# [ODE] 3 out of 4 contacts box->plane?

Kevin Quigley kevin.quigley at gmail.com
Wed Oct 10 16:34:25 MST 2007

```sent this out to just jon, by mistake.
quig
---------- Forwarded message ----------
From: Kevin Quigley
Date: Oct 10, 2007 7:33 PM
Subject: Re: [ODE] 3 out of 4 contacts box->plane?
To: "Jon Watte (ODE)"

This is what I'm seeing, looking down (-Z axis):

got 3 contacts
contact 0 at {0.235, 0.1, 0}                            X-------X
contact 1 at {0.235, -0.1, 0}                           |          |
contact 2 at {-0.235, 0.1, 0}                           0-------X
world time: 0.01
got 3 contacts
contact 0 at {-0.235, -0.1, -1.0791e-11}         X-------0
contact 1 at {-0.235, 0.1, -5.39551e-12}        |          |
contact 2 at {0.235, -0.1, -5.39551e-12}        X-------X
world time: 0.02
got 3 contacts
contact 0 at {0.235, 0.1, -1.18701e-11}        X-------X
contact 1 at {0.235, -0.1, -1.0791e-11}         |          |
contact 2 at {-0.235, 0.1, -9.7119e-12}         0-------X
world time: 0.03
got 3 contacts
contact 0 at {-0.235, -0.1, -1.7913e-11}        X-------0
contact 1 at {0.235, -0.1, -1.40283e-11}        |         |
contact 2 at {-0.235, 0.1, -1.33808e-11}       X-------X
world time: 0.04
....

I tried setting mu = dInfinity, but didn't change anything.  This is
just a static box sitting on a plane. e.g.  box -Z side is == plane.

What is the unit for mu btw?  Is there an SI used there?

thx,
quig

On 10/10/07, Jon Watte (ODE) <hplus-ode at mindcontrol.org> wrote:
> 3 Contacts will give stability. However, depending on stability, you may
> end up with 2 contacts on one side one frame, then 2 contacts on the
> other side next frame, then bouncing back and forth -- usually too small
> a movement to be actually noticed on the screen.
>
> So... are you sure what you're seeing is wrong?
> Btw: you're setting mu to 0, which means no friction in contacts. That's
> usually a bad idea for stability.
>
> Cheers,
>
>           / h+
>
>
> Kevin Quigley wrote:
> > I'm seeing 3 contact points generated by a box geometry sitting on (or
> > through) a plane.  I can't figure out what's gone wrong in my
> > callback.  This is a mixture of various bits I found in the
> > wiki/manual.  Any ideas?
> >
> > The three contact points are not always the same, either.  When drawn,
> > some or all of them flicker as one contact is not drawn during that
> > step.
> >
> >
>
>

--
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.

--
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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