Microsoft KB Archive/174415

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HOWTO: Animate & Apply an Attraction Force to a Constraint

PSS ID Number: Q174415 Article last modified on 09-29-1997

IRIX:3.7; WINNT:3.7

IRIX winnt


The information in this article applies to:

  • Softimage 3D for IRIX, version 3.7
  • == Softimage 3D for Windows NT, version 3.7 ==


By default, when you apply a constraint to an object it sticks to the object that you constrained it to. If your object is constrained to two objects, the constrained object is positioned centrally between the two objects by default.

The DopeSheet allows you to Activate/Deactivate a constraint, which causes the constrained object to stick to the object that has the active constraint. If both constraints are active at the same time, the constrained object positions itself between the two.

In order to position the constrained object closer to one of the two objects that it is constrained to, you must constrain it to a third object. The location of the third object determines which of the two constraints will have the most influence. This can be achieved by using the 3-point constraint or by using three separate position constraints from the same source to three different destinations, as detailed below.


  1. Constrain a sphere to two nulls.

  2. Select the constrained sphere and open the DopeSheet. The Object track that is displayed in the DopeSheet represents the constraint for the sphere.

  3. Left-click in the gray box at the left of the green bar; CNSPOS appears, which represents the constraints.

  4. To see all the constraint tracks, click a second time in the box where CNSPOS is indicated. The track expands, showing the two nulls to which the sphere is constrained.

  5. The vertical tracks at the right of the green bars correspond to individual frames on your active timeline. All constraints are active by default. Therefore, to control the active state of your constraints over time, select a track area for the amount of time you want to deactivate your constraint.

  6. Left-click on the track for Null1 and drag your mouse horizontally for the desired length of time. You can modify your selection on either side of the box afterwards. A white box appears which represents the selected frames.

  7. To deactivate the constraint for the selected number of frames, click DEACT in the title bar of the DopeSheet window. The deactivated area should dim. The sphere’s position constraint to null1 is active during the selected frames.

    You can use the same selection process for re-activating the constraint for any frame selection but click ACTIV.

  8. To determine the frames where the sphere is not constrained to Null2, you must repeat the same procedure for Null1. If you do not offset your track selections between Null1 and Null2, both constraints will be deactivated at that time.

  9. Add a position constraint to a third null. This null is used as the damping value for the constraint. Positioning the third null closer to one of the other two nulls recalculates the average point and as a result offsets your constraint.

  10. To animate the force of the attraction that one constraint has over the other, animate the third constrained object in translation between the two master constraints.


If you have any questions concerning the information contained in this article, contact by e-mail. ====================================================================== Keywords : si si3d si3dconst Version : IRIX:3.7; WINNT:3.7 Platform : IRIX winnt Issue type : kbhowto ============================================================================= Copyright Microsoft Corporation 1997.