You can create a coordinate system based on the Center of Mass. You have two options. You can set the origin at the Center of Mass, or align the principal axis toward or normal to the Center of Mass.
Create and Define a New Local Coordinate System with the Origin at the Center of Mass
Select the Coordinate Systems folder in the Outline.
Select the Coordinate System at Center of Mass option from the Coordinate Systems group in the Coordinate Systems Context tab.
Tip: Alternatively, when the Coordinate Systems folder or an existing coordinate system object is selected, right-click the object, and select > .
Selecting this option inserts a Non-Associative Coordinate System with the origin at the Center of Mass of all unsuppressed bodies and Point Mass objects. Distributed Mass objects are not currently considered in the Center of Mass calculation.
Setting the Principal Axis Using the Center of Mass
Select the Coordinate Systems folder in the Outline.
Select the Principal Axis Using Center of Mass option from the Coordinate Systems group in the Coordinate Systems Context tab.
This option is only active when the current selection consists 1 or 2 points (vertices or nodes).
When a single point is selected, the principal axis is set to Z and defined by a fixed vector that points from the selected point towards the center of mass of all unsuppressed bodies and point masses.
When two points are selected, the principal axis is set to Z and defined by a fixed vector that points normal to the plane formed by the selected points and the center of mass of all unsuppressed bodies and point masses.