Cable-Driven and Tendon-Driven Actuation Explained

Moving the motor away from the joint it drives, the way a human forearm's muscles move fingers they're not attached to.

In cable- or tendon-driven actuation, the motor sits some distance from the joint it moves — often further up the limb — and transmits force through a cable or tendon routed through the structure, much like the tendons in a human forearm move fingers without a muscle in each finger.

Why designers do this

It moves mass away from the extremity being actuated, which matters a lot for hands and fingers where a motor at each joint would make the hand too heavy and bulky to look or move naturally. It also allows several joints to share fewer, more centrally located motors.

The tradeoffs

Cables stretch slightly under load and wear over time, which introduces control complexity and a maintenance item that a rigid gear train doesn't have. Routing also adds friction at every pulley or guide the cable passes through, cutting into the actuator's effective efficiency.