Hi. I'm trying to modify one of the examples, th RBD chain. Basically, I want to attach another object at the end of it. It works, but doesn't look very realistically. With every swing the amplitude get larger and the box flies around on the end as if it weights nothing. I tried a couple of things. If I add a drag, the increasing amplitude of the chain stops happening, but the box still doesn't come to a full stop. I also tried to add a second constrain, constraining the chain to the box, and at this points the whole simulation goes to hell. Do you guys know what I'm doing wrong?
Thank you,
Luka

There were a number of problems with this file. First, you had the box feeding into a separate RBD Solver than the rest of the chain. When you do that, DOPs treats thos as separate simulations. So it was solving the chain first, with no consideration for the box at all. Then it was solving the box, constraining it to the end of the chain, but completely unable to affect the chain in any way. So that's never going to work. You need all your objects going into a single RBD Solver if you want them al to interact with each other.

Second, once you put al objects through the same solver, the rbdconstraint5 node was setting up a constraint from _every_ link to the box (rather than just the last link). So it's no surprise that the simulation blew up. AS Soon as the objects started to rotate it becomes impossible to maintain all the constraints at the same time (notice the white lines that appear, indicating the distance between the actual position of the constraint and its goal). Also, that constraint was set up with a different position than rbdconstraint4. So again when the objects start to rotate, it's impossible to maintain both rbdconstraint4 and rbdconstraint5 at the same tie, so it blows up. To fix this part, change the Objet Location of rbdconstraint5 to “25”, and the “Object Group” to “link_9”.

At this point the simulation no longer blows up. But there is no gravity being a=pplied to the box. So the chain hangs between the origin and the box, while the box moves only slightly. So you want to add gravity to the box.

Now you hit play and the simulation blows up again. But this time it's simply because the box has a mass of 10,000,000, while the chain links each have a mass of about 3. Change the box density to 0.01 to make the masses a little more consistent.

What you end up with is the attached file. I hope that clears some things up for you.

Mark

Thanks a lot, Mark!