Abstract: A control system controlling the movements of a pneumatic percussion tool for breaking crust away from anode butts in an electrolysis cell. The system comprises a control arm extending through first and second plates connected to respective first and second valve stems. In a preferred embodiment, the first valve stem operates a hydraulic scissors jack for extending and retracting the tool, and the second valve stem operates a hydraulic rotator motor for radially rotating a mast supporting the tool. A preferred system also comprises a pneumatic control valve connected to the control arm for positioning and energizing the percussion tool.