An apparatus including a first piston member rotatable about a first rotational axis and a rotor with a first chamber and pivotable about a second rotational axis. The first piston member extends across the first chamber. The rotor and first piston member are rotatable around the first rotational axis, and the rotor is pivotable about the second rotational axis to permit a relative pivoting motion between the rotor and the first piston member linked to the rotor rotating about the first rotational axis.