[ODE] hinge-2 and coordinate systems

[Timothy J. Wood]

   I'm new to ODE and I'm having trouble with joints.  I'm building a 
basic 4-wheel car from a chassis block and 4 wheels (drawn as cylinders, 
but simulated as spheres).

   My code is based fairly closely off the buggy test, but when I use 
hinge-2 joints, the chassis just falls to the ground.  When I use fixed 
joints (just for debugging), the wheels stay attached, but they quickly 
spin 90 degress CCW about the up vector.  This is maybe expected since 
when I create my wheels, I rotate them and fixed joints apparently don't 
support non-identity relative orientations.

   One difference between my code and the buggy code is that I'm using 
the standard OpenGL coordinate system instead of the coordinate system 
that ODE seems to use (with Z being up instead of Y).  Both are 
right-handed, so I would assume all should be OK.  The other difference 
is that I'm not currently using a geometry group since that should just 
optimize stuff, not actually change the results in this case.

   I've positioned and oriented my objects before attaching them.  Are 
there any other obvious things that would cause hinge-2 joints to 
completely fail to keep the anchor points together?  A search on the 
mailing list archive shows only that others are able to make hinge-2 
work, not any failure modes of this variety that I could find.

   Thanks!

-tim