[ODE] three-body joints

[Graham Fyffe]

Hi everybody.  I'm wondering, what are the design issues that caused
Russ to implement only two-body joints?  It seems to me that, from the
point of view of the "big matrix", it's just as easy to implement n-body
joints.  For example, the differentials used in cars can only be
implemented as 3-body joints.  No combination of 2-body joints will do.
 The equations for a differential are in the form e.g. c1 wA + c2 wB +
c3 wC = 0, for bodies A, B, C.  What would it take to add n-body joint
support?  Also, there was some mention of a desire to use the TAUCS
linear solver library, so I figure both changes could be done together
:)  I'd be willing to contribute to the effort, for what it's worth.

- Graham Fyffe
president, Happy Digital