Procedure

To use the MassFX constraint:

The most convenient way to apply a MassFX constraint is from the MassFX toolbar:

1. Create the object or objects to be constrained. Use the Hierarchy panel Pivot controls to position their pivots where you want the constraints to be attached.

   For example, if one object is a door, position its pivot along the vertical edge where the hinge would be attached in the real world.

2. Depending on whether you want to constrain a rigid body to a point in space or to another rigid body, select one or two objects, respectively.

   In the latter case,select the parent object first and then select the child object. The child object is the one that is mainly affected by the constraint; for example, with a hinged door, the door is the child and the door frame is the parent.

   TipThe objects need not be rigid bodies; if not, you're prompted to add modifiers when you apply the constraint.
3. On the MassFX toolbar, click the active constraint preset or choose a different one from the flyout.

   If prompted to apply the MassFX Rigid Body modifier, click Yes to proceed.

   NoteIn all cases you're adding the same helper object: a UConstraint. The different flyout presets simply include different settings based on the type of constraining action to apply. You can adjust these as necessary to create any kind of constraint after applying the constraint.
4. Move the mouse horizontally back and forth in a viewport to adjust the display size of the constraint, and then click to set the size.
   NoteThis applies to most constraints but not all, such as the Slide constraint. In that case, just click in a viewport to finish creating the constraint.

   The command panel switches to the Modify panel and displays the UConstraint settings.

5. Adjust the settings as necessary and position the objects and constraint where they should start out in the simulation.

Connection

Parent

Sets the rigid body to use as the parent of the constraint. Click the button labeled with the name of the associated object, then in the viewport select the rigid body to use as the new parent. The constraint is then linked to the parent object, rotating and moving with it. The parent object can be dynamic or kinematic, but not static.

To remove the parent object, click the X button. When the parent is unset (not linked to any rigid body), as indicated by the "None" label, the constraint is anchored to global space (that is, its current location). Creating a constraint with a single rigid body selected sets that rigid body as the child, with no parent, constraining the rigid body relative to global space.

Child

Sets the rigid body to use as the child of the constraint. Click the button labeled with the name of the associated object, then in the viewport select the rigid body to use as the new child. The child object can be only a dynamic rigid body, not kinematic or static.

You can use the X button to remove the child object, but that results in an invalid constraint.

Breakable

When on, the constraint can be broken during the simulation. If a linear force exceeding Max Force or a twisting force exceeding the Max Torque (see following) is applied between the parent and child object, the constraint "breaks"; that is, it turns off and is no longer applied.

Max Force

When Breakable is on, the amount of linear force beyond which the constraint will break. To make the constraint more difficult to break, increase the value.

Max Torque

When Breakable is on, the amount of twisting force beyond which the constraint will break. To make the constraint more difficult to break, increase the value.

Translation Limits

X/Y/Z

For each axis, choose how to constrain motion along the axis:

• LockedPrevents the rigid bodies from moving along this local axis.
• LimitedAllows the objects to move along this local axis by an amount of the Limit Radius (away from the initial offset between the parent and child). If more than one axis is set to Limited, the motion is limited radially: within a circle or sphere, not a square or box. The distance of the Limit Radius is represented visually in the viewports for each Limited axis.
• FreeMotion of the rigid bodies along the respective axis is unrestricted.

Limit Radius

The distance along the limited axis or axis that the parent and child can move away from their initial offset.

Bounce

For any limited axes, the amount that the objects will rebound off the limit when hit. A value of 0.0 indicates no bounce, while a value of 1.0 is full bounce.

Spring

For any limited axes, the strength of the "spring" that pulls the objects back to the limit if the limit is exceeded. Small values indicate a low spring force, while larger values will pull the objects with increasing force back to the limit. A value of 0.0 is a special value indicating a hard limit, attempting to prevent the objects from exceeding the translation limit.

Damping

For any limited axes, if the translation exceeds the limit, the amount of "mud" they move through beyond the limit.

Swing & Twist Limits

Spring

The Bounce and Spring settings for the constraint limits (see preceding) control how the constraint behaves past the edges of the limits, while settings on Spring rollout are always applied. These settings are more like what you might call a "spring" in the real world.

Advanced

Move to Parent's Pivot

Sets the position of the constraint at the pivot of the parent object. This option is useful for constraints where the child object should rotate around the pivot of the parent, such as a wrecking ball constrained to the tip of a crane.

Move to Child's Pivot

Adjust the position of the constraint to be located at the pivot of the child object. This option is useful for constraints between two bones, for example.

Display Size

The size to draw the constraint helper in the viewports. This property has no effect on simulation; it is just so that you can make your constraints big enough not to be hidden inside the objects they constrain but not too much larger.

Parent/Child Collision

When off (the default), the parent and child rigid bodies connected by a constraint cannot collide with one another. This allows, for example, rigid bodies for a thigh and leg to overlap at the knee without problem. Turn on this option to allow the two rigid bodies to react to each other as well as others.

Use Projection

When on and the parent and child objects violate the limits of the constraint, fixes the situation by forcing them to the limit.

Joint projection is something of a "blunt instrument." It simply moves one actor, disregarding any collisions that might otherwise intervene. This can lead to penetration of collision geometries, so it is recommended that you avoid using joint projection unless there are real problems in terms of joint violation, and then use it judiciously.

After turning on Use Projection, choose a projection method and set the corresponding value(s):

• Linear Only (faster)Projects linear distances only. Set the Distance value.
• Linear and AngularPerforms both linear and angular projection. Set the Distance and Angle values.

Distance

The minimum distance for the constraint violation to exceed for projection to take effect. Errors below this distance will not use projection. Setting this value too low can introduce unwanted oscillations into the simulation.

Angle

The minimum angle (in degrees) that the constraint violation must exceed for projection to take effect. Errors below this angle will not use projection.