Methods of rotational energy harvesting and storage

[physea]

Hello!

What are the available methods to harvest rotational energy?
I was thinking to put a turbine on the shaft and compress air, but the air will get cold and the energy will be lost.
I was thinking to put an electric generator, which is ok but it needs a battery.
I was thinking to use torsional springs.
I was thinking to use a flywheel, but it must have quite large mass to store the energy.

Are there any other methods to harvest and store the rotational energy of a shaft?
Which would be the most efficient?
Are there any products/systems sold? (apart from the electromagnetic generator).

Thanks!

 

[Dr.D]

There is a device called a pulsed alternator that is used to power rail guns. It allows the accumulation of rotational kinetic energy over an extended time period with a quick conversion to a high-current electrical pulse when the energy is dumped.