Lab F: Robot Arm Programming

Today's Lab

Becoming more familiar with the MoveIt ROS package to control the Turtlebot3 OpenMANIPULATOR
Implementing TrafficBot and learning the basics of ROS msg files (here's a link to the example solution code)

Physical Robot Arm Control

This section details how to get the physical turtlebot's OpenManipulator arm up and running. Please refer back to the class meeting 10 page for helpful tips on how to program the arm using the RViz window, GUI, and Python code.

First, run the following commands, which starts ROS, Bringup on the Pi, and the OpenMANIPULATOR Bringup on the PC.

Terminal 1 [PC]:

$ roscore

Terminal 2 [Pi]:

$ ssh pi@IP_OF_TURTLEBOT
$ set_ip LAST_THREE_DIGITS
$ bringup

Terminal 3 [PC]:

$ roslaunch turtlebot3_manipulation_bringup turtlebot3_manipulation_bringup.launch

Next, you need MoveIt to manipulate the arm. Launch the following in a new terminal. You should soon see a message that says, You can start planning now! in the terminal running the move_group node.

Terminal 4 [PC]:

$ roslaunch turtlebot3_manipulation_moveit_config move_group.launch

Finally, you can either (on your PC in a fifth terminal window):

Run the RViz visualization with moveit: roslaunch turtlebot3_manipulation_moveit_config moveit_rviz.launch,
Run the manipulation GUI: roslaunch turtlebot3_manipulation_gui turtlebot3_manipulation_gui.launch, or
Run a python file (via either rosrun or roslaunch) that sends commands to the robot's arm motors.

Again, please refer back to the class meeting 10 page for the details on these three methods of programming the robot's arm and gripper movements.

Lab Exercise: TrafficBot

In this exercise, we will use the arm of the Turtlebot to guide imaginary traffic. You should not use the robot's wheels for this exercise. You will be working the same groups.

Getting Started

To get started on this exercise, update the intro_robo class package to get the lab_f_traffic_bot ROS package and starter code that we'll be using for this activity.

$ cd ~/catkin_ws/src/intro_robo
$ git pull
$ git submodule update --init --recursive
$ cd ~/catkin_ws && catkin_make
$ source devel/setup.bash

Your Goal

Your goal in this exercise will be to have the robot arm move in a distinct manner based on the direction it receives via the traffic_status topic. Here is an example scenario.

Running Your Code

Terminal 1 [PC]: Run roscore.

$ roscore

Terminal 2 [Pi]: Run Bringup on the Pi.

$ ssh pi@IP_OF_TURTLEBOT
$ set_ip LAST_THREE_DIGITS
$ bringup

Terminal 3 [PC]: Run OpenMANIPULATOR Bringup on the PC.

$ roslaunch turtlebot3_manipulation_bringup turtlebot3_manipulation_bringup.launch

Terminal 4 [PC]: Run the move_group node on the PC.

$ roslaunch turtlebot3_manipulation_moveit_config move_group.launch

Terminal 5 [PC]: Run the traffic.py file, which will send the continuous "traffic signals" to your Turtlebot.

$ rosrun lab_f_traffic_bot traffic.py

Terminal 6 [PC]: Run the python node that moves your robot arm.

$ rosrun lab_f_traffic_bot move.py

Steps to Take & Starter Code

There are few steps you would need to take to complete this exercise.

traffic msg: if you look into lab_f_traffic_bot/msg/Traffic.msg, you will see that it is an empty msg file. Update the msg file such that you can encode at least 3 directions with that message. Here are some helpful resources: official wiki and our short intro to ros msgs.
traffic controller node: Update the lab_f_traffic_bot/scripts/traffic.py file such that it publishes a traffic message with a different direction every 10 seconds. After this step, relaunch your gazebo world and make sure that your traffic controller is publishing traffic messages appropriately via rostopic echo traffic_status.
turtlebot traffic controller node: Update the lab_f_traffic_bot/scripts/move.py file such that the turtlebot arm performs something different per msg received in the traffic_status callback function. Once done, run the move.py file and make sure your robot arm moves as it receives different messages.

Example Solution Code

We will release the example solution code later in the week.

Here is the example solution code.

Tips & Hints about the Arm & Gripper

The arm joints have limited movements. Their limits in degrees are listed below.
- Joint 1: -162 to 162
- Joint 2: -103 to 90
- Joint 3: -53 to 79
- Joint 4: -100 to 117
The gripper has limited movement as well; it can only move between -0.019 and 0.019 meters.
Make sure your arm's end goal does not collide with any objects (or the robot itself).
The position of the arm shifts the robot's center of mass and may cause your robot to tilt in some direction if the the arm is pushed too far.
The move_group node will need to get launched every time you wish to control the robot through code using the MoveIt interface.

Acknowledgments

I want to thank former Intro Robotics TAs Pouya Mahdi Gholami and Yves Shum for developing the traffic box exercise.