Abstract: Systems and methods are provided for automatically driving and maintaining oscillation of an assembly system including a mass and a bias member (which may also be referred to as a spring or elastomeric member) at or near a resonant frequency of the assembly system. In one example, apparatus for maintaining oscillation of a moveable subassembly including a mass and a bias comprises a controller operable to receive a signal from a sensor associated with a position or motion of the subassembly, and generate a drive signal for driving the subassembly in response to the received signal from the sensor. In this manner, the controller may monitor the motion of the subassembly and adjust or modulate the driving force over time to maintain the subassembly at or near a resonant frequency. Further, in one example, the subassembly includes a resonant engine comprising a movable mirror of an illumination device.