Guide Particles with Collision Deflectors in Blender

In Blender, collision deflectors allow you to physically redirect, bounce, and shape the paths of emitted particles to create controlled simulations like flowing sparks, guided liquid sprays, or stylized motion graphics. This guide covers how to set up an emitter, assign collision properties to target geometry, fine-tune deflection settings such as damping and friction, and combine multiple deflector shapes to precisely channel particle trajectories.

1. Setting Up the Particle Emitter

  1. Add your emitter mesh by pressing Shift + A and choosing a mesh object (such as a Plane or UV Sphere).
  2. Open the Particle Properties tab in the Properties panel and click the + button to create a new particle system.
  3. Keep the type set to Emitter.
  4. In the Emission panel, configure the Number, Frame Start, Frame End, and Lifetime according to your scene requirements.
  5. Under the Velocity sub-panel, adjust the Normal velocity to give the particles an initial speed and direction.

2. Adding Collision Physics to a Deflector Object

  1. Add or select the mesh object you want to use as a barrier or guide (for example, a curved plane, funnel, or angled cylinder).
  2. Navigate to the Physics Properties tab.
  3. Click on the Collision button to enable collision physics on that object.
  4. Play the animation in the timeline (Spacebar) to verify that the emitted particles interact with the deflector.

3. Configuring Deflection Properties to Shape Trajectories

Once Collision is enabled, adjust the parameters under the Particle sub-panel in the deflector’s Physics tab to alter the particles' rebound behavior:

  • Damping (0.0 to 1.0): Controls how much energy particles lose upon impact. A value of 0 creates a perfectly elastic bounce, while a value of 1.0 absorbs all velocity along the surface normal, making particles slide along the geometry.
  • Randomize Damping: Introduces variation in how much speed particles lose, scattering trajectories naturally.
  • Friction (0.0 to 1.0): Dictates how much resistance particles experience when sliding across the surface. Higher values slow down particles moving parallel to the deflector.
  • Randomize Friction: Adds variation to the slide speed across the deflector surface.
  • Stickiness: Forces particles to adhere to the surface upon contact, useful for creating splatter or cling effects.
  • Permeability (0.0 to 1.0): Sets the percentage chance that particles will pass directly through the deflector without colliding, ideal for partial filters or grates.
  • Kill Particles: Instantly terminates any particle that touches the surface, useful for containing simulations within boundaries.

4. Techniques for Precise Trajectory Guidance

  • Curved Guide Rails: Model curved strips with Damping set to 1.0 and Friction set to 0.0. Particles striking the surface will lose their perpendicular velocity and glide smoothly along the curve.
  • Funneling: Create a cone-shaped mesh with the top and bottom faces removed. Assign collision physics to focus a wide particle spray into a narrow, directed stream.
  • Multiple Stage Bouncing: Place sequential flat planes angled at 45-degree increments to reflect particles around corners, maintaining high velocity by keeping Damping near 0.0.
  • Invisible Guides: If the deflector should guide particles without being seen in the final render, go to the Object Properties tab, expand Visibility, and uncheck Renders.

5. Baking the Particle Simulation

To ensure stable playback and prevent trajectory recalculation issues during rendering:

  1. Select the emitter object and open the Particle Properties tab.
  2. Expand the Cache section.
  3. Set your desired Simulation Start and End frames.
  4. Click Bake to freeze the calculated particle collisions and trajectories to disk or memory.