Powering an electrocautery surgical instrument

A robotic surgical instrument comprising a shaft, an electrocautery end effector powered by an electrocautery element, and an articulation connecting the electrocautery end effector to the shaft. The articulation comprises: a first joint driveable by a first pair of driving elements which permits the electrocautery end effector to rotate about a first axis transverse to a longitudinal axis of the shaft; and a second joint driveable by a second pair of driving elements which permits the electrocautery end effector to rotate about a second axis transverse to the first axis. The electrocautery element is constrained to move around the first axis and constrained to wrap at least one full revolution around the second axis. The path of the electrocautery element between the shaft and the second joint symmetrically opposes the path of a first one of the second pair of driving elements between the shaft and the second joint.