Part Gaps and Overlaps

Before creating a flexible body from rigid group, ensure that there are no gaps or overlapping parts to avoid under constrained parts, incorrect model frequencies, or failure to create the flexible body.

Resolve Gaps Between Parts

If parts within the rigid group have gaps, they may behave as if they are not fully constrained and appear “flop around” in the animation.

By default, when the flex body is called up, parts are bonded based on structural contact bonds. These bonds are detected based on the tolerance settings found under the structure contact Find Options. If the gaps exceed the specified tolerances, no bond is detected and the parts are underconstrained.

You can adjust the tolerance settings to better find bonds at the gaps; however, note that this will result in a new structural contact find and any joints connecting the rigid group to the rest of the model will be deleted and will need to be redefined.

  1. From the Structure tab, select the Contacts tool.
    Tip: To find and open a tool, press Ctrl+F. For more information, see Find and Search for Tools.
  2. Click OK to accept the compatibility message.
  3. Click OK to perform a new contact search.
  4. On the guide bar, select Find Options.
  5. Increase the Gap Tolerance.
  6. Click Find and ensure that a contact is detected at the gap. If not, increase the gap tolerance and repeat until a gap is found.
  7. From the Motion tab, select the Joints tool.


  8. Set the filter to All Parts, and click on Find.
  9. Re-create joints that were lost, that is, any joint that was previously connecting the rigid group to the rest of the model.

Find Part Overlaps

If parts within the rigid group have overlaps, the creation of the flexible body can fail.

  1. You can do one of the following:
    Option A Option B
    1. From the Motion tab, select the Contacts tool.

      Tip: To find and open a tool, press Ctrl+F. For more information, see Find and Search for Tools.

    2. Select the parts to check.

    3. On the guide bar, select Find Initial Intersections.

    4. At the top of the modeling window, a microdialog appears, indicating the number of intersections. Click the arrows to visually step through interfering regions.

    1. In the Run Status window for a failed flex body creation run, click the run name and click View Now.

    2. A message appears, indicating the parts with overlaps.
  2. Now you can modify the parts to avoid overlaps.