Navigation

WARNING: Be careful when running the robot on the table as the robot might fall.

NOTE:

• This instructions were tested on Ubuntu 16.04 and ROS Kinetic Kame.
• This instructions are supposed to be running on the remote PC. Please run the instructions below on your Remote PC.
• The terminal application can be found with the Ubuntu search icon on the top left corner of the screen. The shortcut key for running the terminal is Ctrl-Alt-T.
• Make sure to run the Bringup instructions before running the instructions below.
• The navigation uses the a data created in SLAM. Please make sure to have a map data.

Navigation is to move the robot from one location to the specified destination in a given environment. For this purpose, a map that contains geometry information of furniture, objects, and walls of the given environment is required. As described in the previous SLAM section, the map was created with the distance information obtained by the sensor and the pose information of the robot itself.

The navigation enables a robot to move from the current pose to the designated goal pose on the map by using the map, robot’s encoder, IMU sensor, and distance sensor. The procedure for performing this task is as follows.

Run Navigation Nodes

[Remote PC] Run roscore.

$ roscore

[TurtleBot] Bring up basic packages to start TurtleBot3 applications.

$ roslaunch turtlebot3_bringup turtlebot3_robot.launch

[Remote PC] Launch the navigation file.

TIP: Before executing this command, you have to specify the model name of TurtleBot3. The ${TB3_MODEL} is the name of the model you are using in burger, waffle, waffle_pi. If you want to permanently set the export settings, please refer to Export TURTLEBOT3_MODEL page.

$ export TURTLEBOT3_MODEL=${TB3_MODEL}
$ roslaunch turtlebot3_navigation turtlebot3_navigation.launch map_file:=$HOME/map.yaml

TIP: When you run the above command, the visualization tool RViz is also executed. If you want to run RViz separately, use the following command.

$ rviz -d `rospack find turtlebot3_navigation`/rviz/turtlebot3_navigation.rviz

Estimate Initial Pose

[Remote PC] First, the initial pose estimation of the robot should be performed. When you press 2D Pose Estimate in the menu of RViz, a very large green arrow appears. Move it to the pose where the actual robot is located in the given map, and while holding down the left mouse button, drag the green arrow to the direction where the robot’s front is facing, follow the instruction below.

• Click the 2D Pose Estimate button.
• Click on the approxtimate point in the map where the TurtleBot3 is located and drag the cursor to indicate the direction where TurtleBot3 faces.

Then move the robot back and forth with tools like the turtlebot3_teleop_keyboard node to collect the surrounding environment information and find out where the robot is currently located on the map.

$ export TURTLEBOT3_MODEL=${TB3_MODEL}
$ roslaunch turtlebot3_teleop turtlebot3_teleop_key.launch

When this process is completed, the robot estimates its actual position and orientation by using the position and orientation specified by the green arrow as the initial pose. Every green arrow stands for an expected position of TurtleBot3. The laser scanner will draw approximate figures of wall on the map. If the drawing doesn’t show the figures incorrectly, repeat localizing the TurtleBot3 from clicking 2D Pose Estimate button above.

TIP: The turtlebot3_teleop_keyboard node used for Estimate Initial Pose should be terminated after use. If it does not, the robot will behave strangely because the topic overlaps with the /cmd_vel topic from the navigation node of the next step.

Send Navigation Goal

[Remote PC] When everything is ready, let’s try the move command from the navigation GUI. If you press 2D Nav Goal in the menu of RViz, a very large green arrow appears. This green arrow is a marker that can specify the destination of the robot. The root of the arrow is the x and y position of the robot, and the orientation pointed by the arrow is the theta direction of the robot. Click this arrow at the position where the robot will move, and drag it to set the orientation like the instruction below.

• Click the 2D Nav Goal button.
• Click on a specific point in the map to set a goal position and drag the cursor to the direction where TurtleBot should be facing at the end.

The robot will create a path to avoid obstacles to its destination based on the map. Then, the robot moves along the path. At this time, even if an obstacle is suddenly detected, the robot moves to the target point avoiding the obstacle.

Setting a goal position might fail if the path to the goal position cannot be created. If you wish to stop the robot before it reaches to the goal position, set the current position of TurtleBot3 as a goal position.

Tuning Guide

Navigation stack has many parameters to change performances for different robots. You can get an information about it in ROS Wiki or refer chapter 11 in ROS Robot Programming book.

This tuning guide give some tips for you to configue important parameters. If you want to change performances depends on your environments, this tips might be help you and save your time.

inflation_radius

• turtlebot3_navigation/param/costmap_common_param_$(model).yaml
• This parameter makes inflation area from the obstacle. Path would be planned in order that it don’t across this area. It is safe that to set this to be bigger than robot radius. For more information about it please following page of costmap_2d wiki.

cost_scaling_factor

• turtlebot3_navigation/param/costmap_common_param_$(model).yaml
• This factor is multiplied by cost value. Because it is an reciprocal propotion, this parameter is increased, the cost is decreased.

The best path is for the robot to pass through a center of between obstacles. Set this factor to be smaller in order to far from obstacles.

max_vel_x

• turtlebot3_navigation/param/dwa_local_planner_params_$(model).yaml
• This factor is set the maximum value of translational velocity.

min_vel_x

• turtlebot3_navigation/param/dwa_local_planner_params_$(model).yaml
• This factor is set the minimum value of translational velocity. If set this negative, the robot can move backwards.

max_trans_vel

• turtlebot3_navigation/param/dwa_local_planner_params_$(model).yaml
• Actual value of the maximum translational velocity. The robot can not be faster than this.

min_trans_vel

• turtlebot3_navigation/param/dwa_local_planner_params_$(model).yaml
• Actual value of the minimum translational velocity. The robot can not be slower than this.

max_rot_vel

• turtlebot3_navigation/param/dwa_local_planner_params_$(model).yaml
• Actual value of the maximum rotational velocity. The robot can not be faster than this.

min_rot_vel

• turtlebot3_navigation/param/dwa_local_planner_params_$(model).yaml
• Actual value of the minimum rotational velocity. The robot can not be slower than this.

acc_lim_x

• turtlebot3_navigation/param/dwa_local_planner_params_$(model).yaml
• Actual value of the translational acceleration limit.

acc_lim_theta

• turtlebot3_navigation/param/dwa_local_planner_params_$(model).yaml
• Actual value of the rotational acceleration limit.

xy_goal_tolerance

• turtlebot3_navigation/param/dwa_local_planner_params_$(model).yaml
• The x,y distance allowed when the robot reaches its goal pose.

yaw_goal_tolerance

• turtlebot3_navigation/param/dwa_local_planner_params_$(model).yaml
• The yaw angle allowed when the robot reaches its goal pose.

sim_time

• turtlebot3_navigation/param/dwa_local_planner_params_$(model).yaml
• This factor is set forward simulation in seconds. Too low value is in sufficient time to pass narrow area and too high value is not allowed rapidly rotates. You can watch defferences of length of the yellow line in below image.

References

• Basic Navigation Tuning Guide (ROS Wiki)
• ROS Navigation Tuning Guide by Kaiyu Zheng

References

• Navigation
  • ROS WIKI, Github