A pushable frame includes a plurality of wheels to allow maneuvering due to a rolling motion of one or more wheels. A power generator is operatively connected to the wheels such that kinetic motion of the wheels caused by the frame being pushed or pulled by the user is converted into electric energy. A speed regulator is operatively connected with the plurality of wheels and the power generator such that a rolling speed of one or more wheels is controlled based on a rolling condition of the one or more wheels.
