MORSE CODE - PART 2

Playing around with MORSE 0.6, I was tempted to try out basic obstacle avoidance through ROS (Fuerte) nodes on PR2 and ATRV. An obstacle avoidance approach involves a closed loop control system, which is executed by a laser or sonar scan with a 'see the obstacle => turn left', type of algorithm. After some initial hiccups I was able to get it working.

Here are some details of my efforts,

Fig.1. PR2 simulation and its rxgraph

Fig.2. ATRV simulation

in the PR2 simulation, one can see the closed loop of the system in the rxgraph of the ROS nodes.

I am grateful to Michael (kargm at in dot tum dot de) for his help and suggestions. Michael has also put up a video of the PR2 simulation, http://vision.in.tum.de/~kargm/videos/pr2_obstacle_avoidance.m4v. The codes
can be found at, https://github.com/Arkapravo/laser_obstacle_avoidance_morse

TORTUE

TORTUE is an effort to marry a motion sensor with a Roomba base. It was inspired from Turtlebot, Billibot and Oculus. For the base we used Roomba 560 and for the motion sensor we used ASUS Xtion Pro Live. The software platform is ROS Electric. The project is still in its early days and more is being planned for the future.

Fig.1. Concept development for Tortue

Fig.2. First run on 2nd March 2013, Saturday

The video shows a very basic obstacle avoidance behaviour using point cloud.

The Tortue team comprises of ,

The project has a home page at github, https://github.com/Arkapravo/tortue.

Tortue means Turtle in the French language, which reflects the use of ROS for the robot, ROS has a long term Turtle association and all of their release have a Turtle reference, also ROS softwares (viz. turtlesim) and robots (viz. turtlebot) have such naming. There has been suggestions that tortue has a likeness to wall-e, we do not deny it ! :-)

OBSTACLE AVOID FOR PR2

LASER OBSTACLE AVOIDANCE FOR PR2

One of the basic behaviour a budding roboticist often starts with is obstacle avoidance using sonar or laser scan. While playing with gazebo simulations, we realised that we are yet to try out a very basic laser obstacle avoidance behaviour in the PR2 robot employing the SICK laser. It was not long that we wrote our codes and made our ROS package and started with simulations in gazebo. A surprise awaited us ........

WHAT THE HELL !!!! 

We got an empty world with PR2 and then filled it up with boxes and set our code into action. Much to our surprise the PR2 robot did not try to avoid those boxes, but push them rather awkwardly. 

BOX PUSHING INSTEAD OF OBSTACLE AVOIDANCE

It was after few such 'failed attempts' and cursing our code incessantly that we realised that the issue is with the stretched out arms of the PR2. The distance for the obstacle avoidance to work is at min_range<=0.5, however we never had accounted for the PR2's arms while coding so the obstacle avoidance code is not coming to fore and is restricted by the arm lengths. Thus when the PR2 reaches the obstacle it continues to move and 'push' the obstacles, since gazebo is a physics based simulator thus in a box world it reflects such as a 'box pushing' behaviour. It may be said that such a behaviour arises in the 'emergent' context. Playing around with the code, we finally set it to, min_range<=1.2 which sorted out the issue. 

The codes discussed here can be found at, https://github.com/Arkapravo/laser_obstacle_avoidance_pr2, feel free to write to us at Arkapravo Bhaumik (arkapravobhaumik at gmail dot com) and Koushik Kabiraj (koushik dot atti at gmail dot com).