An apparatus including a drive having motors and at least two coaxial drive shafts; an arm connected to the drive, where the arm is configured to support at least one substrate thereon; and a transmission connected between the drive and the arm, where the transmission includes an eccentric bearing and a linkage, where the linkage is connected between a first one of the coaxial drive shafts and the arm, where the eccentric bearing is connected to a second one of the coaxial drive shafts, where the arm comprises an aperture, where the eccentric bearing is located in the aperture, and where the eccentric bearing is configured to contact the arm in the aperture.