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I am animating a piece of machinery, and am currently trying to simulate rocks falling into a hopper, then being pushed down the screw. I am open to any method that gets this done.

(In the picture below, I have a boolean cutting the objects in half, but the particles etc are still colliding with the whole mesh). The screw is rotating, and should be pushing the rocks along.

Currently I have tried rigid bodies, which work the best, but with the size / amount of particles I want, is not possible on my PC.

I have tried particles with collision objects, but the particles, as in the picture below, merely go underneath the screw.

I've also tried using a curve guide to guide the particles, but as they are falling from below, and can fall into several different slots, that just isn't working.

Any and all help is appreciated!

UPDATE: I am now using the Molecular addon, but my only issue is the extreme bouncing off of particles from each other. Is there any way to reduce that?

UPDATE 2: I am now using a texture to reduce the particles' size over their lifetime - does this scale down the 'collision' shape for the particles too, or just how they look visually?

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In your case, the Molecular Addon works best. To download it, go here: https://github.com/scorpion81/Blender-Molecular-Script/releases and select the zip file for your OS. Do not unzip it. Go to Edit->Preferences->Addons, click Install and select the zip file. Then enable it.

Usage: The molecular add on is a way to make particle systems behave more lifelike, for example, collisions, stickiness, etc.

For your case (follow these):

  1. Create a particle emitter (can be any shape)
  2. Give your mechanical parts collision modifiers
  3. Instance an object on the particle system (I use 1 subdivision Icospheres, low geometry is better)
  4. Press the play button and make sure the particles fall correctly as you want. Note that the molecular addon is still not working right now and particles will still behave normally, which includes clipping through each other.
  5. Once you are happy, scroll down inside the particle system settings and check "Molecular". The add on is now enabled, but in order for you to see the effects you need to bake it. Now we will adjust the settings.
  6. Open the density menu and press the button. Choose "sand", and this will accurately calculate the weights of each particle.
  7. Open the collision menu and enable Self Collision (particles collide) and Collision with Others (particles collide with other things).
  8. In order to see the results, open the simulate menu, choose a frame range, and press "simulate". Once you are done you can view the simulation by playing the animation, and you can also reset it by just pressing "free bake"

Tips:

  • Instance low poly objects on your particle system. Even one less vertex makes a big difference
  • Make sure to increase the particle lifespan so they make it to the end of the animation.
  • Are items still clipping through each other? Increase the timesteps. I usually use around 16 timesteps for relatively fast simulations.
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  • $\begingroup$ I am currenlty using cubes with 1 level of subdivision on them, is low-poly better? Or would it make it act weirdly? Thankyou for this amazing answer, regardless! $\endgroup$
    – Yelefthandman
    Commented Sep 15, 2020 at 22:53
  • $\begingroup$ UPDATE: I am now using the Molecular addon, but my only issue is the extreme bouncing off of particles from each other. Is there any way to reduce that? $\endgroup$
    – Yelefthandman
    Commented Sep 16, 2020 at 1:36
  • $\begingroup$ UPDATE 2: I am now using a texture to reduce the particles' size over their lifetime - does this scale down the 'collision' shape for the particles too, or just how they look visually? $\endgroup$
    – Yelefthandman
    Commented Sep 16, 2020 at 3:45
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    $\begingroup$ @Yelefthandman, inside the collision objects there are settings you can change like particle damping and friction, you can also change the particle settings inside the collision menus in the addon. $\endgroup$
    – Eric Xue
    Commented Sep 16, 2020 at 12:01

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