VaSpoke: A Transformable Leg-Wheel Robot Featuring Variable Spokes

The number of spokes is a key structural parameter influencing motion continuity, smoothness, and obstacle-crossing capability in spoke-wheel robots. However, existing designs typically adopt a fixed spoke number, limiting adaptability to diverse terrains. To address this limitation, this article proposes a transformable spoke-wheel robot, called VaSpoke, with a variable number of spokes. The robot employs four identical spoke wheels, each driven by two motors for wheel rotation and spoke transformation. A planetary gear and rack-and-pinion mechanism enables controlled extension and retraction of six spokes, divided into two independently actuated groups to switch the spoke number. The robot operates in three modes: a wheel mode for smooth motion, a three-spoke mode for enhanced obstacle crossing, and a six-spoke mode that balances both. A dynamic model based on the Lagrange method is developed, and obstacle-crossing and stair-climbing capabilities are analyzed separately. Experimental evaluations on flat ground, steps, stairs, and unstructured outdoor terrains validate the effectiveness of the proposed design. The robot achieved a maximum obstacle-climbing height of 2.24 times its wheel radius, demonstrating its strong terrain adaptability and potential for deployment in complex environments such as inspection and search-and-rescue missions. DOI: 10.1109/TMECH.2026.3726555 Wei, Z., Xue, J., Xiang, S., Yang, Y., & Song, A. (2026). VaSpoke: A Transformable Leg-Wheel Robot Featuring Variable Spokes. IEEE/ASME Transactions on Mechatronics.