Figure from ROBOT, Moravec, Oxford, 1998, Chapter 2: Caution! Robot Vehicle!, page 19
Hopkins Beast

                                                                                                                                       
1964-Two early versions of the ``Hopkins Beast'' feeding at a wall outlet
These machines wandered hallways guided by sonar and found sockets by feeling along walls. In subsequent work, the larger unit was given another layer containing a photocell circuit that allowed it to find contrasting wall plugs optically from a distance.

Courtesy of Johns Hopkins University Applied Physics Laboratory.