An electromechanical flywheel comprising: a top hung core assembly including a motor-generator stator surrounding a stator support; a motor generator rotor surrounding the stator; the stator defining an axis of rotation(x-x), having a field coil (482, 486) that encircles the axis of rotation, and having an armature coil that does not encircle the axis of rotation; the rotor and the stator forming a homopolar motor-generator; a flywheel mass encircling the rotor and coupled to the rotor for rotation with the rotor; an evacuable housing enclosing the rotor and the flywheel mass; characterised by: a central support pin coupled to the flywheel mass via a hub (418; 618) and located between the top-hung stator support and a first bearing carrier assembly for selectively supporting the flywheel mass, the first bearing carrier assembly being supported by a lower wall of the housing so as to selectively engage the support pin; and a second bearing carrier assembly located at a lower end of the top-hung stator support for selectively engaging the support pin; wherein the first bearing carrier assembly includes a first electromagnetic bearing for applying centering and levitating forces to the rotor. a top hung core assembly including a motor-generator stator surrounding a stator support; a motor generator rotor surrounding the stator; the stator defining an axis of rotation(x-x), having a field coil (482, 486) that encircles the axis of rotation, and having an armature coil that does not encircle the axis of rotation; defining an axis of rotation(x-x), having a field coil (482, 486) that encircles the axis of rotation, and having an armature coil that does not encircle the axis of rotation; the rotor and the stator forming a homopolar motor-generator; a flywheel mass encircling the rotor and coupled to the rotor for rotation with the rotor; encircling the rotor and coupled to the rotor for rotation with the rotor; an evacuable housing enclosing the rotor and the flywheel mass; characterised by: a central support pin coupled to the flywheel mass via a hub (418; 618) and located between the top-hung stator support and a first bearing carrier assembly for selectively supporting the flywheel mass, the first bearing carrier assembly being supported by a lower wall of the housing so as to selectively engage the support pin; and a second bearing carrier assembly located at a lower end of the top-hung stator support for selectively engaging the support pin; wherein the first bearing carrier assembly includes a first electromagnetic bearing for applying centering and levitating forces to the rotor. a central support pin coupled to the flywheel mass via a hub (418; 618) and located between the top-hung stator support and a first bearing carrier assembly for selectively supporting the flywheel mass, the first bearing carrier assembly being supported by a lower wall of the housing so as to selectively engage the support pin; and a second bearing carrier assembly located at a lower end of the top-hung stator support for selectively engaging the support pin; wherein the first bearing carrier assembly includes a first electromagnetic bearing for applying centering and levitating forces to the rotor.