particles jerking problem

[seb4d]

Hi !
I simulated a simple thing : coffee beans emitted horizontally from a grid and falling down by gravity. They are simulated with Bullet RigidBody.
I set up my scene at 100fps because I need slow motion, I'll read the render images at 25fps in the compositing program.

My problem is that the particles are not travelling fluently, the motion is a bit jerky. When I scrub frame by frame I can see that, for example, each particle travels 5 units each frame, but every (let's say) 5 frames it travels 8 frames.

Any idea how I can deal with it ? The resulting animation is not good, it's all jerky.

Thanks !

[SamHowell]

Are you playing back your simulation set to realtime instead of all frames?
Are the rigid bodies colliding with anything in the scene?
How dense are you rigid body meshes?
Have you tweaked the precision of the simulation?
Have you altered the scale of your setup?

[seb4d]

Are you playing back your simulation set to realtime instead of all frames?
I play it "all frames", but the problem is not the playback in xsi, after the render is done the sequence is like that too.

Are the rigid bodies colliding with anything in the scene?
Particles are colliding with each other, the point cloud is made of different instances with different shapes (coffee beans, ginger, etc...).
They are first colliding with simple geometry in a tunnel shape in order to give them the right direction and flow (like water pouring out of a pipe), and then they are free in space (jerking appears when they are free too)

How dense are you rigid body meshes?
Meshes are pretty low poly meshes, about 500. Then I cache the simulation and use it back with high res versions of the meshes.

Have you tweaked the precision of the simulation?
Yes, precision is set to 120. Maybe try higher ?

Have you altered the scale of your setup?
I actually scaled up the pointcloud I use to read the cache of the simulated pointcloud yes. But I checked the original simulation at scale 1 and the problem exists too.

[SamHowell]

Scaling the pointcloud won't make a difference, you need to change the scale of the whole setup before the simulation begins. Anything too big or too small could be causing you problems. Peversley, sometimes having the precision too high can cause jittering in my experience. Maybe turn that right down again and see what happens.

[seb4d]

Ok I played with the simulation precision and managed to remove the problem. As you said, setting it up too high causes some problems too.
Thank you for your support, it helped me a lot !

[SamHowell]

Cool, thats a relief!

There is so much tweaking involved with RBD's it can drive you mad learning all of the little idiosyncrasies of the controls.