Douglas Irving Repetto’s Giant Painting Machine (Milano) is pretty much just that. Created with found objects and simple machines and motors, it is essentially a mechanical artist. It operates independently from the inside of a temporary four-walled room with walls of mylar, so the paintings can be viewed from the outside while they are being painted.
The machine works by constantly moving in multiple directions at once as it drags a paintbrush across the canvas. It stops and changes direction at the edges, so each painting is random and unique. Its path can be determined by itself or a person.
The Giant Painting Machine was commissioned for a jewelry fair, and also ran for four days during Fashion Week 2006. During the jewelry fair, four hand shaped metal detectors were used to determine the direction of the moving motor. When jewelry was placed on each hand, the machine would switch directions and keep painting, thus being responsive.