MoGraph 2 - MoDynamics Part 2

Basic cloner stack and animated object collision

The Cloner is used in Grid Array mode to create a simple brick wall and a Sphere is used as the collision object. The cubes used as bricks must not intersect as the dynamics will cause the wall to explode immediately. The Sphere is animated to pass through the wall. Add a Rigid Body tag to the Sphere and press play. The Sphere will collide with the wall and depending on the inherent stability of the wall, either some blocks will be displaced or the whole wall will collapse depending on the thickness of the individual bricks. Thicker bricks will be more stable than thinner narrow ones.

Cloner with object collider

Here is the resulting animation.

Press Play to view animation

Basic Cloner Stack and Cloned Object Collision. (Option 1)

In this case, The collision object is a Cloned Sphere and instead of animating the position of the Sphere, it is given a dynamic Initial Linear and Angular Velocity. This causes it to fall and roll naturally into the wall causing it to collapse realistically. Increasing the Bounce parameter will cause the sphere to bounce more.

Cloned sphere with initial velocity and rotation

Here is the resulting animation. This contains no keyframes. Everything is driven by dynamics.

Press Play to view animation

One thing I wouldn't mind seeing in a future MoGraph version is being able to interactively define initial velocity and rotation. For anyone familiar with trueSpace you would recall that rather than setting up initial direction, velocity, rotation etc numerically, you could do it interactively in the Viewport by dragging handles. Sure have the numerical option but also have an interactive option as well.

If you observe the 2 previous animations you may have noticed the cube wall starts moving straight away. You can prevent this by using the Trigger: On Collision option rather that the default Trigger: Immediately option. What happens here is the dynamics don't kick in until a collision occurs. In this case the cloned sphere hitting the cubes. Look carefully at the following animation. The cubes don't move until the sphere hits them.

Press Play to view animation

When a Rigid Body Tag is added to an object, an extra Rigid Body tab appears in the object's Attribute Managers tabs. This makes it convenient to access all the parameters of the object. This applies to both Cloner Objects and objects used as collision objects.

Animation and Dynamics combined

You can add some life to your MoGraph animations by combining dynamics whilst still retaining the general flow of the animation. After animating your clones using keyframes, effectors etc it's just a matter of adding the Rigid Body tags then adjusting a couple of settings on the Force tab of the Rigid Body tag applied to the Cloner object. To control how closely the clones follow the animation you have to enable the Follow Animation option and select whether you want the clones to follow just the position or position and rotation of the original animation. You then adjust the strength. High strength values make the clones follow the original animation very closely. If you want to use particle modifier objects then you need to add them to the Force List field as per the image below.

Force Tab settings - Combining Animation with Dynamics.

The following animation has 2 identical MoGraph animations where the sphere clones follow a spline using the Rate parameter on the Cloner object. The blue Clones are the default animation. The red clones are with the addition of Rigid Body Tags and a standard particles Turbulence object.

Press Play to view animation

MoDynamics Settings

A new tab in the Project Settings is the MoDynamics Settings (Ctrl+D or Edit>Project Settings) These settings are important and control how the overall dynamics behave. Here are default settings.

MoDynamics Settings

. Briefly the settings are:

• Time Scale - The default value is 1 which I assume is normal speed. Values lower than 1 are slow motion. 0 in fact is completely stopped. So if you want to make the dynamics animation play back in slow motion you would change the value to something like 0.5. The Time Scale value can be animated for some interesting effects. (Note that keyframed animation will still run at normal speed). One thing I find wacky is the maximum value is 10,000,000. Anything much over 20 is far too fast. In my opinion the scale needs changing and the default value and normal speed should be achieved at say 100. This then saves having to use decimal points to achieve slow motion.
• Gravity - The default value is 1000 which equates to the figure of 9.81 that CINEMA 4D users are probably more familiar with. Gravity values can be negative or positive values. I found the speed of gravity to be often too slow so increased this value. Negative gravity just reverses the direction. One thing I would have liked is some control of the direction as it's just up or down. Thinking Particles gravity for example can be rotated to any angle.
• Density - Is more or less how solid an object is. A steel ball for example has more Density and has more Mass than a tennis ball. The Density setting when changed won't actually alter anything in the dynamics animation if you have your Rigid Body tags all set to use World Density. Things get interesting once you change the Density setting on the Mass Tab of one or more Rigid Body Tags to use Custom Density. The animation below has World Density set to the default 1. The wall on the right has the Rigid Body Tag Density set to Use Custom Density and the value is 1000. All other Rigid Body Tags are set to use the World Density value. As you can see the results are quite different.
• Collision Margin - Read the documentation!! In most cases this setting doesn't need to be altered according to the documentation but is available if collisions aren't being calculated correctly.
• Scale - The documentation describes this best: This is the factor by which the CINEMA 4D units of measure will be reinterpreted in the bullet engine. Simply follow this rule of thumb - If you have objects flying through your scene that are 100 CINEMA 4D units in size, leave the Scale value set to 100m. If the objects are 1000 units in size set the Scale value to 1000m. This value only has to be modified if objects start behaving strangely, i.e. if it comes to faulty calculations.
• Substeps - The documentation describes this best: The higher the value, the more precise the calculation will be. This value should be increase in particular when penetration occurs by Clones travelling at high velocity.
• Random Seed - The documentation describes this best: When MoGraph Dynamics are calculated, random numbers are used at various locations. Modifying this value will result in different random numbers being generated, which will affect the Clones' behaviour accordingly.

Press Play to view animation. The wall on the right has Custom Density of 1000.

Mass / Density

Mass Tab on Rigid Body Tag

I left explaining the Mass Tab on the Rigid Body Tab until now. I wanted to cover the Global settings first and prior to the explanation show you an animation. Let's consider a sphere with radius 100m compared to a sphere with a radius 200m. With default settings the 200m sphere has a greater mass but what if the 100m sphere was made of solid steel and the 200m sphere was a plastic beach ball? Obviously the smaller sphere would knock over a wall of bricks but the bigger sphere with a very low density and therefore very low mass would be lucky to knock over any at all and it would just bounce off.

MoDynamics calculates density by multiplying the mass by the volume of the object. The Global Density value is 1 and by default, Rigid Body Tag's use this value. You saw in the animation above where I increased the density of the cubes so that they were like concrete blocks. The sphere bounced off these blocks. As an alternative I could have used a Custom Mass and achieved the same result. So to summarize you can alter the characteristics of objects to simulate real world objects by adjusting the Density / Mass settings.

Following on from this the Use option as shown in the image above when enabled allows you change the position of the Centre of Gravity. By default the Centre of Gravity is in the middle of an object but it doesn't have to be. A sphere for example can be made to wobble as it rolls by moving the Centre of Gravity away from the middle.

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Review by C4D Cafe   © 2009