We recover the energy in a maglev flywheel in the same way we
almost always convert mechanical energy to electrical energy:
with a 3 phase electric power generator/motor, also called an
alternator, with the rotor on the same shaft or otherwise
integrated with the flywheel. In cars with a combined
starter/generator, pumped-storage hydroelectric dams, maglev
flywheels, etc., 3-phase electric power goes into the coils of
the stator, and gets converted to mechanical torque to spin the
rotor. Later, the mechanical energy of the same spinning rotor
pushes a magnetic field around that pushes electrons through
those same coils of the stator, converting mechanical energy to
electrical energy that exits out the wires of the generator.
Such 3-phase motor/generator electric machines don't need
anything to touch the rotor. (Unlike some DC motors/generators
that require a "brush" to touch the rotor). In practice, most of
them do have something that touches the rotor -- a long input
shaft to carry mechanical energy into the