Local planner (DWA, TEB) in ROS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the DWA local planner plugin in ROS.

ROS

#include <[1]/DWAPlannerROS.h>

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Abase_local_planner

Bteb_local_planner

Cdwa_local_planner

Dglobal_planner

Attempts:

3 left

💡 Hint

Common Mistakes

Including the global planner header instead of the local planner.

Confusing TEB planner header with DWA.

The DWA local planner plugin is included with dwa_local_planner header.

2fill in blank

medium

Complete the code to initialize the TEB local planner in a ROS node.

ROS

teb_local_planner::TebLocalPlannerROS planner;
planner.[1]("TebLocalPlannerROS", &tf_listener, &costmap_ros);

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Astart

Binitialize

Csetup

Dconfigure

Attempts:

3 left

💡 Hint

Common Mistakes

Using configure instead of initialize.

Calling start which is not a planner method.

The initialize method is used to set up the TEB local planner with necessary parameters.

3fill in blank

hard

Fix the error in the code to compute velocity commands using the DWA planner.

ROS

geometry_msgs::Twist cmd_vel;
if (!planner.[1](global_plan, cmd_vel)) {
  ROS_WARN("Failed to compute velocity command");
}

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AcomputeVelocityCommands

Bcompute_velocity

CcalculateCmdVel

DgetVelocity

Attempts:

3 left

💡 Hint

Common Mistakes

Using snake_case method names which do not exist.

Using generic method names not defined in the planner.

The correct method to compute velocity commands in DWA planner is computeVelocityCommands.

4fill in blank

hard

Fill both blanks to create a ROS parameter server call to set the TEB planner's max velocity and acceleration.

ROS

ros::NodeHandle nh;
nh.setParam("[1]/max_vel_x", max_vel);
nh.setParam("[2]/acc_lim_x", max_acc);

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Ateb_local_planner

Bdwa_local_planner

Cbase_local_planner

Dglobal_planner

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing namespaces between DWA and TEB planners.

Using global planner namespace for local planner parameters.

Both parameters belong to the teb_local_planner namespace in ROS parameter server.

5fill in blank

hard

Fill all three blanks to create a ROS launch snippet that loads the DWA local planner plugin, sets the controller frequency, and enables oscillation reset.

ROS

<node pkg="move_base" type="move_base" name="move_base" output="screen">
  <param name="base_local_planner" value="[1]" />
  <param name="controller_frequency" value="[2]" />
  <param name="oscillation_reset_dist" value="[3]" />
</node>

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Adwa_local_planner/DWAPlannerROS

B10.0

C0.05

Dteb_local_planner/TEBLocalPlannerROS

Attempts:

3 left

💡 Hint

Common Mistakes

Using TEB planner plugin instead of DWA in this snippet.

Setting controller frequency to an integer without decimal.

Confusing oscillation reset distance units.

The DWA planner plugin is dwa_local_planner/DWAPlannerROS, the controller frequency is typically set to 10.0 Hz, and oscillation reset distance is commonly 0.05 meters.

Practice

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