Thank you,

That placed the cylinder correctly. However, I still have the rotation 
problem.
    <link name="hips">
        <inertial>
            <origin xyz="0 0 0.570" rpy="0 2.2 0"/>
            <mass value="50"/>
            <inertia ixx="1" ixy="0" ixz="0" iyy="0" iyz="0" izz="0"/>
        </inertial>
        <visual>
            <origin xyz="-0.169 0 0" rpy="0 2.2 0"/>
            <geometry>
                <cylinder radius="0.060" length="0.420"/>
            </geometry>
        </visual>
        <collision>
                  <origin xyz="-0.169 0 0" rpy="0 2.2 0"/>
                  <geometry>
                    <cylinder radius="0.060" length="0.400"/>
                  </geometry>
            </collision>
    </link>

    <joint name="knees" type="revolute">
        <parent link="feet"/>
        <child link="hips"/>
        <origin xyz="0 0 0.275"/>
        <axis xyz="0 1 0"/>
        <limit lower="1.31" upper="3.22" effort="30" velocity="1.0"/>
    </joint>

If in the joint, <axis xyz="0 0 1">, the cylinder rotates around the z 
axis. When I set it to <axiz xyz="0 1 0">, it rotates around the y axis 
as I want it to, but the whole robot also jumps and rotates and falls to 
its side...

Kirila

Adolfo Rodríguez Tsouroukdissian wrote:
> On Tue, Jun 1, 2010 at 3:32 PM, Kirila Adamova <kirila.adamova@dfki.de 
> <mailto:kirila.adamova@dfki.de>> wrote:
>
>     Hi all,
>
>     I am currently writing a 3D model in urdf. I have two cylinders, which
>     are connected with a joint. The second cylinder, however, is
>     rotated and
>     can be rotated further in the same direction. When I visualize them in
>     gazebo, the joint is in the center of the second cylinder. Is there a
>     way to make it at the end of the cylinder because that is the point
>     around which I need to rotate it. To make it more clear (or even more
>     confusing), here is sample code:
>
>     <link name="feet">
>            <inertial>
>                <origin xyz="0 0 0.275" rpy="0 0 0"/>
>                <mass value="100"/>
>                <inertia ixx="1" ixy="0" ixz="0" iyy="0" iyz="0" izz="0"/>
>            </inertial>
>            <visual>
>                <origin xyz="0 0 0" rpy="0 0 0"/>
>                <geometry>
>                    <cylinder radius="0.100" length="0.250"/>
>                </geometry>
>            </visual>
>            <collision>
>                      <origin xyz="0 0 0" rpy="0 0 0"/>
>                      <geometry>
>                        <cylinder radius="0.100" length="0.230"/>
>                      </geometry>
>                </collision>
>        </link>
>
>        <link name="hips">
>            <inertial>
>                <origin xyz="0 0 0.570" rpy="0 2.2 0"/>
>                <mass value="50"/>
>                <inertia ixx="1" ixy="0" ixz="0" iyy="0" iyz="0" izz="0"/>
>            </inertial>
>            <visual>
>                <origin xyz="0 0 0" rpy="0 2.2 0"/>
>                <geometry>
>                    <cylinder radius="0.060" length="0.420"/>
>                </geometry>
>            </visual>
>            <collision>
>                      <origin xyz="0 0 0" rpy="0 2.2 0"/>
>                      <geometry>
>                        <cylinder radius="0.060" length="0.400"/>
>                      </geometry>
>                </collision>
>        </link>
>
>        <joint name="knees" type="revolute">
>            <parent link="feet"/>
>            <child link="hips"/>
>            <origin xyz="0 0 0.275"/>
>            <axis xyz="0 0 1"/>
>            <limit lower="1.31" upper="3.22" effort="30" velocity="1.0"/>
>        </joint>
>
>
>     Currently, the axis xyz is set to z, although it needs to be y,
>     because
>     when it's set somewhere else, the whole model goes crazy (jumps and
>     turns around) in gazebo.
>
>
>
> Kirila,
>
> The cylinder primitive makes its center coincide with the 
> corresponding origin (visualization, collision) and is aligned with 
> the z axis. For your robot, it should suffice to specify an 
> appropriate origin for your visualization and collision geometries 
> (with respect to the joint origin). For more details refer to the 
> available documentation:
>
> http://www.ros.org/wiki/urdf/XML/Link
> http://www.ros.org/wiki/urdf/XML/Joint
>
> HTH,
>
> Adolfo
>
>
>     Help will be greatly appreciated,
>
>     Kirila
>
>     p.s. End result must rotate the second cylinder around the point
>     between
>     the two cylinders around the y axis.
>     _______________________________________________
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>
>
>
> -- 
> Adolfo Rodríguez Tsouroukdissian, Ph. D.
>
> Robotics engineer
> PAL ROBOTICS S.L
> http://www.pal-robotics.com
> Tel. +34.93.414.53.47
> Fax.+34.93.209.11.09
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