A surgical tool includes a drive housing, a drive input and input shaft rotatably mounted to the drive housing, and a drive assembly mounted to the input shaft and including an upper capstan rotatably mounted to the input shaft with a first one-way bearing, and a lower capstan rotatably mounted to the input shaft with a second one-way bearing. First and second drive cables are coupled to the upper and lower capstans and extend to an end effector of the surgical tool. Rotating the input shaft in a first angular direction rotationally disengages the lower capstan from the input shaft and drives the upper capstan in the first angular direction, and rotating the input shaft in a second angular direction rotationally disengages the upper capstan from the input shaft and drives the lower capstan in the second angular direction.
