Add technical requirements and refactor nav

Author: fjp

docs/technical_requirements.md

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+# Technical requirements
+
+In the https://github.com/ros-mobile-robots organization on GitHub
+are the required ROS packages to set up a differential drive robot. 
+One of the main software repositories is https://github.com/ros-mobile-robots/diffbot.
+It includes packages for simulation and the configurations and software to operate a real
+robot and interact with it from a development PC. For the hardware, you can build your
+own two- or four-wheeled differential drive robot similar to the one present in the 
+`diffbot_description` package or 3D print a more stable Remo robot with the stl files in
+https://github.com/ros-mobile-robots/remo_description. 
+
+The next two sections describe the technical requirements for the software and hardware.
+
+## Software requirements
+
+For the development PC, you should have ROS Noetic installed on Ubuntu 20.04
+(https://releases.ubuntu.com/20.04/). On the Raspberry Pi 4 B Single-
+Board Computer (SBC) that is mounted on Remo, we use Ubuntu Mate 20.04 for arm64
+architecture (https://ubuntu-mate.org/download/arm64/focal/). To clone
+large stl files from the Git repository we use git-lfs. On both Ubuntu flavors it needs
+to be installed with the following terminal command:
+
+```console
+sudo apt install git-lfs
+```
+
+On both the development PC and the SBC of the robot, you need a connection to the
+same local network and to enable the ssh protocol, to connect from the development PC
+(client) to the robot, which is running an open-ssh server. Install it on Ubuntu Mate
+20.04 with the following:
+
+```console
+sudo apt install openssh-server
+```
+
+Another interface setup that is needed to work with the microcontroller, is to add your
+user to the `dialout` group on both machines, the SBC and the development PC. This can
+be done with the following command, followed by a system reboot:
+
+```console
+sudo adduser <username> dialout
+```
+
+When you clone the diffbot repository in a new catkin workspace, you will find two
+YAML files, `diffbot_dev.repos` and `remo_robot.repos`, that list required source
+dependencies together with their version control type, the repository address, and a
+relative path where these dependencies are cloned. `remo_robot.repos` is here to clone
+source dependencies on the real robot.
+
+To make use of such YAML files and clone the listed dependencies, we use the commands
+from [`vcstool`](http://wiki.ros.org/vcstool), which replaces
+[`wstool`](http://wiki.ros.org/wstool):
+
+1. In a new catkin workspace, clone the diffbot repository inside the src folder:
+
+    ```console
+    ros_ws/src$ git clone https://github.com/ros-mobile-robots/diffbot.git
+    ```
+
+    for a specific tag (e.g. 1.0.0) you can use the following command:
+
+    ```console
+    ros_ws/src$ git clone --depth 1 --branch 1.0.0 https://github.com/ros-mobile-robots/diffbot.git
+    ```
+
+2. Make sure to execute the `vcs import` command from the root of the catkin
+workspace and pipe in the `diffbot_dev.repos` or `remo_robot.repos`
+YAML file, depending on where you execute the command, either the development
+PC or the SBC of Remo to clone the listed dependencies:
+
+    ```console
+    vcs import < src/diffbot/diffbot_dev.repos
+    ```
+
+3. Execute the next command on the SBC of the robot:
+    
+    ```console
+    vcs import < src/diffbot/remo_robot.repos
+    ```
+
+After obtaining the source dependencies with `vcstool`, we can compile the workspace.
+To successfully compile the packages of the repository, binary dependencies must be
+installed. As the required dependencies are specified in each ROS package's `package.xml`, 
+the rosdep command can install the required ROS packages from the Ubuntu repositories:
+
+```console
+rosdep install --from-paths src --ignore-src -r -y
+```
+
+Finally, the workspaces on the development machine and the SBC of the robot need to
+be built, either using `catkin_make` or catkin tools. `catkin_make` comes pre-installed with ROS.
+
+=== "catkin tools"
+
+    ```console
+    catkin build
+    ```
+
+=== "`catkin_make`"
+    
+    ```console
+    catkin_make
+    ```
+
+
+## Hardware requirements
+
+The repository at https://github.com/ros-mobile-robots/remo_description contains the 
+robot description of Remo. Remo is a modular mobile robot platform, which is based on 
+NVIDIA's JetBot. The currently available parts can be 3D printed using the provided 
+stl files in the [`remo_description`](https://github.com/ros-mobile-robots/remo_description) repository. 
+To do this, you either need a 3D printer with a recommended build volume of 15x15x15 cm or to use
+a local or online 3D print service. Further details are found in [hardware setup](hardware_setup/3D_print.md).

mkdocs.yml

@@ -79,7 +79,9 @@ plugins:
 
 nav:
   - Home: index.md
-  - Components: components.md
+  - Getting Started:
+    - Technical Requirements: technical_requirements.md
+    - Components: components.md
   - Robotics Theory:
     - theory/index.md
     - Preliminaries: