ROS 2 Multi‑Machine Recording Guide

Time Synchronisation using Chrony (Critical for Accurate Timestamps)

Install chrony on both machines

sudo apt update && sudo apt install chrony -y

Configure the NUC as the time server

Edit the configuration file on the NUC:

sudo nano /etc/chrony/chrony.conf Ensure the following line is present (adjust the subnet to yours):

allow 192.168.1.0/24 It should also sync with public NTP servers (usually already present):

pool 2.ubuntu.pool.ntp.org iburst

Restart chrony on the NUC:

sudo systemctl restart chrony

Configure the Pi as a client

Edit the configuration file on the Raspberry Pi:

sudo nano /etc/chrony/chrony.conf Comment out or remove any existing pool lines, and add:

server <NUC_IP_ADDRESS> iburst Restart chrony on the Pi:

sudo systemctl restart chrony

Verify synchronisation

On the Pi, run:

chronyc tracking Look for the Last offset value – the closer to zero (e.g., within microseconds), the better your clocks are aligned.

(Raspberry Pi 5 → Intel NUC)

This guide walks you through the necessary steps to record ROS 2 topics from your Raspberry Pi on your Intel NUC, with time‑synchronized timestamps.

1. Network Prerequisites

• Both machines must be on the same local subnet (e.g., both connected to the same router via Ethernet or Wi‑Fi).
• Find the IP address of each machine: ip addr # or ifconfig

Verify connectivity from the NUC to the Pi:

ping <Raspberry_Pi_IP> If you get replies, the network layer is working.

Set a Common ROS_DOMAIN_ID

Both machines must use the same number (0–101).

On both the Pi and the NUC, run in every terminal before launching any ROS node:

echo "export ROS_DOMAIN_ID=42" >> ~/.bashrc
source ~/.bashrc

Verify the setting on both:

echo $ROS_DOMAIN_ID The output must be identical.

Important: Ensure ROS_LOCALHOST_ONLY is not set to 1. If it is, clear it with:

unset ROS_LOCALHOST_ONLY

Firewall Configuration

ROS 2 uses UDP multicast for discovery. Temporarily disable the firewall for testing, or (preferred) allow UDP traffic from your local subnet:

sudo ufw allow in proto udp from 192.168.1.0/24 (Replace 192.168.1.0/24 with your actual subnet.)

Verify ROS 2 Communication

Use the built‑in demo nodes to confirm that the two machines can talk.

On the Raspberry Pi (publisher):

source /opt/ros/<your-ros2-distro>/setup.bash
export ROS_DOMAIN_ID=42
ros2 run demo_nodes_cpp talker

On the NUC (subscriber):

source /opt/ros/<your-ros2-distro>/setup.bash
export ROS_DOMAIN_ID=42
ros2 run demo_nodes_cpp listener

If the NUC receives Hello World messages, the communication is successful.

Record Topics on the NUC

Now you can record the topics published by the Pi directly on the NUC.

• List available topics (from the Pi):

ros2 topic list

• Record specific topics, e.g. /scan and /camera/image:

ros2 bag record /scan /camera/image

• Record all topics:

ros2 bag record -a