Could it be something simple like a combination of measures designed to allow it to rotate for an extremely long time: - Vacuum enclosure (remove air resistance

Could it be something simple like a combination of measures designed to allow it to rotate for an extremely long time: - Vacuum enclosure (remove air resistance) - Perfectly balanced wheel (reduce bearing wear) - Excellent quality bearing / lubrication - Small electric motor & battery to provide enough force to allow for continuity once started externally