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Overview

Swarm_ros_bridge is a lightweight middle interface ROS package mainly based on ZeroMQ. It enables the specified ROS messages transmission among swarm robots through socket communication. The purpose of this package is to replace the traditional way of running ROS across multiple machines in ROS1, which has some drawbacks under swarm robots situation.

Source code:

https://github.com/shupx/swarm_ros_bridge.git

https://gitee.com/shu-peixuan/swarm_ros_bridge.git

csdn blog (in chinese): https://blog.csdn.net/benchuspx/article/details/128576723

An example of two ROS robots communicating with each other through swarm_ros_bridge is shown below:

Compared with ROS1 multi-robot wireless communication way, it has the following benefits:

* Robust: No need for central ROS master launching first. Each robot has its own ROS master and they can launch in a random sequence, connect with each other autonomously and reconnect if disconnected.

* Flexible: You can choose the sending/receiving ROS topics rather than transferring all topic (names) as ROS1 does.

* Easy to use: Specify all the IPs and ROS topics in one configuration file.

Compared with ROS2 DDS communication, it has the following benefits:

* Lightweight: It is a small ROS bridge node subscribing and sending remote ROS topics, so connecting with other ROS nodes is easy.

* Reliable: It uses ZeroMQ socket communication based on TCP protocol while ROS2 is based on DDS, whose default protocol is UDP (unreliable). DDS is mainly designed for data exchange between native processes under wired communication rather than remote wireless communication.

This package is personally developed by Peixuan Shu (PhD, beihang university, China) on Jan. 2023. Any question/suggestion is welcomed at swarm_ros_bridge issue or shupeixuan@qq.com.

Install

Instead of installing from binary form, this package can only be installed from source code since the ROS topic types depend on your need.

First, clone this package:

mkdir -p swarm_ros_bridge_ws/src  # or your own ros workspace
cd swarm_ros_bridge_ws/src
git clone https://github.com/shupx/swarm_ros_bridge.git

or clone its gitee mirror for faster speed:

git clone https://gitee.com/shu-peixuan/swarm_ros_bridge.git

Then, install dependencies with apt:

sudo apt install libzmqpp-dev

or install dependencies using rosdep:

rosdep install --from-path swarm_ros_bridge/

Finally, build this package:

cd ../
catkin_make
source devel/setup.bash

Usage

Make sure that all robots connects to the same network segment.

1. Specify the IP and ROS topic information in config/ros_topics.yaml in the following form:

IP:
  self: '*'   # '*' stands for all self IPs
  robot2: 192.168.1.102  # modify IP in your situation

send_topics:
- topic_name: /topic1
  msg_type: sensor_msgs/Imu
  max_freq: 50
  srcIP: self
  srcPort: 3001 # ports of send_topics should be different

recv_topics:
- topic_name: /topic2
  msg_type: geometry_msgs/Twist
  srcIP: robot2
  srcPort: 3001

,where the IPs and topics can be added and modified in your need. The max_freq will limit the sending frequency once it exceeds max_freq. Set max_freq large enough if you do not want to decrease the sending frequency.

2. Launch the bridge_node:

roslaunch swarm_ros_bridge test.launch

3. Publish messages into send_topics and check that remote recv_topics are receiving these messages. The console will also print INFO the first time recv_topics receive messages.

We also provide a simple latency test demo between two machines. Please refer to scripts/README.md

Advanced

More ROS message types

The default supported ROS message types are only sensor_msgs/Imu, geometry_msgs/Twist and std_msgs/String. If you need more types:

1. Modify the macros about MSG_TYPEx and MSG_CLASSx in include/ros_sub_pub.hpp, then it will generate template functions for different ros message types.

// In ros_sub_pub.hpp
// uncomment and modify the following lines:
#include <xxx_msgs/yy.h>
#define MSG_TYPE3 "xxx_msgs/yy"
#define MSG_CLASS3 xxx_msgs::yy

We support up to 10 types modification. If that is still not enough, then you should modify the topic_subscriber(), topic_publisher() and deserialize_publish() in include/ros_sub_pub.hpp according to their styles.

2. Add the dependent message package in find_package() of CMakeLists.txt:

# in CMakeLists.txt
find_package(catkin REQUIRED COMPONENTS
  roscpp
  std_msgs
  geometry_msgs
  sensor_msgs
  xxx_msgs
)

3. Recompile:

cd swarm_ros_bridge_ws/
catkin_make

More send_topics

We support up to 50 send_topics. Modify the following lines in include/ros_sub_pub.hpp if you need more:

// in ros_sub_pub.hpp
# define SUB_MAX 50 // max number of subscriber callbacks
//...
template <typename T>
void (*sub_callbacks[])(const T &)=
{
  sub_cb<T,0>, sub_cb<T,1>, ... //add more
};

Then recompile:

cd swarm_ros_bridge_ws/
catkin_make

Nodes

bridge_node

Reliable TCP bridge for ros data transfer in unstable network. It will send/receive the specified ROS topics in config/ros_topics.yaml. It uses zeromq socket(PUB/SUB mode), which reconnects others autonomously and supports 1-N pub-sub connection under TCP protocol.

Subscribed Topics

/topic1 (according to your ros_topics.yaml) (sensor_msgs/Imu)

• send_topics specified in config/ros_topics.yaml

Published Topics

/topic2 (according to your ros_topics.yaml) (geometry_msgs/Twist)

• recv_topics specified in config/ros_topics.yaml

Parameters

~IP (XmlRpc::XmlRpcValue, default: none)

• IP_name - IP maps

~send_topics (XmlRpc::XmlRpcValue, default: none)

• sending topics information

~recv_topics (XmlRpc::XmlRpcValue, default: none)

• receiving topics information

Future Work

1. Dynamic RPC, including dynamic node discovery, online topic change, and ground station monitor.

2. Support UDP protocol for mass data transmission like video streams.

3. Support ROS service transmission with ZeroMQ request-reply mode.

4. Support ROS2 topic and service transmission.

Contributor

Peixuan Shu (shupeixuan@qq.com), PhD, beihang university, China, 2023.1.1

Some applications:

pyugvswarm: a python package wrapper around unmanned ground vehicle (UGV) swarm positioning / communication / control ROS1 nodes.