[ODE] velocity constraints vs. acceleration constraints

Bob Dowland Bob.Dowland at blue52.co.uk
Tue Jan 11 10:19:27 MST 2005

Pretty fundamental questions - it'd be great to hear some responses!

In the meantime, one issue with acceleration constraint is friction - from http://www.math.umbc.edu/~potra/fulltext.pdf

"The major obstacle in incorporating the Coulomb friction model in multibody dynamics simulation is that the classical force-acceleration model with a corresponding Newton law is inconsistent: it does not necessarily have a solution in the classical sense."

The rest of that paper is about "Timestepping" - which might be worth googling.



> -----Original Message-----
> From: Achim Moller [mailto:netcom2002 at gmxpro.de]
> Sent: 10 January 2005 09:53
> To: ode at q12.org
> Subject: [ODE] velocity constraints vs. acceleration constraints
> Hi,
> I have some basic question about the pro and cons for using "position
> constraints" vs. "velocity constraints" vs. "acceleration 
> constraints".
> >From the ODE joint creation docs and the ODE source, I think 
> ODE is using a
> "velocity constraint" representation (Right?).
> Some other papers (e.g. thesis of Michael Cline) are talking about
> "acceleration constraints".
> Of course, "acceleration constraints" can be created from "velocity
> constraints" by differentiating the vel. constraints again. 
> But what are the
> general pro and cons for driving a physics engine by either 
> vel. or acc.
> constraints? (Or even positional constraints?)
> Thanks a lot for some thoughts about this.
> Achim
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