What I meant, concerning you model ‘trailer 001.3dm’, was that the cabin is no longer on his original place when you attached (made child) the trailer, because the cabin was displaced as the result of the active Simple constraint (To Path). At the time an object is made child his pivot’s position in regard to his parent’s pivot is recorded. The commands BongoSelectChildren as well as BongoSelectParent have an option ‘SnapIntoPlace’ which specifies whether an eventual parental transform (move/rotate/scale) active at the current tick will be applied to the child object. Unfortunately the use of the second option ‘KeepHierarchy’ - I assume dealing with the effect on the children’s children (grandchildren) or further down the hierarchy - is somewhat obscure and absolutely undocumented in the Helpfile. Anyhow; the dislocation of the cabin is what finally disrupts your trailer (on top of unnecessary constraints and missing hinges).
When the “driver” of an IK-chain is a ToPath or LookAlong constraint, it is wise and handy (although not absolutely necessary) to build the chain before installing the Simple constraint. Conversely it is very hard to get the mutual configuration (position/rotation) of the elements of the chain right. Moreover I find it advisable to position the chain close to the beginning of the path and in the accurate direction, in order to have swift results from the IK-solver.
In regard of your new container problem, I think maybe the same issue is at hand. I don’t understand what you mean by
… so I’m afraid I cannot help you without a more precise description of what you are doing exactly. I suggest you try combining container and trailer while the Simple (driving) constraint is disabled.
I feel you are maybe somewhat confused: Simple constraint versus IK constraint:
- A Simple constraint is merely an active way of animating (making move and/or rotate) an object. It has nothing to do with IK. In your case it only operates as the ‘engine’, the ‘driving motor’ of the IK chain.
- An IK constraint mostly defines a goal which the IK element has to reach. That’s why Bongo sometimes has to report “Constraint goal not reached”.
I would recommend a tutorial with accompanying sample models “The basic Why’s of IK” (http://bongo.rhino3d.com/forum/topics/the-basic-why-s-of-ik) concerning the basic structure of an IK-chain.
Also my video tutorial “Simple constraint versus IK: a clarification” http://bongo.rhino3d.com/video/simple-constraint-versus-ik-in-bongo-2-0-a-clarification may be useful.