A substrate transport apparatus including a frame, a drive section connected to the frame and including at least one independently controllable motor, at least two substrate transport arms connected to the frame and comprising arm links arranged for supporting and transporting substrates, and a mechanical motion switch coupled to the at least one independently controllable motor and the at least two substrate transport arms for effecting the extension and retraction of one of the at least two substrate transport arms while the other one of the at least two substrate transport arms remains in a substantially retracted configuration.