-Gripper: Enabling Multifunctionality through Factorability

Manipulation with legs on multi-pedal robots is not a new concept, but it has rarely been considered on wheel-legged robots due to their mechanical structure. This paper presents a mechanism that transitions between a wheel and a gripper, allowing wheel-legged robots to perform manipulation tasks with their legs. It is capable of storing small objects, liquid, or soil while still functioning as a wheel. The design utilizes two distinctive kinematic modes for these functionalities, and uses only one motor for both wheeled locomotion and gripping, with no new actuator for transitioning or locking. Our analysis showed that those distinctive modes corresponded to the factors of the complex kinematic polynomials of the mechanism. The two modes exist because the polynomials that govern the mechanism's kinematics factor. That is to say, its overall motion is the union of two lower degree irreducible components. A single-leg platform was built to demonstrate its ability to grasp objects and collect water or soil samples, and explore its capability as a contact force sensor through experiments. Such a design could enable wheel-legged robots to perform more diverse loco-manipulation tasks without installing additional limbs.