[ODE] Arbitrarily positioning bodies connected by joints

Shamyl Zakariya shamyl at zakariya.net
Fri Jul 20 15:01:45 MST 2007

Have I asked the question poorly?

I can't imagine that nobody here has ever tried to *move* a  
collection of bodies connected by joints.

In the past, I've just assembled things on the fly at the position  
and orientation I want them to start at, but it seems very useful to  
me to be able to build something at one place, and then arbitrarily  
transform it later.

shamyl at zakariya.net
     "obviously, you're not a golfer"
         -- the Dude

On Jul 17, 2007, at 10:44 AM, Shamyl Zakariya wrote:

> I'm interested in being able to move a set of bodies connected by
> arbitrary joints. That is to say, I want to be able to assemble them
> at, for example the origin, and then move the whole thing to some
> arbitrary position and orientation later. For example I might
> assemble a "car" and then move it to where I want it to go.
> I'm able to move all the bodies retaining their positions in relation
> to one another. But, unfortunately, the joints go bonkers to varying
> degrees. The best behaved is the ball joint, which ( I guess )
> considers its position to be relative to the parent. But other
> joints, such as hinge and slider seem to freak out a little.
> Just to clarify, when I move the bodies I zero out all forces on
> them. I've verified that if I move a bunch of bodies that aren't
> connected by any joints they *do* retain their relative positions
> correctly. So the issue is that the joints don't seem to enjoy being
> suddenly moved/oriented.
> My current approach is simply to not do anything to the joints, and
> assume (hope) that ode considers their attachment points in the
> coordinate systems of the bodies they connect. But as I've described,
> this doesn't really work. I've considered destroying the joints,
> performing the move, and the re-creating them, but this may change
> their zero-points since a connected system ( two bodies connected by
> a "servo", for example ) may have moved before I positioned it.
> Any suggestions for me?
> Shamyl Zakariya
> 	- hobo-raconteur
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