>     I already read that method for friction model before, In the paper
> written by J.C .Trinkle as you recommand me to read before. I know the
> method is to use n friction vector in the tangent place to convex represent
> the friction cone as a friction polyhrdreon.But I have some doubt ,the
> method like the paper said for every contact point we need a matrix D
> belongsR(3 X N)where N is the friction vector.So in every contact point we
> need such a matrix ,so will it take too many memory to store those matrixs?
> Besides,it seems that the model can only choose one friction in the friction
> vectors in most of the time rather than the convex combination of
> them,So when the object is moving it seems impossible to calculate the
> friction force that is directly opposed to the velocity, this situation is
> methioned in Trankle 's paper "Formulations of multibody dynamics as
> complementary" Page .7. figure 6

> So could you give me a little guild about my doubt above.

> <http://count.mail.163.com/redirect/footer.htm?f=http://gouwu.youdao.com>

> It's true that you will need a number of LCP constraints to model
> linearlized Coulomb friction with each contact point. Basically, if you want
> to approximate friction circle by a hexagon then you need 8 friction LCP
> conditions with each contact.

> And it's true that using this model, there will be cases when you can never
> get the friction force that has exactly opposite direction to the tangential
> velocity. Trying to re-align one friction direction according to current
> tangential velocity might help a bit.

> And I think I need to repeat myself: 99.99% of current physics engines are
> NOT using accurate linearized Coulomb friction (described in papers by
> Stewart-Trinkle (1996) and Anitescu-Potra(1997) ). They use some sort of
> constraint that give friction-like behavior ( anything that resist motion
> can give us a feel of friction). And I am not saying that it's a bad or good
> thing, every model is made to serve some specific purposes. So ODE,Bullet,
> PhysX, Havok are great in computer games, film, etc.. but if you used them
> in machine desgin, robotics simulation then you should not expect the same
> results as in experiments.

> --------------------------------------------------
> Binh Nguyen
> Computer Science Department
> Rensselaer Polytechnic Institute
> Troy, NY, 12180
> --------------------------------------------------

> 2009/6/23 fish <fishbo...@163.com>

> > Hi Nguyen Binh:

> >     I already read that method for friction model before, In the paper
> > written by J.C .Trinkle as you recommand me to read before. I know the
> > method is to use n friction vector in the tangent place to convex represent
> > the friction cone as a friction polyhrdreon.But I have some doubt ,the
> > method like the paper said for every contact point we need a matrix D
> > belongsR(3 X N)where N is the friction vector.So in every contact point we
> > need such a matrix ,so will it take too many memory to store those matrixs?
> > Besides,it seems that the model can only choose one friction in the friction
> > vectors in most of the time rather than the convex combination of
> > them,So when the object is moving it seems impossible to calculate the
> > friction force that is directly opposed to the velocity, this situation is
> > methioned in Trankle 's paper "Formulations of multibody dynamics as
> > complementary" Page .7. figure 6

> > So could you give me a little guild about my doubt above.

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