Presentation at Code BEAM America 2021 https://codesync.global/conferences/code-beam-sf-2021 https://codesync.global/speaker/hideki-takase/ How do we install the magic of Elixir into robot systems? One of the solutions is "Rclex", that is a client library for ROS 2 platform. ROS (Robot Operating System) provides publish/subscribe based messaging mechanism between robot modules with the DDS (Data Distribution Service) stack. We suggest that the force of Erlang/Elixir can power up the scalability of ROS 2 communication. This talk will introduce how did we integrate ROS 2 and Elixir by using NIFs, and discuss the possibility of this library in the IoT field.

1. A Library for Robotics meet Elixir
2021/11/05
Hideki Takase
(Univ. of Tokyo / JST PRESTO)

2. Who is ⾼瀬英希?
@takasehideki
­Associate Professor at Univ. of Tokyo
­Researcher at PRESTO Program, JST
üResearch topics: runtime optimization and
design methodology for IoT systems
ナーブスはナウでヤングでcoolなすごいやつです。
“Nerves is awesome!!
because it is now, young and cool!!”
191 members in Japan
https://nerves-jp.connpass.com/
Sapporo.beam

3. 3
(Robot Operating System)
1. Plumbing: pub/sub messaging infrastructure
2. Tools: configuring, debugging, visualizing, etc.
3. Capabilities: broad collection of libraries
4. Ecosystem: world-wide powerful OSS community
Platform for accelerating development of robot software
http://www.ros.org

4. 4
Capabilities
• ROS package:
­a broad collection of libraries for useful robot functionality
­can be installed by apt and built into the project by colcon
ü2,000+ package have been published as open source
• ROS realizes component based development approach
name description
tf 3D coordinate and chain relation
teleop operation of movement direction
usb_cam importing images from USB camera
ros_control control of actuators with abstracted hardware
MoveIt manipulation and controlling of robotics
Navigation localization and mapping for autonomous driving
https://index.ros.org/packages/

5. 5
• Asynchronous comm. between nodes via Topics
­Protocol: DDS (Data Distribution Service, standardized by OMG)
­ROS application can be developed by combining nodes
• Easy to construct loosely coupled architecture
­Pub/Sub nodes can be added/deleted/restarted independently
• Other methods
­ Service: sync. server-client
­ Action: combo of topic/service
­ Parameter: key-value store
Plumbing
node1
node2
node3
node4
topicA
[string]
topicB
[image]
node5
publish subscribe
DDS Domain
msg
msg
msg
msg

6. … …
6
rclcpp rclpy
node.cpp node.py
RCL (ROS Client Library)
RMW (ROS MiddleWare)
DDS B
DDS A
General Purpose OS
• common functions for ROS 2
• implemented by C
• any client library can be
implemented by calling it
• Abstraction layer for DDS
• Able to select prefer DDS
rclrs
node.rs
DDS C
DDS (Data Distribution Service)
• OMG standard specification
• Pub/Sub communication functions
• Automatic search of nodes by RTPS
Software Structure

7. 7
Simple Publisher by Rclpy
https://github.com/ros2/demos/blob/foxy/demo_nodes_py/demo_nodes_py/topics/talker.py
create node from
Talker class
set callback func
and timer interval
publish message
to topic
specify
node name
register as publisher
with topic and type
prepare
massage
class definition

8. 8
• Actors on BEAM send and receive messages
• (I believe) Actor Model is suitable for robot systems🤖
­ "Let it Crash" could also contribute to robot
• (I suggest) Robot programming should be functional!!
­ ROS concept of combining existing packages has a high affinity
System is like,,,
node1
node2
node3
node4
topicA
[string]
topicB
[image]
node5
publish subscribe
DDS Domain
msg
msg
msg
msg
Actor Model!!

9. ROS 2 Client Library for,,,
Rclex
9
rclcpp rclpy
node.cpp node.py node.ex
RCL (ROS Client Library)
RMW (ROS MiddleWare)
DDS B
DDS A
General Purpose OS
rclrs
node.rs
DDS C
github.com/rclex

10. RCL
RMW
DDS
10
OS process space
rclcpp
node1
Erlang VM
rclex
node1
rclex
node2
process
exec. mngr.
process pub1
process sub2
process pub2
...
NIFs
github.com/rclex
calls RCL APIs and converts
Erlang resource objects and
RCL structures to each other
manages Rclex pub/sub functions
(implemented with GenServer)
How to realize Rclex
rclpy
node2
rcl.so
rclex nodes will be created as
Erlang lightweight process!!

11. sub.ex
sub.ex
sub.ex
sub.ex
sub.ex
github.com/rclex
pub.ex
pub.ex pub.ex
pub.ex
pub.ex
11
Ø Massively spawn ROS 2 nodes from Elixir code at the same time
Ø Asynchronously execute pub/sub comm. and corresponding callbacks
Improve ROS 2 communication scalability with
parallel processing of Erlang lightweight processes
pub.ex sub.ex
topic
pub.ex
pub.ex
pub.ex
sub.ex
sub.ex
sub.ex
pub.ex sub.ex
topic
pub.ex sub.ex
topic
pub.ex sub.ex
topic
pub.ex sub.ex
topic
pub.ex sub.ex
topic
pub.ex sub.ex
topic
pub.ex sub.ex
topic
Objective and Advantage

12. 12
Simple Publisher by Rclex
github.com/rclex
number
of nodes
create node by
name and index
create topic
:single-> one topic
:multi-> multiple
set callback func
and timer interval
create list of
messages for
each node
publish message
setting node info.
with pipe operator
processing a data
message with Enum

13. github.com/rclex
論よりRUN!!
😇
😆
pub.cpp x100
(by launch.py)
sub.cpp
(demo_nodes_cpp)
pub.ex x100
sub.cpp
(demo_nodes_cpp)
rclex/rcjp21_demo
RPi4 (CA-72 1.5GHz x4/4GB)
with ROS2 Foxy
"ron yori run"
The RUN is mightier than the word

14. 14
• For ROS developers
­ will acquire better communication performance!
­ will want to employ Elixir/Erlang ecosystem
• For Elixir developers
­ will utilize OSS packages published for ROS!!
More Benefits!! (in the future,,,
MAY THE BEAM
BE WITH
YOUR ROBOT!!
[pic]https://aliexpress.com/
item/32604221183.html

15. 15
Wrapping Up
Give us your contributions!!
https://github.com/rclex/rclex
https://hex.pm/packages/rclex
• Rclex: Robotics meets Elixir!
­ ROS will acquire Elixir's scalability
­ Elixir will utilize ROS packages
• Ongoing/upcoming works
­ Service, Action and Parameter
­ ROS 2 MassageType generation
­ integration into Nerves
­ case study applied to actual robots
­ documentation, and academic paper,,,

16. 16
Thank you so much!
Arigato!!
@takasehideki