The holy grail of a self replicating 3D printer is the ability to print its own drive train. In the long term this may be possible with some form of multi-metal stintering system that can produce a stator layer by layer. However in the near term a more viable DIY option may be to use a piezoelectric “PCB Motor”.
The printing, routing or embedding of wires to form a circuit board track is now common place and with pick and place of components well on its well this could become feasible sooner than thought.
There was already an an entry on the RepRap wiki regarding PCB motors but I cant find any evidence that they have been successfully used.