   generalized coordinates
  Hi,i need help in the following topic:In many papers about rigid body dynamics there is talked about generalized coordinates which appear, if one has some holonomic constraints on an simulated object(for example joints and stuff like that), to make computation easier.Somitimes there are some examples and special cases how to compute them but i have never seen, that there is some algorithm or a general way to compute them. Also it would be nice, if someone would explain, how the equations of motion look like in generalized coordinates and how to convert and compute them on the computer, i.e gives an algorithm.I'm happy for any help, papers, answers... thnx   
  Hmm, let's see.You have one generalized coordinate for each degree of freedom. For instance a hinge joint has one DOF so you'd naturally take rotation as the GC. If you have a hinged joint connected by a bar to a second joint then you have 2 DOG and then you'd have two GC both as angles.The equations of motion are the same (IIRC) which is why this is easier - that sinple hinge joint would require reolving in 2 dimensions normally. It cuts out a lot of redundant calculation.Is this for programming or for school - if the former then search for some theoretical physics course notes online or look in a library.I may still have notes because it might be a module I thought I may actually use in real life.   ;  My Physics-English is not very good, but I will try.The "Newton Equation" in generalized coordinates is the "Lagrange function" (I do not know if there is a differen english expression for this, I just freely translated "Lagrange Funktion").If qi (i being a natrual Number), pi=d(qi)/dt T the kinetic energy and V the potencial (so the the Force F is F=-dV/dx), then the Lagrange function isL=T-Vand the Newton equations are:d/dt(dL/dpi)=dL/dqiMmh .. I gues that does not help much. I would look into some good book for "Lagrange function".Good Luck,Nathan   