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ROSframework~5 mins

Local planner (DWA, TEB) in ROS

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Introduction

A local planner helps a robot decide how to move safely and smoothly in its nearby space. It plans short paths to avoid obstacles and reach the goal.

When a robot needs to navigate around obstacles in real-time.
When a robot must follow a path while adjusting to changes in the environment.
When smooth and safe robot movements are required in tight spaces.
When combining global path planning with immediate obstacle avoidance.
When using ROS navigation stack for mobile robot control.
Syntax
ROS
local_planner:
  type: dwa_local_planner/DWAPlannerROS
  max_vel_x: 0.5
  min_vel_x: 0.1
  max_rot_vel: 1.0
  acc_lim_x: 2.5
  acc_lim_theta: 3.2

# or for TEB planner
local_planner:
  type: teb_local_planner/TEBLocalPlannerROS
  max_vel_x: 0.6
  max_vel_x_backwards: 0.3
  max_vel_theta: 1.0
  acc_lim_x: 3.0
  acc_lim_theta: 3.2

The type field selects which planner to use: DWA or TEB.

Parameters like max_vel_x control the robot's speed limits.

Examples
This sets up the DWA planner with max forward speed 0.5 m/s and rotation speed 1.0 rad/s.
ROS
local_planner:
  type: dwa_local_planner/DWAPlannerROS
  max_vel_x: 0.5
  min_vel_x: 0.1
  max_rot_vel: 1.0
This configures the TEB planner allowing forward and backward speeds with smooth turning.
ROS
local_planner:
  type: teb_local_planner/TEBLocalPlannerROS
  max_vel_x: 0.6
  max_vel_x_backwards: 0.3
  max_vel_theta: 1.0
Sample Program

This launch file starts the move_base node with the DWA local planner configured for safe robot movement.

ROS
# ROS launch snippet to use DWA local planner
<launch>
  <node pkg="move_base" type="move_base" name="move_base" output="screen">
    <param name="base_local_planner" value="dwa_local_planner/DWAPlannerROS" />
    <param name="DWAPlannerROS/max_vel_x" value="0.5" />
    <param name="DWAPlannerROS/min_vel_x" value="0.1" />
    <param name="DWAPlannerROS/max_rot_vel" value="1.0" />
  </node>
</launch>
OutputSuccess
Important Notes

DWA (Dynamic Window Approach) focuses on velocity sampling for safe motion.

TEB (Timed Elastic Band) optimizes the path considering time and robot dynamics.

Both planners require tuning parameters to match your robot's capabilities.

Summary

Local planners help robots move safely in their immediate surroundings.

DWA and TEB are popular local planners in ROS for obstacle avoidance and smooth navigation.

Choosing and tuning the right planner depends on your robot and environment.

Practice

(1/5)
1. What is the main purpose of a local planner like DWA or TEB in ROS?
easy
A. To control the robot's battery usage
B. To map the entire environment for the robot
C. To help the robot navigate safely around obstacles nearby
D. To communicate with other robots

Solution

  1. Step 1: Understand the role of local planners

    Local planners focus on immediate surroundings to avoid obstacles and plan short paths.

  2. Step 2: Compare options

    Mapping the environment is done by global planners or mapping nodes, not local planners.

  3. Final Answer:

    To help the robot navigate safely around obstacles nearby -> Option C

  4. Quick Check:

    Local planner = safe nearby navigation [OK]
Hint: Local planners handle nearby obstacles, not mapping or communication [OK]
Common Mistakes:
  • Confusing local planner with global planner
  • Thinking local planner maps environment
  • Assuming local planner manages robot hardware
2. Which of the following is the correct way to enable the DWA local planner in a ROS navigation stack configuration file?
easy
A. base_local_planner: "dwa_local_planner/DWAPlannerROS"
B. base_local_planner: "teb_local_planner/TEBPlanner"
C. planner: "global_planner/GlobalPlanner"
D. planner: "dwa_local_planner/DWAPlannerROS"

Solution

  1. Step 1: Identify the correct parameter name for local planner

    The parameter to specify the local planner plugin is usually 'base_local_planner'.

  2. Step 2: Match the correct plugin name for DWA

    DWA local planner plugin is 'dwa_local_planner/DWAPlannerROS'. base_local_planner: "dwa_local_planner/DWAPlannerROS" matches this exactly.

  3. Final Answer:

    base_local_planner: "dwa_local_planner/DWAPlannerROS" -> Option A

  4. Quick Check:

    Correct plugin name and parameter = base_local_planner: "dwa_local_planner/DWAPlannerROS" [OK]
Hint: Look for 'base_local_planner' key with DWA plugin name [OK]
Common Mistakes:
  • Using 'planner' instead of 'base_local_planner'
  • Confusing DWA and TEB plugin names
  • Using global planner plugin name for local planner
3. Given the following ROS parameter snippet for TEB local planner: 
teb_local_planner:
  max_vel_x: 0.5
  max_vel_theta: 1.0
  min_turning_radius: 0.2
What will happen if the robot tries to turn with an angular velocity of 1.5 rad/s?
medium
A. The planner will allow the turn at 1.5 rad/s
B. The planner will limit the angular velocity to 1.0 rad/s
C. The planner will stop the robot immediately
D. The planner will ignore the max_vel_theta parameter

Solution

  1. Step 1: Understand max_vel_theta parameter

    This parameter sets the maximum allowed angular velocity for the robot.

  2. Step 2: Compare requested angular velocity with max_vel_theta

    The requested 1.5 rad/s exceeds the max of 1.0 rad/s, so the planner limits it to 1.0 rad/s.

  3. Final Answer:

    The planner will limit the angular velocity to 1.0 rad/s -> Option B

  4. Quick Check:

    Angular velocity capped by max_vel_theta = The planner will limit the angular velocity to 1.0 rad/s [OK]
Hint: Planner caps velocities at max limits set in parameters [OK]
Common Mistakes:
  • Assuming planner allows velocities above max
  • Thinking planner stops robot on limit breach
  • Ignoring max_vel_theta parameter
4. You configured the DWA local planner but the robot keeps colliding with obstacles. Which of the following is the most likely cause?
medium
A. The obstacle distance parameter is set too low, causing late avoidance
B. The global planner is disabled
C. The robot's battery is low
D. The robot's wheels are not calibrated

Solution

  1. Step 1: Identify parameters affecting obstacle avoidance

    DWA uses parameters like obstacle distance to decide when to start avoiding obstacles.

  2. Step 2: Analyze effect of low obstacle distance

    If set too low, the planner reacts too late, causing collisions.

  3. Final Answer:

    The obstacle distance parameter is set too low, causing late avoidance -> Option A

  4. Quick Check:

    Late avoidance due to low obstacle distance = The obstacle distance parameter is set too low, causing late avoidance [OK]
Hint: Check obstacle distance parameter if collisions occur [OK]
Common Mistakes:
  • Blaming global planner for local planner issues
  • Ignoring parameter tuning for obstacle avoidance
  • Assuming hardware issues cause collisions without evidence
5. You want your robot to navigate a narrow corridor smoothly using the TEB local planner. Which combination of parameters should you adjust to improve smooth turning and obstacle clearance?
hard
A. Increase min_turning_radius and decrease obstacle_avoidance_force
B. Increase max_vel_x and decrease max_vel_theta
C. Decrease max_vel_x and disable obstacle avoidance
D. Decrease min_turning_radius and increase obstacle_avoidance_force

Solution

  1. Step 1: Understand min_turning_radius effect

    Decreasing min_turning_radius allows tighter turns, useful in narrow corridors.

  2. Step 2: Understand obstacle_avoidance_force effect

    Increasing obstacle_avoidance_force makes the planner keep safer distance from obstacles, improving clearance.

  3. Step 3: Combine effects for smooth navigation

    Tight turns plus stronger obstacle avoidance helps smooth, safe navigation in tight spaces.

  4. Final Answer:

    Decrease min_turning_radius and increase obstacle_avoidance_force -> Option D

  5. Quick Check:

    Tight turns + strong avoidance = Decrease min_turning_radius and increase obstacle_avoidance_force [OK]
Hint: Tighten turning radius and boost avoidance force for narrow spaces [OK]
Common Mistakes:
  • Increasing turning radius makes turns wider, not tighter
  • Disabling obstacle avoidance causes collisions
  • Confusing velocity limits with turning parameters
Recommended

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