Simcenter 3D Solutions How to model a gear coupler without joints in Simcenter 3D Motion with Body Coupler example

Simcenter 3D


Simcenter 3D Motion (or NX Motion) Body Coupler use case to model a kinematic coupler for rotations when using Bushings instead of Joints. A sample model is attached in version Simcenter 3D 2019.2 (NX 1872) with 3-Motion Bodies type.


The Gear Coupler in Motion allows rotation ratio between 2 Motion Bodies. This is available via selecting the corresponding Joints (Revolute or Cylindrical). You could also use a 2-3 Joint Coupler.
Though, in some use cases, there is no Joint for the Motion Bodies rather a bushing for modeling a bearing compliance. Motion Body Coupler is offering ability to directly define relations between the Bodies DOF. 

Below picture, a use case with 2 Motion Bodies. Both of them connected to the ground via Bushings allowing compliance. Coordinate systems (CSYS) of each body are oriented such as Z is the rotation axis.
The solution via Motion Body Coupler is with the type 3-Motion Bodies. For a constant ratio, Coupling method is 'Scales' and Measurements are set to Rotation for both couples. The rotation couples are both relative to the ground that is the 3rd body. By definition of this Motion object, the Action Body of the 1st couple has to be as well the  Base Body of the 2nd couple. Hence, there is no selection to make for those mentioned, since this common Body is the Ground. Thus, select one Motion body as Base for 1st Couple (see picture and tip), and the other Motion body as Action for the 2nd couple. Adjust the scale for both couples.

Tip: CSYS are defined and belongs respectively to each body. For quick definition of Base or Action, set orientation type to CSYS and simply select that CSYS once selection focus is on 'Select Motion Body'.

File "coupler_sample_motion1.sim" in attached zip file is in version Simcenter 3D 2019.2 (NX 1872).
A sample model is provided with different solutions such as you can compare with joints and gear coupler. Model geometry and Motion objects are all parametric depending on the gear respective diameters. The solution with Motion Body Coupler and bushings is that one active in picture below.


KB Article ID# KB000046591_EN_US



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