Drips and DropsCreating condensation and simulating the way water droplets move on the surface of objects has been a fun thing to attempt in 3D animation for a long time.

This tutorial will cover some of the ways we can use Particle Flow to simulate this idea.

First things first, open up a new scene in 3DS Max and create the surface you want condensation to drip down. I'll use a sphere for this demo because it gives us a nice round surface without a lot of horizontal faces or things to get in the way of our particles.

Once we have our sphere we can open up Particle View (6), or go to the Graph Editors -> Particle View.

First step as usual, is to drag out an Empty Flow to the empty grey flowchart area.

1

Followed by the ever handy, Birth event and connect the blue node dot to the empty circle in our second event.

--------------------->

We want all of our particles to appear the second our scene begins, so I have made both Emit Start and Stop at frame #0. We will more than likely increase this, but for now 500 particles in the Amount: field will do fine and it won't bog down our computers too much.

Next up, we need to tell our particles where to come from. So we need to add a Position Object under our birth in the first Event.

--------------------->

We'll add our sphere to the Emitter Objects and right away you should see tick marks show up on the surface of the sphere showing us where our particles will begin their lives.

Next we'll get these particles some direction, by adding a gravity to our scene.

Our gravity is on the create tab, all the way over to the spacewarps button and is part of the first selection of the dropdown list. Forces.

2

Create it in your top viewport so that the arrow on the icon points down, as gravity should. Then head over to the modify tab to adjust the settings.

I've given my gravity a 0.4 in strength so that my drips don't fall too fast.

Then we'll go back to our Particle View and add "Force" to the list in our first Event.

------------------> and add our gravity to the list in the Force settings.

Next, we'll add a Speed by Surface. This will allow us to force our droplets to follow the contours of the sphere instead of falling straight through it like they do currently.

3

--------------->

This one we will have a lot of settings to adjust.

First click the by list button ad select your sphere as the surface for our particles to pay attention to.

Then make sure at the very top to select Control SpeedContinuously from the drop down, and reduce the Speedand Variations. I chose 12 speed, give or take 5.

And last but not least go down to the Direction settingsand select Parallel to Surface from the dropdown menu so that they follow the outside of the object.

Before we get too far ahead, here might be a good time to realize that our particles are just tick marks still. If we want them to resemble drops we need to give them a shape. Add a Shape event up underneath the Position Object, so that it takes hold right after the particles are born.

-------------> We can always adjust the size more later on when we see our particles in action with a render. I have given mine a Size of 0.6 and made them Sphere 20-sides for now.

4

Your particles should be dripping down the side of your sphere now if you scrub back and forth along your timeline. Our next challenge is to make it so that not all the drops are singular. Let's make some trails on these particles.

Add a spawn up under the Speed by Surface.

---------------------------->

The spawn should be set to Travel by Distance, and we'll reduce the Step Size to 0.5 so our particles stay close together.

We will only make about 30% of our particles spawn trails so we don't make our droplets too predictable.

And down in the Speed settings, be sure to reduce the Inherited number down to a very low value like 5, as well as the Divergence to 0.0 so that our trails follow in line with one another.

Next we'll need to attach the Spawn's blue node to a delete event so that our trails don't spawn continuously and overrun our entire scene. Drag a Delete event out to the empty grey area of your Particle view, and connect the Spawn's blue node to the empty circle above the second event. Then change the delete settings to By Particle Age, and give it 15 with a variation of 10 or so.

-------->

Next we'll head back to our first event list, and we will take this a step further. Lets add an age test so that after a certain amount of time, we can tell our droplets to fall off the sphere like they more than likely would when they get too heavy and engorged with water.

5

------> Give the Age Test a value based on how far down they slip. I've given mine a value of 80, give or take 10.

Then hold down Shift on your keyboard until the mouse icon looks like an arrow with a + sign above it. Click on and drag down the Force from our first Event, into a new event below in the empty grey area of particle view and let go. Select Copy from the resulting dialogue box, and attach the blue node from the Age test to the new event.

This will make a copy of our first Force so that the droplets again start listening to gravity after they reach the age of 80 give or take, and they will fall off the sphere.

We may still see a bit of the particles falling through the faces of the spheres, in order to correct this a bit we will add another speed by surface under the new copy of our Force.

--------> Leave it set to Set Speed Once, and add your sphere to the list of Surface Geometry. Then give it a speed of about 25.

6

This allows our particles the chance to sort of hop off and away from the sphere just slightly so they don't risk falling through any geometry like the faces of the sphere.

Next we'll make some new trails for our falling drops, as not all of those fall individually either.

Add a new spawn under the new speed by surface. Make it a By Travel with a step size of about 0.3, but this time only make about 10% of them Spawnable. So we don't get overloaded with long streams like a shower, but more like just a big long drop every now and then.

-------------------->

Then again make the Inherited speed a low number like 5, and a Divergence of 0.0 so they fall in line.

And lastly we'll add another Delete event to the empty grey area in our Particle View and attach the new Spawn node to the empty circle for the new event.

------------------> Make the life span a lot shorter this time as they are going to be falling a bit faster now. I chose 3 with a variation of 1.

7

One of the final things we can do is add a Cache to the top of our Particle Flow to bake the animation, so that the particles don't slow down our machines too much by having to recalculate every time we scrub back and forth along our timeline.

Now all that's left is to make our particles look less like spheres and more like water.

Go to the Create Tab in your scene, and under Geometry in the drop down list. Select Compound objects.

Create a Blobmesh in your scene, and on the Modify tab. Add our PFSource to the Blob Objects list.

----------->

The blobmesh settings we will change our Evaluation Coarseness to 0.5 inthe Render field.

and I made mine about 3.0 in the Viewport.

8

Now all we have to do is make a water texture and add it to the blobmesh, and Hide our PFSource for the final render!

Enjoy your new droplets!

see a copy of the animation at http://animation.diclementi.com/tutorials/drip.mov

9