Constraints Stretching in Dynamica for Maya 2011

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damonresume
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Joined: Fri Apr 22, 2011 5:48 pm

Constraints Stretching in Dynamica for Maya 2011

Post by damonresume » Fri Apr 22, 2011 5:58 pm

I am very green to dynamica - while playing with the simple scene of 20 spheres generated in Y axis, constrained together and 0 mass on the top sphere - simulation looks great. However, as soon as I set the lower sphere to mass of 1000 the whole thing starts stretching. Whatever settings I change in rigid or constraints option does not change the stretchiness of the chain. Any suggestions on how to basicly make a chain-like setup - with whatever the mass of the object at the end of the chain not stretching the rest of the chain...

Thnx for any help...

Maya 2011 64-bit
Dynamica 2.77 64-bit (updated)

DC

Dirk Gregorius
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Re: Constraints Stretching in Dynamica for Maya 2011

Post by Dirk Gregorius » Fri Apr 22, 2011 7:52 pm

Attaching large masses at the end of a string is as bad for an iterative solver as putting a too heavy object on top of a lighter one. You can search for large mass ration issues on the forum here. As a rule of thumb keep ratios in the range 1 : 10. Also for a string you would like to become lighter towards the free end, not heavier! Same applies for ragdolls (or general tree like structures). You make you limbs lighter as you move from the pelvis towards the "outer" limbs.

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Erwin Coumans
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Re: Constraints Stretching in Dynamica for Maya 2011

Post by Erwin Coumans » Sat Apr 23, 2011 3:14 pm

In the current Dynamica svn trunk there is an option to descrease the internal physics framerate. By default it uses 200 Hertz. If you use 2000 Hertz or higher, you can add a 1000 kilogram sphere at the bottom.

You can download a precompiled version of Dynamica for Maya 2011, Windows 64bit here: http://dynamica.googlecode.com
http://code.google.com/p/dynamica/downloads/list
Thanks,
Erwin
physics_framerate.jpg
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damonresume
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Joined: Fri Apr 22, 2011 5:48 pm

Re: Constraints Stretching in Dynamica for Maya 2011

Post by damonresume » Mon Apr 25, 2011 9:56 pm

Thank you... Reg the 1:10 ratio ... a heavy abject such as a wrecking ball would behave way different due to the fact that the chanlink holding it weights 100-300 times less then the ball itself ...
But the update with the physics frequency works great - thank you so much ...

I really think its an awesome simulation plugin - good luck with it - let me know if you ever need anyone to beta test it and do some nice renderings and lighting of the animations ...

DC

damonresume
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Joined: Fri Apr 22, 2011 5:48 pm

Re: Constraints Stretching in Dynamica for Maya 2011

Post by damonresume » Mon Apr 25, 2011 11:41 pm

Okay - so the stretching is gone ... however after playing with this thing with the new version - the simulation is different everytime I run the simulation... It is different enough that I can't get the simulation of bounces and such the same everytime I run the simulation without changing any settings .... Is this the problem with new version or is that because of "2000" in the physics frequensy !?

DC

abby99
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Joined: Thu Aug 25, 2011 7:16 am

Re: Constraints Stretching in Dynamica for Maya 2011

Post by abby99 » Thu Aug 25, 2011 7:17 am

I just want to say thank you for the information.
It is very valuable for me..newbie here and encountering the same situation.
Thanks and keep up the good work..

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