Stretchable bodies

[Brennan Peter Sellner]

Hi,

This is perhaps more a Coin question, but is there any way to model
stretchable bodies in OpenRAVE?  I'm not interested in springs or the
like, but would like to display a set of cylinders whose length changes
dynamically.

Specifically, I'm modeling an inverted Stewart platform, and would like to
visualize the cables that suspend the platform.

Thanks,

-Brennan

[Rosen Diankov-2]

Hi Brennan,

If this is just for visualization, you can use any of the plotting functions:

drawlinestrip
drawlinelist
drawtrimesh
drawbox (not implemented at the moment, but tell me if you need it)

At every new frame, just delete the old plot and start a new one. This
is fast, so you won't notice any lag unless you render 100,000+
primitives.

rosen,

2008/8/28 Brennan Peter Sellner <[hidden email]>:

> Hi,
>
> This is perhaps more a Coin question, but is there any way to model
> stretchable bodies in OpenRAVE?  I'm not interested in springs or the
> like, but would like to display a set of cylinders whose length changes
> dynamically.
>
> Specifically, I'm modeling an inverted Stewart platform, and would like to
> visualize the cables that suspend the platform.
>
> Thanks,
>
> -Brennan
>
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[Seth Koterba]

Rosen,
  I'm trying to set the linear and angular velocity of a knibody.  From
the openrave API I found the KinBody::SetVelocity function that would
appear to do what I want.  However, when I looked closer at the openrave
code, it appears that this function passes the velocities on to the
physics engine interface, which just outputs a message saying that this
is not supported.

Is there a non-physics based way to do this within openrave, or should a
create my own monitoring function that increments the position for all my
bodies at each simulation step?

Seth

[Rosen Diankov-2]

Hi Seth,

In order to set velocities through the physics engine, you'll have to
switch to a non-dummy engine. Currently the only one supported is ODE.
Check out this tutorial on how to do it:

http://openrave.programmingvision.com/index.php?title=Tutorials:Simulations

However, all your bodies will now be affected by collisions and
gravity, so it might be very hard to work with.

Another way is to create a Trajectory file with waypoints and
timestamps and SetTrajectory on the robot. You can control both joint
velocities and velocity of the entire body. I recommend this method
over creating your own monitoring function.

Rosen,

PS: I'll add functionality for no joint limits in a week or two
necessary for physics experiments (if you can wait).

2008/9/5 Seth Koterba <[hidden email]>:

> Rosen,
>  I'm trying to set the linear and angular velocity of a knibody.  From
> the openrave API I found the KinBody::SetVelocity function that would
> appear to do what I want.  However, when I looked closer at the openrave
> code, it appears that this function passes the velocities on to the
> physics engine interface, which just outputs a message saying that this
> is not supported.
>
> Is there a non-physics based way to do this within openrave, or should a
> create my own monitoring function that increments the position for all my
> bodies at each simulation step?
>
> Seth
>
>
> -------------------------------------------------------------------------
> This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
> Build the coolest Linux based applications with Moblin SDK & win great prizes
> Grand prize is a trip for two to an Open Source event anywhere in the world
> http://moblin-contest.org/redirect.php?banner_id=100&url=/
> _______________________________________________
> Openrave-users mailing list
> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/openrave-users
>

[Seth Koterba]

Rosen,
  What is the difference between creating a KinBody and a Robot?  Within a
plugin, I'm trying to create a robot with env->CreateRobot(name), but
the result is NULL, however creating a kinbody does not return NULL.  By
looking at the difference between CreateKinBody and CreateRobot, it
seems that there is something fundamentally different between the two.
Is it possible to create a robot from within a plugin?

Seth

[Rosen Diankov-2]

Hi Seth,

CreateRobot takes a robot type. For a list of the current types
supported by plugins type

./openrave -listplugins

For example, env->CreateRobot("GenericRobot") should work. KinBodies
do not have types, that is why you can create a KinBody without
specifying anything.

Once you create a robot, you should call RobotBase::Init and specify
and xml file to load the robot with geometry.

rosen,

2008/9/5 Seth Koterba <[hidden email]>:

> Rosen,
>  What is the difference between creating a KinBody and a Robot?  Within a
> plugin, I'm trying to create a robot with env->CreateRobot(name), but
> the result is NULL, however creating a kinbody does not return NULL.  By
> looking at the difference between CreateKinBody and CreateRobot, it
> seems that there is something fundamentally different between the two.
> Is it possible to create a robot from within a plugin?
>
> Seth
>
>
> -------------------------------------------------------------------------
> This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
> Build the coolest Linux based applications with Moblin SDK & win great prizes
> Grand prize is a trip for two to an Open Source event anywhere in the world
> http://moblin-contest.org/redirect.php?banner_id=100&url=/
> _______________________________________________
> Openrave-users mailing list
> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/openrave-users
>