Run demo

ros2 launch webots_ros2_epuck example_launch.py

and you can use teleop_twist_keyboard in another window to control the robot:

ros2 run teleop_twist_keyboard teleop_twist_keyboard

but make sure you have the teleop-twist-keyboard ROS package installed.

Topics Overview

Here you can find a full list of ROS2 topics:

$ ros2 topic list -t
/cmd_vel [geometry_msgs/msg/Twist]
/gs0 [sensor_msgs/msg/Range]
/gs1 [sensor_msgs/msg/Range]
/gs2 [sensor_msgs/msg/Range]
/image_raw [sensor_msgs/msg/Image]
/camera_info [sensor_msgs/msg/CameraInfo]
/imu [sensor_msgs/msg/Imu]
/led0 [std_msgs/msg/Bool]
/led1 [std_msgs/msg/Int32]
/led2 [std_msgs/msg/Bool]
/led3 [std_msgs/msg/Int32]
/led4 [std_msgs/msg/Bool]
/led5 [std_msgs/msg/Int32]
/led6 [std_msgs/msg/Bool]
/led7 [std_msgs/msg/Int32]
/ls0 [sensor_msgs/msg/Illuminance]
/ls1 [sensor_msgs/msg/Illuminance]
/ls2 [sensor_msgs/msg/Illuminance]
/ls3 [sensor_msgs/msg/Illuminance]
/ls4 [sensor_msgs/msg/Illuminance]
/ls5 [sensor_msgs/msg/Illuminance]
/ls6 [sensor_msgs/msg/Illuminance]
/ls7 [sensor_msgs/msg/Illuminance]
/odom [nav_msgs/msg/Odometry]
/ps0 [sensor_msgs/msg/Range]
/ps1 [sensor_msgs/msg/Range]
/ps2 [sensor_msgs/msg/Range]
/ps3 [sensor_msgs/msg/Range]
/ps4 [sensor_msgs/msg/Range]
/ps5 [sensor_msgs/msg/Range]
/ps6 [sensor_msgs/msg/Range]
/ps7 [sensor_msgs/msg/Range]
/scan [sensor_msgs/msg/LaserScan]
/tf [tf2_msgs/msg/TFMessage]
/tf_static [tf2_msgs/msg/TFMessage]
/tof [sensor_msgs/msg/Range]

Infra-red, Light Sensors, and LEDs

E-puck2 has 8 infra-red sensors (named as ps0-7) all of which are mapped to the same name ROS2 topics of type sensor_msgs/Range. Therefore, you can obtain a distance from a sensor as follows:

ros2 topic echo /ps1

Besides infrared sensors, e-puck2 is upgraded with long-range ToF sensor positioned just above the camera. Data from this sensor is also exposed through the sensor_msgs/Range topic with name tof.

All distance sensors are combined to create sensor_msgs/LaserScan so you can use it directly in SLAM packages. You can test it as:

ros2 topic echo /scan

The same infra-red sensors act as light sensors. In the ROS2 driver, data from the sensors is published as sensor_msgs/Illuminance message (unit is lux) and you can subscribe to it as follows:

ros2 topic echo /ls1

Notice in the image above, there are 8 LEDs as well-positioned around the robot. LEDs led0, led2, led4 and led6 can be only turned on or off, while LEDs led1, led3, led5 and led7 have controllable RGB components. Therefore, in the case of binary LEDs, you can test them as:

ros2 topic pub /led0 std_msgs/Bool '{ "data": true }'

and RGB as:

ros2 topic pub /led1 std_msgs/Int32 '{ "data": 0xFF0000 }'

where 3 lower bytes of Int32 represent 3 bytes of R, G and B components.

Velocity

Standard geometry_msgs/Twist topic with name /cmd_vel is exposed for velocity control.

ros2 topic pub /cmd_vel geometry_msgs/Twist "linear:
  x: 0.1
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 0.0"

Note that only linear.x and angular.z are considered as e-puck2 is differential wheeled robot.

Odometry

Standard ROS2 messages nav_msgs/Odometry are used to publish odometry data. You can subscribe to it with:

ros2 topic echo /odom

In case you are not interested in covariance matrices, you can use --no-arr parameter to hide arrays:

ros2 topic echo --no-arr /odom

Note that ROS uses REP convention (x-forward, y-left and z-up) while Webots inherited convention from VRML (x-right, y-up, z-backward). Therefore, you will see translations in Webots as following , and .

You can also visualise odometry in rviz :

ros2 launch webots_ros2_epuck example.launch.py rviz:=true

Camera

Camera data and details are described through image_raw (type sensor_msgs/Image) and camera_info (type sensor_msgs/CameraInfo) topics. Compared to the physical robot driver there is no sensor_msgs/CompressedImage since the images are not meant to be transfer thourgh a network.

You can run rqt , navigate to Plugins > Visualization > Image View and for topic choose /image_raw. Note that the image encoding is BGRA.

IMU

There are 3D accelerometer and 3D gyro hardware on e-puck2. You can access to this data through imu topic (type sensor_msgs/Imu), e.g.:

ros2 topic echo --no-arr /imu

Ground Sensors

Ground sensors come as an optional module for e-puck2. If the module is present, the ROS2 driver will automatically detect it and publish data. You can test them as:

ros2 topic echo /gs1

To put the ground sensor module, select groundSensorsSlot in e-puck2 robot tree, click + button and find E-puckGroundSensors (check the image bellow).

Transformations

Dynamic transformations are only used for the odometry and you can show it as:

ros2 topic echo tf

All other transformations are static and they are exposed as latched topics, so you show them with the following command:

ros2 topic echo --qos-profile services_default --qos-durability transient_local tf_static

Changelog for package webots_ros2_epuck

0.0.1 (2020-03-31)

• Initial version