A C-Legged Monopedal Robot and Its Transition From Multiple Locomotion Modes

This paper introduces a minimalistic design of a monopedal robot (monobot) with C-shaped legs which can achieve multiple locomotion modes (multi-mode) such as walking, leaping, as well as backward and forward flipping. We introduce a methodology to design and develop a direct-drive robot with only six necessary parts, possessing at least four general locomotion modes. The monobot contains an actuator, speed controller, 3D printed base frame and legs and battery set. The weight of the whole robot is less than 80 grams. Dimensional parameters are optimized to simplify the design process and to identify effective factors for locomotion. Potential locomotion modes of the robot are analysed by dynamics simulation. A simplified virtual prototype is tested within multibody simulation software. All potential locomotion modes are achieved by adjusting the speed of the actuator. An experimental platform of monobot is then developed. The speed of the platform is adjusted to verify the correspondence between actuator speed and locomotion mode as obtained by simulation. Experimental testing of the monobot confirms the predictions obtained through simulation and thus provides a proof of our design approach. The monobot with multiple locomotion modes (multi-mode monobot) provides mobility and adaptability to the ambient environment such as crossing obstacle or rough terrain, fast transportation, climbing etc. Potential applications of the multi-mode monobot include disaster rescue, planet exploration and reconnaissance. INTRODUCTION Legged morphologies have the ability of behavioural alternatives in a wide range, such as walking, running, selfrighting and jumping. Animal-inspired quadruped robots have been well developed to compete in running speed or energy efficiency, such as Boston Dynamics BigDog[1], MIT Cheetah robot[2], EPFL Cheetah-Cub robot[3], ETH Zurich ANYmal[4], IIT HyQ2Max[5] and Minitaur developed by Ghost Robotics[6]. These biomimetic quadruped robots are all well designed and developed with precisely controlled actuator, many sensors for balancing and delicate structure design for locomotion and navigation. In addition, spoke-like legged robots provide another vision to improve mobility of robot. This concept starts from PROLERO, a PROtotype of LEgged ROver, known as WAlking RObot for Mars Applications (WAROMA) [7]. The robot was developed in European Space Agency. The micro mobile robot was intended to apply instruments in the surroundings of a small lander. The mission requirements of the robot constraint mass and power of the microrover. RHex [8] is also an example to demonstrate how biological inspiration can help improve mobility of robot. RHex has six actuators-one located at each hip. The mechanical simplicity promotes reliable and robust operation in real-world tasks. Legged amphibious robot [9] is an evolution of RHex capable of both sea and land-based locomotion. Three types of robot share the same body with same software, electronic and mechanical structures. Quattroped and TurboQuad are two wheel-leg transformable robots [10, 11]. The modes transition between wheel and leg make the robot adaptive to flat or uneven terrains.