Subject:
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Re: Autonomous Robot
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 8 Aug 2000 05:01:44 GMT
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Original-From:
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Steve Baker <sjbaker1@+spamless+airmail.net>
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Reply-To:
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sjbaker1@airmail.netSTOPSPAMMERS
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Viewed:
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813 times
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Ian Warfield wrote:
>
> I thought of another possibility for robot coordinate recognition. It's
> rather unorthodox, however, and requires some special equipment and setup to
> make it work. Still, in the interest of creative discussion...
>
> Building off the base station idea mentioned earlier, set up a single station
> in the middle of the room/arena/whatever. This station incorporates an extra
> RCX, two motors, two rotation sensors, and two laser pointers, one mounted on
> the tower at ground level and one mounted about two feet high. The robot
> itself sports a laser detection sensor.
>
> Here's the tricky part... use polar coordinates. Suppose the robot wants to
> know where it is relative to the tower. It stops, sends out an IR call for
> help, and enables its laser detection sensor. The base station receives the
> call, turns on the ground-level laser pointer, and starts rotating the tower.
> As soon as the robot detects the ground-level laser it signals again, and the
> tower stops rotating. Next the base station switches off the ground-level
> laser and switches on the high-level laser. The high-level laser zeroes
> itself perpendicular to the floor and starts sweeping upward towards
> parallel. When the robot detects this laser, it signals again, and the tower-
> based laser stops.
>
> Now the base station records the orientation of the tower via the turntable
> rotation sensor and the angle of the high-level laser via the laser rotation
> sensor. The base RCX stores the turntable orientation provides the angle
> reference. It then multiplies the height of the tower (two feet in this case)
> by the tangent of the angle of the tower-based laser to get the distance from
> the base station to the robot. Finally, it sends the ordered coordinate pair
> to the robot, which updates its internal odometry and continues on its way.
Clever! ...Food for thought!
The only snag I can see is that when the first laser is being acquired, both the
tower and the robot have to spin. It might take a LOT of rotations for them
both to happen to be pointing in the right direction for an acquisition. I suppose
you can fix that by using an omni-directional light on the tower (rather than a
laser) to get the robot pointed the right way - and then (after another IR handshake)
have the tower sweep the floor with the high-up laser in a spiral until it lights
up the robot.
Another idea might be to put patches of retro-reflective tape on the robot. That
stuff is *supposed* to reflect all light back to it's source - no matter where it
comes from (does that *really* work?). Now the tower can scan the floor until
it gets a strong reflection from the laser in the tape and the tower can continually
track the tape as the robot moves around the room.
The tower can even use cartesian coordinates directly by using two motors placed
at right angles to deflect the laser and pick up the returned light.
You don't get the orientation of the robot from that - but if the robot drives
in a straight line then you can infer its' direction from consecutive coordinates.
I suppose that once the tower knows where the robot is, it can do a little spiral
search to re-aquire it when it gets lost - so it won't be necessary to track
the robot all the time. Knowing that would allow one tower to track MULTIPLE
robots at once!
Best of all, the robot can be told where it is without it having to have any on-board
measurement stuff - so you have all three RCX inputs free for important stuff.
The tower now needs all the smarts - two motors to deflect the laser - two rotation
sensors to know where the laser is - and a third sensor two detect the reflected
laser light.
I guess this all depends on how truly retro-reflective that tape is. The stuff they
put on kids clothes for traffic safety *seems* pretty good...I played with some bicycle
reflectors - and they do retro-reflect suprisingly well over a reasonable angle (maybe
+/- 45 degrees) but they also produce lots of other reflections too. I guess that so
long as enough light makes it back into the detector that's OK. However, all those
spurious reflections are going to shine into people's eyes - and that can be dangerous
- even at the relatively low power of a laser pointer.
Thinking about precision - how accurate can you make a lego gear train/rotation sensor
point? Seems to me like the slop in the gears would limit you to perhaps 1 degree
precision. If the tower is in the middle of a 10m x 10m room, then that 1 degree
error translates to a worst case error of about 10cm - not enough to reliably
find a robot unless it has about a 10cm reflective area on it. Smaller rooms
are easier of course.
Another idea would be to use a digital camera with some simple motion detection
software. Mount that in the middle of the ceiling looking vertically down with
a wide angle lens to capture all the action.
With a 'typical' 1k x 1k resolution camera, you could image a 10m x 10m area with
a precision of about a centimeter or two. With care you could probably extract the
heading of the robot at the same time.
What precision is the new Lego camera supposed to be?
Fine until the robot drives under the sofa!
--
Steve Baker HomeEmail: <sjbaker1@airmail.net>
WorkEmail: <sjbaker@link.com>
HomePage : http://web2.airmail.net/sjbaker1
Projects : http://plib.sourceforge.net
http://tuxaqfh.sourceforge.net
http://tuxkart.sourceforge.net
http://prettypoly.sourceforge.net
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Message has 1 Reply:
 | | Re: Autonomous Robot
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| (...) Thanks! (...) Not if you used an omnidirectional laser sensor. Picture, instead of only one face of paper, a paper cylinder. There would be a tube of paper mounted on top of a circular LEGO piece (or *pieces* arranged in a circle) with a paper (...) (24 years ago, 8-Aug-00, to lugnet.robotics)
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Message is in Reply To:
| | Re: Autonomous Robot
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| I thought of another possibility for robot coordinate recognition. It's rather unorthodox, however, and requires some special equipment and setup to make it work. Still, in the interest of creative discussion... Building off the base station idea (...) (24 years ago, 8-Aug-00, to lugnet.robotics)
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