2. Reduce energy to approximately 400J in 2sec and this would translate to slighty under 720 degrees of rotation of the spring
3. The spring must be very light and maximum outer diameter would be about 3.5"

Does any have any experience with clock springs or know of a spring selection calculator that could help me? This is for a prototype of a pet project so an off-the-shelf item is necessary. I can vary the rotation and accelerations in the name of cost so long as they are ballpark. The 720 degress is only there because this is what I see as a minimum and I have been told that after 360 degrees a springs resistance increases rapidly due to the coils of the spring coming into contact with each other.

Any help on this would be greatly appreciated.