A drive assembly for a centrifugal processing system is provided for rotating the yoke assembly (36) about a first axis at a first angular velocity and rotating the chamber assembly (30) coaxially with the yoke assembly at a second angular velocity A drive motor (54) is provided for rotating the yoke assembly at the first angular velocity and simultaneously rotating the chamber assembly at the second angular velocity by a sun gear (66) mounted to the chamber assembly for rotation about the first axis and a planetary gear (64) mounted to the yoke assembly that is operatively connected to the sun gear such as to impart rotation to the sun gear as it orbits thereabout upon rotation of the yoke assembly.