   Rotational Springs
  What is a good model for a rotational spring..Is there such thing as an orientational spring?   
  I'm not sure what you mean by orientational spring. For simple springs I've used Hooke's Law on its own, is that what you are referring to?Did you google for rotational spring? I found many formula and examples.   ;  In 3D, how can we define the behavior of the rotational spring.As for an orientation spring, well visualize yourself being in a cockpit (an advanced one that I will just describe). If you roll along the axis of sight (the forward vector) the Moments will push you back to your initial orientation. Samewise, if you yoke pack your cockpit, the orientational spring will revert you back to where you were.I have actually seen the orientational spring only in my dream! My mind simulated it or something... Weird   ;  Normal springs work by applying a force per unit displacement, ie "F = -cD",  F = Force, c = spring stiffness, D = Displacement.The same idea could be applied in theory for spinny springs, so the formula turns into:"T = -cA",  T = Torque, c = spring stiffness, A = Angle offset.Although measuring the angle might get a bit tricky when it spins more than 360 degrees as it would loop back round again.  Erm, you're on your own with that one :)   