CAD-Line | Mass Properties tab

Terminology: Solids, CAD-Line, Kinetostatic Force


To calculate Forces correctly, it is important that the Mass Properties of each Part are correct.

Use the  in the CAD-Line dialog-box | Mass Properties tab to:

Import mass properties from the active SOLIDWORKS document
Use the 'User Mass Properties' separator to specify other Mass Properties.

Mass Properties include:

Mass [kg]
Position of the Centre-of-Mass [mm]
Moment-of-Inertia (at it Centre-of-Mass), or
OR defined as a Mass[kg] and Radius-of-Gyration[mm] = [kg.m2]

All mass properties are co-planar with the Mechanism Plane.


Note: The mass-properties of Profile and Extrusions elements are also added to the total mass-properties in this dialog.


Mass Properties tab

Dialog-13.2-CADLine-Masstab

Separators:

tog_minus User Mass Properties 

Dialog-13.2-CADLine-Mass-User

Mass : [kg]

Centre-of-Mass X–axis [mm] relative to the Origin CAD-Line's coordinate-system.

Centre-of-Mass: Y–axis [mm] relative to the Origin and CAD-Line coordinate-system.

Radius-of-Gyration* [mm]

or

Moment-of-Inertia* [kg.m2] [NOT kg.mm2 ]
Units of 'kilogram.metres2.'

Notes: *

If you do not enter a Radius of Gyration OR a Moment of Inertia, then the Mass is a 'Point -Mass' at a distance defined by the X and Y-axis coordinate values.

If you do enter a Radius of Gyration or Moment of Inertia, then the Point-Mass becomes a mass with a real mass distribution in the body.

The same Mass applies at the X and Y-axis coordinates, but now the body has an Inertia about the centre of Mass and a corresponding Radius of Gyration.


MechDesigner uses the Parallel Axis Theorem to calculate the Moment-of-Inertia about the Part's Origin.

After you have entered the mass of the Part, then:

If you enter 'Moment-of-Inertia', then MechDesigner calculates the 'Radius-of-Gyration'

If you enter 'Radius-of-Gyration', then MechDesigner calculates the 'Moment-of-Inertia'

Radius of Gyratio2

tog_minus SolidWorks Mass Properties 

Dialog-13.2-CADLine-Mass-SW

Usually, the Mass-Properties will show after you import a SolidWorks document. However, you may want to update the Mass Properties to those of the active document in SolidWorks.

8s Import Mass Properties button

MechDesigner imports the Mass Properties of the active document in SolidWorks, as Read-Only values:

Mass : [Units: kg]
Centre-of-Mass : X-axis: [mm]

Coordinates along the X–axis of the CAD-Line.

Centre-of-Mass Y-axis [mm]

Coordinates along the Y–axis of the CAD-Line.

Moment-of-Inertia (CoG) [kg.m2]

MechDesigner uses the Parallel Axis Theorem to calculate the Moment-of-Inertia about the Part's Origin.


9s Clear SolidWorks Mass Properties button

When you do not want to use the Mass Properties of the active document in SolidWorks , then:

1.Click the button 9s to set the Mass-Properties to zero[0].

tog_minus        Total Mass Properties 

Dialog-13.2-CADLine-Mass-Total

The Total Mass Properties includes masses from other CAD-Lines in addition to those defined for this CAD-Line.

Parallel-Axis Theorem
Inertia about Part's Origin = Inertia about Centre-of-Mass  + Mass × (Distance to Part's Origin)2

Relationship between Moment-of-Inertia and Radius of Gyration
Moment-of-Inertia(about Center-of-Mass) = Mass×(Radius-of-Gyration)2

Total Mass of Part =

Mass of Extrusion + Mass from SolidWorks Mass Properties + User Mass Properties + Total mass of other CAD-Lines in the same Part.

Total Moment-of-Inertia about the Part's Origin =

Inertia of Extrusion + Inertia from SolidWorks Mass Properties + User Inertia Properties + Total Inertia of other CAD-Lines in the same Part.

 

Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd