Towards Dynamic Trot Gait Locomotion—Design, Control and Experiments with Cheetah-cub, a Compliant Quadruped Robot

We present robot design and results from locomotion experiments with a novel, compliant quadruped robot: Cheetah-cub. The robot's leg configuration is based on a spring-loaded, panthograph-mechanism with multiple segments. A dedicated open-loop, joint-space locomotion controller was derived and implemented. Experimentally, we found high speed and dynamic gaits, and evaluated the robot's locomotion characteristics. Experiments were run in simulation and in hardware on flat terrain, and at a step-down obstacle. The robot reached a running trot with maximum speed of 1.42m/s, in the hardware experiments. This speed corresponds to a Froude number of 1.3, or 6.9 body lengths per second. Besides typical control parameters, also morphological parameters such as the leg design played a role for maximum robot speed. Our robot platform has several advantages, especially when compared to larger and stiffer quadruped robot designs. 1) It is the fastest (Froude number) trotting quadruped robot of its kind, light-weight, compact, electrically powered, and made from many off-the-shelf components. 2) The robot shows self-stabilizing behavior at increasing robot speed, with open-loop control. 3) It is cheap, easy to reproduce, robust, and safe to handle. This makes it an excellent tool for research of multi-segment legs in quadruped robots.