Design and motion planning of a compact direct-drive leg-wheel robot: DTransleg

Existing articulated-leg leg-wheel robots suffer from complex structures and morphing mechanisms. To address this issue, this paper presents a transformable leg-wheel robot named DTransleg. The robot is propelled by four identical leg-wheel mechanisms that can switch between wheel mode and articulated-leg mode. Wheeled locomotion is introduced by designing the thigh segment as a circular rim, eliminating the need for additional actuators. In leg mode, each mechanism possesses three active joints, whereas, in wheel mode, active motion is realized using the hip-pitch actuator. To enhance agility and stability, DTransleg also incorporates waist yaw and pitch joints. This paper details the design methodology, establishes a kinematic model, and devises motion plans for four-wheeled, quadruped, and carriage modes together with the transition strategies among them. Both simulations and physical experiments validate the feasibility of the design and the correctness of the modeling and motion planning.