According to various embodiments, there is provided a robot including: a spherical shell; a cart in the spherical shell, the cart including a plurality of wheels rotatable to move the cart along an inner surface of the spherical shell; a sensor coupled to the cart, the sensor configured to provide an inertial measurement of the cart; a motion encoder configured to measure an angular velocity of each wheel of the plurality of wheels; and a localizer configured to determine a location of the robot, based on the angular velocities of the plurality of wheels and the inertial measurement of the cart.