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.

[Pratham-Pandey]

@ahcorde the controller PR has been merged. Have made some changes in config and URDF of this PR. Let me know if any other changes are required and we could get this PR merged.

[christophfroehlich]

@Pratham-Pandey be aware that iron is EOL and we won't release the mecanum controller or gazebo_ros2_control any more to iron. please rebase your PR to rolling/master branch, and we might backport it to humble if the controller will be merged into humble

[ahcorde]

do you mind to target rolling ?

[Pratham-Pandey]

To target rolling, I need to create a separate PR?

[christophfroehlich]

no,you can rebase yours on top of master, force push, and change the target of the PR