[ODE] clock stepping and ODE

Kevin Quigley kevin.quigley at gmail.com
Sat Nov 17 09:48:57 MST 2007

Interesting.  As I care more for the output of the simulation than
running real-time graphics, hopefully I won't get bit as much.

Since it will be a while before I have time to look, how deeply
integrated are the first-order integrator and constraints?  If it's a
matter of creating a higher order set w/ the same API as the current
ones, I can look to make replacements later on.  If not, I'm going to
have to rething what I'm doing.

My goal is to be able to run an ODE simulation while connecting to my
robot's processor, so real-time is very important for my
hardware-in-the-loop setup.  If I can do this, I can work on the
control algorithms while building the physical bot in parallel.


On Nov 15, 2007 5:23 PM, Jon Watte (ODE) <hplus-ode at mindcontrol.org> wrote:
> ODE uses a first-order integrator, and first-order response constraints.
> This means that time step variability will introduce energy in joints
> and contacts.
> To solve the seeming discrepancy between real-time and stability, use a
> quantized main loop.
> http://www.mindcontrol.org/~hplus/graphics/game_loop.html
> Cheers,
>           / h+
> Kevin Quigley wrote:
> > On Nov 11, 2007 4:42 PM, Jon Watte (ODE) <hplus-ode at mindcontrol.org> wrote:
> >
> >> 3) To make a simulation stable, make sure that you're using a fixed time
> >> step. Variable time step sizes, say based on the clock, will introduce
> >> energy into the system.
> >>
> >
> > This was from the "sliding box on plane" thread earlier this week, but
> > I was wondering what kind of instability using the system clock would
> > generate?  The user's guide specifically mentions that "ODE is
> > designed to be used in interactive or real-time simulation."  That
> > implies that ODE will be able to use an outside clock in some fashion,
> > although it shouldn't be variable stepping if you want to keep it
> > real-time.
> >
> > Did I misunderstand something from the previous post?  I was hoping to
> > use ODE on an RT system.
> >
> > quig
> >
> >
> >

There was a pirate's parrot who got a bad case of sunstroke and was
heard crowing, "Pieces of seven, pieces of seven," which was clearly a
parroty error.

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