Torsion Springs

Use the Add/Edit Torsion Springs tool to apply a rotational spring-damper force about the pivot axis for two parts.

Location: Motion ribbon, Forces group, Springs icon

Click the satellite icon that appears when you hover over the Springs icon to view a list of all coil springs or torsion springs in your model.

Add/Edit Torsion Springs

Position the torsion spring, then define the preload torque, torsional stiffness, and torsional damping rates.

  1. Select the Add/Edit Torsion Springs tool on the Springs icon.

  2. Select a hole, location on a surface, or pin where you want to apply a torsion spring.
    • For pins, the pin axis defines the pivot axis.
    • For holes and surfaces, click once to place the pivot point for the torsion spring, and a second time to finish connecting it. (You can select the same hole or surface twice, in which case the second click is interpreted as reacting against ground.) Hold down the Ctrl key to deselect a feature.
  3. Enter the torsional stiffness (KT) and torsional damping (CT) rates, or enter zeros to disable them.

  4. Enter a magnitude for the preload torque in the microdialog. Click the +/- icon to reverse the direction of the preload torque in the spring.
  5. Optional: Enter the free angle (θ f) of the spring in its resting state rather than the preload torque. (The preload torque is automatically calculated based on the free angle and the torsional stiffness.)
  6. Optional: Enter the installed angle (θ i) of the spring, or reposition with the graphical endpoint manipulator. The manipulator includes a snapping feature that helps you easily align the torsion spring arms to an edge in your model. As you drag the manipulator over an edge, the orientation of the x-axis snaps into alignment with the edge, and positive (or negative) direction is based on proximity to the edge.
  7. Right-click and mouse through the check mark to exit, or double-right-click.
  • If you want a damper rather than a spring, change the spring Type in the microdialog and select Damper.
  • Color attributes for the spring can be set using the Property Editor.
  • Suppress/Unsuppress a torsion spring to understand its effect on your model. On the spring, right-click and select Suppress. From the Model Browser or Table, right-click and select Unsuppress.

Nonlinear Spring Dampers

Nonlinear stiffness and damping characteristics can be entered for spring dampers for motion analysis.

Using the Profile Editor you can import test data and then edit graphically or through cells in the table. Three interpolation types are available (Akima, Cubic, Linear) and if desired, you can visualize the derivative and extrapolation tails.
  1. For a nonlinear spring damper, deselect the check boxes for the spring stiffness (K) and damping (C) rates as desired.

  2. Click the table icon to open the Profile Editor. (The stiffness curve example below is for a coil spring. Similar profiles are available for dampers and torsion springs.)

    Figure 1. Example of a Coil Spring Stiffness Curve
  3. If you have test data in the expected .csv format, you can drag and drop to import it. (Save a sample file to view the expected format.)
  4. Inspect your data and make changes as needed. Use the options in the Visualization section to help understand how the data is being interpolated/extrapolated.
  5. Edit the data in the table, or use the buttons to remove or reflect the curve as desired.
  • Sometimes it is easier to remove the left side data, work on the right side data, and then use the Reflect to Left Side button to reflect your data.
  • Clicking the Replace with Linear Equivalent button will use the Stiffness value (shown greyed out on the microdialog) and display it as an editable curve in the graphical area of the Profile Editor.
  • The Derivative button in the legend is helpful for the Akima and Cubic interpolation methods because it helps you visualize discontinuities in your data. Introducing more points may help you smooth the profile.
  • The Provide Signals to Plant option is available for spring dampers in motion, but is disabled by default. It can be found in the Property Editor and when enabled, the motion Export operation will include the necessary plant signals in the .mdl file for use in MotionView, MotionSolve, and Altair Activate.
  • See the Profile Editor for an explanation of the buttons and visualization options.

Microdialog Options

Use the options in the primary microdialog to edit the behavior of a torsion spring. Click the to view advanced options.

Figure 2. Torsion Springs Microdialog
The default type is spring damper. You can also select just the spring, or just the damper. It is advisable to include some damping.
Set Torsional Stiffness
Enter a positive value for the torsional stiffness rate of the spring. (To have no torsional stiffness, set the spring Type to Damper.)
Set Torsional Damping
Enter a positive value for the torsional damping rate of the spring.
Reverse Preload Torque
Reverse the direction of the preload torque in the spring.
Set Preload Torque
Enter a magnitude for the preload torque in the spring.
Set Free Angle (θ f)
The free angle is the angle of the spring in its resting state. If you enter a preload torque, the free angle is automatically calculated from the torsional stiffness.
Installed Angle (θ i)
The angle of the spring as installed in the mechanism.
Flip to the Other Side
Flip the torsion spring to the other end of the hole or pin. This only changes the appearance of the spring.
Align to Global X, Y, or Z Axis
Align the pivot axis to the global X, Y, or Z direction. Not applicable for holes or pins.
Align Normal to Face
Align the pivot axis to be perpendicular to the first surface. Not applicable for holes or pins.
Move Torsion Spring
Open the Move tool to place the spring at a distance. Not applicable for holes or pins.

Torsion Spring Properties

Refine the behavior and appearance of torsion springs using the properties available in the Property Editor (F3)

Restrain Centerline
When enabled, the pivot axis of the torsion spring is restrained to essentially create a cylindrical joint between the parts.

Springs Table

The Springs table lists all of the coil and torsion springs in your model and allows you to edit various attributes. Click the Torsion tab to view torsion springs.

Location: Springs tool, satellite icon

Figure 3. Springs Table
To Do this
Rename a spring Select the cell in the table and then click again to make the field editable.
Change a value Select the cell in the table and then click again to make the field editable. Some fields are for display only.
Sort a column Click the column header. Click repeatedly to toggle between ascending and descending order.
Add or remove columns Right-click on a column header.


To Do this
Deselect a feature Hold down the Ctrl key and left-click a selected (red) feature.
Exit the tool Right-click and mouse through the check mark to exit, or double-right-click.