Angle constraint Flipping 180 degrees in Inventor

Question

Angle constraint keeps flipping 180 degrees in Inventor.

Answer

Here are some useful tips for when your angle constraint keeps flipping 180 degrees (either when using positional representations or driving constraints in your assembly);

Generally a more robust solution can be obtained by combining the following;

1. Try to not either switch or drive a constraint to (or past) zero degrees in your constraints. If you are switching between 0 degrees and 90 degrees on your angle constraint, then create a work plane offset by 20 degrees to the original and constrain to this, so that now you are switching between 20 degrees and 110 degrees. Going to (or across) zero degrees can sometimes confuse Inventor.
2. Use the explicit vector angle constraint type for angles you are driving or overriding with a positional representation (see shot below). Use an edge instead of a face for specifying this as it is more robust.
3. Occasionally, if the above do not work, you can persuade Inventor not to flip the direction by using an ‘intermediate’ positional representation, that leads Inventor in the right direction so that it doesn’t have to make such a large jump when switching constraints. E.g. if you were going from 20 to 160 degrees, try going via a positional rep. of 90 degrees.