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 00:29:46 GMT
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Original-From:
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Steve Baker <{sjbaker1@}stopspam{airmail.net}>
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Reply-To:
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sjbaker1@airmail./nospam/net
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Viewed:
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748 times
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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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Message has 1 Reply:
 | | Re: Autonomous Robot
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| How exactly do the retroreflectors work? I was under the impression that you couldn't selectively reflect light unless you had a parabolic dish - and then it would all focus on one point. Do your reflectors have a convex mirror, or some other (...) (24 years ago, 9-Aug-00, to lugnet.robotics)
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Message is in Reply To:
| | RE: Autonomous Robot
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| 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. -----Original Message----- From: Ian Warfield [mailto:ipw47@hotmail.com] (...) (24 years ago, 8-Aug-00, to lugnet.robotics)
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