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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Wed, 9 Aug 2000 13:34:12 GMT
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Original-From:
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Sattler Chris-QA1406 <CHRISTOPHER.SATTLER@antispamMOTOROLA.COM>
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Viewed:
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872 times
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No' I don't think you correctly understood what I am proposing. The
reflective surface would be on the outside of the funnel shaped piece with
the narrow tip of the funnel resting on the center of the sensor.
Funnel
\ / light beam
\ /______________
\ /|
______V__
Sensor
The light beam would have to arrive parallel to the sensor. If the outside
surface of the funnel/cone was at a 45 degree angle to the sensor the sensor
would have to be as large around as the widest part of the cone and this
would determine how much the height of the beam above the sensor could vary.
By curving the surface of the cone you could change this do some degree.
Getting the light beam to arrive parallel to the sensor would be a problem
in and area of uneven terrain. I suppose you could use some kind of system
to keep the sensor horizontal.
In any kind of laser based system like this where you are only interested in
the angle from the tower it would help to spread the laser beam in the
vertical direction. This would allow for more variation in the height of the
sensor, for situations where the robot may be going up and down slopes. I
have a laser pointer that when you rotate the tip unfocuses the beam in one
direction to produce a line instead of a point. At 10 feet the line is a
little over 3 inches long and about one inch wide, but still pretty bright.
-----Original Message-----
From: Steve Baker [mailto:sjbaker1@airmail.net]
Sent: Tuesday, August 08, 2000 7:30 PM
To: Sattler Chris-QA1406
Cc: lego-robotics@crynwr.com
Subject: Re: Autonomous Robot
Sattler Chris-QA1406 wrote:
>
> I had a similar idea, but I was picturing a funnel-shaped mirror above a
> light sensor so that no matter what angle you hit it at the light is
> reflected down at the sensor.
Yes - but that wouldn't be a funnel shape - it would need to be a
'retro-reflector'
that reflects all light back to it's source - no matter the direction.
That's why I was babbling on about the retroreflective tape they have on
kids clothes and bicycle reflectors. Both of those (theoretically) have
that property.
However, experiments I did last night with a laser pointer showed that for
at least one kind of bicycle reflector, it only retro-reflects when the
incident light beam is within about 45 degrees of the primary axis of the
reflector.
Beyond that angle there is a pretty sharp cutoff when no light is reflected
back to the laser at all. That might be good enough for the scanning tower
position finder idea - providing the robot never drives much further from
the
base of the tower than the tower is high. If you put the spinning laser on
the ceiling - you could probably get the entire room.
The MUCH more troublesome problem (for me at least) is that there are TONS
of spurious reflections in other random-looking directions. That must mean
that something quite a bit less than 100% of the light is being
retro-reflected
back to the detector (which we could probably live with) - but much nastier,
it means that laser light is bouncing off around the room where it could do
damage to someone's eyes. Even a $5 hand-held laser pointer has enough
energy
to harm someone's vision.
Also, at close ranges, the retro-reflection was a bit TOO good - and the
laser
light was reflected back so accurately into the transmitter that you
wouldn't
be able to get a Lego light detector close enough to pick it up! I suppose
you could fix that with a 'beam-splitter' (a semi-silvered mirror) - or once
again, ensure the tower is tall enough that the beam has enough room to
diverge
some more after it bounces back off the robot.
I have to admit that I was suprised at just how good a 25 cent
retroreflector
could be.
--
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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