Design and Control of a Miniature Bipedal Robot with Proprioceptive Actuation for Dynamic Behaviors

As the study of humanoid robots becomes a world-wide interdisciplinary research field, the demand for a cost-effective bipedal robot system capable of dynamic behaviors is growing exponentially. This paper presents a miniature bipedal robot named Bipedal Robot Unit with Compliance Enhanced (BRUCE). Each leg of BRUCE has five degrees of freedom (DoFs), which includes a spherical hip joint, a knee joint, and an ankle joint. To lower the leg inertia, a cable-driven differential pulley system and a linkage mechanism are applied to the hip and ankle joints, respectively. With the proposed design, BRUCE is able to achieve a similar range of motion to a human's lower body. The proprioceptive actuation and contact sensing further prepare BRUCE for interactions with unstructured environments. For real-time control of dynamic motions, a convex formulation for model hierarchy predictive control (MHPC) is introduced. MHPC plans with whole-body dynamics in the near horizon and simplified dynamics in the long horizon to benefit from both model accuracy and computational efficiency. A series of experiments were conducted to evaluate the overall system performance including hip joint analysis, walking, push recovery, and vertical jumping.