[ODE] Silly question, Is ODE based on accurate physics ?

Konstantin Slipchenko slipch at gsc-game.kiev.ua
Fri Feb 11 12:29:41 MST 2005

Hello Chris,

Friday, February 11, 2005, 12:15:58 AM, you wrote:

CR> Hello there, it just dawned on me, is ODE based on 
CR> real time physics ?

It is based on First Type Lagrange's equations of motion.
They are equations of motion for systems with holonomic constraints.
Holonomic constraints are constrains which reaction forces do no
mechanical work during system motion. Simply saying the constrains can newer
be broken.
   If we had joints error and and CFM always zero we would be within the
bounds of the theory of mechanical systems with holonomic constraints.
CFM can not be set to zero at least for exact LCP method due to
problems with singularities. Supporting zero error for all joints is
a much more difficult task, I think.
  On other hand with real holonomic constraints it would be simulation
for perfectly rigid bodies, which does not exist in real world. In
this case we would never see bouncing when dContactBounce param is not set.
      Unfortunately, since the simulation breaks the theory on
which it based it is rather difficult to make real numerical
estimations. As far as I understand there are some estimations on
deviation from the theory. At least we have equations for spring and
damping via ERP, CFM and time step.

Best regards,
 Konstantin Slipchenko                           mailto:slipch at gsc-game.kiev.ua

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