[ODE] How to realize natural interaction?

[Roland Landertshamer]

Hi all,

This is my first post to this list and since it probably will be not the last 
one i think i should introduce myself. My name is Roland Landertshamer, i'm a 
student and i'm working on my master thesis about physics simulation in 
networked virtual environments.
For the implementation of my work i'd like to use ODE as physics engine. In my 
application world entities are represented by rigid bodies. The users of the 
application should be able to interact with this objects in the sense of 
grabbing an entity via a virtual hand and moving it around. The virtual hand 
should only be visible and not collide with other rigid bodies. In my current 
implementation i realized the virtual hand as a body without geometry to 
ignore collisions. Before each simulation step the transformation of the 
virtual hand is set manually and the velocities and forces are zeroed. When 
the virtual hand moves into the bounding box of an entity the user can grab 
this object. I realized the grabbing by adding a fixed joint between the 
virtual hand and the entity. This works quite well so far. The simulation 
fixes the joint error produced by the manual positioning of the virtual hand 
quite well.
My problem now is that i can interact with all objects independent of their 
mass. For example i can grab an object with mass 1000 and throw it away the 
same way as it would be with an object with mass 1. The desired behaviour 
would be that an object with more mass should be harder to move and rotate. I 
thougt about realizing this via a linear and angular spring. Any ideas how to 
implement this in ODE?

Roland