CubiXMusashi: Fusion of Wire-Driven CubiX and Musculoskeletal Humanoid Musashi toward Unlimited Performance

TL;DR

CubiXMusashi addresses the control and task limitations of high-DOF musculoskeletal humanoids by fusing Musashi with the environment-connected wire-driven CubiX. The approach combines dual-robot hardware with a synchronized control architecture: Musashi is steered via neural-network-based whole-body mapping from target joint angles to muscle lengths, while CubiX handles wire-length regulation with a weight-compensation feedforward term. Through three experiments—pull-up, rising from a lying pose, and mid-air kicking—the system demonstrates new capabilities enabled by external wire actuation, including lifting the body, transitioning to a standing posture, and performing kicks while rotating in the air. These results highlight the potential for environment-connected actuation to augment both musculoskeletal and general humanoids, reducing natural physical constraints and expanding motion repertoires, with implications for training platforms and multi-robot integration.

Abstract

Humanoids exhibit a wide variety in terms of joint configuration, actuators, and degrees of freedom, resulting in different achievable movements and tasks for each type. Particularly, musculoskeletal humanoids are developed to closely emulate human body structure and movement functions, consisting of a skeletal framework driven by numerous muscle actuators. The redundant arrangement of muscles relative to the skeletal degrees of freedom has been used to represent the flexible and complex body movements observed in humans. However, due to this flexible body and high degrees of freedom, modeling, simulation, and control become extremely challenging, limiting the feasible movements and tasks. In this study, we integrate the musculoskeletal humanoid Musashi with the wire-driven robot CubiX, capable of connecting to the environment, to form CubiXMusashi. This combination addresses the shortcomings of traditional musculoskeletal humanoids and enables movements beyond the capabilities of other humanoids. CubiXMusashi connects to the environment with wires and drives by winding them, successfully achieving movements such as pull-up, rising from a lying pose, and mid-air kicking, which are difficult for Musashi alone. This concept demonstrates that various humanoids, not limited to musculoskeletal humanoids, can mitigate their physical constraints and acquire new abilities by connecting to the environment and driving through wires.

Figures (9)

• Figure 1: The overview of CubiXMusashi. CubiXMusashi is a robot that combines Musashi, a musculoskeletal humanoid, with CubiX, a wire-driven robot capable of connecting to the environment.
• Figure 2: The hardware structure of CubiXMusashi. CubiX and Musashi were assembled on the back pelvic area of Musashi using connector parts. CubiX is equipped with 8 wire modules, sensors, and a computer. Musashi's body consists of muscle modules representing muscles, joint modules functioning as joints, and bone frames serving as the skeleton.
• Figure 3: The system configuration of CubiXMusashi. Separate controllers run for Musashi and CubiX, and CubiXMusashi is controlled by synchronizing the planners in each controller. Musashi was controlled using inference by neural networks, and CubiX used wire length control.
• Figure 4: Pull-up motion experiment. (A) Experimental setup. (B) Pull-up motion. By winding the 4 wires connected to the environment, it was possible to perform a pull-up motion, lifting the entire body.
• Figure 5: Time series data of height position $z$ and target wire tension $\bm{f}^\mathrm{ref}_\mathrm{CubiX}$ during the pull-up motion experiment. By controlling the length of the 4 wires, it shows that the entire body of CubiXMusashi was lifted while compensating for its own weight.