The center of mass is the point that represents the mass distribution. 

For example: a hammer has a light handle and a heavy iron head. So, the center of mass for the hammer would be closer to the head. 

By knowing and adjusting the position of the center of mass, you can make the animation more realistic and even more attractive! 



Character rigs in Cascadeur consist of rigid bodies. Every rigid body has its own weight value. These rigid bodies are used to calculate the position of the character's center of mass.



If the pose of the character changes, the center of mass changes as well. Sometimes the center of mass might even end up outside the body.

When the center of mass is above the fulcrums, the object is in equilibrium!

Many of you probably know funny toys with such levitation effects. Due to the increased weight of its wings, this bird's center of mass is exactly in its beak, so it only needs to touch the surface with the tip of its beak to keep its balance.




And in Cascadeur, you too can take the Center of Mass into account when you set up poses for your character.


 

Observing how balanced the character's pose is can be made easier by activating the center of mass projection.

• Click the View Mode icon with the Right Mouse Button.
• Enable the Center of mass grounder option.

Now a line connects the Center of Mass to the ground. This line is the projection.
If the projection of the Center of Mass is in a fulcrum area (between the supporting limbs, for example), the pose can be considered balanced. 



 Also in the Settings menu you can adjust the display of the center of mass projection more accurately. For example, set whether the projection is always visible or only when the center of mass is selected

The position of the center of mass is responsible for balance not only in static postures, but also in movements.

For example, to get up from a chair, a person first leans forward slightly. This movement is necessary just to shift the center of mass closer to the feet - points of fulcrum. Also, people move their feet closer to the chair before standing up. 





Similarly, when lifting weights, a person assumes a posture in which the combined center of mass of the body and the object being lifted is above the fulcrum points. In this example, the body is tilted backward to maintain equilibrium. 


 

In fast motion, the center of mass may not always be over the fulcrum points.

Timing and trajectories play a large role in these motions. When the center of mass moves away from the fulcrums, the character begins to tilt.



The center of mass continues to move along its trajectory, gaining speed. If a supporting fulcrum (e.g. a foot) does not appear in time, the person will fall. 



For example, walking is essentially a series of small controlled falls! Before the first step, the person's body leans forward slightly, and then the person catches themselves by stepping a foot forward. This happens with every step! 



And the trajectory of the center of mass while walking is in the shape of a wave.



We don't notice it, but by changing our posture we are constantly affecting the position of the center of mass in different movements. In fact, that's why we change our posture in certain ways! So it is the trajectory of the center of mass that plays a huge role in movements!

 

The physics corrector can adjust animations to keep a character balanced.

For example, in a given animation, the character rolls backwards and then rolls up again without any external influence..



Once the center of mass is no longer above the pivot points, the fall must begin. This fall cannot suddenly stop in the middle without external influence. Nor can the center of mass suddenly start moving backwards again. This is only possible if the person is supported by wires or if they lean on something.

This is what the animation looks like after adding a physics corrector.



The physics corrector cannot add new keys and poses to the animation, because it is important to keep that particular animation that was intended by the creator.

In this case, it is assumed that the animator intended for both feet to be on the ground, hands not moving, etc. These are exactly the poses that the animator put in the keys. Therefore, the Physics Corrector cannot add to this animation any movement of the arms or legs that would cause the character to step on the ground to stop falling! Nor can the physics corrector turn the second part of the animation into a continuation of the fall - because that would also break the animator's idea that the character should be on his feet at the end of the animation, rather than lying on the floor. 

Thus, in order to keep the movement as close to the original as possible, but make it more physically correct, the tool will have to shift the character's center of mass so that it doesn't extend beyond the fulcrums! 



The result of the tool is not the final version of the animation. It is just a suggestion of how to solve the problem in that interval. You can apply these changes and then edit the poses again to make them more appealing. This process can be repeated until you are happy with the result! 



Or you can abandon the original idea altogether if you find that it doesn't work from a physical point of view. For example, I could add leg movement to this animation to maintain balance. Or I can decide to have the character actually fall to the ground.



Often, though, physical corrections can be quite minor and won't affect your animation that much. For example, the tool might add small shifts in the center of mass while walking. Sometimes even these small refinements make the animation more lively and appealing! 

But, of course, you can always choose not to use the Physics Corrector at all for some parts of the animation, or use other tweaks to get the physical accurate version as close to your vision as possible! 


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