Abstract: The leg structure is crucial to the legged robot's motion performance. With the size and load of the legged robot increasing, the difficulty of leg design increases sharply. Inspired by biomechanics, this paper proposes a leg design approach based on effective mechanical advantage (EMA) for developing the heavy-duty legged robot. The bio-inspired design approach can reduce the demand for joint actuation forces during walking by optimizing the ratio relationship between the joint driving force and ground contact force. A dimensionless EMA model of the leg for the heavy-duty legged robot is constructed in this paper. Leg dimensions and hinge point locations are optimized according to the EMA and energy-optimal criterion. Based on the optimal leg structure, an electrically driven tri-segmented leg prototype is developed. The leg's joint hinge points are located near the main support line, and the load-to-weight ratio is 15:1. The leg can realize a swing frequency of 0.63 Hz at the stride length of 0.8 m, and the maximum stride length can reach 1.5 m.

Key words: Legged robot , · EMA , · Heavy-duty , · Bio-inspired