 During motion of the train, the frame-suspended motors constantly move relative to the axles, which requires some kind of flexible drive to accommodate this motion.On early ER2s this was achieved by means of a jaw coupling between the motor shaft and the intermediate drive shaft, but on later trains, rubber rag joints were used instead.The first such joint was fitted to an ER2 in 1964 as an experiment; in late 1965, five more prototypes with rubber couplings were built, and from 1966 onward these became standard on all new ER2s.