A robotic surgical instrument comprises a shaft, a first end effector element, an articulation connecting the first end effector element to a distal end of the shaft, the first end effector element being movable relative to the articulation, and a drive mechanism at a proximal end of the shaft. The drive mechanism comprises a first actuator connected to the first end effector element by a first pair of driving elements. The first pair of driving elements are configured such that a tension force applied by the first actuator to a first one of the first pair of driving elements causes the firstend effector element to move relative to the articulation in a first motion direction, and the tension force applied to a second one of the first pair of driving elements causes the first end effectorelement to move relative to the articulation in a second motion direction. The first one of the first pair of driving elements has a first path between the first actuator and the first end effector element, and the second one of the first pair of driving elements has a second path between the first actuator and the first end effector element. The first path has a lower tension force loss than thesecond path such that the first motion direction transfers a greater proportion of the tension force to the first end effector element than the second motion direction.