A data storage disk cartridge library system includes a rack having an array of bays, at least some housing disk media cartridges and/or media drives, and a pair of horizontal and vertical guide rails bordering each bay. A media transport robot includes fixed-position drive wheels at each corner for driving the robot along the guide rails, and pivoting guide wheels corresponding to each drive wheel for guiding the drive wheel horizontally along a horizontal guide rail and vertically along a vertical guide rail. With each guide wheel coupled with a horizontal guide rail the robot can travel horizontally on the rack, and with each guide wheel coupled with a vertical guide rail the robot can travel vertically on the rack. Electrical power can be supplied to the robot via the guide rails, and gear portions of the wheels mechanically interface with a mechanical portion of the guide rails.