behavior-stack-example

 

Repository containing a simple example of the Behavior Stack

 

The stack is partitioned into different layers of abstractions, each addressing different concerns; the separation of the layers allows level-specific efficient solutions. The number and separation of the layers are the subject of controversial discussions; in this example we use the abstraction layers defined by the RobMoSys Robotic Software Component Following the abstraction above, we categorize the robotic software in:

 

• Task Layer, the layer where we design how the robot accomplishes a goal, disregarding the implementation details. In this example, it describes the a Behavior Tree (BT).

• Skill Layer , the layer where we design the basic capabilities of a robot (e.g. grasp an object); It describes the implementation of a leaf node of a BT that that can run in mainly two fashions with respect to the BT engine:

  • In the same executable, where the source code of the skill is written inside a leaf node of the BT engine that implements the Tick() and (for actions) the Halt() methods.

  • -In a separate executable, where the source code of the skill is written in a separate program that exposes the interface for calling the Tick() and (for actions) the Halt() methods. Over the network. A leaf node of the BT engine forwards the calls to the corresponding executable.

  A middleware usually handles these calls over the network.

 

• Service Layer, the layer that contains system-level entities that serve as the access point for the skills to command the robot (e.g. move mobile base destination, read sensor input); It described the server side of a service called by a skill to perform its basic capability (e.g. get battery level).

 

This example contains:

 

run_bt: An executable that runs a Behavior Tree (a task).

 

SimpleCounter: An executable that implements a counter and exposed 3 services, implemented as YARP Remote Procedure Calls: one to increase, one to decrease, and one to reset the counter.

 

ActionExample A skill that when starts request to SimpleCounter to increase the counter by 1 every second. When the skill stops, it resets the counter.

 

ConditionExample: A skill that when starts request to SimpleCounter its counter value and returns to the BT on a success state if the counter is lower than 10; it returns a failure state otherwise.

 

The skills ActionExample and ConditionExample are implemented in three ways:

 

• As leaf nodes in the BT (In the same executable of the BT).

• As YARP RF Modules (in a separate executable).

• As State Charts, using the QtSCXML engine (in a separate executable).

 

Dependencies

 

• YARP
• BehaviorTree.cpp
• Groot (For behavior trees visualization, optional)
• GammaRay (State Chart visualization, optional)

 

Installation (Tested on Ubuntu 20.04)

 

Install Dependencies:

 

• YARP: Follow the instructions here.

• Behavior Tree.cpp: (use a specific commit) run :

  git clone https://github.com/BehaviorTree/BehaviorTree.CPP.git

  git checkout 5e8e2da2d93139fdf5f5d188e6dedf4e8180cf15

  Then install the library:

  cd BehaviorTree.CPP

  mkdir build;cd build

  cmake ..

  make

  sudo make install WARNING! this installs the library system wide

• Groot: Follow the instructions here.

• GammaRay:

  add the following ppa :

  sudo add-apt-repository -s -y ppa:robotology/test

  `sudo apt install -y \

      gammaray \
      gammaray-plugin-quickinspector \
      gammaray-plugin-statemachineviewer`
  

 

Clone and compile this library:

 

git clone https://github.com/hsp-iit/behavior-stack-example

 

mkdir build;cd build

 

cmake ..

 

make

 

Execute the examples

 

Example with skills as Leaf nodes

 

Go to the bin directory:

 

cd bin

 

and run the following executables:

 

1. ./simple_counter
2. ./run_bt --from ./BT_leaf_nodes_example.xml

 

If you have Groot installed, execute it in "Monitor Mode" and then click "Connect" to see the execution of the BT, as in the figure below

 

 

Example with skills as RFModules

 

Go to the bin directory:

 

cd bin

 

and run the following executables:

 

1. ./simple_counter
2. ./rf_module_condition_example
3. ./rf_module_action_example
4. ./run_bt --from ./BT_state_chart_example.xml

 

If you have Groot installed, execute it in "Monitor Mode" and then click "Connect" to see the execution of the BT, as in the figure below

 

 

Example with skills as State Charts

 

Go to the bin directory:

 

cd bin

 

and run the following executables:

 

1. ./simple_counter

2. ./state_chart_condition_example

3. ./state_chart_action_example

4. ./run_bt --from ./BT_state_charts_example.xml

 

if you have GammaRay installed, run the executables 2. e 3. as:

 

gammaray ./state_charts_condition_example

 

gammaray ./state_charts_action_example

 

and then select the tab "State Machine" to see the execution of the skill, as in the figure below:

 

 

If you have Groot installed, execute it in "Monitor Mode" and then click "Connect" to see the execution of the BT, as in the figure below