This tutorial will explore using Maya's particle system and instancer to simulate planets with several moons orbiting the Sun. With a few expressions you can control the positions and rotations of individual particles which can control geometry through Maya's instancer.
One of the first things we learn about space is that it's big - really big. We'll recreate the orbit of Jupiter and four of its major moons somewhat accurately while fudging a few numbers to make the scene more manageable. First we will need 6 spheres which will represent the Sun, Jupiter, Io, Europa, Ganymede and Callisto.
Let's start by creating the Sun. Go to Create > NURBS Primatives > Sphere > Option box (Fig.01). If we assume that a radius of 1 is the size of Earth, the radius of the Sun would be about 109 times that which is a bit big for our scene. Set the radius to 20 and leave all other settings at their default. Name the sphere "Sun_geo".
The next planets can be set to a more accurate size relative to Earth. Create 5 new nurbs spheres naming and setting the radiuses to the following values:
- Jupiter_geo = radius: 11.2
- Io_geo = radius: 0.28
- Europa_geo = radius: 0.24
- Ganymede_geo = radius: 0.41
- Callisto_geo = radius: 0.25
Now you can apply textures to the spheres if you choose (Fig.02)
Before we move on it is important to note how the instancer handles geometry. When geometry is instanced, it is placed at a particle using the geometry's pivot point. If the pivot is not centered then the geometry will be placed off center and will not behave properly. Also if the transforms are frozen and the geometry does not reside at the origin, the geometry will be instanced onto the particle offset the same distance the geometry is away from the origin. Since we created spheres from the menu we do not have to worry about this as their pivots are centered and transforms are frozen at the origin.
Now create an emitter by going to the dynamics module Particles > Create Emitter > Option box (Fig.03).
Set the type to omni. Open the outliner by going to Window > Outliner (Fig.04).
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