[ODE] Picking objects

[Manohar B.S]

Ya, spring-damper works nice when tuned properly. But
I didn't get the cear idea what you have done with the
Robot Arm. Can you explain with a small code.

 when you say follow the 'Proxy' at best => it means
to 'Constrain' the physical object to the position of
the proxy as in a joint (LCP). Some people do this by
connecting the 'proxy' and the ODE body with a
spherical joint (or any other joint). This should work
fine I guess.

 When you say 'Clamp' acceleration and velociy it
means you are playing with State params as per your
'taste' => in other words fuzzyfication.

 -- Manohar BS.
www.scientifik.org

--- Bob Dowland <Bob.Dowland at blue52.co.uk> wrote:
> Guys,
> 
> some time ago I had to simulate a robotic arm and
> control the pos/ori of the end effector using output
> from a 6d pos/ori tracker - lots of fun. What I did
> with that might be of interest and might not but
> there we are.
> 
> I used what you might call a "reference proxy" which
> responded perfectly (ie kinematically not
> dynamically) to the user input. The motion of this
> proxy was totally free and unsullied by the ravages
> of physics/collision response - it could go through
> walls, outreach the arm and so on.. The arm then
> just "did the best it could" to follow it. Where
> "doing the best it could" meant not violating it's
> various dynamic and geometric constraints. This
> worked very nicely.
> 
> As far as spring and damper mechanisms go the main
> problem seems to be the tuning issue. In particular
> in graphical sims the spring (and underlying
> metaphor :) ) will often get "stretched" far beyond
> any reasonable physical limits / dynamic operating
> range - so in a sense the model breaks down. One
> awful hack that works quite well is to treat the
> spring damper as a black box, tune stiffness and so
> forth to taste (so that things are good where you
> mostly need them) then maintaining a very clear idea
> of what velocity/acceleration ranges you want to
> allow just clamp the outputs.
> 
> Bob.
> 
> > -----Original Message-----
> > From: Manohar B.S [mailto:sciphilog at yahoo.com]
> > Sent: 30 June 2004 10:55
> > To: Olivier Parisy
> > Cc: ode at q12.org
> > Subject: Re: [ODE] Picking objects
> > 
> > 
> > Hello James,
> > Hello Olivier,
> > 
> > > It's sad we have to get to such tricks as soon
> as
> > > model control is needed... Perhaps someone who
> > > developped a stable servo example could
> contribute
> > > it in ODE distribution someday ? I know it would
> > > solve most of my animation/interaction needs !
> > 
> > Well, I think there's a serious need for model
> control
> > or Motion controller interface with the physics
> > engines (which ever it be). Well, oscillations are
> > part of the physics and the physics engine is
> happy
> > becos it is honestly doing what it is supposed to
> do.
> > We always expect some thing that we get convinced
> of
> > due to our past experience with the nature
> > (irrespective of right mathematical
> justification).
> > 
> >  At this time I am not very much informative about
> how
> > to make a very "convincing" and "Accurate" motion
> > control interface but I believe that Fully logic
> based
> > contoller is the best option. But the requirements
> are
> > like this:
> > 
> >  1. The Physics body/geom should follow the
> position
> > and orientation of the Motion sensor as quickly as
> > possible (with accuracy).
> >  2. Oscillations should be minimum or atleast
> > invisible.
> >  3. Forces applied on the physics body/geom should
> be
> > clean enough to be applied to the forcefeedback
> > device.
> >  3. The algorithm should be computationally lite.
> > 
> > ___________
> > Fuzzy Spring-Damper will have variable spring
> konst
> > and variable damping konst, depending on the rule
> > table entries.
> > 
> >  I would be happy to dedicate time for research in
> > this like.
> > 
> >  -- \
> > Manohar BS
> > 
> > 
> > 
> > 		
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