Ground burst debris effect?

I have Hitfilm pro-2017, I'm currently using the particle system and I am using the inbuilt appearance rock debris.  My question is how do I set up the particle system to have the rocks fly up and get pulled down by gravity?   My end goal is to have a zombie hand coming out of the ground. 


  • Triem23Triem23 Moderator
    edited September 2017

    You'll want to have multiple emitters in a single particle layer. You'll create one first, then duplicate it and make some changes.

    You'll need a 3D plane aligned with your ground surface to be a deflector. If you're using your grave you might need several planes arranged to leave a "hole" where the grave is.

    You'll want your emitters to be Circle emitters with Cone trajectories. You'll adjust the trajectory angle so the cone is perpendicular to the circle emitter.  For your first emitter, go ahead and check Boundary as well.

    You'll align your circle emitter to lie flat on the ground plane.

    At the bottom of the particle emitter controls are the menus for forces and emitters. Click the "+" icon to create a new force. The default force is gravity. Rather than the default strength of 25%, take this down closer to 3-5%.

    Under Forces is Deflectors. Click the "+" icon and select Layer Deflectors and choose your planes. Note if you're not worried about the hole you could use a cubic deflector to be your ground.

    Now you'll have to twiddle around with particle speed and gravity strength until your motion dynamics are correct. You'll also need to tweak the bounce and friction parameters. Take note of the Mass parameter. We'll talk about that in a minute. 

    Once you have the motion of the first emitter correct, duplicate it a couple of times. On the duplicates you'll want to make changes to particle size and speed, and the angle of the cone trajectory. Basically to add realistic variation. Big rocks will have less velocity than small rocks, for example. You can vary the size of your circle emitters, and, for one or two, turn off boundary. 

    Consider some mobile emitters. The mobile emitters would be invisible (scale 0%) but would spawn lots of tiny particles to be dust. This is where Mass comes in. Turning up particle Mass reduces the effects of Forces. Oddly enough turning mass (and mass variation) UP is better for the dust! Reducing the effect of gravity (via increasing mass) will have the particles "hang" in the air longer. Dust, caught in the moving air...

    Remember, the particle sim can use 3D models as particle textures. If you bring in a rock model you would probably get better results than the built-in rock/concrete textures. You could build multiple rocks for different emitters... Maybe one with a "flat" edge and some grass texture for the surface layers and some "pure" rocks for deeper layers.

    For inspiration, this is a test building a procedural ground explosion in the particle sim. It's built using the exact principles and techniques discussed above. Pretty much the only difference between this and what you want to do is choice of textures and texture colors.

  • @Triem23 how do I stop the particles from going through the ground plane?

  • Use the Deflector controls to define something for the particles to bounce off. You'll have the option to use a plane layer (or several) or a cuboid.

    You might need to check in the "General" Settings for the individual Particle System and make certain "Affected by Forces/Deflectors" is on. 

  • @Triem23 do you mind If I look at your project file if you have one?

  • And how do I keep it from regenerating or aka cycling the particles 

  • @Triem23 I finally go the right projectile, now I do I get that gravity force like in your video?


    This is what I have so far.... I need help with the gravity part.  Once the debris reaches its peak its needs to fall back to the ground

  • Triem23Triem23 Moderator
    edited September 2017

    Yeah, I'll find the project. Hopefully I remember to upload after work.

    In Emitter>General is a property called "Active." This controls whether or not an emitter spews particles. Keyframe this to turn off after a frame or two. Alternatively, keyframe "Particles per Second" to drop to zero.

    To get the particles to fall, you have to add a force as described above. Again, the default force is... Gravity. 

    The particle sim is Hitfilm's most complex and powerful tool. Until I get around to it, Axel's Hitfilm 2 Ultimate breakdown is the best tutorial for the basic controls, although it misses some features added in HF 3 and 4.

    This covers textures.

    These next two cover mobile emitters.

    These next two cover some use of forces and deflectors:

    And these discuss using 3D models as particles:

     And some good general tips:

    I did say the particle sim was complex, right? 

    That's starting to look good. You'll make this work. 



    Test 2,  I got gravity finally but now how do I manipulate the gravity so the debris doesn't get sucked back into the floor?

  • How did you get the particles to suck back to the emission point to begin with? Looks like you used a Cuboid force set to Attraction, which would be what pulls particles to the center of the zone. You should be using a Global force set to Direction.


    Test 3,  I got the result but now what should I add to it...

  • Motion dynamics are getting there. Maybe a sharper burst at the start?

    I think you're ready to add your textures. Decide which systems are rocks and assign a concrete/rock texture. Dust, assign colors from your BG plate. See how that's looking.

    Once you get the textures in, you might want to add some dust/smoke stock footage if you have any. You've got a good start already, now it's refinement, and that's just taking the time to tweak. 

  • @Triem23 What property would I manipulate to have a sharper burst?

  • edited September 2017

    @Andersen01498 ; Nice slow "bubbling" before the eruption.  I like it!  It will build suspense before the "whatever" crawls out if the ground/grave.

    Edit: This was supposed to post at 11:20 am from my phone.  Don't know what happened.

    @Triem23 I've starred this thread for the wealth of knowledge you're tossing out like candy at a parade!  Thanks, man.

  • Andersen without seeing your project, tough to tell. Do you WANT the bubbling before the burst? It looks like you may have keyframed particle speed to start low for the bubbling then raised it for the burst. Am I close? 

  • I'm rendering out my project so you'll see soon I hope :)


  • (To clarify, I meant without seeing the particle sim settings. Like I said, the particle sim is very complex.)

  • I keyframed the percentage of gravity that's what I did

  • Oh, interesting! So you have high gravity for the bubbling, low gravity for the burst, then turning gravity back up?

    That's different. In general when I'm using a force for gravity I set it to a desired value and don't animate that as gravity is basically constant (as a given location).

    Consider locking your gravity value and keyframing speed instead.

    Whether you keyframe speed or gravity, consider making changes very sharp. Like frame 100 has gravity (say) 25 and frame 101 has gravity at 5. So you get a sharp change in dynamics. At a guess I would say your gravity keys are three to five frames apart which is why the bubbling "swells" to your burst.

    Grab reference footage. Look on YouTube for ground bursts, and check out the library at ActionVFX. Seeing what you're trying to recreate will help you judge how close it is.

    Don't get discouraged. I keep saying it, but the particle sim is complex and often just requires a lot of tweaking values to dial it in. That one particle explosion (and I'm on my third day in a row of 12-14 hour gig, so I've not had a chance to upload the project) was several hours of tweaking. It's actually still incomplete since the next step would be to replace the static fire textures with an video texture of fireball stock. 

  • @Andesen01498 ; I've been watching this intently since I too wish to simulate a ground burst.   Please do not take this a an insult.   I thought you were going for a creature or entity bursting out of the ground.  What you posted @ 12:02 is a perfect simulation of what an in the ground lawn sprinkler looks like when it starts up.   Or possibly a fountain    If you decided to do massive changes please save that project as well as it is also valuable.


    This is way far from done but this gives you just a general idea of what my project entails.  

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