An ablation instrument (e.g., an ablation balloon catheter system) includes an elongate catheter having a housing with a window formed therein. An energy emitter is coupled to the elongate catheter and is configured to deliver ablative energy. A controller is received within the window and is coupled to the energy emitter such that axial movement of the controller within the window is translated to axial movement of the energy emitter and rotation of the controller within the window is translated into rotation of the energy emitter. The instrument includes a motor that is at least partially disposed within the housing of the catheter; a first gear that is operatively connected to and driven by the motor; and a second gear that is coupled to the energy emitter and is driven by the first gear to cause rotation of the energy emitter, while allowing the energy emitter to move axially.