Added Gazebo Demo for Mecanum Drive Controller

[Pratham-Pandey]

Added Holonomic Drive(Mecanum Wheel Based) Demo:

Updates:
- Added a 4 wheeled mecanum wheel base cart demo to try out the mecanum drive controller.
- Updated the documentation.
- Added new folder named "mesh" under "gazebo_ros2_control_demos/urdf" for storing mesh.

NOTE:

• Gazebo is not loading at all when relative path for mesh is used in URDF. For example:
  <mesh filename="package://gazebo_ros2_control_demos/urdf/mesh/holonomic_drive/roller.stl" scale="0.001 0.001 0.001"/>
• But is loading properly when absolute path is used. For example:
  <mesh filename="file:///home/Desktop/roller.stl" scale="0.001 0.001 0.001"/>

[ahcorde]

@Pratham-Pandey Thank you for your contribution. Do you mind to open the PR against or retarget this one to master ? then we can backport this to rest of distros.

I'm not completely against adding meshes for the model, Maybe we can keep roller.stl and use a rectangle as the base ? What do you think ?

[Pratham-Pandey]

PR against or retarget this one to master

What does that means? This pull request is for ROS Iron and i feel it would be better to merge it with Iron branch. Can it be merged with Master Branch? I don't have much idea about git.

I have this pull request as draft because the cart is not loading in Gazebo when relative path for mesh is used(using "package://"). It is working fine with absolute path, though. Do you have any idea how can I get it working with relative path?

I'm not completely against adding meshes for the model, Maybe we can keep roller.stl and use a rectangle as the base ? What do you think ?

Yes it is Good. But having mesh for roller is a must for the cart to behave like a holonomic drive cart. Apart from that, what is the downside of using mesh in this repo? The base mesh dose'nt look that bad 😆

[ahcorde]

Hey @Pratham-Pandey I made same changes in this commit https://github.com/ros-controls/gazebo_ros2_control/tree/ahcorde/iron/mecanum

I didn't try the mecanum controller but the robot is there with the mecanum wheels. Do you mind to cherry-pick the commit and try again?

[Pratham-Pandey]

@ahcorde ok. I will open this PR for review once done.

[Pratham-Pandey]

@ahcorde The controller is still working after your changes. I have opened the Pull Request.

Question:

• Any reason for removing rviz from the launch file?
• Do I need to add license to the launch file like:

# Copyright 2020 Open Source Robotics Foundation, Inc.
#
# 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.

Let me know if any other changes are required.

Thanks!

[ahcorde]

@ahcorde The controller is still working after your changes. I have opened the Pull Request.

Question:

* Any reason for removing rviz from the launch file?

* Do I need to add license to the launch file like:

# Copyright 2020 Open Source Robotics Foundation, Inc.
#
# 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.

Let me know if any other changes are required.

Thanks!

• The reason to remove rviz is that I didn't find a rviz configuration file. If you add a configuration file, happy to add it.
• Yes, please. Add the license at the top of the file

[ahcorde]

This PR requires this controller ros-controls/ros2_controllers#512. PR is still open.

[Pratham-Pandey]

This PR requires this controller ros-controls/ros2_controllers#512. PR is still open.

The controller PR needs to be merged before this PR could be merged?

• Have added the License.
• It is ok without rviz.

[ahcorde]

The controller PR needs to be merged before this PR could be merged?

Yes, It's a requirement, otherwise the example will not work with the debian packages.