# [ODE] Infinite sliding... ?

Nguyen Binh ngbinh at gmail.com
Wed Aug 16 15:22:29 MST 2006

```What's the mass of your box?
If it's too small, you could possibly have that effect.

On 8/16/06, Jeff Kershner <jeff at jeffkershner.com> wrote:
>
> This is what I did:
>
> First: set mu to 10.0
>
> Second:  This is the third time I have heard that stepping at variable
> times
> wrong.  In
> a normal game loop that is operation almost all the time at 75 Hz, how
> much
> should the step size be and how often should it be called every frame?
>
> Third: can't do this since I need to interact with the bodies after they
> lay
> at rest.
>
> Forth: I saw in the FAQ/WIKI this question: "How do I stop things from
> rolling into infinity..."  This says to compute the velocity, multiply by
> a
> damping coefficient like -0.01 and apply with dBodyAddForce.
>
> This is what I do:
> const dReal* v = dBodyGetLinearVel(it->body);
> dBodyAddForce(it->body, v[0] * -0.01, v[1] * -0.01, v[2] * -0.01);
>
> // Also so this for angular vel with a coefficient greater than 1
> const dReal* av = dBodyGetLinearVel(it->body);
> dBodyAddForce(it->body, av[0] * 2.0, av[1] * 2.0, av[2] * 2.0);
>
> This is done at every frame when I update the graphical positions and
> rotations.
>
> After doing these steps, I am still getting boxes to slide forever.
>
> Any suggestions?
>
>
> -----Original Message-----
> From: Jon Watte (ODE) [mailto:hplus-ode at mindcontrol.org]
> Sent: Wednesday, August 16, 2006 12:42 PM
> To: Jeff Kershner
> Cc: ode at q12.org
> Subject: Re: [ODE] Infinite sliding... ?
>
> First, you should probably use a mu that's not infinity. Try 10.
>
> Second, you need to make sure you use fixed time steps. All calls to
> dWorldStep() (or the faster equivalents) need to pass in the same value
> for delta-time -- no exceptions!
>
> Third, you may want to enable auto-sleeping (disabling) of bodies at
> rest, if it isn't already.
>
> Fourth, you probably want to add dampening forces and torques to each
> non-sleeping body for each step. There's an entry in the FAQ/Wiki about
> this, IAICR. The most important part is actually the dampening torque,
> in my experience.
>
> Cheers,
>
> / h+
>
>
>
> Jeff Kershner wrote:
> >
> > I have a room where I drop random boxes. The boxes seems to collide
> > very accurately but don't ever stop moving.
> >
> > I am using surface mode dContactFDir1 | dContactApprox1 with mu =
> > dInfinity. Everything else in that structure is zeroed out.
> >
> > The floor is a geom without a body so that it will never move like it
> > says in the FAQ.
> >
> > Any suggestions?
> >
> > /jk
> >
> > ------------------------------------------------------------------------
> >
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> >
>
>
>
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--
--------------------------------------------------
Binh Nguyen
Computer Science Department
Rensselaer Polytechnic Institute
Troy, NY, 12180
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