A galvanometer mirror rotates in one direction when the galvanometer mirror is used. The generator includes an RF output stage configured to supply electrosurgical energy to tissue via at least one active electrode configured to apply electrosurgical energy to tissue; sensing circuitry configured to measure impedance of tissue; and a controller. A second idler is mounted to the frame and positioned further away from the drive tower than the first idler such that, as the chain moves toward the drive tower, the chain contacts the second idler before contacting the first idler.