[ODE] how to glue bodies together ?

[Nate W]

On Thu, 29 Jan 2004, Brian Clarkson wrote:

> >Our application aims on very accurate collision detection.
> >So, computation time is not critical, but accuracy is .
> >Detecting breaking is not our goal either.
> 
> I think the detection of break forces on joints is very much part of
> body physics. Just as much as collision. A very efficient fixed joint
> would be very useful for this. There are several benefits to breakable
> joints for sub bodies which need to break apart.

I haven't actually tried this, but:

It seems to me that it should be pretty straightforward to NOT use
fixed joints, and instead compute the amount of force (torque and/or
linear) present at the location of the 'virtual joint.'  If that force
exceeds a certain limit, then create a second body and give it the mass
and geoms of the object that is supposed to be breaking away.

I'm pretty sure that would take much less CPU time than a fixed joint
would require.

> All this is for free once you implement Roel's breakable joints. I did
> and it has introduced another level of realism to our RTS.

Does Roel implement the mass-combining and mass-separating functions, or
is his code implemented as multiple ODE bodies connected with fixed
joints? 

I have no doubt that fixed joints speed development - and that's a good
thing - but I wonder about the CPU demand of a joint that removes all
degrees of freedom.


Nate Waddoups
Redmond WA USA
http://www.natew.com/