Subject:
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RE: Line Followers
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 16 Nov 1999 05:15:31 GMT
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Viewed:
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595 times
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On Tue, 16 Nov 1999, Ralph Hempel wrote:
> > With just one light sensor, the problem is that you have to guess which
> > direction you just fell off the line. i.e., your sensor suddently goes
> > from dark to light. Is the dark to your left? Your right? There's no real
> > way of telling, is there?
>
> One way around it is a specially graded line. It's black on one side and
> light on the other, sort of a dark grey in the middle. Try to keep the sensor
> in the dark grey area.
At some point, my letter had a point about "cheating" by shading the line
or edges of the line, which I guess I took out. I've built a large "sumo
pit" built on this principle (the floor is shaded with flat black and
glossy white spray paint) but have not had time to write the intended sumo
wrestling code. I intend to use one light sensor, and guess the proper
direction based on previous observations.
> > With two light sensors, this suddenly becomes much easier, and with
> > three, you can build a great light sensor. However, forks still aren't
> > dealt with well- you need depth as well as breadth to be able to analyze
> > those robustly and on the fly (in my opinion). Anyone have any thoughts
> > on that one?
>
> Yes. Now that I have solved the maze problem on paper with the mazewalker
> at:
>
> <http://www.hempeldesigngroup.com/lego/mazewalker/index.html>
>
> It uses depth and breadth techniques to "map" and "solve" the maze.
I didn't mean depth/breadth-first search, but rather (say) a 3x3 grid of
light sensors, which would provide depth and breadth of vision. In a line
following bot, "backing up" to look in more detail at a junction becomes
difficult (unlike, as I understand it, your mazewalker.) Instead, it is
"best" to look at the complete junction at once in order to make
on-the-fly decisions (which is what you need for line-following, as
opposed to maze-traversal.)
Certainly, for good maze traversal, some combo of DFS and BFS are necessary.
> I'm going to eventually try a wheeled bot that follows a maze on the floor.
> Once again, I'll keep to the idea of line segments of fixed length and
> and only four directions, but once the simple problem is solved, more
> general solutions would be fun.
I like that idea. Mayhaps someday when I have time (Christmas? Next
summer?:) it'll get implemented in legOS...
-Luis
> Cheers,
>
> Ralph Hempel - P.Eng
>
> --------------------------------------------------------
> Check out pbFORTH for LEGO Mindstorms at:
> <http://www.hempeldesigngroup.com/lego/pbFORTH>
> --------------------------------------------------------
> Reply to: rhempel at bmts dot com
> --------------------------------------------------------
>
>
#######################################################################
Profanity is the one language that all programmers understand.
-Anonymous
#######################################################################
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Message is in Reply To:
 | | RE: Line Followers
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| (...) One way around it is a specially graded line. It's black on one side and light on the other, sort of a dark grey in the middle. Try to keep the sensor in the dark grey area. (...) Yes. Now that I have solved the maze problem on paper with the (...) (25 years ago, 16-Nov-99, to lugnet.robotics)
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