A motor-driven articulated haptic interface arm includes: a frame an arm linked to the frame and rotationally mobile about an axis and a motor, which delivers at least one torque about the axis countering at least one part of forces applied to the arm by its environment. A main transmission transmits the torque to the arm and includes a capstan-type cable reducer, and an auxiliary transmission transmits the torque to the arm. The auxiliary transmission is capable of taking at least two states: an inactive state, when the forces applied to the arm by its environment are below a predetermined threshold, in which the auxiliary transmission transmits no torque to the arm and an active state when the forces applied to the arm by its environment are higher than a predetermined threshold, in which the main transmission transmits no torque to the arm.
