When a character moves, some parts of the body ‘lead’ the motion, while others follow them. This causes laggings, overlaps and swings.
Cascadeur includes a dedicated tool for imitating these effects.
The exact way Secondary Motion works is defined by the parameters set for controllers in various parts of the character’s body.
After enabling this mode, you’ll have to manually set the body part to which secondary motion should be applied.
The secondary animation mode can work independently from other modes. This means it can be used for animations that won’t work with more conventional physics tools, for example, for magical, levitating characters.
To test this feature, you can use this scene.
- Disable Physics corrector.
- Enable Spring Secondary motion.
- Run the physics ghost.
- Select the point in the character’s arms and legs
- Open the Spring secondary motion tab on the Object Properties panel.
- Select every frame of the animation
- Turn on Apply on selected interval button
- Set Dynamic for the selected points.
The effect of Secondary Motion can be increased or decreased for each individual body part by changing corresponding parameters.
To better understand how this works, imagine the physical assistant’s rigid bodies as if they were tied to the original character’s body parts by little springs. So, the assistant’s body parts sort of oscillate around their animation counterparts. The parameters of these springs are what we can adjust.
The tool is also affected by gravity in a significant way. The gravity makes the springs stretch. Because of this, the physical character would behave in a different way when the gravity is enable than when it is disabled.
Increasing the Stiffness value makes the corresponding spring more rigid. This causes the amplitude of the resulting oscillation to lower while the frequency of the oscillation, on the contrary, rises.
The Damping parameter, in essence, controls the force of friction and defines the difference between the speeds. Increasing its value makes the motion more smooth. When 0 < Damping < Stiffness, the oscillations fade away slowly. But if you set Damping > Stiffness, the friction increases to the point oscillations stop before they can really begin.
For snapping secondary animation, there is a dedicated button called Snap with additional motion.
This is done so secondary animation won’t be applied to itself. Otherwise, be it snapped in a regular manner, the effects of the secondary animation would sum up after each snapping.
This way you can view the physical assistant with secondary motion taken into account, and still be able to make adjustments after snapping regular tools.
Snapping to Secondary Motion should be used at the very last stage, when other physics-based tools are already applied to the animation.
Sometimes, changes generated by Secondary Motion might end up looking a bit weird.
For example: you try to animate an arm moving, but on some of the frames the arm bends in the opposite direction.
What is important to remember here is that at the moment the tool has no information about the character’s anatomy or about how to ‘make things look pretty’. For it, the character’s limbs are mere rigid bodies connected by joints.
Also, the animation might sometimes come off as rather chaotic, but this is actually close to how such contraptions move in real life.
Because of this, it’s better to apply the tool not to the whole animation, but rather only to the specific intervals; you also shouldn’t set the degree of freedom for the tool too high.
