  This article presents the design, implementation, and performance evaluation
of SWheg, a novel modular wheel-leg transformable robot family with minimalist
actuator realization. SWheg takes advantage of both wheeled and legged
locomotion by seamlessly integrating them on a single platform. In contrast to
other designs that use multiple actuators, SWheg uses only one actuator to
drive the transformation of all the wheel-leg modules in sync. This means an
N-legged SWheg robot requires only N+1 actuators, which can significantly
reduce the cost and malfunction rate of the platform. The tendon-driven
wheel-leg transformation mechanism based on a four-bar linkage can perform fast
morphology transitions between wheels and legs. We validated the design
principle with two SWheg robots with four and six wheel-leg modules separately,
namely Quadrupedal SWheg and Hexapod SWheg. The design process, mechatronics
infrastructure, and the gait behavioral development of both platforms were
discussed. The performance of the robot was evaluated in various scenarios,
including driving and turning in wheeled mode, step crossing, irregular terrain
passing, and stair climbing in legged mode. The comparison between these two
platforms was also discussed.
