[ODE] Jitters and GeomTransforms

Andrew Schroeder schroe2a at gmail.com
Wed Feb 2 10:14:11 MST 2005

I'm having simalar problems with geom Transforms.  I use one attached
to the same body as the head of my robot, and use it's position to
drive the location of a third-person camera.  This works really good,
the camera doens't affect the mass of the head, you can detect
collitions with the camera and stuff and do all the nice things you
want a third person camera to to.  However, I find that as my robot
moves around, the geom transform jerks around and it's motion is not
smooth like that of the body it's attached to.
One hunch is that Chris Calef is on the right track with the scaling
thing. Maybe when ode calculates the position of the geom transform
relative to the body small rounding errors cause the postion to be
slightly different each timestep causing jitter and even penetration
into the floor.  If this is correct then Chris is right that scaling
up the units would HELP, but not solve the problem.

If you find any solutions or have more insight, I would be very interested...

On Mon, 31 Jan 2005 11:50:37 -0700, matt stephure <stephure at gmail.com> wrote:
> Hi all,
> I'm working on a multiple robot simulator project. I'm currently
> having the following problem with ODE.
> I'm using a spring/dampening friction style (CFM/ERP calculated along
> the fly, along with the dContactApprox1). My solid plain geoms when
> dropped sit nice and still on the Plane.
> However, my transforms (created, iirc, correctly) have a jitter. When
> I built my robot up the jitter becomes more and more extreme.
> I had less of this problem, or it was less noticable, when creating
> large geoms. Most of the parts I'm making now are on the order of
> 50cms or so.
> I've tried adjusting the global CFM/ERP and I haven't had much
> success. I've added in BodyDampening and played around with those
> values, also without much success. Additionally, increasing the step
> size does help, but never fully correctly the problem.
> I'm willing to live with some jitter, but I can't have my robots
> blowing themselves apart after a while.
> Any insight would be great. Excellent work with ODE in general, I do
> not have a physics background, but I have been able to develop fairly
> complex simulations -- kudos. If it is a problem with the
> 'squishiness' of the plane, how can I make it more solid? My kp is
> already quite large.
> Thanks for your time,
> Other variables of interest:
> Max contacts: 10
> Step size: 0.002 .. 0.02
> Kd = 0
> Kp = Large (100000)
> Dampening = -0.001
> --
> | Matt Stephure
> | stephure at gmail.com
> +----------------------------------------------------------
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