Editing Constraint Properties

In the Vortex® Studio Editor, you can define how the attached parts will react in the simulation environment by defining the constraint's properties:

editor_assemb_cns.png
Note
In order to verify proper functioning of a constraint after it has been modified, you should run the simulation to see the behavior of the relationship between the part and the constraint in motion. When a simulation is running, the physics engine is activated and the parts and constraints behave accordingly based on the environmental settings.

Basic Constraint Properties

  1. Select the constraint from the Explorer panel of the Assembly editor.

    The constraint properties appear in the Property panel. On the Attachments tab you can see that Vortex Studio has already calculated and is displaying the offsets. For more about offsets, see Customizing Offsets.

  2. You can modify the following values:

    • Position
    • Primary Axis
    • Secondary Axis
  3. Click the Orthonormalize button to recalculate the axis dimensions, based on the primary axis being dominant. The secondary axis direction will be set orthogonal to the primary axis.

    The primary axis' dimensions will be normalized, and the orthonormal vector nearest to the specified secondary axis (and in the same plane) will be assigned to the secondary axis.

  4. If you click the Orthonormalize button and Vortex cannot perform the computation (for example if you enter [0,0,0]), the following message appears:

    editor_assemb_cns_ortho_warning.png

Setting Limits on the Constraint

There are two really important things to consider when setting constraint limits:

  • By default, a new constraint does not have limits, so you may need to set the lower and upper limit properties to ensure the correct behavior.
  • You must make sure you explicitly activate limits for the constraint; otherwise, any limit values you set will be ignored.

Follow this procedure to set limits on a constraint:

  1. Select the constraint in the Explorer panel of the Part editor.

  2. In the Property panel, select the Controlled Axes tab.

  3. Enable the limits by selecting the box next to Limits.

  4. Set the values under Lower Limits and the Upper Limits sections (you may need to scroll down to find them).

  5. Depending on the mode of your controllable coordinate, you may also need to set one of the following values:

    • In Motorized mode, edit the Desired Velocity and Loss values on the Motor tab.
    • In Lock mode, edit the Damping, Position, and Stiffness values on the Lock tab.
  6. If the Control is set to Lock, you can enable the Plastic parameter to enable deformation.

Setting the plastic option results in the part, when the maximum force is reached, to stay in the position that the force applied to the part, even when the force is removed.

Changing the Mode of the Controllable Coordinates

You can modify the mode of a controllable degree of freedom before and during simulation (see Working with Constraints for information about the controllable coordinate constraints).

The type and number of Controlled Axes will depend on the constraint and its numbers of degrees of freedom (DoF). For example, aHingewill only have an Angular controllable DoF, a Prismatic constraint will have a Linear controllable DoF, a Cylindrical will have a Linear and Angular DoF (see images below).

Controllable Axes for a Hinge Controllable Axes for a Prismatic Controllable Axes for a Cylindrical
  1. Select the constraint in the Explorer panel.

  2. In the Properties panel, select the Controlled Axes tab.

  3. Under the Angular or Linear section, choose one of the options from the Control drop-down list.
    By default the Control is set to Free and the values associates with the other modes are grayed out. The grayed-out container can still be expanded and the values changed but they will not be used by the simulation until the mode changes to the related control. This enables you to set proper values beforehand to be ready once the mode is switched.

    Changing the value of a grayed-out Control
  4. Depending on the mode of your controllable coordinate, you may also need to set one of the following values:

    • In Motorized mode, edit the Desired Velocity and Loss values on the Motor tab.
    • In Lock mode, edit the Damping, Position, and Stiffness values on the Lock tab.

    When the Motor or the Lock is selected, the corresponding container is un-grayed and expanded to make it obvious to the user that some properties need to be defined for this control type.

    Control mode selected with expanded parameters
  5. In the Lock options, you can select Plastic to enable deformation if the maximum force is reached.

Selecting the Plastic option results in the part, when the maximum force is reached, to maintain the position that the force applied to the part, even when the force is removed. Plastic deformation is done in a Plastic Lock by internally updating the lock position. This is done by monitoring the Lock Stiffness, Lock Position, Lock Maximum and Lock Minimum, and the coordinate current force properties of the Locked Coordinate. When using the Plastic mode, you must carefully set the Maximum and Minimum Forces, stiffness of the lock, and apply a proper damping value. Leaving these fields to their default values will not work with this mode of the constraint.

Note
You must set the Lock Velocity property of a non-drifting motor after you select the control mode to Locked and select Plastic.

Customizing Offsets

The position of the attachment is given as an offset in the local frame of the part used for the attachment.

Attachments tab

Sometimes, this reference frame might not be the best method to represent the offset. In these cases, click the Browse button beside the Offsets (Relative) to open a dialog box where the offset can be specified with respect to any reference.

Attachment Offset Window for Part 1

The Attachment Offset dialog tells you which attachment you are currently working on (Part 1, Part 2, Part 3, etc.). The new position of the offset is presented in the 3D view by bold, color-coded arrows attributed to the corresponding axes.

World position of the Attachment Offset

When opening the Attachment Offset dialog, the reference object is always the attachment part. The reference can changed and replaced by any object, selected from the Explorer panel or the 3D View. At this point, the position and the orientation of the axis (displayed in the window) might have changed since the position and axis orientation are relative to the referenced object, but its position in 3D space did not change (see image below). This can be really useful to double-check that the offset position is still at the right place with respect to a given object which is not the attachment part.

Attachment Offset with respect to a different IMobile

To change the position and orientation of the offset, you need to manually change the value of the Position, the orientation of the Primary Axis or the orientation of the Secondary Axis. It is also possible to change the values by copying those of another attachment of this constraint using the Copy From drop-down menu, and selecting which offset to copy. This feature is useful since most of the constraints need to have their attachments at the same position. Copying values from another attachment ensures that the offsets coincide.

These changes are not in effect until you press Ok, after which the world 3D position is converted to be relative to the part selected for the attachment.