Recovery behaviors in ROS

Introduction

Recovery behaviors help a robot fix problems when it gets stuck or lost. They make the robot try simple fixes before giving up.

When a robot hits an obstacle and cannot move forward.

If the robot's path is blocked and it needs to find a new way.

When the robot loses localization and needs to reset its position.

If the robot gets stuck in a tight space and needs to back up.

When the robot needs to clear costmaps or sensor data to continue.

Syntax

ROS

class RecoveryBehaviorName : public nav_core::RecoveryBehavior {
public:
  void initialize(std::string name, tf2_ros::Buffer* tf, costmap_2d::Costmap2DROS* global_costmap, costmap_2d::Costmap2DROS* local_costmap) override;
  void runBehavior() override;
};

Recovery behaviors are classes that inherit from nav_core::RecoveryBehavior.

They must implement initialize() and runBehavior() methods.

Examples

This recovery behavior clears the robot's costmap to remove old obstacle data.

ROS

class ClearCostmapRecovery : public nav_core::RecoveryBehavior {
public:
  void initialize(std::string name, tf2_ros::Buffer* tf, costmap_2d::Costmap2DROS* global_costmap, costmap_2d::Costmap2DROS* local_costmap) override {
    // setup code
  }
  void runBehavior() override {
    // clear costmap data
  }
};

This recovery behavior makes the robot spin in place to find a clear path.

ROS

class RotateRecovery : public nav_core::RecoveryBehavior {
public:
  void initialize(std::string name, tf2_ros::Buffer* tf, costmap_2d::Costmap2DROS* global_costmap, costmap_2d::Costmap2DROS* local_costmap) override {
    // setup code
  }
  void runBehavior() override {
    // rotate robot 360 degrees
  }
};

Sample Program

This simple recovery behavior logs a message and would back up the robot to get unstuck.

ROS

#include <nav_core/recovery_behavior.h>
#include <pluginlib/class_list_macros.hpp>
#include <ros/ros.h>
#include <tf2_ros/buffer.h>
#include <costmap_2d/costmap_2d_ros.h>

class SimpleBackUpRecovery : public nav_core::RecoveryBehavior {
public:
  void initialize(std::string name, tf2_ros::Buffer* tf, costmap_2d::Costmap2DROS* global_costmap, costmap_2d::Costmap2DROS* local_costmap) override {
    initialized_ = true;
    ROS_INFO("SimpleBackUpRecovery initialized");
  }

  void runBehavior() override {
    if (!initialized_) {
      ROS_ERROR("Recovery behavior not initialized");
      return;
    }
    ROS_INFO("Backing up robot to recover...");
    // Here you would add code to command the robot to move backward safely
  }

private:
  bool initialized_ = false;
};

PLUGINLIB_EXPORT_CLASS(SimpleBackUpRecovery, nav_core::RecoveryBehavior)

Important Notes

Recovery behaviors run automatically when navigation fails.

You can create custom recovery behaviors to handle special cases.

Always test recovery behaviors carefully to avoid unsafe robot moves.

Summary

Recovery behaviors help robots fix problems during navigation.

They are classes implementing initialize() and runBehavior() methods.

Common recovery actions include clearing costmaps, rotating, or backing up.

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