at least two axially collinear drive wheels;

a robot body mounted on said drive wheels;

a control system on the robot body utilizing, at least in part, a ded-reckoning navigational system;

a cart attaching mechanism on said robot body for coupling a cart to said robotic vehicle; and

a positioning error reducing system for reducing accumulated error in the ded-reckoning navigational system, said positioning error reducing system including at least a calibration system having at least one proximity sensor mounted on the robot body, said control system coupled to said at least one proximity sensor for adjusting a calculated robotic position, wherein the control system sets up virtual checkpoints along known fixed features of a predetermined length, takes a statistically significant number of proximity readings along an adjacent fixed feature, removes statistically anomalous readings and automatically adjusts the calculated robotic position based upon statistically significant readings.