MORSE CODE - PART 3

Since there are a good lot of robot simulators, Gazebo and Stage for the ROS enthusiast, V-REP and webots in the more commercial domain, OpenRave and Microsoft Robotics Developer's Studio are other options one can explore into, therefore when one comes across a new robot simulator, the obvious question is - so what is special about it ? I have been asked this question a few times about MORSE, and is usually accompanied with a comparison with Gazebo. 

My answer is, 

• MORSE is not limited to few robots (10 for Gazebo), I have used Morse for (i) 176 small robots (ATRV) and (ii) 9 PR2 robots, in 2 separate simulations. The limit to the number of robots is not a limitation of the simulator, but rather the limitation of the CPU and graphics card.

Pic.1. Multiple PR2 simulations

• MORSE has bindings with various middlewares ROS, YARP and MOOS, which enables it more versatility [1]. 

Pic.2. ROS binding, rviz visualisation and mapping of MORSE simulation

• There is facility for human robot interaction. Like in motion gaming, direct input from the motion sensor (Microsoft Kinect, ASUS Xtion or Nintendo Wiimote) enables human avatar in the simulator [2]. 

Pic.3. Human avatar

• Since everything happens through Python scripts,one need not care about compilation and executable files. MORSE is 'pythonic' [3] and can be arguably said to be an extension of Blender.

• It is based on Blender and not Ogre, so it doesn't take up a hell lot of resources. Also, the texture and the graphics are more sleeker than Gazebo.

• New robot models can be developed through Blender, and the developmental process is simple [4]. 

Pic.4. Blender model of the robots

• Blender has a huge online community. Hence help and support is easy to find.

I would not be giving a very honest opinion if I do not talk about the shortcomings of MORSE,

• Binding with ROS is a laborious process and often discourages the novice ROS user, particularly due to Python 3 and also because only certain versions of Blender works well with the MORSE + ROS + Python 3 set-up.

• Physics simulation in Blender/MORSE is inferior to Gazebo. Getting force, torque values etc is not yet possible.

The latest release is MORSE 1.2 and more details can be found at http://www.openrobots.org/wiki/morse. A good part of this post came out of discussions at the MORSE mailing list, morse-users at laas dot fr .

REFERENCES

[1] http://www.openrobots.org/morse/doc/latest/user/integration.html
[2] http://www.openrobots.org/morse/doc/stable/user/advanced_tutorials/mocap_tutorial.html

[3] http://www.openrobots.org/morse/doc/stable/user/basic_morse.html

[4] http://www.openrobots.org/morse/doc/stable/user/advanced_tutorials/a_journey_to_a_new_simulation.html

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 made a video of the PR2 obstacle avoidance simulation, https://www.dropbox.com/s/66rpmuyhzkm2ka4/pr2_obstacle_avoidance.m4v .

The codes can be found at, https://github.com/Arkapravo/laser_obstacle_avoidance_morse

MORSE CODE PART - I

MORSE 0.6

I installed MORSE 0.6 and linked it up with ROS on Ubuntu 12.04 and  it was fun to try out simulations of PR2 and ATRVs. I was interested in simulating a 2 robot system where one robot was guided by ROS nodes while the other was controlled by MORSE. This article is a brief on how I got that working ! 

THE kb_control CODE

Koushik and I have been tying to use kbhit() function to model teleoperation in ROS, however lack of a conio.h  in gcc made us channel our efforts differently (fcntl.h), and develop our codes.

SETTING IT UP IN MORSE

Instead of a single ATRV, I put in 2 ATRVs in my simulation, Castor and Pollux. Castor controlled by ROS nodes while Pollux was by MORSE keyboard. In the Python script (two_atrv.py) it was easy to 'connect up' Castor to ROS and Pollux to MORSE;

To link up ROS nodes with MORSE, remapping of the launch file (kb_control_morse.launch) is done,

The remapping is done by checking the rxgraph and enabling publisher/subscriber connectivity to ensure the interconnectivity of all the nodes. A working rxgraph for this simulation is as shown,

THE SIMULATION

Download the kb_control package from https://github.com/Arkapravo/kb_control and install it, rosmake kb_control

Place the file kb_control/morse/two_atrv.py at /opt/ros/morse/share/morse/examples/scenarii/

Start an instance of the master

Start the morse simulation, cd /opt/ros/morse/share/morse/examples/scenarii/ && morse run two_atrv

Start the kb_node, roslaunch kb_control kb_control_morse.launch

Now you should be able to control Castor with ROS and Pollux with MORSE.Click on the blender screen, the arrow keys will move Pollux around.Click on the kb_control terminal window, the arrow keys will move Castor around.

MORSE 1.0

MORSE 1.0 is slated for release in February 2013, with various improvements and newer features.

ACKNOWLEDGEMENTS

I am thankful to the morse-user mailing list (morse-users at laas dot fr) particularly, Florian Lier (flier at techfak dot uni-bielefeld dot de), Michael Karg (kargm at in dot tum dot de) and Séverin Lemaignan (severin dot lemaignan at laas dot fr). I am also thankful to my friend Vasileios Lahanas (vasileios dot lahanas at hotmail dot com) for his suggestions regarding kbhit() function. 

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