Compensation motion

The Compensation motion feature works differently from other similar tools. It is best used without combining it with other tools for correcting physics.

This tool runs on complex mathematical calculations, but if we’d try to explain the process as simply as possible, we could say that it works in the following way:
It tries to recreate the original animation frame by frame, but while taking into account the set limitations. These limitations prevent the tool from simply copying the animation, instead forcing it to alter it in a specific manner.

It’s a bit like what an untrained person would do if they were trying to copy movements of an athlete. An average person simply wouldn’t have muscles strong enough to make some of the motions, so those motions would come off differently, no matter how much this person tries to copy everything as closely as possible. Alternatively, it can be compared to one athlete trying to copy another, but while standing on a more slippery surface. Both these comparisons are, of course, very rough.

It’s just important to know that this tool has no knowledge of what is happening in the original animation, nor does it try to make the motions any more ‘meaningful’, much less ‘pretty’... it’s just the outcome can very well be both these things if the settings are right.
 

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Rotation Filter Settings

The first method of using the tool is setting a limit for the rotation.
The value of 100 means the physical ghost has no limitations, and it can completely retread the original animation.
But lowering this value means the tool is able to make more and more alterations to the animation. Moreover, the difference between 50 and 10 is actually not as big as between 5 and 4!

  • Open the scene for testing the instrument.
  • Enable Compensation motion, but turn off other physical filters.
  • Open the tab with the settings for the tool.
  • Enable Rotation cut-off% by setting any value below 100.
  • See how much the animation on the physical ghost would change with the tool set to low values.
  • Set the value back to 100 to disable the filter.

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Translation cut-off

The second way of working with this tool is to limit the translation.
Using both filters at the same time is not recommended.

  • Open the scene for testing the tool.
  • Enable Compensation motion, but turn off every other physics filter.
  • Open the tab with the tool’s settings.
  • Enable Translation cut-off% by setting any value below 100.
  • See how much the animation on the physical ghost would change with the tool set to low values.
  • Set the value back to 100 to disable the filter.

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Compensation by altering the pose

By default, the tool tries to evenly change the coordinates for every body part.
But you can also set up the degrees of freedom for various parts in greater detail.
For example: people rarely try to balance themselves with the whole of their body. More often they keep the balance using their arms.
Physics tools know nothing about the character’s anatomy. On one hand, this can lead to some unnatural motions, but on the other, enables working with characters of any kind, including non-humanoid ones.

  • Take the test scene with the dinosaur. This scene includes an animation of the dinosaur jumping.
  • Disable Physics corrector and enable Motion compensation.
  • Set Rotation cut off to 5. Enable the physical ghost.

Now if you move the physics ghost to the same place as the original mesh (by setting Ghost Offset to 0, 0, 0), you’ll see clearly how the tool has rotated the entire character on some of the frames.

In addition: the tail in this animation is left to be completely straight-lined. Later, we could research how we could use the tail to compensate this motion with fixed physical parameters.
 

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Setting up body parts for compensation

So, we’d like the dinosaur to use its tail for compensating the rotation.

  • Switch to the Point Controller mode and select the points in the dinosaur’s tail.
  • In the Object Properties, open the Physics point tab.

The values of these parameters are animatable, meaning they can have different values on different frames. To set one value for every frame, you’ll need to use Interval edit Mode.
  • Select every frame of the animation. ​
  • Enable Interval Edit Mode.

Then you’ll have to adjust the Muscle stiffness value. This parameter defines how much the points will ‘try’ to correspond to the local positions they had in the original animation. Lowering the value means the original animation would have lower influence on the points, giving them an increased degree of freedom.
  • Set Muscle stiffness for the points in the tail to 5.
  • Set the offset for the physical ghost to 0, 0, 0, and compare the frames where the physical ghost rotates the character.

As you can see, now, instead of rotating the entire body, the dinosaur simply raises its tail. This means that now we compensate the rotation by moving the tail.
You can set very specific and detailed settings for various body parts. For example, different parts of the tail can have different Muscle stiffness values, which would help to make the tail more flexible.

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How to choose fitting settings for various cases

Unfortunately, there aren’t yet definitive guidelines for every possible case.
When you set up the parameters, it’s best to go by the visual results and the characteristics of your model and animation.

We’d recommend trying different values and see how they affect your animation. Most of the time, it’s enough to only set the main settings: Rotation cut-off or Translation cut-off, and sometimes Muscle stiffness as well, when it is needed.

You can learn more about the rest of the settings in the documentation.
And if you have any questions, or are facing difficulties, we recommend you contact us via Discord or by email.

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Snapping to the physical ghost

To apply the changes suggested by the AutoPhysics tool to your character, you need to snap the animation to the physical ghost.
The Compensation motion mode uses its own snap button!

This is necessary so you could work with both the regular physics corrector tools and the compensation mode at the same time, and to make adjustments to the animation after snapping it. Also, the animation should first be snapped to the regular corrector while the compensation motion or secondary motion should be applied at the very last moment. This way the effects of these modes will be applied on top of the regular physics corrector and nothing else.
Otherwise, however, they will be applied on top of themselves, which can lead to undesired results.

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