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Add an example with a passive joint (backport #172) #306

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Apr 30, 2024
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Add an example with a passive joint (backport #172) #306

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541939c
Add an example with a passive joint (#172)
christophfroehlich Apr 30, 2024
4518f47
Fixed docs
ahcorde Apr 30, 2024
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56 changes: 51 additions & 5 deletions doc/index.rst
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Expand Up @@ -220,7 +220,12 @@ gazebo_ros2_control_demos

This package contains the contents for testing gazebo_ros2_control. It is running Gazebo Classic and some other ROS 2 nodes.

There are some examples in the *Gazebo_ros2_control_demos* package. These examples allow to launch a cart in a 30 meter rail.
There are some examples in the *Gazebo_ros2_control_demos* package.

Cart on rail
-----------------------------------------------------------

These examples allow to launch a cart in a 30 meter rail.

.. image:: img/cart.gif
:alt: Cart
Expand All @@ -232,9 +237,6 @@ You can run some of the configuration running the following commands:
ros2 launch gazebo_ros2_control_demos cart_example_position.launch.py
ros2 launch gazebo_ros2_control_demos cart_example_velocity.launch.py
ros2 launch gazebo_ros2_control_demos cart_example_effort.launch.py
ros2 launch gazebo_ros2_control_demos diff_drive.launch.py
ros2 launch gazebo_ros2_control_demos tricycle_drive.launch.py


When the Gazebo world is launched you can run some of the following commands to move the cart.

Expand All @@ -243,11 +245,35 @@ When the Gazebo world is launched you can run some of the following commands to
ros2 run gazebo_ros2_control_demos example_position
ros2 run gazebo_ros2_control_demos example_velocity
ros2 run gazebo_ros2_control_demos example_effort

Mobile robots
-----------------------------------------------------------

You can run some of the mobile robots running the following commands:

.. code-block:: shell

ros2 launch gazebo_ros2_control_demos diff_drive.launch.py
ros2 launch gazebo_ros2_control_demos tricycle_drive.launch.py


When the Gazebo world is launched you can run some of the following commands to move the robots.

.. code-block:: shell

ros2 run gazebo_ros2_control_demos example_diff_drive
ros2 run gazebo_ros2_control_demos example_tricycle_drive

Gripper
-----------------------------------------------------------
The following example shows a parallel gripper with a mimic joint:

.. image:: img/gripper.gif
:alt: Cart

.. code-block:: shell

The following example shows parallel gripper with mimic joint:
ros2 launch gazebo_ros2_control_demos gripper_mimic_joint_example_position.launch.py

.. image:: img/gripper.gif
:alt: Cart
Expand All @@ -264,3 +290,23 @@ Send example commands:
.. code-block:: shell

ros2 run gazebo_ros2_control_demos example_gripper

Pendulum with passive joints
-----------------------------------------------------------

The following example shows a cart with a pendulum arm. This uses the effort command interface for the cart's
degree of freedom on the rail, and the physics of the passive joint of the pendulum is solved correctly.

.. code-block:: shell

ros2 launch gazebo_ros2_control_demos pendulum_example_effort.launch.py
ros2 run gazebo_ros2_control_demos example_effort

.. note::

If the position command interface is used instead, the motion of the pendulum is not calculated correctly and does not move at all, see this `PR <https://github.com/ros-controls/gazebo_ros2_control/issues/240>`__. This also holds true if a mimicked joint with position interface is used. To demonstrate this, run

.. code-block:: shell

ros2 launch gazebo_ros2_control_demos pendulum_example_position.launch.py
ros2 run gazebo_ros2_control_demos example_position
86 changes: 86 additions & 0 deletions gazebo_ros2_control_demos/launch/pendulum_example_effort.launch.py
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# Copyright 2024 ros2_control Development Team
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import os

from ament_index_python.packages import get_package_share_directory


from launch import LaunchDescription
from launch.actions import ExecuteProcess, IncludeLaunchDescription, RegisterEventHandler
from launch.event_handlers import OnProcessExit
from launch.launch_description_sources import PythonLaunchDescriptionSource

from launch_ros.actions import Node

import xacro


def generate_launch_description():
gazebo = IncludeLaunchDescription(
PythonLaunchDescriptionSource([os.path.join(
get_package_share_directory('gazebo_ros'), 'launch'), '/gazebo.launch.py']),
)

gazebo_ros2_control_demos_path = os.path.join(
get_package_share_directory('gazebo_ros2_control_demos'))

xacro_file = os.path.join(gazebo_ros2_control_demos_path,
'urdf',
'test_pendulum_effort.xacro.urdf')

doc = xacro.parse(open(xacro_file))
xacro.process_doc(doc)
params = {'robot_description': doc.toxml()}

node_robot_state_publisher = Node(
package='robot_state_publisher',
executable='robot_state_publisher',
output='screen',
parameters=[params]
)

spawn_entity = Node(package='gazebo_ros', executable='spawn_entity.py',
arguments=['-topic', 'robot_description',
'-entity', 'cartpole'],
output='screen')

load_joint_state_controller = ExecuteProcess(
cmd=['ros2', 'control', 'load_controller', '--set-state', 'active',
'joint_state_broadcaster'],
output='screen'
)

load_joint_trajectory_controller = ExecuteProcess(
cmd=['ros2', 'control', 'load_controller', '--set-state', 'active', 'effort_controller'],
output='screen'
)

return LaunchDescription([
RegisterEventHandler(
event_handler=OnProcessExit(
target_action=spawn_entity,
on_exit=[load_joint_state_controller],
)
),
RegisterEventHandler(
event_handler=OnProcessExit(
target_action=load_joint_state_controller,
on_exit=[load_joint_trajectory_controller],
)
),
gazebo,
node_robot_state_publisher,
spawn_entity,
])
87 changes: 87 additions & 0 deletions gazebo_ros2_control_demos/launch/pendulum_example_position.launch.py
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# Copyright 2024 ros2_control Development Team
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import os

from ament_index_python.packages import get_package_share_directory


from launch import LaunchDescription
from launch.actions import ExecuteProcess, IncludeLaunchDescription, RegisterEventHandler
from launch.event_handlers import OnProcessExit
from launch.launch_description_sources import PythonLaunchDescriptionSource

from launch_ros.actions import Node

import xacro


def generate_launch_description():
gazebo = IncludeLaunchDescription(
PythonLaunchDescriptionSource([os.path.join(
get_package_share_directory('gazebo_ros'), 'launch'), '/gazebo.launch.py']),
)

gazebo_ros2_control_demos_path = os.path.join(
get_package_share_directory('gazebo_ros2_control_demos'))

xacro_file = os.path.join(gazebo_ros2_control_demos_path,
'urdf',
'test_pendulum_position.xacro.urdf')

doc = xacro.parse(open(xacro_file))
xacro.process_doc(doc)
params = {'robot_description': doc.toxml()}

node_robot_state_publisher = Node(
package='robot_state_publisher',
executable='robot_state_publisher',
output='screen',
parameters=[params]
)

spawn_entity = Node(package='gazebo_ros', executable='spawn_entity.py',
arguments=['-topic', 'robot_description',
'-entity', 'cartpole'],
output='screen')

load_joint_state_controller = ExecuteProcess(
cmd=['ros2', 'control', 'load_controller', '--set-state', 'active',
'joint_state_broadcaster'],
output='screen'
)

load_joint_trajectory_controller = ExecuteProcess(
cmd=['ros2', 'control', 'load_controller', '--set-state', 'active',
'joint_trajectory_controller'],
output='screen'
)

return LaunchDescription([
RegisterEventHandler(
event_handler=OnProcessExit(
target_action=spawn_entity,
on_exit=[load_joint_state_controller],
)
),
RegisterEventHandler(
event_handler=OnProcessExit(
target_action=load_joint_state_controller,
on_exit=[load_joint_trajectory_controller],
)
),
gazebo,
node_robot_state_publisher,
spawn_entity,
])
108 changes: 108 additions & 0 deletions gazebo_ros2_control_demos/urdf/test_pendulum_effort.xacro.urdf
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<?xml version="1.0"?>
<robot xmlns:xacro="http://www.ros.org/wiki/xacro" name="pendulum on cart">

<xacro:macro name="quadr_block" params="mass width height name">
<link name="${name}">
<collision>
<geometry>
<box size="${width} ${width} ${height}"/>
</geometry>
<origin xyz="0 0 0"/>
</collision>
<visual>
<geometry>
<box size="${width} ${width} ${height}"/>
</geometry>
<origin xyz="0 0 ${height/2}"/>
<material name="blue">
<color rgba="0 0 .8 1"/>
</material>
</visual>
<inertial>
<origin xyz="0 0 ${height/2}" rpy="0 0 0"/>
<mass value="${mass}"/>
<inertia
ixx="${mass / 12.0 * (width*width + height*height)}" ixy="0.0" ixz="0.0"
iyy="${mass / 12.0 * (height*height + width*width)}" iyz="0.0"
izz="${mass / 12.0 * (width*width + width*width)}"/>
</inertial>
</link>
</xacro:macro>

<link name="world"/>

<link name="slideBar">
<visual>
<geometry>
<box size="30 0.05 0.05"/>
</geometry>
<origin xyz="0 0 0"/>
<material name="green">
<color rgba="0 0.8 .8 1"/>
</material>
</visual>
<inertial>
<mass value="100"/>
<inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>
</inertial>
</link>

<xacro:quadr_block name="cart" mass="10" width="0.5" height="0.2"/>

<xacro:quadr_block name="pendulum" mass="1" width="0.2" height="1.0"/>

<joint name="world_to_base" type="fixed">
<origin rpy="0 0 0" xyz="0 0 1"/>
<parent link="world"/>
<child link="slideBar"/>
</joint>

<joint name="slider_to_cart" type="prismatic">
<axis xyz="1 0 0"/>
<origin xyz="0.0 0.0 0.0"/>
<parent link="slideBar"/>
<child link="cart"/>
<limit effort="1000.0" lower="-15" upper="15" velocity="30"/>
<dynamics damping="0.3" friction="0.0"/>
</joint>

<joint name="cart_to_pendulum" type="revolute">
<axis xyz="0 1 0"/>
<origin xyz="0.0 0.35 0.0" rpy="0 0.1 0"/>
<parent link="cart"/>
<child link="pendulum"/>
<limit effort="10000.0" lower="-100000" upper="100000" velocity="100000"/>
<dynamics damping="0.1" friction="0.0"/>
</joint>

<ros2_control name="GazeboSystem" type="system">
<hardware>
<plugin>gazebo_ros2_control/GazeboSystem</plugin>
</hardware>
<joint name="slider_to_cart">
<command_interface name="effort">
<param name="min">-1000</param>
<param name="max">1000</param>
</command_interface>
<state_interface name="position">
<param name="initial_value">1.0</param>
</state_interface>
<state_interface name="velocity"/>
<state_interface name="effort"/>
</joint>
<joint name="cart_to_pendulum">
<state_interface name="position">
<!-- this does not work if no command interface is set -->
<!-- <param name="initial_value">1.57</param> -->
</state_interface>
<state_interface name="velocity"/>
<state_interface name="effort"/>
</joint>
</ros2_control>

<gazebo>
<plugin filename="libgazebo_ros2_control.so" name="gazebo_ros2_control">
<parameters>$(find gazebo_ros2_control_demos)/config/cart_controller_effort.yaml</parameters>
</plugin>
</gazebo>
</robot>
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