Add internal forces and torques

When you add standard joints , regardless of the method you use to add them, they are initially perfect. They have no internal forces, torques, or imposed motions. You can add internal forces and torques to each degree of freedom in the joint.

1. In the Dynamic Simulation browser , right-click the standard joint and select Properties.
2. On the Properties dialog box, click the DOF tab for the degree of freedom to which you want to add internal forces or torques.
   Note: There is a DOF tab for each degree of freedom in the joint. Each tab has a title consisting of "DOF," the number identifying that degree of freedom, and a T (for translational) or an R (for rotational) in parentheses.
3. On the DOF tab, click Edit joint force or Edit joint torque, depending upon whether this DOF is a translational or a rotational degree of freedom.
4. Click Enable joint force or Enable joint torque, depending upon whether this DOF is a translational or a rotational degree of freedom.
   Note: None of the other fields on this tab are available until you enable the force or torque.
5. For all of the remaining fields on this tab, determine the type of value you want to add and define the value.

   For these fields, you have the option of entering a constant value or a value that varies during the simulation . Do the following to select a type of value and define the variable:

   • Click the arrow at the right of the field.
   • From the menu, select Constant value if you want to enter a value that stays constant during the simulation or Input grapher if you want to enter a value that varies during the simulation.
   • If you select Constant value, enter that value in the text box and skip to step 6. If you select Input grapher, click the icon that the software has added to the text box.
   • Using the Input Grapher dialog box that appears when you click the icon, define the value you want for this force component.
6. In the Damping text box, enter a value for damping.

   Because this value depends upon the qualities of the lubricant you use between the two components, the lubricant manufacturer or a standard mechanics reference book should give you the value.

7. In the Free length text box in the Spring group, enter the length of the spring at which it exerts 0 force or torque.
8. In the Elastic Stiffness text box in the Spring group, enter the value for the Elastic stiffness of the spring.

   The software calculates the force or torque exerted by the spring by multiplying the stiffness by the difference between the distance between the two components minus the spring free length.

   Elastic stiffness depends on the material of the spring and the way it is made (for example, the number and radii of turns in the spring). Therefore the spring manufacturer or a standard mechanics reference book should give you the value.

9. In the Coefficient text box in the Dry friction group, enter the Coefficient of dry friction .

   This value depends upon the materials of the two components of the joint. The value of this coefficient for two components both made of steel is 0.15. A standard mechanics reference book should give you the value for the materials composing the two components in your joint.

   Note: For standard joints and 3D contact joints, velocity must exceed 0.01 meters per second for translational DOF and 0.01 radians per second for rotational DOF for tangential effort (friction) to be applied. When velocity is less than 0.01 or null, an approximation of friction is used. For small velocity values, we recommend that you define a 2D contact joint and set the friction coefficient for the face selections.
10. In the radius text box in the Dry friction group, enter the radius or distance of the torque from the center of rotation.

    Radius is available only for torque.

11. Click OK.

    The program applies the resulting force or toque in the joint.

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