Chengnan Liu

I'm doing scales sim for animated snake.I'm using constraint to make scales follow the body and solve collisions. My scales are packed RBD, i have a position constraint to lock the scales to snake body, which work fine. And i need to set up another rotation constraint, which controls the scales to only rotate in one direction. I tried Spring Constraint Relationship, it seems no where to set up the angle? By default it lock the rotation to initial state.