The Selective Compliance

Contact is not uniform across a hand. Impacts concentrate at joints — where fingers bend, where objects first touch. Links between joints carry load but rarely absorb impact. Standard robotic hands are either rigid everywhere (strong but brittle at contact) or soft everywhere (compliant but weak under load).

CRAFT places soft material at joints and keeps links rigid. The hybrid matches the contact distribution: compliance where impacts happen, rigidity where load transfers. Rolling contact joint surfaces keep flexion on repeatable motion paths despite the soft material. Fifteen tendon-driven motors mount directly on the fingers, keeping the form factor compact.

The result: 33 out of 33 grasps in the Feix taxonomy — complete coverage of the standard grasp classification — with improved handling of fragile and low-friction objects compared to rigid alternatives. The full design costs under $600 and is open-source.

The through-claim: the design principle is not “make it soft” or “make it rigid” but “match the compliance to the contact distribution.” Uniform compliance wastes structural capacity. Uniform rigidity wastes the opportunity to absorb impact. The right answer requires knowing where the forces are — and in a hand, the answer is anatomically obvious: joints take impact, links take load. The principle generalizes: any mechanical system that interacts with variable environments should distribute compliance according to the spatial distribution of contact uncertainty, not uniformly.