There's already a lot of clockwork and gearpunk mechanisms in Create, but so far, it sorely lacks a method to STORE rotational energy. There's an abundance of ways to move it from point A to point B, and make it faster/more powerful, but no way to store it. Therefore, I propose the following:

A 1x1x1 block, crafted with brass casing and lots of brass and string, called a Mainspring. This block would have shaft connections on 2 opposite sides, and when powered from either side, would store that rotational energy as tension, where one unit of tension equals 16 stress units over a period of 1 second. A Mainspring would be able to hold a maximum of 256 SU, which could be delivered for a maximum of 16 seconds, giving 16 SU/sec. This doesn't seem like much, but Mainsprings can be chained together to form more powerful Mainsprings, both horizontally and vertically, for a max of a 9-tall, 9-long and 5-wide spring, capable of storing 103680 SU and delivering a maximum of 1024 SU/sec over a period of about 100 sec. The amount of connections a Mainspring can have is never more than 2, one per side. A Mainspring can also never be comprised of an even number of blocks on a face. A Mainspring can also be configured to transmit power either when needed (to maintain a constant stress value in the network), when a redstone signal is applied, or when no winding force is applied. A Mainspring on a minecart contraption will power the minecart contraption.

Complimenting the portable power functionality of the Mainspring are two blocks. The Portable Shaft Interface, which acts like a constant-velocity joint that can move power to/from a moving structure, and the Slip Clutch. The Slip Clutch is a simpler version of the regular Clutch. Instead of stopping rotational transmission when powered, the Slip Clutch will stop rotational transmission when the stress value on the output side of the Slip Clutch exceeds the input stress value.

This has been suggested a lot. But I personally don't find any use for this, since all rotation energy (except furnace engine) is constant, so moving energy from point A to point B would be easier directly and not with springs.

This has been suggested a lot. But I personally don't find any use for this, since all rotation energy (except furnace engine) is constant, so moving energy from point A to point B would be easier directly and not with springs.

That's a fair point.