[ODE] Center of Mass of Mesh

Jon Watte (ODE) hplus-ode at mindcontrol.org
Mon Jun 25 21:05:44 MST 2007

The reference point for trimesh geoms is the origin. If you have another 
center, you need to offset the geom.

Note that the translation part of the mass is ignored by the body 
simulation code, so don't expect to use it. Offset the geoms instead.

Joints are not between geoms; joints are between bodies. Perhaps that's 
what you mean. Note that the impulse is torque*time/inertia, and your 
time step is typically 1/100th of a second.


          / h+

yyd_iris at yahoo.com wrote:
> Hi, 
> In ODE, center of mass must coincide with geom
> reference points. I have read some posts about setting
> center of mass of geoms. Basically there are two ways
> to do it: 1. use geom-translate and 2. geom offset. 
> I have some questions about the case of TriMesh geom.
> 1. Is there default defintion of TriMesh reference
> point? I have mesh models of some manufacture parts.
> Their reference points are just somewhere in the
> middle of the models. I also have the dynamics data:
> center of mass and the inertia at the center of mass. 
> The next two questions are general to all geoms. 
> 2. In my understanding, dMassSetParameters is equal to
> dMassTranslate plus setMassRoate, if I do the right
> computation, right? 
> 3. If I apply a torque to a hinge joint with two gemos
> (one end is fixed), I should be able to get an
> acceleration of q_dotdot = torque/inertia. But in my
> experiments, I need to apply a much bigger torque to
> get the accelerations. Is there any parameters I
> should pay attention to? 
> Thanks!
> Iris
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