CRAFT: A Tendon-Driven Hand with Hybrid Hard-Soft Compliance

Venue: RSS 2026 (Sydney, Jul 13–17) · Session: Robot & Sensor Design · paper #192 Authors: Leo Lin, Shivansh Patel, Jay Moon, Svetlana Lazebnik, Unnat Jain (University of Illinois Urbana-Champaign · UC Irvine) arXiv: 2603.12120 · program page

Summary compiled from the arXiv paper (v2); all numbers quoted from the paper. Trend context: RSS 2026 survey.

Figure 1: The CRAFT Hand. (A) Full anthropomorphic hand with forearm-mounted actuators; (B) holding chopsticks to show dexterity; (C) grasping a tennis ball at human-like scale; (D) a single finger built from rigid PLA links and soft TPU joints; (E) the hand passively conforming to a surface under contact, illustrating compliance concentrated at the joints.

Problem

Rigid dexterous hands break when contact concentrates at joints, while fully soft hands lose load capacity and have configuration-dependent, hard-to-repeat kinematics. Both failure modes stem from applying a uniform material choice across the whole hand, whereas impacts concentrate at joints and links must stay rigid to transmit load.

Method

CRAFT is a tendon-driven anthropomorphic hand with hybrid hard-soft compliance: soft material (TPU) at the joints where impacts and contact uncertainty concentrate, and rigid links (PLA) where load paths and geometric predictability matter. Coupled bidirectional rolling-contact PIP–DIP joints keep flexion on repeatable motion paths while absorbing impact. Fifteen motors are mounted off the fingers (in the forearm) and drive the hand through tendons, keeping the form factor compact (≈198 mm: 95 mm palm + 103 mm finger) and the fingers light (~800 g total). The full design costs under $600 and is released open-source with vision-based teleoperation and simulation integration; structural benchmarks compare against a same-servo LEAP hand.

Results

In structural tests CRAFT matches the rigid LEAP baseline in repeatability and pull-out strength while improving strength and endurance, maintaining a joint-angle tracking error < 0.01 rad over one hour of operation. In teleoperation it achieved 100% success on fragile objects and improved handling of low-friction items, and it covers all 33/33 grasps in the Feix taxonomy — full taxonomy coverage that competing designs (e.g. RUKA, ORCA) do not reach.

Significance

A durable, low-cost, open-source hand aimed at repeatable dexterous data collection and policy learning, feeding the hardware side of Review-Dexterous-Manipulation and Review-Tactile-VLA.

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