A graphic recorder has a string drive for the recording pen, the string being secured to and passing around a pulley mounted to a clutch hub. A potentiometer is also mounted to the clutch hub. A servomotor drives a bull gear having a clutch ring affixed thereto. The clutch ring drives the hub through a pair of "O" -rings, frictionally fit therebetween, the torque capacity being adjustable by an axially adjustable retainer.
