Animate Particles with Forces
Blender 3d tutorial
The particle system in Blender is typically used for grass or fairly basic particle effects. However, force fields can be quite powerful in drastically turning your typical boring particles into well controlled or even vaguely directed particles that go where you want them to go.
To gain control of particles in Blender 3D, we will cover some basic particle emission setup, how to use force field physics objects to control particle animations, and how to create a particle material that changes as the particle ages.
Setup: The Emitter
Before playing with particles, we are going to set up all the components of our scene. If you have the default cube, delete it. We will not be using it in this tutorial.
In its place, add a plane (Shift-A --> Mesh --> Plane). Scale it along the X axis by a factor of .250 (Press S, X, 0.25) and along the Y axis by a factor of .4 (Press S, Y, 0.4). This plane going to act as our emitter, which we will come back to later.
Next, we want to add an empty (Shift-A --> Empty). The empty is going to act as our first force field. If they are not already, ensure that both the plane and the empty are centered at the origin.
Setup: Empties and Camera
There are also two other empties in our scene that will be exactly the same as each other except for their position in the scene. Because of this, we will make one now and then duplicate it after we have added the force field later on. For now, select the empty currently in the center of our scene, duplicate it (Shift-D), and move it along the X-axis by 8 units.
The next object we need to set up is the camera. With the camera selected, open up the Transform Panel by pressing 'N', if it isn't open already. Then change the X, Y, and Z values under Location to 0.000, 0.000, and 40.000. Then change the X, Y, and Z values under Rotation to 0, 0, and 0. This puts the camera into a top down view. You can see these settings in the image here. Lastly, down in the timeline menu, change End to 400.
Let's add a particle system into our scene now. Since our plane is going to be the emitter, select the plane and go to the Particles settings. Once there, add a new particle system to the plane by clicking on the button with the plus sign on it.
The first batch of settings we are going to change are in the Emission section. To recreate the video, we want quite a large number of particles which emit until partway through the video and live throughout nearly the whole video. With that in mind, we will change Amount to 15000, End to 150, and Lifetime to 250. Other settings to change include changing the Normal setting in the Velocity section to 0.000, turning off the Emitter setting in the Render section, and changing the Gravity setting in the Field Weights section to 0.000.
If you play the animation at this point (Alt-A) then you should see the particles appear on the plane and do absolutely nothing. This is exactly what should be happening since we have turned off gravity and we have changed the Normal initial velocity to zero.
Now for the fun part! Let's start by selecting the empty located at the origin of our scene. In the Properties panel go to the Physics settings. There should be one button labeled Force Field. Click on that and you should see a set of options appear. By default, the force field will be set to the most basic force, however, we want to change the Type from Force to Vortex.
We will then change the Strength setting, which you will want to set to 10.000. If you play the animation (Alt-A) now, you should see the particles move in a circular motion and outward, with the particles moving faster as they are farther away from the center of the vortex.
However, since we do not want the vortex to affect the particles everywhere in our scene, we are going to turn on Maximum by checking the box next to the setting and changing the value to 2.000. In the 3D viewing window, you should see a dashed circle appear around our vortex showing the area that it affects. Feel free to replay the animation to see this in action.
Lastly, we are going to change Power to 0.500. This setting changes how strongly the force field effects particles based on the distrance from the center of the force field. The higher the value, the less strongly the field works at the edges of its maximum boundary.
The Force Fields
The other type of force we will use is the basic force field. Select the empty that is off to the side of the emitter, go to the Physics section and click on the Force Field button. Similar to the vortex force, we want to set the maximum distance in which the Force field will work. In this case, we turn on Maximum and change it to 8.000. Also, change Power to 0.900. With the maximum distance on this force field and the other force field (which we will make soon!) we will split the group of particles into two groups.
Without the maximum value turned on, having many force fields with the same strength would cause a group of particles to move to where the forces are equal and cause the particles to eventually sit in one spot. If they have different strengths, the particles will be pulled towards the greatest force.
Side Note: If you've never used forces, this is a pretty good time to test out the other types of forces available. While exploring, keep in mind some forces may require something else to get started. For instance, the magnetic force doesn't do much without an initial velocity on the particles and the Charge force won't work unless you give the particles themselves an initial charge (this can be done in the Force Field Settings section in the particles panel. Make Type1 Charge and particles will be given that charge).
Animating the Force Field
Unlike the vortex force, we will animate the strength of this force field. To start, make sure we are on frame 1 in the timeline and make sure the Strength of the force field is at 0.000. Then right click on the Strength setting and choose Insert Keyframe. Now move to frame 90 in the timeline and change the Strength setting to -50.000. Insert another keyframe by right click on the Strength setting again. Finally, move to frame 100, change the Strength setting to -100.000 and add a new keyframe.
If you remember, we still need one more force in our scene, but because it is exactly the same as the one we just created, we do not have to add a new empty. Instead, we duplicate (Shift-D) the force field we just made move it along the X-Axis by -16. This puts it on the opposite side of the vortex force and the edges of the two force fields touch right in the middle. Playing the animation now should give us the final particle movement that we are looking for.
Rendering the current set up will get us some pretty ugly results. To fix this, we'll change the material of the emitter. Select the emitter and go to the Materials settings in the Properties panel. Click on New to create a new material for our particles. Then change the materials type to Halo so we can tweak the way the particles look.
The material itself is pretty simple. We are only going to change Alpha to 0.000, Size to 0.070 and Add to 1.000. The particles will look very tiny in the preview, but since there are so many of them in our scene, we will have no problem seeing them in the render. Add also brightens up the particles so that we can see them more easily.
In the video, a simple blend texture is used to get the nice color changing effect to our particles. To do this, make sure the emitter is selected and go to the Texture settings. Click on the New button and change the Type of the texture to Blend. In the Colors section we want to turn on Ramp. This is where our colors are chosen. The first color will be on the left and the last color is on the right end of the gradient. Feel free to use whatever colors you like. Also, note that you can choose color values greater than 1. Sometimes this gives you a brighter color. For instance, the red in my gradient is RGB(1.650, 0, 0).
To get this blend texture to effect the particle based on its age, we have to go to the Mapping section. In here, change the Coordinates to Strand/Particle. This effects the color of the particles based on their age rather than on where they were created on the emitter. We also want to go into the Influence section. Make sure both the Color and the Alpha settings are on and change the Color value to 1.600.
Now we have colors and the movement of the particles complete, however, you may notice it is quite sparse. There are many ways to remedy this, such as adding more particles, making the particles larger in the materials section, or by adding children particles. Since I wanted small particles, I added children. Adding children doesn't slow down the calculation of the particles, especially compared to simply increasing the number of particles.
To add children we need to select our emitter and go to the Particles settings. There should be a section called Children with three buttons to choose from. Click on Simple. New settings should appear. Then change Render to 10, Radius to 0.300, and Roundness to 1.000. This will give us 10 times as many particles in our render without the extra time to calculate the particles. Stray particles may look a bit clumpy, but when packed together you can't tell the difference.
That's all for now! Go ahead and render an animation of your controlled particles!
No single tutorial will cover everything, so if you want to dig deeper, here are some resources for you to check out. If you have other resources you think I should add to this list, feel free to let me know!