On Mon, Apr 2, 2012 at 6:15 PM, pagnol <pagnol@posteo.de> wrote:

Recently I've been toying around with Lego NXT during a project at uni.
We've built the usual line following and obstacle avoiding robots.  As we've
had to return the packages, I'd like to take these experiments to
Player/Stage.  I've been searching for an equivalent to the "light sensor"
which comes shipped with the NXT.  (This sensor measures the ambient light,
thus allowing the software to differentiate between the black line and the
white background.)  I'd greatly appreciate any advice on how to setup a
sensor with similar behavior in Player/Stage.


I am far from being a player/stage expert, but since no one is replying, I'll give it a try. More expert users may have better ideas.

There is no light sensor in player/stage, as far as I can tell. You can emulate a light source with a fiducial, get the distance and then apply some math transformation to emulate light fall-off. This works if you are interested in simple phototaxis simulations (which is what I was interested in), but obviously it won't work for detecting light reflected off surfaces, which seems to be what you'd need for line-following behaviors of the kind you've played with with the NXT.

Suggestions:
1. Look into gazebo as an alternative to stage. Here is a starting point (first link on a google search:http://answers.ros.org/question/10175/how-to-simulate-a-simple-light-sensor-in-gazebo)

2. For line-following experiments: use a wall as your line, but set its parameter so that your robot can sense it but never bumps into it. (If I remember correctly, setting obstacle_return=0 in the object's parameters should do the trick.) J Owen tutorial is also very good.

3. Use a camera or perhaps a blob-finder as a replacement for a light sensor.

4. :-( Find a different simulation environment that comes with NXT models built in. Webots (commercial and quite expensive) is one.

More expert users may be able to give better advice.

Cheers,

Stefano

 
Thank you very much for maintaining this bundle of great programs!
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Stefano Franchi
Associate Research Professor
Department of Hispanic Studies            Ph:   +1 (979) 845-2125
Texas A&M University                          Fax:  +1 (979) 845-6421
College Station, Texas, USA

stefano@tamu.edu
http://stefano.cleinias.org