Autodesk Inventor Angle Constraint

The Angle constraint permits three solutions within this constraint type. The solutions are Directed Angle, Undirected Angle, and Explicit Reference Vector.

The Directed Angle solution always applies the right-hand rule, meaning that the angle rotation will function in a counterclockwise direction.

The Undirected Angle allows either counterclockwise or clockwise direction, resolving situations where a component orientation will flip during a constraint drive or drag operation.

The Explicit Reference Vector solution allows for the definition of a z-axis vector by adding a third click to the selection. This option will reduce the tendency of an Angle constraint to flip to an alternate solution during a constraint drive or drag.

You will probably find that using edges rather than faces for angle constraints will provide more predictable results particularly when setting up constraints to be used in creating positional variations for animation or documentation purposes. The Explicit reference vector solution will provide you the most predictable results as it defines the angle completely with in the angle constraint, whereas the other solutions may be dependent upon other assembly constraints.