An apparatus and method are described for utilizing internally generated angular momentum for supplementing the propulsion of a mobile spherical vehicle capable of motion by rolling over terrain, thereby enabling such vehicles to climb steeper inclines and overcome larger obstacles. Torque generated by counter-rotating gyroscopes was used to supplement gravity generated torque produced by a pendulum drive propulsion system. Precession torque may be generated along a desired axis by changing the angular momentum of the gyroscopes while leaving its magnitude unaffected.