[Sserver-three-d] Re: Reg friction in Robo-3D simulation

[Markus R. <rol...@un...>]

Hi,

Shaik Shadab Sayani wrote:
> Is there any frictional force acting on the objects in the soccer 
> field.If so from where can I get this info(like friction co-efficient
>  etc.,).

As I said before:
> Ode does models friction for contact surfaces only
[...]
> The default collisionhandler is a 'ContactJointHandler' that creates
>  'ode contact joints'

The ContactJointHandler creates so called ODE contact joints, see the
ODE manual [1] at section 7.3.7 [2]. The default contact surface
parameters used in the server (see contactjointhandler.cpp:34) are:

     // set up default contact surface parameters
     mSurfaceParameter.mode = dContactBounce;
     mSurfaceParameter.mu = dInfinity;
     mSurfaceParameter.bounce = 0.8f;
     mSurfaceParameter.bounce_vel = 2.0f;

They are currently used as they are for the soccer simulation.

The second source of friction,
> a simple air drag is simulated with a so called 'DragController' (see
>  rcssserver3d.rb:65 and lib/oxygen/physicsserver/dragcontroller.*)

This Dragcontroller appllies a linear force that is proportional to the 
current velocity of a player (see dragcontroller.cpp:46):

         Vector3f vel = mBody->GetVelocity() * mLinearDrag * -1;
         mBody->AddForce(vel);

Additionaly an angular drag is applied to dampen the torque of an object 
over time (see dragcontroller.cpp:53)

         Vector3f vel = mBody->GetAngularVelocity() * mAngularDrag * -1;
         mBody->AddTorque(vel);

The paramters used here are at a default value of 0.1 each) (see 
DragController constructor) but are set to 12.0 each in the 
rcssserver3d.rb (line 66)

Shaik Shadab Sayani wrote:
 > Also does this frictional force produces a torqus on the
 > object.

Concerning the actual mathematics behind ODE I can't tell give you that 
much detail. However on the ODE page are some useful links that give 
more background about Rigid Body Dynamics, please see [3]. Maybe you can 
find out yourself ;)

cheers,
Markus

[1] http://ode.org/ode-latest-userguide.html
[2] http://ode.org/ode-latest-userguide.html#sec_7_3_7
[3] http://www.d6.com/users/checker/dynamics.htm