This is a tool that analyzes the animation you’ve created and suggests a physically accurate version of it.

AutoPhysics Controls

AutoPhysics is controlled by a set of buttons on the Toolbar:

(1) AutoPhysics
Enables and disables AutoPhysics.

(2) Snap to AutoPhysics
Snaps the animation to the AutoPhysics simulation.

(3) Snap to AutoPhysics on interval
Snaps the animation to AutoPhysics on the selected interval.

(4) Update AutoPhysics
Click this button to recalculate the AutoPhysics simulation.
By default, the simulation is not updated when you adjust the animation.

(5) Auto Update AutoPhysics
If this is enabled, AutoPhysics simulation is recalculated after any kind of change is made to the animation.

Enabling AutoPhysics

If the character has only one Center of Mass, simply click the AutoPhysics button on the Toolbar:

The tool will be activated and should work without issues.

But if the character has multiple centers of mass, you should first select the one that fits the kind of animation you’ve created.
For example:

-If the character performs a jump holding a sword, the character’s and the sword’s composite center of mass should be used (1).
-If the character performs some action without a sword, the character’s center of mass should be used (2).
-If the character throws the sword, the sword’s center of mass should be used (3).

After selecting the Center of Mass you need, click the AutoPhysics button on the Toolbar.

Using AutoPhysics

After enabling the tool you should see a differently colored copy of you character:

Take a note of the differences in the trajectories.

This is the Physical Assistant. It shows how your animation would look if it was completely physically accurate.
The Physical Assistant can be colored differently on different frames:

Green color means that there’s nothing wrong with the original animation, outside of maybe some minor deviations.
The way the ghost moves is the solution suggested for these deviations. You can apply this solution to your animation by clicking Snap to AutoPhysics:

Red means that a physically accurate solution is not possible under given circumstances. In a case like this, the animation can only be fixed by manually altering poses and/or timings.

Blue means that there were changes made to the initial animation that the simulation does not reflect. It should be recalculated by clicking Update AutoPhysics:

Alternatively, you can enable Auto Update AutoPhysics:

This way, the simulation will be updated automatically every time any change is made to the animation.
Keep in mind, however, that this option can be rather taxing on the performance.

When AutoPhysics is enabled, a gradient line is shown on top of the Timeline:

The color of this line signifies how close is the initial animation to the physical simulation:

Green means there’s nothing wrong with the animation.

Yellow means there are some deviations, but the algorithm is able to find a way to fix them.

Red means that the algorithm is unable to find a solution under current circumstances. The corresponding part of the animation has to be adjusted manually.

Gray means there’s no animation on the corresponding frames.

Common Issues

Feet Distortions

If the character’s feet include several Rigid Bodies and subsequently several Point Controllers, some of these points might not be designated as Fulcrum Points. Because of that, they might shift along with the Center of Mass, causing distortions seen above.

To fix this issue:

1. Go to a keyframe after the frames where the issue occurs.

2. Enable Is_enforce for the points that should not move:

This setting can be found on the Object Properties panel, under the Fulcrum point tab:

A similar effect might occur when the character performs a kick. Here, the left foot rotates, leaving only the heel point as the fulcrum:

This can also be fixed by enabling Is_enforce for the heel controllers.
Another way is to increase the Max_distance parameter:

This parameter defines how far the Point Controllers can shift while still remaining fulcrum points:

Timing Issues

Sometimes AutoPhysics can cause distortions like this:

Take a note of the difference in the position of the character’s legs on the simulation in comparison with original animation.

This happens because AutoPhysics does not have enough frames to better position the character. To improve the situation:

1. Remove the Ballistic trajectory.
It is not required, but recommended to avoid complications.

2. Use Tracks stretching mode to increase the length of the part of the animation that displays this issue (the landing sequence in our example).

3. Set Bezier interpolation for the stretched intervals (or Bezier Clamped for feet and such).

4. Create a new Ballistic trajectory and snap the character to it.

As you can see, the stretched animation is significantly longer than the original (over 200 frames instead of about 165). However, because of that the AutoPhysics is able to display a solution much closer to the original.


See Also

AutoPhysics Settings

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