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Newton's Cradle


Symbolic

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Hi,

I am trying to re-create the "newton's cradle" example from the Gnomon RBDs DVD. Some how I got stuck... something is wrong. I have to systems.

One uses "RBD Pin Constrains" the other one uses "RBD Spring Constrain"...

In the system with the Pin constrains, the balls just go through each other. I do not know what is wrong?

:(

Sorry it is a very messy file. I wanted to be able to control the position of everything with nulls... ended up with a totally non-procedural system.

:(

newton_15_wrong.hipnc

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Yeah... but when I use it then the ball keeps leveled when moving up and down... like there is a rod passing through it...

I just wanted the DOPs system to be correct as possible... maybe I will use just one "RBD Pin Constrain" going through the center of the ball...

Instead of trying to make like the real toy... guess cheating is the word :)

It is not that important... I just got confused about this... I wish the example was in the DVD... i guess it is not...

and the RBDContrain is not there in H9... thats what confused me.

Sorry for wasting your time.

:(

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I tried to get the collision in your hipnc to work but couldn't - now I'm confused too ;)

(being a relative noob might explain that, though)

The other branch does work, but the one with pin constraints just refuses to collide.

eetu.

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Jeff Lait solved this one. The Rotational Stiffness parameter on the RBD Objects was set to zero. The help for this parameter says that a lower value makes the object easier to spin. But what the help doesn't say is that a value of zero breaks the system completely. Setting this value to zero is like giving an object a zero mass - it makes the value physically meaningless.

Generally when a simulation suddenly breaks, the best thing to do is hit Undo a few times until it starts working again. Then figure out what parameter is was that you changed to make it break. Fixing a simulation as soon as it breaks is always the best time to do it. Another good way to debug these problems is to rebuild the simulation from scratch, and more often than not it will work. Then you just need to start comparing parameters (opscript output can be useful here) until you find what is different.

Mark

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