A surgical instrument includes an end effector, a handle assembly, and a knife drive assembly. The end effector includes a pair of jaws, a knife, and an RF electrode assembly. The knife actuates between a pre-fired position and a fired position. An arm of the handle assembly is configured to pivot the second jaw between the open position and the closed position. The knife drive assembly includes an input assembly, a rotary assembly, and an output assembly. The input assembly travels a first proximal distance to rotate the rotary assembly. The rotary assembly rotates in response to travel of the input assembly along the first proximal distance to drive the output assembly a first distal distance to thereby actuate the knife from the pre-fired position toward the fired position. The first distal distance is greater than the first proximal distance.
