ROSbot 2R workspace

This folder contains the files for starting the sensors of the ROSbot 2R, from Husarion.
This README contains the instructions to setup the ROSbot and to make it usable when launching ROS among multiple machine. It is also shown how to broadcast the time over the Wi-Fi in order to have all the agents synchronised with the master.

The folder of the workspace has to be put in the ros_ws of each robot needed and properly built through catkin_make.

ROSbot start packaged

The starting packages can be download from the official Github Page.
In particular the packages needed are:

• rosbot_ekf
• rosbot_description

IMPORTANT

All the files are setup with a namespace (robot_0 in this case), becuase there was the need to use multiple robots of the same type. Remeber to change the files parameter and the folder names.
The files in the [rosbot_navigation] need the namespace robot_i addition to the existing name. Be careful to not add / in front of the name if not alredy present. n particular:

• start_pkg:
  • start.launch: robot_ns line 3
• rosbot_navigation:
  • costmap_common_params.yaml: change the namespace of the following parameters:
    • map_topic: line 4
    • laser_scan_sensor: sensor_frame and topic line 7
    • robot_base_frame: line 9
    • map_topic: line 13
  • exploration.yaml: change the namespace of the following parameters:
    • robot_base_frame: line 7
    • map_topic: line 14

ROSbot setup

These instructions are needed to setup the ROSbot in order to make the robots work correctly.

.bashrc file

Before starting check the .bashrc file and change the following settings.
Comment the one needed for the localhost and set the one for the shared master by adding new lines.
At the end you should have something as:

# Local host master
#export ROS_MASTER_URI=http://localhost:11311
#export ROS_HOSTNAME=localhost

# Shared master with rosbot
export ROS_MASTER_URI=http://PC_IP:11311
export ROS_IP=PC_IP

where the PC_IP can be retrieved with hostname -I once connected to the Wi-Fi.
Remember to source the .basrch file once modified otherwise the changes will not be taken into account.

Once in this situation, when launching the roscore on the master PC you can see some topics also from the other machines which are sharing the master.

Broadcast the time on the Wi-Fi

For the ROSbot in the Lab sometimes the clock is lost so the program will have problems in running cause of mismatch in the TF with the timestamps.
To avoid this, the master PC can broadcast its own clock over the Wi-Fi in order to have all the devices sharing the same. To do so follow these steps:

• on the master PC create a dedicated file ntp.conf in the /etc folder and set it as:

# Use the local clock
server 127.127.1.0 prefer
fudge  127.127.1.0
driftfile /var/lib/ntp/drift
broadcastdelay 0.008

# Give localhost full access rights
restrict default

# Give machines on our network access to query us
restrict PC_IP.0 mask 255.255.255.0 nomodify notrap

broadcast PC_IP.0

where PC_IP is nnn.nnn.nnn.0: important to set to 0 the last one set.

• on each of the agent that has to retrieve the clock create a file ntp.conf int the /etc folder and write this inside

# Point to our network's master time server
server PC_IP iburst

restrict default

driftfile /var/lib/ntp/drift

minpoll 4
maxpoll 5

where PC_IP is the complete IP of the master PC over the wifi (retrieved with hostname -I form the master PC).

Once all the files are set up, reboot the agents (sudo reboot now) to be sure teh changes are applied and the clock will be correctly shared.