[ODE] contact joints / attaching them

[gl]

> Not really. A penetration is an "error" in the rigid body configuration
> (if bodies are rigid, they should not ever penetrate). Since ODE is a
> discrete simulator, it makes these "errors."
>
> The Error Reduction Parameter (ERP) reduces error by pushing bodies apart.
> Also, the Constraint Force Mixing allows slight errors (violations of
> constraints) to be tolerated.

OK, that sounds right, but then let's say that the errors will be different,
and that this will produce different results.  With tuning those differences
may be minimal, but it's worth bearing in mind, and it might be significant
in certain setups.
--
gl