I'm modelling a part that requires what we call a "differential pitch".  Imagine a gear that the teeth aren't equally spaced around the OD.  I want to create a circular pattern with 20 instances of a feature, but I want to vary the angle between each instance.  For example, I want 18, then 17, 19, 20, 16 etc.  How can I accomplish this in Solidworks?  I've looked at Sketch driven and curve driven, but these don't seem to work.  Thanks,