[Robotics] Linked group and rigid body constraints - problem.

[Morten Lind]

Hi all
 
 Background: In a manufacturing simulation I use a lot of work pieces which 
are handled by robots an transported by AGVs, as well as hung on conveyor 
carriers for painting. A very simple workpiece is an L-shaped, square cross 
section aluminium tube; a part of an office chair. 
 
 Having many such workpieces, like 100s, it is practical to make it in a group 
and then link all others, possibly from an external .blend-"library". Due to 
the non-convex nature of the L-shape, and the fact that this non-convexity is 
exploited in stacking the workpieces, I wish to model it as two box-shaped 
rigid bodies, each bounded by "box". These rigid bodies are invisible, and one 
should be doubly hinged to the other. To one of these, all other geometric 
parts are attached, notably a non-colliding object representing the actual 
geometric shape of the workpiece, and a small invisible cube for a gripper 
tool to sense contact with.
 
 The method and the structure of the L-shaped compound works splendid, so that 
I get a very fine and realistic scenario if the work piece is dropped into a 
box with other parts or dropped on top of an AGV. This can be verified when 
douplicating the group directly, creating a couple of workpieces.
 
 However, when linking the group to make linked duplicates, it seems that the 
constraints disappear, and the two rigid bodies just separates. Trying out 
another method where everything is parented to the "master" rigid body does 
not work, since the other rigid body will then have a parent and not move; 
dynamics for a rigid body with a parent seems to totally disable dynamics for 
that body. Trying to mend this parenting-problem by un-parenting and replacing 
by a couple of hinge-constraints on start-up does not alter the immobility of 
the rigid body that was born with a parent.
 
 I have been trying various ways to solve the problem for some days now. I 
have searched a lot on Blender Artists, as well as generally with Google, and 
I have read a lot of docs and examples. Nothing seems to even hint on the 
existence of this problem. If anyone has any suggestions on how to solve it, 
it would be received warm-heartedly by me! Alternatively, but not preferably, 
if anyone could inform me that this is un-acheivable with Blender 2.49b and 
it's game engine, I would be grateful for that information, and settle with 
what I can get then.
 
 Best regards,
 Morten Lind.