Inventors have been more successful with robots that can help with housework. The Roomba, for example, is a robotic vacuum cleaner. Made of lightweight plastic, it is low and round, with wheels. Before it begins cleaning a room, Roomba first moves all around it to "learn" about the shape of the room and the furnture in it. Then it starts vacuuming, avoiding the walls and furniture. When it begins to run out of power, it returns to a base to recharge. It does all of this without any human dircetion. With a price tag of only about $200, the Roomba has sold well about 2million Roombas were sold in its first four years. The same company that makes Roomba has now developed a floor-washing robot called the Scooba.