How do joints work?

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How do joints work?

Repiphany
Hey,

I've modified the ExampleModel.cc and .hh so that I now have two
bodies(segment1 & 2) and a joint attaching them(I don't exactly know
how this works).  I think I have it set to rotate around the Z axis.

I set the joint rotational velocity to a value, and the max force to a
value, and nothing happens(unless I put in very large numbers).  The
two bodies seem to be rotating with one another, when I want segment2
to work like an arm, while segment1 stays stationary.

The way I have it now, I think it's trying to rotate around the center
of segment2, but I want it to rotate around the end nearest segment1.

Any ideas on how to solve this?

I've attached the source files and the world file.

Thank you,
Ryan

example.world (1006 bytes) Download Attachment
ExampleModel.cc (5K) Download Attachment
ExampleModel.hh (2K) Download Attachment
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Re: How do joints work?

Nate Koenig
Hello,

Have you read the ODE documentation?
www.ode.org

And also take a look at the Bandit model in Gazebo CVS. It has two
articulated arms. You can use this model as a reference point.

-nate

On 11/27/05, Repiphany <[hidden email]> wrote:

> Hey,
>
> I've modified the ExampleModel.cc and .hh so that I now have two
> bodies(segment1 & 2) and a joint attaching them(I don't exactly know
> how this works).  I think I have it set to rotate around the Z axis.
>
> I set the joint rotational velocity to a value, and the max force to a
> value, and nothing happens(unless I put in very large numbers).  The
> two bodies seem to be rotating with one another, when I want segment2
> to work like an arm, while segment1 stays stationary.
>
> The way I have it now, I think it's trying to rotate around the center
> of segment2, but I want it to rotate around the end nearest segment1.
>
> Any ideas on how to solve this?
>
> I've attached the source files and the world file.
>
> Thank you,
> Ryan
>
>
>


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Re: How do joints work?

Repiphany
Bandit, just so happens to use sgix as the render method, wich, as you
noted in my other post, doesn't work on my card.  I tried glxp, glx,
xlib, and auto, and none of them worked.  They all resulted in the
server dying without displaying anything.  Is there some way I can
render this scene?

-Ryan

On 11/28/05, Nate Koenig <[hidden email]> wrote:

> Hello,
>
> Have you read the ODE documentation?
> www.ode.org
>
> And also take a look at the Bandit model in Gazebo CVS. It has two
> articulated arms. You can use this model as a reference point.
>
> -nate
>
> On 11/27/05, Repiphany <[hidden email]> wrote:
> > Hey,
> >
> > I've modified the ExampleModel.cc and .hh so that I now have two
> > bodies(segment1 & 2) and a joint attaching them(I don't exactly know
> > how this works).  I think I have it set to rotate around the Z axis.
> >
> > I set the joint rotational velocity to a value, and the max force to a
> > value, and nothing happens(unless I put in very large numbers).  The
> > two bodies seem to be rotating with one another, when I want segment2
> > to work like an arm, while segment1 stays stationary.
> >
> > The way I have it now, I think it's trying to rotate around the center
> > of segment2, but I want it to rotate around the end nearest segment1.
> >
> > Any ideas on how to solve this?
> >
> > I've attached the source files and the world file.
> >
> > Thank you,
> > Ryan
> >
> >
> >
>
>
> -------------------------------------------------------
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Re: How do joints work?

Repiphany
Nate,

If nothing else, do you have some images of this model somewhere?
This way I can reference the image while looking through the code.

-Ryan


On 11/28/05, Repiphany <[hidden email]> wrote:

> Bandit, just so happens to use sgix as the render method, wich, as you
> noted in my other post, doesn't work on my card.  I tried glxp, glx,
> xlib, and auto, and none of them worked.  They all resulted in the
> server dying without displaying anything.  Is there some way I can
> render this scene?
>
> -Ryan
>
> On 11/28/05, Nate Koenig <[hidden email]> wrote:
> > Hello,
> >
> > Have you read the ODE documentation?
> > www.ode.org
> >
> > And also take a look at the Bandit model in Gazebo CVS. It has two
> > articulated arms. You can use this model as a reference point.
> >
> > -nate
> >
> > On 11/27/05, Repiphany <[hidden email]> wrote:
> > > Hey,
> > >
> > > I've modified the ExampleModel.cc and .hh so that I now have two
> > > bodies(segment1 & 2) and a joint attaching them(I don't exactly know
> > > how this works).  I think I have it set to rotate around the Z axis.
> > >
> > > I set the joint rotational velocity to a value, and the max force to a
> > > value, and nothing happens(unless I put in very large numbers).  The
> > > two bodies seem to be rotating with one another, when I want segment2
> > > to work like an arm, while segment1 stays stationary.
> > >
> > > The way I have it now, I think it's trying to rotate around the center
> > > of segment2, but I want it to rotate around the end nearest segment1.
> > >
> > > Any ideas on how to solve this?
> > >
> > > I've attached the source files and the world file.
> > >
> > > Thank you,
> > > Ryan
> > >
> > >
> > >
> >
> >
> > ----------------------------
---------------------------

> > This SF.net email is sponsored by: Splunk Inc. Do you grep through log files
> > for problems?  Stop!  Download the new AJAX search engine that makes
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> > Playerstage-gazebo mailing list
> > [hidden email]
> > https://lists.sourceforge.net/lists/listinfo/playerstage-gazebo
> >
>


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Re: How do joints work?

Repiphany
Nate,

Apparently the bandit model relies on the pioneer2dx which I was
forced to disable during compilation because of the following error
during 'make':

Pioneer2DX.cc: In member function `virtual void Pioneer2DX::Update(double)':
Pioneer2DX.cc:446: error: 'class HingeJoint' has no member named 'SetTorque'
Pioneer2DX.cc:447: error: 'class HingeJoint' has no member named 'SetTorque'

This being disabled was causing the segfault I mentioned earlier.
Any idea why this compile error is happening?

-Ryan

On 11/28/05, Repiphany <[hidden email]> wrote:

> Nate,
>
> If nothing else, do you have some images of this model somewhere?
> This way I can reference the image while looking through the code.
>
> -Ryan
>
>
> On 11/28/05, Repiphany <[hidden email]> wrote:
> > Bandit, just so happens to use sgix as the render method, wich, as you
> > noted in my other post, doesn't work on my card.  I tried glxp, glx,
> > xlib, and auto, and none of them worked.  They all resulted in the
> > server dying without displaying anything.  Is there some way I can
> > render this scene?
> >
> > -Ryan
> >
> > On 11/28/05, Nate Koenig <[hidden email]> wrote:
> > > Hello,
> > >
> > > Have you read the ODE documentation?
> > > www.ode.org
> > >
> > > And also take a look at the Bandit model in Gazebo CVS. It has two
> > > articulated arms. You can use this model as a reference point.
> > >
> > > -nate
> > >
> > > On 11/27/05, Repiphany <[hidden email]> wrote:
> > > > Hey,
> > > >
> > > > I've modified the ExampleModel.cc and .hh so that I now have two
> > > > bodies(segment1 & 2) and a joint attaching them(I don't exactly know
> > > > how this works).  I think I have it set to rotate around the Z axis.
> > > >
> > > > I set the joint rotational velocity to a value, and the max force to a
> > > > value, and nothing happens(unless I put in very large numbers).  The
> > > > two bodies seem to be rotating with one another, when I want segment2
> > > > to work like an arm, while segment1 stays stationary.
> > > >
> > > > The way I have it now, I think it's trying to rotate around the center
> > > > of segment2, but I want it to rotate around the end nearest segment1.
> > > >
> > > > Any ideas on how to solve this?
> > > >
> > > > I've attached the source files and the world file.
> > > >
> > > > Thank you,
> > > > Ryan
> > > >
> > > >
> > > >
> > >
> > >
> > > ----------------------------
> ---------------------------
> > > This SF.net email is sponsored by: Splunk Inc. Do you grep through log files
> > > for problems?  Stop!  Download the new AJAX search engine that makes
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> > > _______________________________________________
> > > Playerstage-gazebo mailing list
> > > [hidden email]
> > > https://lists.sourceforge.net/lists/listinfo/playerstage-gazebo
> > >
> >
>


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Re: How do joints work?

Nate Koenig
Hello,

I have fixed the Pioneer2DX model. The latest CVS has the changes.

Bandit doesn't rely on the Pioneer2DX. All models are independent of
each other.

No model requires a specific <renderMethod>. The renderMethod is used
by a camera to determine how to create a pixel buffer. Since none of
the render methods work for you, I must assume you have an ATI
graphics card. These cards do not completely support the opengl
standard. I believe some people have managed to get them to work. Try
searching the mailing lists:
http://sourceforge.net/mailarchive/forum.php?forum_id=33909

I really must stress that you read the documentation, which has
pictures of bandit.
http://playerstage.sourceforge.net/doc/Gazebo-manual-cvs-html/group__Bandit.html

-nate

On 11/28/05, Repiphany <[hidden email]> wrote:

> Nate,
>
> Apparently the bandit model relies on the pioneer2dx which I was
> forced to disable during compilation because of the following error
> during 'make':
>
> Pioneer2DX.cc: In member function `virtual void Pioneer2DX::Update(double)':
> Pioneer2DX.cc:446: error: 'class HingeJoint' has no member named 'SetTorque'
> Pioneer2DX.cc:447: error: 'class HingeJoint' has no member named 'SetTorque'
>
> This being disabled was causing the segfault I mentioned earlier.
> Any idea why this compile error is happening?
>
> -Ryan
>
> On 11/28/05, Repiphany <[hidden email]> wrote:
> > Nate,
> >
> > If nothing else, do you have some images of this model somewhere?
> > This way I can reference the image while looking through the code.
> >
> > -Ryan
> >
> >
> > On 11/28/05, Repiphany <[hidden email]> wrote:
> > > Bandit, just so happens to use sgix as the render method, wich, as you
> > > noted in my other post, doesn't work on my card.  I tried glxp, glx,
> > > xlib, and auto, and none of them worked.  They all resulted in the
> > > server dying without displaying anything.  Is there some way I can
> > > render this scene?
> > >
> > > -Ryan
> > >
> > > On 11/28/05, Nate Koenig <[hidden email]> wrote:
> > > > Hello,
> > > >
> > > > Have you read the ODE documentation?
> > > > www.ode.org
> > > >
> > > > And also take a look at the Bandit model in Gazebo CVS. It has two
> > > > articulated arms. You can use this model as a reference point.
> > > >
> > > > -nate
> > > >
> > > > On 11/27/05, Repiphany <[hidden email]> wrote:
> > > > > Hey,
> > > > >
> > > > > I've modified the ExampleModel.cc and .hh so that I now have two
> > > > > bodies(segment1 & 2) and a joint attaching them(I don't exactly know
> > > > > how this works).  I think I have it set to rotate around the Z axis.
> > > > >
> > > > > I set the joint rotational velocity to a value, and the max force to a
> > > > > value, and nothing happens(unless I put in very large numbers).  The
> > > > > two bodies seem to be rotating with one another, when I want segment2
> > > > > to work like an arm, while segment1 stays stationary.
> > > > >
> > > > > The way I have it now, I think it's trying to rotate around the center
> > > > > of segment2, but I want it to rotate around the end nearest segment1.
> > > > >
> > > > > Any ideas on how to solve this?
> > > > >
> > > > > I've attached the source files and the world file.
> > > > >
> > > > > Thank you,
> > > > > Ryan
> > > > >
> > > > >
> > > > >
> > > >
> > > >
> > > > ----------------------------
> > ---------------------------
> > > > This SF.net email is sponsored by: Splunk Inc. Do you grep through log files
> > > > for problems?  Stop!  Download the new AJAX search engine that makes
> > > > searching your log files as easy as surfing the  web.  DOWNLOAD SPLUNK!
> > > > <a href="http://ads.osdn.com/?ad_idv37&alloc_id865&opclick">http://ads.osdn.com/?ad_idv37&alloc_id865&opclick
> > > > _______________________________________________
> > > > Playerstage-gazebo mailing list
> > > > [hidden email]
> > > > https://lists.sourceforge.net/lists/listinfo/playerstage-gazebo
> > > >
> > >
> >
>
>
> -------------------------------------------------------
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Re: How do joints work?

Repiphany
Hello Nate,

I must apologize, when I said Bandit model, I actually meant the
bandit world.  In the bandit world the bandit model is attached to the
pioneer2DX model.

Also, the reason it wasn't rendering was not due to the render method,
it was due to my disabling of the pioneer2dx ie:

'./configure --disable-pioneer2dx'

Since in bandit.world the pioneer2dx is included by default, and that
model hadn't been built, gazebo oh so gracefully segfaulted.  After I
fixed the perpetrating code in the pioneer2dx model, everything
compiled fine, and I was able to direct render again using the glxp
method.  Thanks for fixing that in CVS, it makes it just that much
easier for someone who downloads CVS naively expecting it to compile.
;-)

I must also apologize for asking about the images.  I had seen them
before, but I didn't make the connection when I was looking at the
code, and by that point I had already lost a lot of interest in
reading pure code labeled as "documentation."  Doxygen is a nice tool,
but it's not meant to replace *actual* documentation, just to aide in
it's creation.  I have a few reservations about the current state of
documentation, but I will address those more thoroughly later.  This
is one of the things I would like to improve upon.  Any suggestions on
where to post a message dealing with docs?  I'll default to the gazebo
list, since that's mostly all I'm interested in.

Also, I have no problems with my video card rendering using the glx
and glxp methods.  I was able to get these to work some time ago by
reading your conversations with numerous other individuals.
Fortunately, I already had direct rendering configured, and I simply
needed to download CVS and use the glxp method.

Back to the original intent of this thread.  I was able to
successfully hinge two bodies together by modifying my code to more
closely resemble the  bandit model.  I was not correctly setting the
initial position of the bodies of the segments, and the position of my
anchor was off.  I will clean up the code for this very simple joint
and post it with a simple hinge joint howto ( after I learn :-P ).
There are still a couple things that I couldn't glean from the ode
docs, but hopefully I'll figure them out from a little more
experimentation.  You don't necessarily have to answer these, I'll
post my findings later.
(These are still very rough, and wholly based on guesses)

-What effect does moving the Body have?  I tried changing the position
of the body in all three axes, but I couldn't tell any difference in
it's reaction to being dropped from various heights.  The Body holds
the mass information, but apparently the position of the body is
different from the Center of Mass?

-When using setRelativePos() during geometry setup, what determines
the point that this vector is relative to?  Is this determined from
whether or not the geom is attached to a canonical body?  It seems
that when I change the values for the geom attached to the first body,
it's absolute(relative to the origin), because if I change the values
of the body position, the block doesn't appear to move, is this right?

Thank you for all of your help, I couldn't have gotten my simulation
to work without it.

-Ryan

P.S. - Yesterday I registered an IRC channel called #gazebo on the
FreeNode server.  I think this will be a beneficial forum for gazebo
users/developers to discuss things a bit more...interactively.  I'm
always signed in, so feel free to stop by.  Is there some place we can
publicize this?




On 11/29/05, Nate Koenig <[hidden email]> wrote:

> Hello,
>
> I have fixed the Pioneer2DX model. The latest CVS has the changes.
>
> Bandit doesn't rely on the Pioneer2DX. All models are independent of
> each other.
>
> No model requires a specific <renderMethod>. The renderMethod is used
> by a camera to determine how to create a pixel buffer. Since none of
> the render methods work for you, I must assume you have an ATI
> graphics card. These cards do not completely support the opengl
> standard. I believe some people have managed to get them to work. Try
> searching the mailing lists:
> http://sourceforge.net/mailarchive/forum.php?forum_id=33909
>
> I really must stress that you read the documentation, which has
> pictures of bandit.
> http://playerstage.sourceforge.net/doc/Gazebo-manual-cvs-html/group__Bandit.html
>
> -nate
>
> On 11/28/05, Repiphany <[hidden email]> wrote:
> > Nate,
> >
> > Apparently the bandit model relies on the pioneer2dx which I was
> > forced to disable during compilation because of the following error
> > during 'make':
> >
> > Pioneer2DX.cc: In member function `virtual void Pioneer2DX::Update(double)':
> > Pioneer2DX.cc:446: error: 'class HingeJoint' has no member named 'SetTorque'
> > Pioneer2DX.cc:447: error: 'class HingeJoint' has no member named 'SetTorque'
> >
> > This being disabled was causing the segfault I mentioned earlier.
> > Any idea why this compile error is happening?
> >
> > -Ryan
> >
> > On 11/28/05, Repiphany <[hidden email]> wrote:
> > > Nate,
> > >
> > > If nothing else, do you have some images of this model somewhere?
> > > This way I can reference the image while looking through the code.
> > >
> > > -Ryan
> > >
> > >
> > > On 11/28/05, Repiphany <[hidden email]> wrote:
> > > > Bandit, just so happens to use sgix as the render method, wich, as you
> > > > noted in my other post, doesn't work on my card.  I tried glxp, glx,
> > > > xlib, and auto, and none of them worked.  They all resulted in the
> > > > server dying without displaying anything.  Is there some way I can
> > > > render this scene?
> > > >
> > > > -Ryan
> > > >
> > > > On 11/28/05, Nate Koenig <[hidden email]> wrote:
> > > > > Hello,
> > > > >
> > > > > Have you read the ODE documentation?
> > > > > www.ode.org
> > > > >
> > > > > And also take a look at the Bandit model in Gazebo CVS. It has two
> > > > > articulated arms. You can use this model as a reference point.
> > > > >
> > > > > -nate
> > > > >
> > > > > On 11/27/05, Repiphany <[hidden email]> wrote:
> > > > > > Hey,
> > > > > >
> > > > > > I've modified the ExampleModel.cc and .hh so that I now have two
> > > > > > bodies(segment1 & 2) and a joint attaching them(I don't exactly know
> > > > > > how this works).  I think I have it set to rotate around the Z axis.
> > > > > >
> > > > > > I set the joint rotational velocity to a value, and the max force to a
> > > > > > value, and nothing happens(unless I put in very large numbers).  The
> > > > > > two bodies seem to be rotating with one another, when I want segment2
> > > > > > to work like an arm, while segment1 stays stationary.
> > > > > >
> > > > > > The way I have it now, I think it's trying to rotate around the center
> > > > > > of segment2, but I want it to rotate around the end nearest segment1.
> > > > > >
> > > > > > Any ideas on how to solve this?
> > > > > >
> > > > > > I've attached the source files and the world file.
> > > > > >
> > > > > > Thank you,
> > > > > > Ryan
> > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > > > ----------------------------
> > > ---------------------------
> > > > > This SF.net email is sponsored by: Splunk Inc. Do you grep through log files
> > > > > for problems?  Stop!  Download the new AJAX search engine that makes
> > > > > searching your log files as easy as surfing the  web.  DOWNLOAD SPLUNK!
> > > > > <a href="http://ads.osdn.com/?ad_idv37&alloc_id865&opclick">http://ads.osdn.com/?ad_idv37&alloc_id865&opclick
> > > > > _______________________________________________
> > > > > Playerstage-gazebo mailing list
> > > > > [hidden email]
> > > > > https://lists.sourceforge.net/lists/listinfo/playerstage-gazebo
> > > > >
> > > >
> > >
> >
> >
> > -------------------------------------------------------
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Re: How do joints work?

Nate Koenig
Hi Ryan,

Responses are below.

On 11/29/05, Repiphany <[hidden email]> wrote:
> Hello Nate,

> -What effect does moving the Body have?  I tried changing the position
> of the body in all three axes, but I couldn't tell any difference in
> it's reaction to being dropped from various heights.  The Body holds
> the mass information, but apparently the position of the body is
> different from the Center of Mass?

The position of a Body is it's abosulte location in the world. So if
you move a body to (1,2,3),   it will be positioned at x=1, y=2, z=3.
The center of mass of a body is relative to the body. Take a look at
Body::UpdateCoM in Body.cc

> -When using setRelativePos() during geometry setup, what determines
> the point that this vector is relative to?  Is this determined from
> whether or not the geom is attached to a canonical body?  It seems
> that when I change the values for the geom attached to the first body,
> it's absolute(relative to the origin), because if I change the values
> of the body position, the block doesn't appear to move, is this right?

SetRelativePos moves the Geom relative to the body it is attached to.
Try creating and moving the body, then attach a geom to it and set its
relative position.

> P.S. - Yesterday I registered an IRC channel called #gazebo on the
> FreeNode server.  I think this will be a beneficial forum for gazebo
> users/developers to discuss things a bit more...interactively.  I'm
> always signed in, so feel free to stop by.  Is there some place we can
> publicize this?

You can send a message out the gazebo mailing list informing people of
the IRC channel.

-nate


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Re: How do joints work?

Repiphany
Hello Nate,

Do you have any idea why the joint interface would not be displayed
for the bandit model?  The position iface works for other models, but
when I click the check box for the joint iface, nothing shows up.  I
compared the initializations of both interfaces, and they look nearly
identical with the exception of a missing assert() in the bandit
model.

Thanks,
Ryan


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Re: How do joints work?

Nate Koenig
Hello,

I haven't implemented a GUI for the joint interface yet. You have to
go directly through libgazebo right now.

-nate

On 12/5/05, Repiphany <[hidden email]> wrote:

> Hello Nate,
>
> Do you have any idea why the joint interface would not be displayed
> for the bandit model?  The position iface works for other models, but
> when I click the check box for the joint iface, nothing shows up.  I
> compared the initializations of both interfaces, and they look nearly
> identical with the exception of a missing assert() in the bandit
> model.
>
> Thanks,
> Ryan
>
>
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