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Madrid,  January 2019

ROBOTIS Co., Ltd has chosen eProsima Micro XRCE-DDS (Data-Distribution Service for Extremely Resource Constrained Environments) for the CommXel microcontroller firmware to integrate their XEL Network into ROS 2.

ROBOTIS Co., Ltd is a leading developer of smart servos, industrial actuators, manipulators, open-source humanoid platforms, and educational robotic kits. They have been working on the XEL Network project which was recently released as announced on the XEL Network site.

XEL NETWORK

The primary purpose of this project is to standardize a modular embedded open-source-hardware for robots so that robot hardware can be configured more easily using the features of DDS adopted in ROS 2. It has been achieved communicating the existing DYNAMIXEL protocol with ROS 2 integrating eProsima Micro XRCE-DDS as an enabler protocol.

XEL Network allows the Dynamixel modules to be integrated into a DDS space as ROS 2. XEL Network achieves it using a CommXel board which enables communication from an XEL Network to ROS 2 using eProsima Micro XRCE-DDS.

The CommXel board must be able to:

  • communicate with the DDS for communication with the ROS (for which ROBOTIS used Micro XRCE-DDS in the firmware)
  • periodically collect data (via the Dynamixel protocol) from embedded slave devices
  • be able to publish via Micro XRCE-DDS at specified intervals.
  • to subscribe to specific topics to change the table value of each embedded slave device, or to control the actuator.

XEL Network

The XEL Network integrates two more boards - one dedicated to sensor and power management. SensorXEL enables the connection of multiple devices to an XEL network using UART, I2C, or SPI. Ideally, as can be seen in the picture above. Any sensor device using those interfaces could be easily attachable.

Sensor XEL

XEL NETWORK APPLICATION

XEL Network application can be found in mobile robots area. Please see below video for more details.

EPROSIMA MICRO XRCE-DDS 

ROBOTIS Co., Ltd selected the eProsima open source Micro XRCE-DDS product for this project. eProsima Micro XRCE-DDS implements a client-server protocol to enable resource-constrained devices (clients) to take part in DDS communications. eProsima Micro XRCE-DDS Agent (server) makes possible this communication. Micro XRCE-DDS Agent acts on behalf of the Micro XRCE-DDS Clients and enables them to take part as DDS publishers and/or subscribers in the DDS Global Data Space. Micro XRCE-DDS provides both, a plug and play Micro XRCE-DDS Agent and an API layer, which allows you to implement your Micro XRCE-DDS Clients.

eProsima Micro XRCE-DDS is an implementation of the brand new OMG DDS XRCE standard.

eProsima Micro XRCE-DDS provides some interesting features:

  • Resilience to recurrent connection-disconnection of clients. Support for sleep cycles.
  • Client-side with no dynamic memory allocations.
  • Client reduced memory footprint.
  • Modular transports between client and agent.
  • Reliable or best effort communications.
  • Usage of DDS QoS.
Architecture of eProsima Micro XRCE-DDS environment
The architecture of eProsima Micro XRCE-DDS environment

DYNAMIXEL PROTOCOL

Together with the eProsima Micro XRCE-DDS, ROBOTIS Co., Ltd opted to use the Dynamixel protocol to sense from each embedded sensor or to control the actuator. Dynamixel can control the actuator and read the information (position, speed, etc.) of the actuator.

Currently, Dynamixel is widely extended on different areas (used mainly at university, research lab, military & government research lab, and robotic competition worldwide) being their actuators popular in robotic manipulators, which are quite common in Industrial Environments.

As an example we can find following manipulators that use Dynamixel:

MICRO XRCE-DDS ON INDUSTRIAL ENVIRONMENTS 

There is an increasing interest in bringing ROS 2 to embedded systems. Currently, multiple initiatives are chasing this. Part of the efforts follows a similar pattern, using DDS-XRCE to enable communication between embedded devices and a DDS global data space.

Using DDS-XRCE provides a native communication between ROS 2 and embedded systems, as ROS 2 uses DDS as default protocol and DDS-XRCE is a protocol to communicate microcontrollers with DDS. This new protocol between microcontrollers and DDS simplifies the implementation, usage, and integration of MCUs in a ROS 2 system.

Currently, the most used implementation of DDS-XRCE is eProsima’s open source Micro XRCE-DDS. Micro XRCE-DDS is being used in some real applications by notable companies as Renesas and Robotics. It is also the basis of growing robotics community efforts and projects as micro-ROS.

MORE INFORMATION ABOUT EPROSIMA MICRO XRCE-DDS:

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