Detachable Wire Drive:
Reconfigurable Robot Architecture with Shared Actuators

Reconfigurable robots provide high adaptability to diverse tasks, but traditional centralized systems require dedicated heavy actuators for every module, accounting for 30–50% of total system weight and cost. To eliminate this redundancy, we present Detachable Wire Drive, a reconfigurable robotic architecture that consolidates heavy motors into a shared base unit and transmits actuation power to interchangeable limb morphologies via detachable wire paths.

The key innovation enabling this architecture is the Wire Detach Unit, a novel mechanism capable of physically disconnecting and reconnecting wire drive lines while preserving structural rigidity and power transmission capability.

Mechanical Design and Modular System

The Detachable Wire Drive system comprises a central motor-unit, interchangeable robotic arms, and specialized end-effectors, seamlessly interconnected through quick-coupling detacher mechanisms.

1. Wire Detach Unit: Housed in a modular sector-shaped shell, this unit features a winding pulley, a wire alignment pulley, and convex-concave axial features for torque engagement. Bundles of up to 6 units can be arranged in a circular configuration. Driven by high-strength 1 mm Vectran wires (1000 N tensile strength), each unit supports robust power transmission and quick physical coupling.

2. Motor-Unit and Motor-Arm Detacher: The central motor-unit integrates four quasi-direct-drive (QDD) motors providing up to 15 Nm peak torque and 312 N continuous wire tension. The motor-arm detacher uses a spring-loaded pin-and-latch mechanism with a rotating outer ring, enabling simple push-to-attach and rotate-and-pull-to-detach operations.

3. Interchangeable Arms: - 2-DOF Rigid Arm: Features shoulder and elbow joints actuated by three routed wires plus a Bowden cable for end-effector power, achieving a 10 kg payload capacity. - Continuum Arm: An underactuated hyper-redundant arm composed of seven spring-plate modules with flexible wrapping constraints, providing flexible multi-DOF bending and contracting capabilities.

1. End-Effectors and Arm-EE Detacher: An arm-end-effector detacher transmits power via a single integrated Wire Detach Unit to interchangeable tools, including a parallel-jaw gripper and a 3-fingered adaptive gripper.

Unified Control Framework

To manage reconfiguration across diverse morphologies without adding joint-embedded sensors, the system relies on a state machine and a kinematics-based joint controller driven entirely by motor encoder readings.

• State Transition Machine: Operates across four discrete states: FREE (unpowered motors for manual swapping), ATTACH (low-velocity rotation for convex-concave engagement), CALIBRATE (gravity-settled or limit-pushed wire zeroing), and CONTROL (closed-loop joint tracking).

• Joint Angle Estimator: Formulates joint angle estimation $\hat{\boldsymbol{q}}$ as an optimization problem minimizing wire displacement error $\| \boldsymbol{l} - \boldsymbol{l}_0 - \boldsymbol{H}(\hat{\boldsymbol{q}}) \|^2$ using motor encoders $\boldsymbol{\theta}$, the geometric kinematic model $\boldsymbol{H}(\boldsymbol{q})$ and zero wire position $\boldsymbol{l}_0$. Constant-curvature joint constraints are introduced to handle underactuation in continuum limbs.

• Joint Angle Follower: Computes required joint torque $\boldsymbol{\tau}_{ref}$ through PID control with gravity and spring elasticity compensation. The target torque is then mapped to target wire tensions $\boldsymbol{f}_{ref}$ via constrained quadratic optimization involving the Tendon Jacobian $\boldsymbol{G} = \frac{\partial \boldsymbol{H}}{\partial \boldsymbol{q}}$.

Experimental Validation

We conducted comprehensive physical experiments to evaluate component durability, mechanical reconfigurability, and control accuracy.

• Unit Mechanical Performance: Tensile cycling up to 450 N demonstrated zero structural damage in the Wire Detach Unit, with an average internal friction deviation of only $\pm 16\text{ N}$.

• Sequential Arm Attachment and Control: Both the 2-DOF rigid arm and the continuum arm were successfully attached, calibrated, controlled, and detached sequentially from the common motor-unit. Attachment required ~10 seconds for mechanical alignment, while detachment was executed in ~1 second. Closed-loop tracking verified seamless control continuity.

• End-Effector Swapping and Manipulation: The rigid arm demonstrated quick end-effector swapping (~1 s) between the parallel gripper and the multi-fingered adaptive gripper, achieving stable grasping and manipulation of diverse items including boxes, frames, and glue sticks.

• Tracking Accuracy: Evaluation across 225 spatial postures measured by AprilTag visual ground truth confirmed precise joint estimation and tracking, with an actual-to-estimated joint angle RMSE of 0.087 rad and actual-to-reference RMSE of 0.177 rad.

Bibtex

@inproceedings{hattori2026detachable,
  title={{Detachable Wire Drive: Reconfigurable Robot Architecture with Shared Actuators}},
  author={Takahiro Hattori and Kento Kawaharazuka and Kei Okada},
  booktitle={IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)},
  year={2026}
}

Contact

If you have any questions, please feel free to contact Takahiro Hattori (gmail: t-hattori @ jsk.imi.i.u-tokyo.ac.jp).