[ODE] RE: attn: Erin Catto, concerning: fixed path constraint

[jnilson_99 at yahoo.com]

actually the more i think about using a universal, the
more i think it won't work.

here's my problem, i only want the upper arm to follow
a plane for a portion of the throw. around the point
the ball is released i want to "release" the upper
arm. that is i just want it to flow freely and follow
it's own momentum. just like in a real pitcher's
motion, he accelerates, throws and then releases.
after the release his arm follows whatever path it
wants.

if i were to use a universal joint here, after the
release the arm would still follow a plane, it
wouldn't look natural. after the release i need the
upper arm to act like it does in reality, it moves
based on the fact it's attached to a ball and socket
joint.

john

--- Erin Catto <erincatto at sbcglobal.net> wrote:

> Yeah, just recreate the joint to get the required
> plane of motion. The first
> axis is perpendicular to the plane.
> 
> 
> -----Original Message-----
> From: jnilson_99 at yahoo.com
> [mailto:jnilson_99 at yahoo.com] 
> Sent: Thursday, July 21, 2005 11:15 PM
> To: Erin Catto; 'ode'
> Subject: RE: [ODE] RE: attn: Erin Catto, concerning:
> fixed path constraint
> 
> 
> ok, using a universal joint makes sense. my only
> question would be: how do i allow the user to change
> the plane of the upper arm? this would be necessary
> to
> change the type of throw,i.e. slider, side arm etc.
> 
> if "The first axis is the vertical axis", then to
> change the plane at run time, do i just tweak the
> direction of this vertical axis? 
> 
> thanks,
> 
> john
> 
> --- Erin Catto <erincatto at sbcglobal.net> wrote:
> 
> > Okay, this is clearer.
> > 
> > You have just two rotation axes:
> > 
> > 1. The first axis is the vertical axis.
> > 2. The second axis is along the axis of the upper
> > arm.
> > 
> > For this constraint you can use a universal joint.
> > No ball joint or planar
> > joint is needed.
> > 
> > Erin
> > 
> > -----Original Message-----
> > From: jnilson_99 at yahoo.com
> > [mailto:jnilson_99 at yahoo.com] 
> > Sent: Thursday, July 21, 2005 9:03 PM
> > To: Erin Catto; 'ode'
> > Subject: RE: [ODE] RE: attn: Erin Catto,
> concerning:
> > fixed path constraint
> > 
> > "Perhaps you could explain the specific thing you
> > are
> > trying to model."
> > 
> > i'm trying to model various motions in sports,
> like
> > swinging, throwing, etc. all must use the
> > ball/socket
> > joint because that's the joint humans are using to
> > accomplish this task.
> > 
> > take throwing a baseball for example, the upper
> arm
> > moves along a plane roughly parallel to the ground
> > while rotating the lower arm from back to front.
> > this
> > motion requires a ball/socket joint because all
> > three
> > axis are being used. i could use a hinge to
> restrict
> > the upper arm to follow a plane, but then i
> couldn't
> > twist the lower arm.
> > 
> > i could use Russ's CMAC/Fox controller but for
> > various
> > reasons i don't want to do that. the biggest
> reason
> > being i want to allow the user to change the
> motion
> > of
> > the shoulder in realtime without requiring
> thousands
> > of training steps. using mathematical constraints
> > like
> > requiring motion only along a plane i would be
> able
> > to
> > change the motion of the shoulder and arm
> > immediately.
> > 
> > 
> > john
> > 
> > --- Erin Catto <erincatto at sbcglobal.net> wrote:
> > 
> > > I guess I don't understand what you're after.
> > > Perhaps you could explain the
> > > specific thing you are trying to model.
> > > 
> > > Erin
> > > 
> > > -----Original Message-----
> > > From: jnilson_99 at yahoo.com
> > > [mailto:jnilson_99 at yahoo.com] 
> > > Sent: Wednesday, July 20, 2005 1:32 AM
> > > To: Erin Catto; 'ode'
> > > Subject: Re: [ODE] RE: attn: Erin Catto,
> > concerning:
> > > fixed path constraint
> > > 
> > > "You cannot base a planar joint off a ball joint
> > > because a ball joint has 3 position constraints
> > > while
> > > a planar joint has only 2. "
> > > 
> > > maybe i'm incorrect in using the word "planar".
> > > after
> > > a few google searches, it seems planar joints
> are
> > in
> > > fact a real joint type. by planar i simply mean
> > > confining either a universal or ball/socket to
> > > follow
> > > a plane through the joint anchor. this would be
> > > something like defining a spline and making an
> arm
> > > follow the spline's path.
> > > 
> > > i'm also a little confused on constraints. yes a
> > > ball
> > > and socket has 3 constraints per se. but it also
> > has
> > > "limit" constraints which confine the joint to
> > > certain
> > > angle ranges of motion,i.e. hi/lo stops.
> > > 
> > > is it possible to add my planar constraint like
> an
> > > additional limit constraint?  i could go through
> > the
> > > laborious process of updating the hi/lo stops
> > every
> > > time step to the exact angle made by the plane
> and
> > > the
> > > ball/socket joint arm. i'd rather find a more
> > > elegant
> > > solution though.
> > > 
> > > thanks,
> > > 
> > > john
> > > 
> > > 
> > > 
> > > 
> > > 
> > > john
> > > 
> > > --- Erin Catto <erincatto at sbcglobal.net> wrote:
> > > 
> > > > You cannot base a planar joint off a ball
> joint
> > > > because a ball joint has 3
> > > > position constraints while a planar joint has
> > only
> > > > 2. I would implement a
> > > > completely new joint type and use the code for
> > > other
> > > > joint types as a guide.
> > > > The planar joint needs to use the position
> > errors
> > > I
> > > > wrote along with their
> > > > Jacobian rows.
> > > > 
> > > > Erin
> > > > 
> > > > -----Original Message-----
> > > > From: jnilson_99 at yahoo.com
> > > > [mailto:jnilson_99 at yahoo.com] 
> > > > Sent: Monday, July 18, 2005 1:36 AM
> > > > To: Erin Catto; 'ode'
> > > > Subject: attn: Erin Catto, concerning: fixed
> > path
> > > > constraint
> > > > 
> > > > Erin,
> > > > 
> > > > I've given this a lot of thought as I'd like
> to
> > > > create
> > > > an additional "planar" constraint for any
> joint.
> > > > Take
> > > > a ball and socket joint for example. You
> mention
> 
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