Employed on the lowest layer of the A.s.a. H. hierarchy Arduinos are adequate for some light preprocessing, postprocessing (like PID control), and for simple reflexes. (Raspberry Pis are suitable for somewhat heavier computing tasks. Arduinos can be plugged into them and the Raspberry Pis used as a next higher layer. See, for example, Beginning Robotics with Raspberry Pi and Arduino, Jeff Cicolani, Apress, 2018) The Arduinos can then also do analog to digital conversions for the Raspberry Pis.