Define a "Pickup objects" task using behavior trees

This lab uses the turtlebot3 simulator in ROS noetic Gazebo to complete an object collecting task making use of the py_trees library.

`py_trees` library

This lab uses the py_trees library. To install the py_trees library do:

pip install py_trees

You can find information about how to use this library at this github page.

There is also a tutorial included in this package. Check it for a brief introduction.

Task description

We have a robot with the follwong behaviors:

move: The robot move to the x, y location. This behavior is provided by the node turtlebot_controller_node.py from this package.
check_object: A service provided by the manage_objects_node.py. It returns False if no object is close to the robot and True plus the object's name if an object is close to it.
get_object: A service provided by the manage_objects_node.py. It returns False if no object is close to the robot and True if an object is close to it. It also moves this object over the robot.
let_object: A service provided by the manage_objects_node.py. It returns False if no object is over the robot and True if an object is over it. It also moves this object to the floor.

Using these behaviors, you have to implement the following task.

The robot has to navigate to a list of points and in each one it has to check if there is an object on it. If there is an object, it picks it up and takes it to (-1.5, -1.5) if the object was a beer can or to (1.5, 1.5) if the object was a coke can. Once there, the robot leaves the object and goes to the next point. The task ends once two objects have been collected or all provided points have been explored. The points where the objects can be found are:

(1.25, 0.5)
(1.25, -1.25)
(0.0, -1.25)
(-0.5, 1.25)
(-1.25, 0.5)

An execution example can be found here.

Notice that in the video a task planning node is used instead of a simple controller as the one provided in this package.

Included code

Three code files are included: turtlebot_controller_node.py, manage_objects_node.py and pickup_behaviors_no.py:

turtlebot_controller_node.py: This file is a ROS node that contains a basic move to point controller. When a PoseStamped message is published to the topic /move_base_simple/goal, this controller moves the turtlebot to this position.
manage_objects.py: This file is a ROS node that contain the following ROS services:
- check_object
- get_object
- let_object
pickup_behaviors.py: Contains 3 behaviors ready to be called from the py_trees library. Modify this file to add the necessary additional behaviors.
- CheckObject: Behavior for calling check_object task and if True, store object name to Blackboard
- GetObject: Behavior for calling get_object
- LetObject: Behavior for calling let_object

Additionally, a launch file named pick_up_objects_task.launch is also included. Launch it and run the pickup_behaviors.py node to play the behavior tree that executes the autonomous task.

Work to be done

Define a behavior tree to complete the task at hand. Once the behavior tree is being approved by your lab assistant, implement it using ROS and py_trees. Despite there is a py_trees implementation for ROS1, here, we propose you to use the standard py_trees library and add by hand any necessary call to ROS services, publishers or subscribers. However, feel free to use whatever package is more convininent for you.

Extra bonus

You can override the turtlebot_controller_node.py by the path planning controller that you developed in the first lab. If you do that, you should be able to execute the task in the turtlebot3_stage_3.world. Modify the launch file turtlebot3_stage.launch to include this world.

Deliverable

Deliver a zip file containing these package completed. For the pick_up_objects_task package replace or complete the current README.md file with:

The name of all group members (max. 2)
If it is required to install some package, detailed instructions of how to do it.
Detailed instructions of how to execute the task (i.e., launch file, rosrun nodes, ...).
A figure of the behavior tree you have implemented.
An explanation of the behavior tree used and how each behavior have been implemented.
A video of the task execution.
Problems found.
Conclusions

WARNING:

We encourage you to help or ask your classmates for help, but the direct copy of a lab will result in a failure (with a grade of 0) for all the students involved.

It is possible to use functions or parts of code found on the internet only if they are limited to a few lines and correctly cited (a comment with a link to where the code was taken from must be included).

Deliberately copying entire or almost entire works will not only result in the failure of the laboratory but may lead to a failure of the entire course or even to disciplinary action such as temporal or permanent expulsion of the university. Rules of the evaluation and grading process for UdG students.

^{Narcis Palomeras -
Last review March 2024.}

narcispr / pick_up_objects_task