Even without a brain, metal-eating robots can search for food

This 'metal-eating' robot can follow a metal path without using a computer or needing a battery. By wiring the power-supplying units to the wheels on the opposite side, the robot autonomously navigates towards aluminum surfaces and away from hazards that block its energy source.

source https://www.sciencedaily.com/releases/2021/03/210331173716.htm