Part-4-Simulation-Jan23.md

Prerequisites

• installed ROS (See video Getting Ready for ROS Part 3: Installing ROS and cfr. my notes in Part-1-Getting-ready-ROS2-Aug22-Jan23.md)

• watched Intro video Why do I think you should build this robot?

  • copied template from github: https://github.com/joshnewans/my_bot, created a workspace and built with colcon:

  $ cd ~ 
  $ mkdir dev_ws && cd dev_ws
  $ mkdir src && cd src
  $ git clone https://github.com/mhered/manolobot_uno.git
  $ cd ..
  $ colcon build --symlink-install

• watched TF overview video: ROS Transform System (TF) | Getting Ready to Build Robots with ROS #6. See my notes in Part-1-Getting-ready-ROS2-Aug22-Jan23.md

  • installed xacro and joint state publisher GUI

• watched URDF Overview video How do we describe a robot? With URDF! | Getting Ready to build Robots with ROS #7. See my notes in Part-1-Getting-ready-ROS2-Aug22-Jan23.md

Describing the robot in URDF

Video: Creating a rough 3D model of our robot with URDF Blog: Making a Mobile Robot #2 - Concept Design URDF Discussion: Discourse

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• root link must be called base_link

• orientation is:

  • x forward (red)

  • y left (green)

  • z up (blue)

3 things to take into consideration when saving changes in URDF:

1. build workspace with $ colcon build --symlink-install. This avoids having to rebuild with every change (except if you add new files)

2. quit (ctrl+c) and relaunch the robot state publisher with. $ ros2 launch manolobot rsp.launch.pyevery time you make a change

3. click Reset to refresh RVIZ so it picks up changes. If this does not work tick/untick display items or close/reopen as last resource

4. To get started, go to the workspace and source it:

(Terminal 1):$ cd dev_ws
$ source install/setup.bash

2. With every change run the launch file:

$ ros2 launch manolobot_uno rsp.launch.py

If new files are present rebuild the workspace with colcon before the launch file:

$ colcon build --symlink-install

3. to view run RVIZ in another terminal

(Terminal 2):$ rviz2 -d dev_ws/src/manolobot_uno/config/view_bot.rviz

4. to publish dynamic joints run joint_state_publisher_gui in another terminal

(Terminal 3):$ ros2 run joint_state_publisher_gui joint_state_publisher_gui

To save the state of RVIZ: Save as... in ./config/view_bot.rviz then open rviz with the rviz file as parameter:

$ rviz2 -d dev_ws/src/manolobot_uno/config/view_bot.rviz

Merging manolobot_uno into the main repo manolobot

Based on The good way to download code from internet, see notes on ETH Zurich course.

Rather than having multiple repos I copy the folder into the main one and symlink to dev_ws/src.

This is way cleaner:

1. copy the contents of the repo to a folder inside manolobot

$ mv ~/dev_ws/src/manolobot_uno ~/manolobot/

2. Symlink it to dev_ws

$ ln -s ~/manolobot/manolobot_uno/ ~/dev_ws/src/

3. Build it and re-source environment

$ colcon build --symlink-install
$ cd ~/dev_ws
$ source install/setup.bash

4. Then, to launch the robot_state_publisher:

$ ros2 launch manolobot_uno rsp.launch.py

Simulating the robot in Gazebo

Blog: https://articulatedrobotics.xyz/mobile-robot-3-concept-gazebo/

Check also: https://articulatedrobotics.xyz/ready-for-ros-8-gazebo/

1. Launch robot_state_publisher with sim time:

(Terminal 1):$ ros2 launch manolobot_uno rsp.launch.py use_sim_time:=true

2. Install - if not done before - and launch gazebo with ROS compatibility:

$ sudo apt install ros-foxy-gazebo-ros-pkgs
(Terminal 2):$ ros2 launch gazebo_ros gazebo.launch.py

3. Spawn the robot:

(Terminal 3):$ ros2 run gazebo_ros spawn_entity.py -topic robot_description -entity manolobot

Prepared launch_sim.launch.py to achieve the same effect (launch gazebo and spawn the robot) but with a single command:

(Terminal 1):$ ros2 launch manolobot_uno launch_sim.launch.py

• Createdgazebo_control.xacro , a new file with the configuration of the diff_drive plugin for gazebo

• Properties definition (robot dimensions etc) need to be used now as well by gazebo_control.xacro so I moved their definition from robot_core.xacro to a separate file properties.xacro and included it from robot.urdf.xacro.

• Modified robot.urdf.xacroto add calls to both properties.xacro and gazebo_control.xacro

• Modified robot_core.xacro:

  • added gazebo tags to define colors for each link

  • added very low friction coefficients mu1 mu2 for caster wheels

With this it is possible to control the robot in the simulation using teleop_key:

(Terminal 2):$ ros2 run teleop_twist_keyboard teleop_twist_keyboard

• Adjusted the masses to get a proper behavior of the simulation. Note: the values are not real ones, need to make measurements!!
• Created launch file joystick.launch and parameter file joystick.yaml to configure and launch support for PS4 gamepad as follows:
  • Dead man switches: L button (left shoulder) for normal speed, R button (right shoulder) for turbo
  • Control on left stick: vertical axis for forward/backward motion and horizontal axis for rotation.
• See details of the setup of the gamepad in ./BOM/gamepad.md

Launch with:

(Terminal 2):$ ros2 launch manolobot_uno joystick.launch.py

• Driving manolobot_uno around in Gazebo:

Tips & tricks

• to open Gazebo in a world:

(Terminal 1):$ ros2 launch manolobot_uno launch_sim.launch.py world:=./src/manolobot_uno/worlds/cones.world use_sim_time:=true

• to force Gazebo to update changes in the model: close all other terminals, source, if necessary kill hung up processes with:

$ sudo killall -9 gazebo gzserver gzclient