Secondary Motion

 

This feature improves animation generated by AutoPhysics by making it more smooth and accentuated.

Enabling Secondary Motion

This effect can be enabled or disabled by enabling or disabling the Secondary motion parameter.

1. Go to the the Physics settings panel.

2. On the AutoPhysics tab, enable the Secondary motion parameter:

This will enable the Secondary Motion feature, but with default settings, its effect won't differ from the original animation.
Next, you'll need to define parts of the character to apply it to.

3. Select the Point Controllers associated with the parts of the character you'd like to use Secondary Motion on.

4. (optional) If you'd like to only apply Secondary Motion to selected frames, select these frames on the Timeline.

5. On the Object Properties panel, go to the Secondary motion tab and turn on the Powered option for the points you've selected:

6. Enable Interval Edit Mode.
This way, the tool would be applied to every (selected) frame.

After this, the effect of Secondary Motion should become visible the scene.
Keep in mind, however, that the effect would be applied exclusively to the selected Point Controllers on the selected frames. The rest of animation won't be affected by it.

Applying Secondary Motion

Secondary Motion is generated automatically, but has to be manually snapped to the current animation.
To do this, click the Snap with additional motion button on the Toolbar, under the Auto Physics panel:

Note

Secondary Motion should only be applied after the rest of animation work is complete.
Otherwise, it will be applied to itself, overlaying and amplifying the effect, especially if you click the button several times.
(This is also the reason there's a dedicated button for applying the effect)

Point Settings for Secondary Motion

How much Secondary Animation impacts the character’s motion is defined by the dedicated set of parameters.

These parameters can be found on the Object properties panel, under the Secondary Motion tab (this tab is specific to Point Controllers):

Translation Settings

The first group of settings controls translation, i.e. how the selected objects are moved to produce Secondary Motion effect.

Local/Global
This switch defines if translation should be be performed in Global (world) or Local (object) space.
Global means that the selected objects on the physical ghost would follow the original animation, trying to preserve their positions in the world (global) space.
The Local value means that the tool would try to preserve the objects' positions in relation to their respective parents.

In most situations, we recommend to use the Global setting. The Local setting is intended for overlappings, increasing the effect of the local Rotation (see below). Also, for high Translation stiffness values, using Local can lead to instabilities in the simulation.

Translation stiffness
Controls the amplitude and frequency of the oscillations that make up secondary motion effect.
Increasing this value decreases the amplitude and increases frequency.

Translation damping
Controls how fast the oscillation should fade.
Increasing this value accelerates the fading.
If the value is equal to the Translation stiffness, oscillations fade out evenly; if it is lower, the objects oscillate more; if it is higher, oscillations stop quickly.

Rotation Settings

The next group of settings controls the rotation of the selected objects.

Local/Global
This switch defines if the rotation should be performed in Global (world) or Local (object) space.
Global means the tool would try to preserve the objects' orientation in the world coordinates by rotating the objects.
Local means the tool would try to preserve their local coordinates (in relation to their parents).

Rotation stiffness
Controls the amplitude and the frequency of the oscillations that make up rotation part of the secondary motion.

Rotation damping
Defines how fast rotation should fade.
Works on the same principle as Translation damping described above.

Powered/Kinematic
This switch defines the method used to change the objects' positions:

  • Powered means that the objects are moved by applying physical force to them. Objects accelarate in proportion to their masses and the force applied.
  • In the Kinematic mode the objects follow their local movements in the original animation.
    • If Kinematic is used for the entirety of the Timeline, the objects' movements would coincide with their movements in the original.
    • If a Kinematic interval follows a Powered interval, the tool would try to pull up the obejcts to their original positions on the respective frames.
    • This motion does not involve forces, masses etc.

Pull up Settings

The final two settings are intended for controlling the pull-up effect, i.e. how the objects are moved to their original positions on intervals with the Kinematic setting enabled.

Pull up stiffness
Sets the strength used to pull the physics assistant to the original animation.

Pull up damping
Sets how fast the pull-up effect should fade.

Aside from these parameters, Secondary Motion is affected by the Gravity setting. The same set of settings with different Gravity values would produce different results.

Examples

The effects these parameters have on the animation can be better understood by seeing them in action:


1. Here, Translation damping is set to 1, while every other parameter is 0. Gravity causes the arm to fall down and wave.


2. If we increase the Rotation damping value to 10, the arm's osicllation quickly fades away.


3. Increased Rotation stiffness (to 50) causes the arm to keep closer to its original position, although oscillation still happens.


4. Setting Translation damping to 10 instead of 1 causes the whole motion to become slower and less pronounced, as if the environment has become more dense.


5. Finally here the parameters for the arm are the same as in the previous example, but the hand has increased Translation stiffness (15).
Because of this, the hand 'tries' to keep its original position and sort of drags the entire arm after it.

Other Settings

Aside from Point Controller settings, a set of parameters for Secondary Motion tool as a whole can be found on the Physics settings panel, under the Secondary Motion tab:

Currently, this tab only includes one parameter:

Interframe count
This parameter sets the number of subframes used for calculating Secondary Animation.

Increasing this value increases the stability of the effect.
Decreasing the value, on the other hand, decreases the impact on performance.

It is recommended to increase the value when Secondary Animation becomes distorted, and decrease it when the AutoPhysics simulation becomes too slow to work comfortably.
The default value is 100.

 

See Also

AutoPhysics

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