I remember a fly wheel battery concept from the early 90's. Spin light weight tiny flywheels on magnetic bearings in a near vacuum and take advantage of the fa

I remember a fly wheel battery concept from the early 90's. Spin light weight tiny flywheels on magnetic bearings in a near vacuum and take advantage of the fact that energy storage is linear with mass, but the square of velocity. Put the flywheels in opposing directions and spin them really fast. If I remember correctly, there still was a bit of a safety problem: my understanding was if one of the tiny flywheels fell off the magnetic bearing it would rip through 9 feet of steel. Not great for a battery in a vehicle. However I don't see why you can't tune the amount of energy you decide to store, and the amount of safety barriers to handle catastrophic failure. Makes me wonder if there is anyway to do something akin to a MEMS flywheel.