sometimes objects fall, sometimes not (beginner)

Discussions about rigidbody simulation in Realflow 4
Anaxarchos
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Joined: Wed Mar 19, 2008 4:21 pm
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sometimes objects fall, sometimes not (beginner)

Postby Anaxarchos » Wed Mar 19, 2008 6:54 pm

Hi,

maybe you are able to explain this strange sort of behaviour to me:

I built a scene. First, I started out with a plane (Sim active, Rigid Body, Primitive: Plane, Collision Outside, Dyn Motion: No). Then I added a sphere, also as a rigid body but with dynamic motion turned on. I moved the sphere a little distance above the plane and added a gravity demon (default settings).

I pressed the "Simulate" button and everything happend as I expected it to hawppen. The sphere dropped on the plane and kept lying there.

So I rolled the frames bar back to zero and pushed "Simulate" again. Everything worked fine again. So I set it back to zero another time, pushed the button...and nothing happened. The sphere kept staying in the air.

The gravity values hadn't changed at all, so hadn't the other object's values. I decided on deleting the gravity node and added a new one. As a reault everything was still working fine. I pushed the simulate button after rolling back the animation frame bar over and over again, as suddenly, after abot 5 runs, the sphere wasn't moving, again. This time, pushing the "Reset" button, next to "Simulate" solved the problem.

What is the cause for this?
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shaun_michael
Posts: 4766
Joined: Sun Sep 10, 2006 8:04 am

sometimes objects fall, sometimes not (beginner)

Postby shaun_michael » Wed Mar 19, 2008 7:57 pm

Well this is indeed odd.

Try this:-

Add a plane and position it at zero on the y
Add a sphere and position it at 1.0 on the y
Ensure the plane is a rigid body, motion set to no, plabe primitive, all other values at default
Ensure the sphere is set to "Motion:Yes" and all other values at default.

Set the sim for 20 frames and simulate.

Without resetting the sim, drag (or use the transport controls) to take the sim back to frame zero and hit simulate.
Accept the usual warning about losing data from frame 1.

What happens?

Now, reset the sim, and set the height of the sphere to 2.0 on the y (y-up by the way).
Run the sim, take the slider back to zero manually, and hit sim again. Accept the warning.

What happens?

Anyone getting the sim to repeat at 2.0 for the sphere nd not 1.0?

Now, clearly, if you want to run a simulation from zero you should reset the scene, but if you wish to interrupt a scene and take it a few frames back - will it work? It should do but with the sphere set to 1.0 it doesn't.

RF 4.3.8.0123

Shaun

Anaxarchos
Posts: 843
Joined: Wed Mar 19, 2008 4:21 pm
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sometimes objects fall, sometimes not (beginner)

Postby Anaxarchos » Fri Mar 21, 2008 5:49 pm

thanks for your answer.

Resetting the scene was the key to success, here. Some stuff was still in memory and I confused the engine.
www.fk-fx.com

shaun_michael
Posts: 4766
Joined: Sun Sep 10, 2006 8:04 am

sometimes objects fall, sometimes not (beginner)

Postby shaun_michael » Fri Mar 21, 2008 5:55 pm

Well I'm not convinced thats the case you know. Why would having the sphere at 1.0 on the y axis not work, when having it at 2.0 on the y axis work?

Weird!

Shaun


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