I have been working on a WWII German u-boat for a while now. You may have seen the prelim model on the homepage. Anyway I was messing around with particle systems in Strata Pro so I thought I would pass along how I make bubbles under water.

I have modeled a prop for the torpedo by extruding a besier line and then torqued it with a deform lattice. I used a simple cone primitive for the center hub. Once the pieces were arranged into a prop then I linked the prop blades to the center cone. That way when I rotate the center cone the prop blades follow right along.

The next step is to put down a sphere primitive to be our particle emitter. Set it some where out by the tip of one of the blades. Make sure it doesn't intersect with the blade.

Now what we need to do is duplicate this sphere and line it along the edge of the prop blade.

Okay, now let's duplicate the whole lot of them and arrange the others around each prop blade like you see below.

Now for the particles. In the resource pallet select the "FX" tab and then the "new" drop down. From that choose "Fountain" from the drop down list.

These are the settings I choose when I made my bubble particles. Once the particles are made they show up on the "FX" tab just like a texture shows up under the "Textures" Tab. Select the spheres and apply the particle FX to them.

Once you have the particles applied to the spheres we need to make sure they don't show up when we render them. To do this turn down the tab for each sphere in the "Project window" and check the "Anti-matter" check box.

Okay, now we have to "link" each sphere (emitter) to the prop blades. Choose your link tool and then drag from a sphere to a prop blade to link them. This will make the sphere follow the prop blade they are attached to when we rotate the prop.

Okay, what I've done here is rotate the prop by the center cone by 45 degrees four times. With the the prop blades linked to the cone and the spheres linked to the prop blades everything rotates together when you rotate the cone. Once you have that done save it as something like "rotatingProp.s3d"

Next, open a new file and make the torpedo body. I used a lathed spline. Then "import" the file you named "rotatingProp.s3d" into the scene. Position the prop at the end of the torpedo, use the scale and rotate tool if you need to. When you import an animation like this into another file it keeps all the animation setting that you made to the prop. It's kind of like a nested animation or a movie clip in flash. Very handy when you have something spinning around. Now use the "Link" tool and link the prop to the torpedo body, like below.

Now we we need to make this prop spin forever. Double click on the prop. It will open up the details of the animated prop when you double click on it. In the "project Window" you will see all of the objects that make up the prop. Select the "Cone" and then click on the +arrow icon at the top right corner of the window. Choose "Add Attribute" then "Cycle Attribute". This will add a new attribute to the cone that allows you to specify how many times to cycle through the animation.

Once you have the "Cycle" attribute available, turn down the arrow and type in "inf" for infinite. That means it will loop through the animation forever until you hit the end of your main animation timeline.

If we leave the sphere emitters like they are the bubbles will look pretty uniform and not very random when they come off the prop. What you need to do is move the sphere emitters around randomly so it will produce a better looking bubble cloud.

Now all you need to do is animate the torpedo along a path and set up a camera and animate! This is what mine looked like when I got done.

Watch the animation here...
(91kb .mov)