Development of a novel leg-wheel module with fast transformation and leaping capability

We report on the development of a novel two-degrees-of-freedom module capable of transforming its shape between a wheel and a leg, with the length of the latter approximately 3.4 times the wheel radius. The leg-wheel module was empirically built and experimentally evaluated. It utilizes a linkage mechanism and can perform a smooth yet rapid leg-wheel transition within 0.25 s. The design concept, selection of the linkage parameters, and kinematics are described in this paper. The rapid transition from a wheel to a leg endows the robot with wheel-to-leap behavior. The general motion planning strategy of the leg-wheel, as well as the wheel-to-leap behavior, are explained in the demonstration example. The results confirm that the module can perform wheel-to-leap behavior with a height of up to 4.6 times the wheel radius. (c) 2021 Elsevier Ltd. All rights reserved. Several thousand years of man-made civilization have changed the environment, including the terrain, in many ways. In addition to natural terrain (such as mountains), the engineered landscape includes flat surfaces, surfaces with smooth curvatures, terraced fields, stairs, and single steps. While legged robots are highly capable of negotiating uneven terrain, wheeled robots are advantageous for cruising over flat terrain because of their smoothness, power efficiency, and high speed. Therefore, leg-wheel hybrid robots can effectively negotiate existing flat and rough terrains [1] . Several leg-wheel hybrid robots have been reported in the literature. They can be categorized into three types, as shown in Table 1 . The robots in the first category have wheels mounted on the feet. The wheels are typically small and actively actuated. The wheels and legs are coordinated and act together to achieve locomotion. The new version of the quadruped ANYmal [2] is equipped with four non-steerable and torque-controlled wheels, achieving power-efficient motion on flat