[ODE] are torque and force measures available for all joints in ODE?

Jon Watte (ODE) hplus-ode at mindcontrol.org
Mon Aug 28 15:11:25 MST 2006

The easiest way to get these forces is to measure the delta-velocity for 
each body, and multiply that by mass, divided by timestep size. This 
will give you the net force that acts on an object. If you are using 
gravity, but measure movement in world space, then add the gravity force 
to this value.

You can sometimes also use the joint feedback to get an approximation of 
this information, although that's on a per-joint basis, not per-body.

The most important thing to realize is that the step-to-step forces will 
be very jittery (because ODE is penetration based), so you have to 
integrate over some amount of time to get a smoother value that you can 
actually do anything useful with.


/ h+

Armand Prieditis wrote:
> I’d like to access the torques and forces that external forces cause 
> upon a set of joints connected through bones. For example, when a foot 
> in on the ground, the forces from the ground presumably propagate to 
> the knee, hips, pelvis. Are these available through some function 
> call? If not, is it easy to get these? It seems like ODE must have 
> these easily accessible since it must use such information to compute 
> the result of external forces upon a connected object.

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