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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Thu, 10 Aug 2000 01:50:39 GMT
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Original-From:
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Steve Baker <sjbaker1@#NoMoreSpam#airmail.net>
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Reply-To:
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{sjbaker1@airmail.}saynotospam{net}
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Viewed:
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1029 times
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Doug Weathers wrote:
>
> in article Fz036w.F10@lugnet.com, Ian Warfield at ipw47@hotmail.com wrote on
> 8/8/00 6:08 PM:
>
> > 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 arrangement?
>
> Here's a picture of a marine radar reflector.
>
> http://www.oceanmark.com/manufacturers/safety_manuf/Safety-Davis.html
Yep - that's what I was thinking of.
> The back of a bicycle reflector is a hexagonal array of little triangular
> right-angle pyramids packed edge to edge. Seen from the front, each pyramid
> looks like an inside corner of a radar reflector.
But they seem (in practice) to splatter reflections in all sorts of weird
directions (as well as the direction you want). That might not matter in
some applications.
The corner reflector ought not to suffer from *that* problem - but it looks
like you'd have to hit it fairly accurately near the middle if the angle
is close to 45 degrees - which is probably why the bicycle has so many little
reflectors.
> Incidentally (pun!) this is why bicycle reflectors only reflect within 45
> degrees of their surface - the corner reflectors only spread out 90 degrees,
> which is 45 degrees off of perpendicular in any direction.
Yep.
> The white reflective road paint uses little spherical glass beads mixed into
> the paint. The surface of the paint is covered in glass spheres half buried
> in paint and half exposed. The light enters the exposed part, bounces
> around inside, and exits roughly in the direction it entered.
Not as accurately as a corner reflector though. I work in flight simulation
and we use retro-reflective paint for projection screens - some of that stuff
is pretty sophisticated these days. Smaller *shaped* beads that orient themselves
in the paint layer using the surface tension in the liquid of the paint as it
dries ... it has to be applied with a special spray gun - it's destroyed if you
touch it - you can't clean dust from it - you can't repaint it ... hairy stuff
like that.
(If you want a REALLY bright image on a projection screen - then put the projector
right next to the viewer's head and use a retro-reflective screen and nearly most of
the light from that bright arc lamp ends up inside your victims eyes!)
> I don't know how reflective tape works.
It *looks* like a bunch of hexagonal cells from what I remember. I can't find
any around the house to test with.
--
Steve Baker HomeEmail: <sjbaker1@airmail.net>
WorkEmail: <sjbaker@link.com>
HomePage : http://web2.airmail.net/sjbaker1
Projects : http://plib.sourceforge.net
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Message is in Reply To:
 | | Re: Autonomous Robot
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| in article Fz036w.F10@lugnet.com, Ian Warfield at ipw47@hotmail.com wrote on 8/8/00 6:08 PM: (...) Here's a picture of a marine radar reflector. (URL) back of a bicycle reflector is a hexagonal array of little triangular right-angle pyramids packed (...) (24 years ago, 9-Aug-00, to lugnet.robotics)
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