[ODE] Help with joint Constraint forces

[Sergey Kurdakov]

Hello Mostafa

> > If yes, what is lambda? and how does it relate to
> > the
> > force acting on the two bodies to preserve the joint
> > constraints ?  

I think paper here http://ode.org/joints.pdf  will answer quite a it in general,

having a contact or joint you have

 F = Fc + Fext

where Fc the force from contact and Fext is the sum of external forces such as gravity now
you have

Fc = J^T * lambda where  is a 'transpose' operator ( ie  J^T is a transposed J)

for the meaning of the last equation  - I suggest you to look at  Baraff paper http://www-2.cs.cmu.edu/~baraff/papers/sig94.pdf or
Jeff Trinkle  http://www.cs.rpi.edu/~trink/rigid_body_dynamics.html papers or
thesis by James A. Tzitzouris http://www.mts.jhu.edu/~jimt2/

there are number of other sources but hope this will answer your question.

Sergey


> > 
> >   I am having trouble understanding how ode computes
> > the joint constraint forces. Here is what I
> > understand
> > till now, please correct me if i am wrong.
> > 
> > The equation used is:
> >   J1*v1 + Ohm1 * Omega1 + J2*v2 + Ohm2* Omega2= c+
> > C*lambda
> > 
> > J1,J2,Ohm1,Ohm2 vary according to the type of joint,
> > so does c and C. Am I solving the equation for
> > lambda?
> > If yes, what is lambda? and how does it relate to
> > the
> > force acting on the two bodies to preserve the joint
> > constraints ?  If no, then what am I solving for?
> > Please reply to the mailing list and to my email
> > address just in case.
> 
> 
>