Cinema 4d Handbook: Chapter 9

28Oct11

I’m finally in the last week of Cinema 4D chapters and posts. It’s been a good run, but I’m glad to be on the final stretch. Some of the last few chapters are really short, and I will combine multiples into the same post. Chapter 9 is by itself, so here we go…

Chapter 9: Dynamics

Physics in the real world dictate how things move and react to each other. “One of the most difficult things to do as an animator is to mimic real physics.” To help with this C4D has a module called Dynamics. There are to types of dynamic interactions: Hard (Rigid) Body and Soft Body. Rigid bodies are things that have definitive shapes. Soft bodies are objects that are flexible; like flesh or Jell-O.

Tutorial 9.1: Rigid Body Dynamics

Rigid Body Dynamics only need to worry about mass, velocity, and collision detection. But each of these properties has a group of subsets that can make working in dynamics tricky. Using Save Incremental will help you if you have to go back to a previous state. When working with Dynamics, work with low-poly proxy models because Dynamics chugs with high-poly counts.

Solver Object
“Dynamics requires a Solver Object. The Solver will eventually be the parent of everything you want to be a part of the simulation.” Anything that is linked to a Solver also needs to have a Dynamics Tag attached to it. *NOTE: Dynamics won’t work on NURBS or primitives.
To Add a Solver:
1) Create a Solver Object. Dynamics> Solver Object

The Solver has a number of editable settings. Here’s a brief overview of what they do:
Start/ Stop Overall length of the simulation.
Integration Method Different methods that C4D uses to calculate.
Oversampling/ Subsampling- Tells the computer how much to sample for the render.
Energy Loss- Simulates entropy, or the rate that energy is released.
Collision Eps. (Inside the “Details” tab) The distance buffer Dynamics uses to separate objects.

While the book does give a tutorial about editing the settings, most of the dynamics need to be adjusted by guess-and-check. It’s all about making it look realistic for your particular environment.

Forces
Forces
are objects that exert some sort of influence on Dynamic geometries. The three force options are Gravity, Drag, and Wind. When using forces, be sure to pay attention to the size of your objects. A large object will fall differently than a small object.
To Add Forces:
1) Create a force object. Dynamics> Gravity, Dynamics> Drag
2) Use the Attributes Manager to adjust settings for any created Forces.

Rigid Body Dynamic Tag
None of your objects will fall under Dynamics without a tag. For hard surfaces, use a Rigid Body Dynamic Tag. The tags tell your objects how to interact with the Solver and Forces.
To Add and Edit a Rigid Body Dynamic Tag:
1) Select the object you want to add to, then Right+Click and choose Dynamics> Rigid Body Dynamics
2) Make adjustments in both the “Mass” and “Collision” tabs so that the physics work in a way that makes sense in your scene.
3) Copy the Rigid Body Dynamics Tab to any objects that share the same dynamics, or create new ones if needed.
4) If your objects are interacting with a base, or floor, object, be sure to add tags for this as well.

The Rigid Body Dynamics Tag has many properties. Here’s a quick run-through of what they do:
Total Mass- Determines how the object reacts to Gravity and Drag forces.
Rotational Mass- Tells you how much force is needed to rotate the object.
Collision Detection- Calculates the collision rate.
Elasticity- How much bounce an object has.
Static- Determines the amount of friction an object has.
Dynamic- Determines friction for objects that move in the scene.






Hierarchy
Just like with every other action you perform in 3D, the hierarchy can be critical. Once you have all of your elements created, you link them to the Solver Object.

Bake Solver
Once everything is ready, you need to Bake the Solver. This is essentially like rendering the elements. Once you bake, the animation will play back without having to run through all of the Dynamics calculations.
To Bake the Solver:
1) Select the Solver Object.
2) Start the animation by choosing Dynamics> Bake Solver
3) Play bake the animation to check for accuracy. *NOTE: To undo the bake, select Dynamics>Clear Solver, then turn the Solver Back on.

Tutorial 9.2: Soft Body Dynamics

Soft bodies are objects that’s vertices are controlled by springs. Basically, anything that moves organically. Soft Body Dynamics are edited in their own window, not in the Attributes Manager.
To Add a Soft Body Spring Tag:
1) Select the object and add the tag by Right+Clicking on it then choosing Dynamics Tags> Soft Body Spring
2) In the new window, select Springs> Add Soft Springs
3) In the window that pops up, go into the “Method” Section and choose your spring type then click “OK.”
4) Adjust the settings to the springs in the “Springs” tab.
5) In the “Collision” tab adjust the settings for Collision Detection and Elasticity.

Initialize Objects
“The Initialize Objects in the Dynamics menu will make it so that each object can have its own starting position.” If you were to leave this out, and copied a Soft Body Tag to multiple objects, they would overlap. You also have to use Initialize when you want to change an object’s position. *NOTE: If a Solver Object already exists, then you must also turn it off to move objects.
To Initialize and Object:
1) Copy/ create all the Soft Body Spring Tags that you need in your scene.
2) Initialize the objects. Dynamics> Initialize All Objects

Solver Object
Whenever you use Dynamics you need to include a Solver Object. If your scene is all soft bodies, then use the Solver to add Gravity.
To Add a Solver and Its Hierarchy:
1) Add Gravity then make adjustments to it. Dynamics> Gravity
2) Add a Solver. Dynamics> Solver Object
3) Link all of the objects in your scene to the Solver Object.
4) Bake




Like much of the “final touches” of 3D modeling and animating, working with the physics is a lot of guess-and-check. Keep working with the options until it works for your individual scene.

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