Operating in environments too harsh or inaccessible for humans is one of the critical roles expected of robots. However, such environments often pose risks to electronic components as well. To overcome this, various approaches have been developed, including autonomous mobile robots without electronics, hydraulic remotely actuated mobile robots, and long-reach robot arms driven by wires. Among these, electronics-free autonomous robots cannot make complex decisions, while hydraulically actuated mobile robots and wire-driven robot arms are used in harsh environments such as nuclear power plants. Mobile robots offer greater reach and obstacle avoidance than robot arms, and wire mechanisms offer broader environmental applicability than hydraulics. However, wire-driven systems have not been used for remote actuation of mobile robots. In this study, we propose a novel mechanism called Remote Wire Transmission Mechanism that enables remote actuation of mobile robots via wires. This mechanism is a series connection of decoupled joints, a mechanism used in wire-driven robot arms, adapted for power transmission. We experimentally validated its feasibility by actuating a wire-driven quadruped robot, which we also developed in this study, through Remote Wire Transmission Mechanism.

Methods

Remote Wire Transmission Mechanism: A Flexible Power Conduit

The core of this research is the Remote Wire Transmission Mechanism, a mechanism that transmits mechanical power over a distance through a flexible body. For a mobile robot to move freely, this "power transmitter" must bend and twist without affecting the power transmission.

A simple tube or a basic series of pulleys would improperly constrain the robot's movement or turn it into a conventional robot arm. Instead, we constructed the Remote Wire Transmission Mechanism from a series of decoupled joints. A decoupled joint is a special mechanism with two synchronized pulleys that allows the joint to bend freely without changing the length of the wire passing through it.

By linking these joints in series, we created a flexible structure. This design is highly efficient and maintains consistent performance, unlike alternatives like Tendon Sheath Mechanisms (TSMs) which suffer from high and variable friction.

A Wire-Driven Quadruped Robot

To test the Remote Wire Transmission Mechanism, we built a quadruped robot designed to be powered by it. To minimize complexity and avoid onboard electronics, the robot uses a simple mechanical design. The front and back legs are mechanically coupled to produce a trot gait (where diagonal legs move in unison). The mechanical coupling parameters were mathematically optimized to apploximate an ideal trot foot trajectory, with one pair of legs providing support (stance) while the other pair swings forward.

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Experiments

We conducted experiments to validate the system, both with the robot suspended in the air and walking on the floor. The key finding was that the robot could successfully perform a walking motion while being powered through the flexible Remote Wire Transmission Mechanism.

During the walk, the Remote Wire Transmission Mechanism was observed to bend and change its shape to follow the robot's movement, all without interrupting the robot's gait. This successfully demonstrated that the core concept is viable: a serially-connected decoupled joint system can function as an effective remote actuation mechanism for a mobile robot.

We also conducted a midair walking motion experiment, to evaluate the tracking performance of the foot trajectory. Swing phase and stance phase altenated, and stance phase trajectory followed virtual ground plane as planned.

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Bibtex

@inproceedings{hattori2025remotewire,
  title={{Design and Development of a Remotely Wire-Driven Walking Robot}},
  author={Takahiro Hattori and Kento Kawaharazuka and Kei Okada},
  booktitle={2025 IEEE-RAS 24th International Conference on Humanoid Robots (Humanoids)},
  year={2025},
}