Tag Archives: Physics

Getting started with Bullet Physics in Poser

RigidBody2

Bullet is an open-source physics engine which was integrated with the release of Poser 10 and Poser Pro 2014. It allows us to use soft and rigid body dynamics in our scenes.

Rigid bodies are solid objects that do not deform when they collide with other objects. Think of bowling pins that are hit by a ball. Soft bodies on the other hand deform upon impact, like cloth or rubber.

I had always assumed that Bullet Physics has something to do with projectiles being fired from guns, perhaps for use in game engines. Turns out that it’s just the name of the engine itself, which is also part of many other 3D applications like Blender.

Here’s a quick overview on how to use this thing in Poser.

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Creating a waving flag in Carrara using Soft Body Modifiers

Waving-Flag

Carrara lets you turn any object in your scene into a Soft Body object with the help of a Soft Body Modifier. To create a waving flag we need to use a combination of two modifiers: one that makes the object a “soft body”, and one that attaches it to something else, such as a flag pole.

Here’s how to do it in Carrara 8.5.

The objects in my scene are:

  • a thin cylinder for the flag pole
  • a grid (or squished up cube) as the flag
  • optional: to create some wind I’m also using a Directional Force, but that’s more of a fine-tune

All our work is happening in the Assemble Room.

Select the flag, head over to Modifiers and add a Soft Body modifier. This is where you can setup the physical properties of your object, such as stiffness, how it reacts to air flow, how much internal surface pressure it has, and if you would like it to collide with itself in case it folds.

Screen Shot 2014-11-18 at 13.10.43

The values here are largely self-explanatory and require a bit of experimentation. Notice that nothing appears to happen if you change any of these. To see your object take on the new properties of this modifier, click on the Simulate Physics icon at the top left (the “bone in a dotted circle with an arrow” button).

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As soon as you click it Carrara will go to work with all physics calculations in your scene. It will render an animation which is governed by the duration you’ve set with the little yellow arrow icon in the timeline (not the actual animation duration). By default this is set to 4 seconds. If you want to see what happens beyond this, simply move that little yellow triangle in your timeline, then hit Simulate Physics again.

The flag is not attached to anything yet, so it will either stay in place, drop to the floor, or if you’ve already added a directional force it may drift away outside your scene. To attach it to the flag pole we need to add another modifier, this time it’s a Soft Body Attach Modifier.

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With it we’ll tell Carrara which other object our flag is attached to. In the first box, select your Flag Pole Cylinder. In the second box (edit) you’ll open a kind of paint mode. This will let you select which vertices you’d like to attach. In our case, we only want the points closest to the pole to be attached to the pole. Red points are selected, white points are unselected.

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Selection can be a bit tricky: I’ve not managed to find a way to change the size of the paint selection brush – I’m sure there is one, but I find it easier to select too many at first, and then choose the little minus icon and unselect what I don’t need.

Notice the three new icons in the top left corner: those are “select points” (plus), “deselect points” (minus), and “we’re done here” (tick icon). When you’re done, select Simulate Physics again to see your result.

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To render one particular image, simply drag the animation playhead to a desired position and select render. You can also render the entire animation of course.

The quality of physics relies on the amount of points your object has: the more points, the more accurate the waving will be, but at the same time the longer it will take Carrara to calculate the effect. Especially with cloth type objects, increase the tessellation for better results.

Using the Physics Engine in Carrara

Carrara has a built-in physics engine which is very capable of calculating dynamic animations. Here’s how to setup a basic scene with physics.

Physics are already setup in every new scene with a default gravity. Feel free to change the Simulation Accuracy and Geometric Fidelity different results before messing with each single object. You can find these properties under Scene – Physics:

physics

All we have to do next is to make our objects participate in the engine and have Carrara calculate the physics. Select an object, then head over to Motion and change the drop down menu to Physics (it’s set to Keyframe by default).

Here you can change the starting behaviour of your object, but the defaults work well for a quick test. Repeat this setup for every object you’d like to participate.

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To change the properties of an object (such as weight, bounciness, etc) head over to the Effects tab and look for a section called Physical Properties. There are some materials to choose from (such as Clay, Ice, Metal, etc) or you can create your own based on Density, Bounce and Friction.

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Animate this thing

Once setup, decide how long you’d like the simulation to be and adjust your animation duration accordingly. The default is 4 seconds, but you may be interested in events that happen beyond that. Simply drag the little yellow triangle in the timeline to change the duration.

Now we need to ask Carrara to Simulate Physics by pressing that “bone dipped in sauce” icon on the far left side in the top bar, next to the greyed out hand icon. You need to do this every time you make a change to the scene or the objects that participate in the physics engine.

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Either move your timeline scrubber to a desired frame, or render the animation out.