Wireframe Pro
TUTORIALS
Animate an elliptical orbit
Animate an elliptical orbit
uses Cognito

Carrara 6 or better tip

Many of these tutorials were written before the scene scaling functionality was added in Carrara 6. If the tutorial does not mention it, assume the scene should be a small scale scene. If you would like to build the scene as a medium or large you will need to adjust any size attributes listed.
Cognito doesn't directly support elliptical motion, but this tutorial will show you how to fake it using a couple of Cognito motors. 

Tutorial

  1. Launch Carrara and select File|New.
  2. To fake the elliptical motion, we'll need two Cognito motors. Select Insert|Sphere twice, rename the first one Planet and the second one Rack Motor. Set Rack Motor's Visible property to unchecked.
  3. Select the Planet object, scale it to 200%, and add the Cognito modifier. This object will drive the rotation in the scene. Set the following properties:

    X = 0.0
    Y = 0.0
    Z = 1.0

    Flip to the Effects tab and set the following properties on the Cognito Data Effect:

    Teeth = 250
    Motor = Checked
  4. Select the Rack Motor object and add the Cognito modifier. This object will be used to stretch the rotation into an elliptical shape. Flip to the Effects tab and set the following properties on the Cognito Data Effect:

    Teeth = 48
    Motor = Checked
  5. Move the timeline to 10 seconds, with the Rack Motor still selected, set Rotation property on the Cognito Data Effect to 1.0. Do the same thing for the Sun object. Click on the tweener for the Sun object, change it to a Linear tweener. Click on the tweener for the Rack Motor, change to the Oscillate tweener and set the number of Oscillations to 2. These are the only two keyframes you need to set. Move the timeline back to 0 seconds.
  6. Select Insert|Cube, on the Properties panel, set Y = 24.00 in. Add the Cognito modifier, and set the following properties on the Cognito Data Effect:

    Teeth = 16
    Slave = Checked
    Driver = Rack Motor
    Linkage = Rack

    This object will move back and forth, but we don't want to see it. Flip to the texture room, set the Color value = 0, Transparency value = 100, and check the No Light Interactions When Fully Transparent.
  7. Flip back to the Assemble room and select Insert|Sphere. This sphere will rotate around the cube while it slides back and forth. Rename it to Moon, set Y = 48.00 in., the Hotpoint Y = 24.00 in, and drag it on the timeline so that it is a child of the Cube object. You should have a timeline that looks something like Figure 1.
  8. Add the Cognito modifier, set Y = 0.0, Z = 1.0, and set the following values on the Cognito Data Effect:

    Teeth = 100
    Slave = Checked
    Driver = Planet
    Linkage = Gears

    Notice that the ratio of teeth to Planet's teeth is the same as number of times our Rack Motor will move back and forth.
  9. Finally light and shade to taste then render. Click on Figure 2 to see the final QuickTime animation, spiced up with a liberal application of a StarBright background and Shader Ops shaders.

Figure 1. The object hierarchy

Figure 2. The final animation

Download the complete scene for Mac or PC.

Advanced Exercises

  1. Figure out how to make the moon spin. This moon always has the same face towards the planet, make the moon spin. Hint: the getting started with Cognito shows you how to group objects so they can spin and orbit another object.
  2. Add more moons with different orbits, or even a Sun for the planet to orbit around.
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