Adding Hokuyo Laser Range Finder to Turtlebot¶

Installing the Hokuyo Related Packages¶

Hokuyo Node (UTM-04G) is a laser scanner that can scan with an opening up to 270 degrees with a range up to 4 meters. TurtleBot comes with the Kinect sensor that has a laser scanner with a scan opening up to 57 degrees with practical range of 3 meters. Hokuyo LRF is more accurate than the Kinect sensor and it would be more useful in making maps with gmapping and SLAM applications. ROS provides a driver for Hokyuo LRF, referred to as urg_node in ROS Hydro distribution. You have to install the urg_node as follows:

sudo apt-get install ros-hydro-urg-*

It is also possible to use the hokuyo_node and for this you need to install hokuyo_node as follows:

sudo apt-get install ros-hydro-hokuyo-node

Copying Hokuyo description in meshes folder¶

After the installation of above package is completed, we should now make the changes in Turtlebot URDF. First we should add the hokuyo.dae file into /opt/ros/hydro/share/turtlebot_description/meshes folder. Meshes file contain all the properties that are needed to define hokuyo_node

Editing and adding the Hokuyo URDF file¶

Now go the folder /opt/ros/hydro/share/turtlebot_description/urdf/sensors and create a new file called as hokuyo.urdf.xacro. And add the following lines in the file:

<?xml version="1.0"?>
<robot name="sensor_hokuyo" xmlns:xacro="http://ros.org/wiki/xacro">
<xacro:include filename="$(find turtlebot_description)/urdf/turtlebot_gazebo.urdf.xacro"/>
<xacro:include filename="$(find turtlebot_description)/urdf/turtlebot_properties.urdf.xacro"/>

<xacro:macro name="sensor_hokuyo" params="parent">
<link name="laser_joint">
<collision>
<origin xyz="0 0 0" rpy="0 0 0"/>
<geometry>
<box size="0.1 0.1 0.1"/>
</geometry>
</collision>
<visual>
<origin xyz="0 0 0" rpy="0 0 0"/>
<geometry>
<mesh filename="package://turtlebot_description/meshes/sensors/hokuyo.dae"/>
</geometry>
</visual>
<inertial>
<mass value="1e-5" />
<origin xyz="0 0 0" rpy="0 0 0"/>
<inertia ixx="1e-6" ixy="0" ixz="0" iyy="1e-6" iyz="0" izz="1e-6" />
</inertial>
</link>
<joint name="hokuyo_joint" type="fixed">
<axis xyz="0 0 1" />
<origin xyz="0 0.22 0.05" rpy="0 0 1.570796"/>
<parent link="${parent}"/>
<child link="laser"/>
</joint>
</xacro:macro>
</robot>

Code Explanation¶

The code focuses on two things one is description about Hokuyo that is in meshes folder, and other is the defining join with its location and its relation with parent frame (joint). For finding the location of hokuyo sensor, you may need to calculate the location that will be in meters and the representation is in x,y,z . Turtlebot assumes 0 0 0 at it base center.

<collision>
<origin xyz="0 0 0" rpy="0 0 0"/>
<geometry>
<box size="0.1 0.1 0.1"/>
</geometry>
</collision>

Collision do provide the opportunity to take a decision before going to collide.In above code we have defined collisions for more explanation look into Adding Collisions.It is necessary to set the parameters to avoid collisions.

<joint name="hokuyo_joint" type="fixed">
<axis xyz="0 0 1" />
<origin xyz="0 0.22 0.05" rpy="0 0 1.570796"/>
<parent link="${parent}"/>
<child link="laser"/>
</joint>

In above code, first thing we did is specifying the joint name that is Hokuyo (but can be changed to any other thing), the type we select as fixed then we defined where the Hokuyo is attached with respect to origin, Next thing the joints are defined by parent and child, You can also specify some fixed frame like map or base_footprint or make it link to default parent

Adding Hokuyo URDF description to Turtlebot URDF description¶

In order to be Hokuyo a part of URDF description, we need to add Hokuyo LRF description to the Turtlebot URDF so that it can be visualized in rivz and other simulators. For that purpose, go to the folder /opt/ros/hydro/share/turtlebot_description/urdf and add the following line in turtlebot_library.urdf.xacro file:

<xacro:include filename="$(find turtlebot_description)/urdf/sensors/hokuyo.urdf.xacro"/>

This will call the hokuyo description created in urdf. In order to launch the description , it is just required to launch mininal.launch and it will work, in order to see a hokuyo sensor in rviz we need to add its definition in gazebo that is not covered in this tutorial but can be borrowed from Building Visual Robot

Creating a Launch File for Hokuyo Node¶

Its is better to create a Hokuyo Launch file in order to launch the Hokuyo node. It will also allow Hokuyo node dynamic re-configuration of Hokuyo node. Create a launch file in any package and call it as hokuyo.launch. Copy and paste the following code in hokuyo.launch

<launch>
<node name="hokuyo" pkg="hokuyo_node" type="hokuyo_node" respawn="false" output="screen">
<param name="calibrate_time" type="bool" value="true"/>
<param name="port" type="string" value="/dev/ttyACM0"/>
<param name="intensity" type="bool" value="false"/>
<param name="min_ang" value="-2.356194437"/>
<param name="max_ang" value="2.35619443"/>
<param name="cluster" value="1"/>
</node>
</launch>

Using SLAM With Hokuyo LIDAR Sensor¶

In order to use Hokuyo for SLAM as described in tutorial Building SLAM hokuyo-turtlebot. Following are the steps to be done at turtlebot Launch the Turtlebot

roslaunch turtlebot_bringup minimal.launch

run the Hokuyo node:

roslaunch turtlebot_test_launch hokuyo.launch

Launch the gmapping for map building

roslaunch turtlebot_navigation gmapping_demo.launch

You can view the map at workstation using rviz

roslaunch turtlebot_rviz_launchers view_navigation.launch