A vehicle comprising: a frame comprising a plurality of axles having a plurality of axes; a plurality of self-contained wheels , each wheel rotatably connected to a separate one of the plurality of axles , each wheel defining an inner volume and comprising: a frame mount positioned within the inner volume of the wheel and connected to the separate one of the plurality of axles , the frame mount having a portion extending below an axis of the axle ; a propulsion unit supported within the inner volume and below the axis by the portion of the frame mount extending below the axis, the propulsion unit drivingly coupled to the wheel ; an energy source supported within the inner volume and below the axis by the portion of the frame mount extending below the axis; wherein the center of gravity of the wheel is below the separate one of the plurality of axles to which the wheel is rotatably connected, and the center of gravity of the vehicle is below the plurality of axes, characterized in that the vehicle further comprises a control unit supported within the inner volume by the portion of the frame mount extending below the axis, wherein a first axis of a first one of the plurality of axles is substantially parallel to but not coaxial with a second axis of a second one of the plurality of axles . a frame comprising a plurality of axles having a plurality of axes; a plurality of self-contained wheels , each wheel rotatably connected to a separate one of the plurality of axles , each wheel defining an inner volume and comprising: a frame mount positioned within the inner volume of the wheel and connected to the separate one of the plurality of axles , the frame mount having a portion extending below an axis of the axle ; a propulsion unit supported within the inner volume and below the axis by the portion of the frame mount extending below the axis, the propulsion unit drivingly coupled to the wheel ; an energy source supported within the inner volume and below the axis by the portion of the frame mount extending below the axis; wherein the center of gravity of the wheel is below the separate one of the plurality of axles to which the wheel is rotatably connected, and the center of gravity of the vehicle is below the plurality of axes, a frame mount positioned within the inner volume of the wheel and connected to the separate one of the plurality of axles , the frame mount having a portion extending below an axis of the axle ; a propulsion unit supported within the inner volume and below the axis by the portion of the frame mount extending below the axis, the propulsion unit drivingly coupled to the wheel ; an energy source supported within the inner volume and below the axis by the portion of the frame mount extending below the axis; wherein the center of gravity of the wheel is below the separate one of the plurality of axles to which the wheel is rotatably connected, and the center of gravity of the vehicle is below the plurality of axes, characterized in that the vehicle further comprises a control unit supported within the inner volume by the portion of the frame mount extending below the axis, wherein a first axis of a first one of the plurality of axles is substantially parallel to but not coaxial with a second axis of a second one of the plurality of axles . <EOS>