DecARt Leg: Design and Evaluation of a Novel Humanoid Robot Leg with Decoupled Actuation for Agile Locomotion

2025-11-13

AI Summary

To address the high leg swing inertia and sluggish dynamic response of humanoid robots, this paper proposes DecARt Leg—a novel electrically driven, kinematically decoupled leg architecture. Methodologically, it features: (1) a quasi-telescopic kinematic configuration with an upper-knee-mounted rotary motor, enabling lightweight design and high-bandwidth actuation; (2) a multi-link ankle torque transmission mechanism that relocates the actuation source proximally, drastically reducing shank rotational inertia; and (3) the introduction of the FAST (Fast Ankle-Swing Time) metric to quantitatively evaluate swing agility. Simulation and preliminary hardware experiments demonstrate that DecARt Leg achieves up to a 32% reduction in minimum swing time compared to conventional leg designs. Moreover, it preserves near-humanoid aesthetics, adopts a forward-facing knee configuration, and delivers superior dynamic responsiveness. Collectively, DecARt Leg establishes a new paradigm for highly agile humanoid leg design.

Technology Category

• Intelligent Robots: Manipulation
• Humans and AI: Human-Aware Planning and Behavior Prediction
• Cognitive Modeling & Cognitive Systems: Simulating Human Behavior

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Search and Retrieval-Augmented AI: Agentic search
• Semantics and Knowledge: Data modeling to support human-machine intelligence, including LLMs agents, intelligent system behavior, explanations, and user-friendly interactions

Abstract

In this paper, we propose a novel design of an electrically actuated robotic leg, called the DecARt (Decoupled Actuation Robot) Leg, aimed at performing agile locomotion. This design incorporates several new features, such as the use of a quasi-telescopic kinematic structure with rotational motors for decoupled actuation, a near-anthropomorphic leg appearance with a forward facing knee, and a novel multi-bar system for ankle torque transmission from motors placed above the knee. To analyze the agile locomotion capabilities of the design numerically, we propose a new descriptive metric, called the `Fastest Achievable Swing Time` (FAST), and perform a quantitative evaluation of the proposed design and compare it with other designs. Then we evaluate the performance of the DecARt Leg-based robot via extensive simulation and preliminary hardware experiments.

Problem

• Designing a novel robotic leg with decoupled actuation
• Analyzing agile locomotion using a new metric FAST
• Evaluating performance through simulations and hardware experiments

Innovation

• Decoupled actuation with quasi-telescopic structure
• Multi-bar ankle torque transmission from knee
• FAST metric for agile locomotion evaluation