Group in dops [SOLVED]

[Alain2131]

Hello !

I'm trying to apply a force in dops to some packed geometry based on some rule.
For the test, I use a group that have "@P.y<2.5" in its expression box, and use this group inside of a drag node.

But for some reasons, it's not working properly. I never used the group node in dops before, so maybe I'm missing something.
Not working properly being the force still applied to the geometry, even though the geometry is clearly above 2.5 in y position.

Anyone have an idea ?

Thanks !

group_in_dops.hipnc

Edited May 17, 2018 by Alain2131

[3dome]

that group is for grouping Simulation Objects. 

in your case a POP Group should work, since all the pieces in a single RBD Packed Object are represented as points.

Cheers

[Alain2131]

Hey Dominik,
thanks for you answer !

I actually tried the Pop Group, but I get an error on the node (

merge1:
Error: Connection to input 1 is the wrong type.
Connection to input 2 is the wrong type.

)

I don't know what I did wrong. Why is it throwing me this error ?
I never used POP Forces in dops, I don't know if there is a certain way to plug them up.

Thanks !

group_in_dops.hipnc

Edited May 17, 2018 by Alain2131

[3dome]

oh yes sorry forgot to tell you that this one needs to be plugged into the second or third input of rigidbodysolver.

second input = pre-solve means that whatever is plugged into it will be executed before the solver does its magic
third input = post solve => solver updates the pieces and all that stuff and then does all operations of that stream

so in your case i would plug it into the second input, followed by a pop drag (instead of the one you are using now) because in that way the pieces will enter the next simulation step with a reduced force/velocity (because of drag)

 

[Alain2131]

Well, that did the trick !

Thanks a lot !
Have a good day

group_in_dops[SOLVED].hipnc

[Alain2131]

Weird things happens sometimes though - I get "-nan(ind)" positions, and my object(s) dissapear. Strange. If you know right away what the problem is, great ! If not, then that's alright, I'm going to investigate !

group_in_dops_nan.hipnc

EDIT : Well, there doesn't seem to be much people on the internets who have this problem, so, darn it
But ! I think this happens only when the drag force is too strong. In my case this doesn't pose a problem, but it's still a bit strange. [SOLVED]... kinda

Good day !

Edited May 17, 2018 by Alain2131

[3dome]

25 minutes ago, Alain2131 said:

Weird things happens sometimes though - I get "-nan(ind)" positions, and my object(s) dissapear. Strange. If you know right away what the problem is, great ! If not, then that's alright, I'm going to investigate !

group_in_dops_nan.hipnc

EDIT : Well, there doesn't seem to be much people on the internets who have this problem, so, darn it
But ! I think this happens only when the drag force is too strong. In my case this doesn't pose a problem, but it's still a bit strange. [SOLVED]... kinda

Good day !

i'll have a look at that tonight but with a clean sop you can remove NANs (if that helps for now)

[Alain2131]

The answer is here, in the third paragraph -"If the drag value is very large with respect to the timestep, some solvers can experience instability."
Upping the substep significantly solved the problem (to 15 in my case, although it depends on the drag's value).

For the clean sop, I'm not sure how you would use it to correct a dop's nan error, plugging it before or after the dopimport in sopland didn't do the trick. But hey, upping the substep helps !
Thanks again

[3dome]

well instead of going crazy with the drag values you could just use a pop wrangle to mess with velocities directly
then there's no reason for increased substeps

switch between the 2 and see that the results are about the same (or maybe even THE same)

dm_group_in_dops_nan.hipnc

Edited May 17, 2018 by 3dome