Is vellum scale dependent?

   1966   3   2
User Avatar
Member
548 posts
Joined: Nov. 2005
Offline
I have to work on rather small object/creature, about 10cm, and I can not get the attributes for stiffness to work like it it would be in a 100cm scale
so I prepared a little test setup to demonstrate my current problem


the box has a stiffness attribute ranging from 0.001 (blue) to 200 (red). The upper box is scaled down by factor 10 before it goes into the solve.
The lower box is the desired motion, but somehow the sharp contrast in stiffness does not appear in the scaled down sim version?
I can not see any way to prevent this, other than creating it in a scaled up version, but I would prefer to stay in real world scale

thanks for Your time

Martin
Edited by sanostol - Dec. 2, 2020 16:04:19

Attachments:
sad_box.jpg (222.7 KB)
scale_dependent.hipnc (542.5 KB)

User Avatar
Staff
95 posts
Joined: Dec. 2010
Offline
Hi Martin, this is mostly an issue having to do with the mass being calculated per point based on the size (volume) of the tet mesh and the supplied Density value. The smaller object effectively has a total mass of 0.001 times the larger box. Try setting your Mass Density to 1000 and increasing Substeps. Try at least 4 substeps for the sim to converge properly. This should get you in the ballpark where you can start adjusting stiffness values.
-j
john mariella
Senior Technical Director
SideFX
www.sidefx.com
User Avatar
Member
548 posts
Joined: Nov. 2005
Offline
Hi John, thanks for Your help.
This does solve the problem, but would it be possible to have a world scale parameter here?
Your solution does fix the problem at the price of 4 steps to get a result, that is faster and, at least on the at the first impression, easier to achieve in another scale.

would this be possible at all to have something like a global scale parameter?

martin

Edit:
As soon as You adjust gravity to the new scale it behaves quite similar
Edited by sanostol - Dec. 4, 2020 06:25:06
User Avatar
Staff
779 posts
Joined: July 2006
Offline
There are options to set the Unit Length and Unit Mass in Preferences | Hip File Options. If you set these *before* creating any Vellum SOPs or DOPs, then physical parameters like gravity should be scaled appropriately.
  • Quick Links