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nomojosh

RBD/Bullet solver not accurately colliding with ground plane

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Hi all, 

I'm exploring some basics in Houdini and wanted to make a simple sphere bounce on a ground plane. However I'm struggling to get the sphere and ground plane to make contact - the sphere seems to bounce above the floor for some of the fast bounces?
I wondered if it's a framerate but ramping that up to 240 fps doesn't reveal any hidden subframe contact.

What parameters are needed in order to improve accuracy? I appreciate I'm using fairly small scale (ping pong ball @ 40mm)


I'm absolutely stumped! 

Thanks

 

Simple_RBD_Collision.hipnc

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in the Global Anim Options (bottom left corner), I disabled integer Frame values, step 0.01

Sim substeps 5-8

There's probably other settings which I don't know about.

 

Simple_RBD_Collision2.hipnc

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10 hours ago, Noobini said:

in the Global Anim Options (bottom left corner), I disabled integer Frame values, step 0.01

Sim substeps 5-8

There's probably other settings which I don't know about.

 

Simple_RBD_Collision2.hipnc

Thanks Noobini, that certainly shows it colliding with the floor. Obviously when you render out with integer frames, the issue returns.

Is it simply an optical illusion and the hit is simply not captured on a frame (using 24fps). Contrary to what I said in my first post increasing the framerate does actually improve the accuracy (with substeps at 8). But something feels off. Some of the slower bounces still seem to collide quite high above the floor.

I also tried scaling the ball up to 1 unit (metre?) and the gap between the ball and the floor also increases!?


Of all the complex stuff I've done in Houdini, I can't believe I'm struggling with a bouncing ball! :D
 

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13 hours ago, nomojosh said:

Thanks Noobini, that certainly shows it colliding with the floor. Obviously when you render out with integer frames, the issue returns.

Is it simply an optical illusion and the hit is simply not captured on a frame (using 24fps). Contrary to what I said in my first post increasing the framerate does actually improve the accuracy (with substeps at 8). But something feels off. Some of the slower bounces still seem to collide quite high above the floor.

I also tried scaling the ball up to 1 unit (metre?) and the gap between the ball and the floor also increases!?


Of all the complex stuff I've done in Houdini, I can't believe I'm struggling with a bouncing ball! :D
 

yeah I actually don't know the rendering process myself, hopefully some expert will chime in.

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