Joint Elasticity
The Joint Elasticity subnode is automatically added to a joint node when Elastic joint is chosen under Joint Elasticity. You use it to specify elastic and viscous data for the constrained degrees of freedom in a joint.
The contents of the Joint Elasticity settings adapt to the type of joint used.
For specifying elastic or viscous properties for the degrees of freedom which are not constrained by the joint, see Spring-Damper.
Coordinate System Selection
Select a coordinate system in which the elasticity and viscosity matrices are described. The default is Joint coordinate system, in which case the directions are the same as those specified for the joint itself.
Elastic Degrees of Freedom
Select the degrees of freedom that are to be treated as elastic. The default is all constrained degrees of freedom for this type of joint. If you deselect a certain degree of freedom, it reverts to being treated as rigidly constrained. The axis directions always refer to the directions of the joint coordinate system, irrespective of the settings in the Coordinate System Selection section.
Check boxes are shown only for the degrees of freedom which are constrained by the current joint type.
Spring
Specify the elastic properties of the joint. For joints constraining both translational and rotational degrees of freedom, select Translational-rotational coupling to enable input of stiffness terms coupling translation and rotation.
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In ku, enter the translational stiffness matrix.
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In kθ, enter the rotational stiffness matrix.
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For Translational-rotational coupling also enter the coupling matrices kuθ and kθu.
Viscous Damping
In this section, you specify the viscous damping properties of the joint. For joints constraining both translational and rotational degrees of freedom, select Translational-rotational coupling to enable input of viscous terms coupling translation and rotation.
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In cu, enter the translational damping matrix.
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In cθ, enter the rotational damping matrix.
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For Translational-rotational coupling also enter the coupling matrices cuθ and cθu.
The stiffness and damping matrices are always entered with the largest possible size (for example as 3x3 matrices in 3D). Values entered in directions that are not part of the degrees of freedom declared as elastic are ignored.
The rotational and coupling matrix inputs are not available for the Ball Joint, Slot Joint, Hinge Joint in 2D, and Reduced Slot Joint in 2D. These joint do not have any rotational constraints.
Elasticity in Joints
Location in User Interface
This node is automatically added when Elastic joint is selected in the parent joint node. It cannot be added or removed manually.