Recovery behaviors in ROS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a recovery behavior node in ROS.

ROS

ros::NodeHandle nh;
std::shared_ptr<[1]> recovery_behavior = std::make_shared<ClearCostmapRecovery>(nh);

Drag options to blanks, or click blank then click option'

ARecoveryNode

BMoveBaseRecovery

CRecoveryBehavior

DClearCostmapRecovery

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic RecoveryBehavior instead of a specific recovery class.

Confusing MoveBaseRecovery with ClearCostmapRecovery.

The ClearCostmapRecovery class is a common recovery behavior in ROS navigation stack.

2fill in blank

medium

Complete the code to call the recovery behavior's runBehavior method.

ROS

if (!recovery_behavior->[1]()) {
  ROS_ERROR("Recovery behavior failed");
}

Drag options to blanks, or click blank then click option'

Aexecute

BrunBehavior

Cstart

Dperform

Attempts:

3 left

💡 Hint

Common Mistakes

Using execute() which is not defined in recovery behaviors.

Using start() or perform() which are not standard methods.

The runBehavior() method triggers the recovery action in ROS navigation.

3fill in blank

hard

Fix the error in the recovery behavior initialization code.

ROS

std::shared_ptr<ClearCostmapRecovery> recovery_behavior = std::make_shared<ClearCostmapRecovery>([1]);

Drag options to blanks, or click blank then click option'

Anullptr

Bros::NodeHandle()

Cnh

Dnode_handle

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a temporary NodeHandle instead of the existing one.

Passing nullptr or an undefined variable.

The ClearCostmapRecovery constructor requires a valid NodeHandle object, usually named nh.

4fill in blank

hard

Fill both blanks to create a recovery behavior and run it safely.

ROS

auto recovery = std::make_shared<[1]>(nh);
if (!recovery->[2]()) {
  ROS_WARN("Recovery failed");
}

Drag options to blanks, or click blank then click option'

AClearCostmapRecovery

BrunBehavior

Cexecute

DMoveBaseRecovery

Attempts:

3 left

💡 Hint

Common Mistakes

Using execute() instead of runBehavior().

Using MoveBaseRecovery class incorrectly.

ClearCostmapRecovery is a recovery class and runBehavior() runs it.

5fill in blank

hard

Fill all three blanks to define, initialize, and run a recovery behavior with error handling.

ROS

std::shared_ptr<[1]> recovery_behavior = std::make_shared<[2]>(nh);
if (!recovery_behavior->[3]()) {
  ROS_ERROR("Recovery behavior execution failed");
}

Drag options to blanks, or click blank then click option'

ARecoveryBehavior

BClearCostmapRecovery

CrunBehavior

DMoveBaseRecovery

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same class name for pointer and instance incorrectly.

Using execute() instead of runBehavior().

RecoveryBehavior is the interface type, ClearCostmapRecovery is the concrete class, and runBehavior() executes it.

Practice

1. What is the main purpose of recovery behaviors in ROS navigation?

easy

A. To help the robot fix problems when it gets stuck

B. To speed up the robot's movement

C. To map the environment faster

D. To reduce battery usage

Solution

1. Step 1: Understand recovery behaviors role

   Recovery behaviors are designed to help the robot when it encounters problems like being stuck or blocked.

2. Step 2: Compare options with purpose

   Only To help the robot fix problems when it gets stuck matches this purpose. Other options describe unrelated functions.

3. Final Answer:

   To help the robot fix problems when it gets stuck -> Option A

4. Quick Check:

   Recovery behaviors fix stuck robot = C [OK]

Hint: Recovery behaviors fix stuck robots, not speed or mapping [OK]

Common Mistakes:

• Confusing recovery behaviors with mapping functions
• Thinking recovery behaviors save battery
• Assuming recovery speeds up navigation

2. Which YAML configuration snippet correctly enables a recovery behavior in ROS navigation?

easy

A. recovery_behaviors:
- clear_costmap_recovery
- rotate_recovery

B. recovery_behaviors = [clear_costmap, rotate_recovery]

C. recovery_behaviors:
clear_costmap: true
rotate_recovery: true

D. recovery_behaviors:
- name: clear_costmap
type: "clear_costmap_recovery/ClearCostmapRecovery"

Solution

1. Step 1: Identify correct YAML syntax for recovery behaviors

   ROS navigation expects a list of recovery behaviors with name and type keys in YAML format.

2. Step 2: Check each option's format

   recovery_behaviors: - name: clear_costmap type: "clear_costmap_recovery/ClearCostmapRecovery" uses correct YAML list with name and type. Options B, C, and D use invalid syntax or missing keys.

3. Final Answer:

   YAML list with name and type keys -> Option D

4. Quick Check:

   YAML recovery behaviors need name and type keys = A [OK]

Hint: YAML lists need dash and key:value pairs for recovery behaviors [OK]

Common Mistakes:

• Using equal signs instead of colon in YAML
• Missing name or type keys in recovery behavior
• Using Python list syntax instead of YAML

3. Given this ROS recovery behavior configuration snippet, what will happen when the robot is stuck?

recovery_behaviors:
  - name: rotate_recovery
    type: "rotate_recovery/RotateRecovery"

medium

A. The robot will clear its costmap to remove obstacles

B. The robot will rotate in place to find a new path

C. The robot will stop and wait indefinitely

D. The robot will move backward quickly

Solution

1. Step 1: Understand rotate_recovery behavior

   The rotate_recovery behavior makes the robot spin in place to scan surroundings and find a new path.

2. Step 2: Match behavior to options

   The robot will rotate in place to find a new path correctly describes rotation. The robot will clear its costmap to remove obstacles describes clearing costmap, which is different. Options C and D do not match rotate_recovery.

3. Final Answer:

   The robot will rotate in place to find a new path -> Option B

4. Quick Check:

   rotate_recovery spins robot = B [OK]

Hint: RotateRecovery spins robot to find path, not clear or stop [OK]

Common Mistakes:

• Confusing rotate_recovery with clear_costmap_recovery
• Thinking robot stops instead of rotating
• Assuming robot moves backward

4. You configured a recovery behavior in ROS but it never triggers when the robot is stuck. What is the most likely cause?

medium

A. The recovery behavior is not listed in the YAML file

B. The robot's battery is low

C. The robot is moving too fast

D. The map is too large

Solution

1. Step 1: Check recovery behavior configuration

   If the recovery behavior is not listed or enabled in the YAML file, it will not run.

2. Step 2: Evaluate other options

   Battery level, speed, or map size do not prevent recovery behaviors from triggering directly.

3. Final Answer:

   The recovery behavior is not listed in the YAML file -> Option A

4. Quick Check:

   Missing YAML config stops recovery trigger = A [OK]

Hint: Recovery behaviors must be listed in YAML to trigger [OK]

Common Mistakes:

• Blaming battery or speed for recovery not triggering
• Ignoring YAML configuration
• Assuming map size affects recovery behavior

5. You want the robot to first clear its costmap and then rotate if still stuck. How should you configure the recovery behaviors in YAML?

hard

A. recovery_behaviors:
- name: rotate_recovery
type: "rotate_recovery/RotateRecovery"
- name: clear_costmap
type: "clear_costmap_recovery/ClearCostmapRecovery"

B. recovery_behaviors:
- clear_costmap_recovery
- rotate_recovery

C. recovery_behaviors:
- name: clear_costmap
type: "clear_costmap_recovery/ClearCostmapRecovery"
- name: rotate_recovery
type: "rotate_recovery/RotateRecovery"

D. recovery_behaviors:
clear_costmap: true
rotate_recovery: true

Solution

1. Step 1: Understand order matters in recovery behaviors

   ROS runs recovery behaviors in the order listed in YAML. To clear costmap first, it must be listed first.

2. Step 2: Check YAML syntax and order

   recovery_behaviors: - name: clear_costmap type: "clear_costmap_recovery/ClearCostmapRecovery" - name: rotate_recovery type: "rotate_recovery/RotateRecovery" lists clear_costmap first, then rotate_recovery, with correct YAML syntax. recovery_behaviors: - name: rotate_recovery type: "rotate_recovery/RotateRecovery" - name: clear_costmap type: "clear_costmap_recovery/ClearCostmapRecovery" reverses order. Options B and C have invalid syntax.

3. Final Answer:

   List clear_costmap first, then rotate_recovery with correct YAML -> Option C

4. Quick Check:

   Order in YAML controls recovery sequence = D [OK]

Hint: List recovery behaviors in YAML in desired run order [OK]

Common Mistakes:

• Reversing order of recovery behaviors
• Using invalid YAML syntax
• Assuming order does not matter