[ODE] Arbitrarily positioning bodies connected by joints

Szabo Gabor uchimata at t-online.hu
Mon Jul 23 04:25:26 MST 2007


Ok, I just waited for answers too. All I can do in this topic to ensure 
that it would be a useful feature. It could save a lot of time for 


Shamyl Zakariya wrote:
> 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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