Package Summary

An interface to the Dynamixel actuators for ROS control

Introduction

This package provides a hardware interface for ROS control. Its aim is to allow generic software controllers to control a set of Dynamixel actuators. ROS control is a framework to design software control loops in ROS (Robot Operating System) where the controller code is decoupled from the actual hardware. Dynamixel is a popular servo range for robots with all-in-one module (reductor, PID controller, profil speed / acceleration, encoder...).

Features

  • simple, ROS-style control interface for your dynamixel-based robot
  • not specific to a given number or set of actuators
  • position and velocity control
  • works with both version of Dynamixel protocol (1 and 2)
  • uses radians uniformly over all Dynamixel models (no need to worry about ticks-to-angle conversion)
  • you can set an offset for each actuator's position
  • set names for your dynamixels in a configuration file
  • joint limits

Limitations

We are currently working on the following features:

  • add support for the more exotic control modes (including current and multi-turn)
  • it would be great to offer a service to reset one actuator after an overload error

Installation and usage

dynamixel_control_hw depends on the libdynamixel library. Please install it, it's light and quick.

Then, you'll need to store the installation path of libdynamixel in the LIBDYNAMIXEL environment variable.

Install the ros package ros_control. In apt-get, it is called ros-YourDistro-ros-control (where *YourDistro* must be changed by the ROS distribution's name, like indigo or jade).

Clone the dynamixel_control_hw repository in your catkin workspace's source directory and run a catkin_make.

Parameters

For sample configuration files, see the ones in config/. Here are the accepted parameters.

Parameters

~serial_interface (string, default: auto)
  • path to the USB to serial interface for example "/dev/ttyUSB0"
~baudrate (int, default: 0)
  • baud-rate for the serial communication with actuators (in bauds)
~loop_frequency (float, default: 0.0)
  • frequency at which the control loop will run (in Hz)
~cycle_time_error_threshold (float, default: 0.0)
  • how much delay is tolerated on the control loop (in s)
~read_timeout (float, default: 0.0)
  • timeout on the reception of replies from the servos (in s)
~servos (Servo, default: auto)
  • object which keys are the name of the joints and which values contain
~id (int, default: 0)
  • actuator's ID to its name (the one used in the controller list and in URDF)
~offset (float, default: 0.0)
  • correction to be applied to the angle of the joint (in rad)
~command_interface (string, default: position)
  • the command mode (velocity or position)
~max_speed (float, default: 0.0)
  • maximal allowed velocity (rad/s)
~default_command_interface (string, default: position)
  • if no 'command_interface' is defined for a joint, this value is used instead

Testing the hardware interface

If you want to use the sample launch files or to use one of the default controllers, please install with apt-get:

- ros-YourDistro-ros-controllers and - ros-YourDistro-joint-state-publisher.

Have a look at the launch/sample.launch file. It will by default launch two feed-forward only controllers (one position and one velocity) and a virtual controller that publishes the states of the two actuators.

*Before starting* it, check config/sample.yaml for the id parameters, the serial_interface and baudrate settings. Once you are sure that it's correct, you can roslaunch dynamixel_control_hw sample.launch. By looking at the available topics, you should find two, for the commands the joints, and one for the joint state.

== Troubleshooting read time ==

If the reading time seems too long, check the value of the USB latency timer. On ubuntu this value is retrieved with this command cat /sys/bus/usb-serial/devices/ttyUSB0/latency_timer. It is the time, in milliseconds, for which the device driver buffers data before making it available.

You can change this timer with the command echo 4 | sudo tee /sys/bus/usb-serial/devices/ttyUSB0/latency_timer which sets it to 4 ms for the device /dev/ttyUSB0.

Alternative software

If you know of an other software offering similar functionalities to this one, feel free to open an issue so that we can add it here.

Support and contact

This software is developed as part of the ResiBots project. We do our best to keep it free of bug and to implement relevant features. Should you face an issue or have a suggestion, please open an issue.

Projects using this software

- ResiBots

License

Unless stated otherwise, the license for this repository is CeCILL-C (see LICENSE and LICENSE.fr).

ResiBots: http://www.resibots.eu libdynamixel: http://github.com/resibots/libdynamixel ROS: http://www.ros.org/ ROS control: http://wiki.ros.org/ros_control

Wiki: dynamixel_control_hw (last edited 2019-03-28 12:44:59 by PierreDesreumaux)