How do I troubleshoot a Houdini particle sim that's ignoring gravity?

[Madison_W]

I'm diving into Houdini for the first time, coming from a Blender background, and I'm completely stuck on something that feels basic. I'm trying to set up a simple houdini particle simulation for dust falling off an object, but my particles are just shooting out in random directions instead of falling with gravity. I think I've messed up the force node, but the network is already a spaghetti mess. Where's the best place to start troubleshooting when a sim just doesn't behave?

[OliviaXH]

Nice problem to tackle. Treat Houdini like a workflow puzzle: start simple and verify each assumption. Build a tiny scene with a single emitter above a ground plane. Put a POP network on it and add a gravity force node. If you’re not seeing downward motion, bake or cache a frame or two to confirm gravity is actually acting. Also check units: Houdini uses meters by default, so a scale mismatch can make gravity feel wrong. Ensure gravity is along the Y axis, not Z. Once you confirm gravity in isolation, you can gradually reconnect collision and surface forces and see where things drift. What does your current node layout look like for the core bits?

[JasonDA]

Skeptical but practical. Often the issue isn’t gravity at all but how the particles are emitted. If your initial velocity is high or random, they’ll shoot out before gravity does much. Turn down the initial speed or zero-out velocity, and check for any random velocity noise in the POP. Also verify the seed so you’re not chasing the same outcome. How is your emitter configured right now, especially the velocity parameter?

[James79]

Two quick tests you can run: 1) a tiny demo with a flat ground and a left-to-right emitter to see gravity pull; 2) a test with collisions active to confirm contact response. Compare the results to your real scene and keep your workflow simple so you can isolate where gravity is breaking.

[RichardS]

Increase substeps in the DOP/POP solver. If the frame rate is 24 or 30, try 8–12 substeps to get a smooth gravity curve. Also check the time scale in the solver; a slow time scale can make gravity feel too weak. After adjusting these, re-evaluate with the same asset and see if the motion matches the expectation.

[IsabellaNR]

Use a helper node to visualize velocity and acceleration. A color ramp on velocity can tell you quickly whether velocity is pointing outward due to emission or gravity pulling inward. This helps you refine the node logic without wrecking the whole network.

[Samuel_D]

Share a screenshot or file if you want. We can sketch a lean troubleshooting plan or a minimal working node tree to help you debug while keeping your spaghetti network intact.

[AdamDM]

Finally, consider documenting a small 'gravity test' workflow you can reuse across scenes. It saves time and reduces frustration when you bring in more objects. Are you comfortable posting a small sample node tree or a screenshot so we can tailor a minimal fix?