[ODE] several questions from new user

Martin C. Martin martin at metahuman.org
Mon Jan 26 20:17:17 MST 2004

Ary Setijadi Prihatmanto wrote:

> 1. I tried to make capped-cyllinder chains (only like chain sample just 
> with capped cyllinder element) with zero forces on it (free fall 
> movement). When the body hit the ground, I noticed that the geoms 
> sometimes overlap each other. I try to adjust global ERP and CFM but it 
> seems the results in not change. How can I  solve the problem.

I think you can't solve the problem.  ODE doesn't try to force geoms
apart until they've collided.  So you'll always have some overlapping,
at least for a little while.  Also, if ERP < 1, they may overlap in
steady state.  Although, if you don't have gravity, then probably not.

> 2. I want to make a system with a complex visualization but still with 
> simple physical simulation & collision detection. Making a visualization 
> as a puppet of physical simulation. For that purpose, I think i will 
> going to need joint information especially if we want to use 
> skeleton-based mesh. There are methods available for hinge, hinge-2 and 
> slider joint types, but not for ball and universal.
> I realize that it is not trivial to get the angle change for ball and 
> universal joint, but maybe relative transformation matrix between 
> attached bodies will be usefull to get (with jointID parameter) not only 
> global transformation matrix(function with GeomID/BodyID parameter).

Sure the universal joint does, although you might need to get the latest
version from CVS.  For ball and socket, try attaching an AMotor to it,
with FMAX = 0.  You can read the joint angles from the AMotor (I think).

> 3. I also want to have a physical simulation only a part of the body 
> system and make it fix for other part for several simulation periods.
> I know it is possible to disable the simulation for the whole "island", 
> but is there any way to do the similar for the part of the island?
> I dont want to ruin my ODE copy ^_^

I think this is answered in the fact.  You can have a joint or motor
between the part you want fixed & the world.

- Martin

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