Subject:
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Re: NXT Program: How to avoid stop-and-go? (US-Sensor in angle)
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Newsgroups:
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lugnet.robotics
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Date:
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Sat, 22 Dec 2007 15:45:57 GMT
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Viewed:
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6033 times
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In lugnet.robotics, bigboss97 <bigboss97.geo@yahoo.com> wrote:
> Why does the sensor detects < 30cm, but misses < 20cm for flat angle?
At a glancing angle (not approaching the wall "head on" at 90°, but at an angle)
very little sound energy will be reflected back towards the sensor. If there
isn't enough energy reflected back for the sensor to "hear" the echo, it won't
detect the wall. This is complicated by the fact that the field of view of the
sensor change with distance - very close to the sensor, the sensor can't detect
something that is only off center by a couple of cm, but further away, something
that's just 5 cm of the midline is only a small angle away from the midline.
> Shouldn't the sensor be more reliable when the distance is smaller?
In general, yes, except for the field of view issues mentioned above. In
particular, the two "eyes" of the sensor have different purposes: one sends the
sound out, while the other listens for the return. It's really the angle that
those two points make with the object being detected that matters, so for
objects at an angle to the sensor, it might be more "blind" to the left or
right.
--
Brian Davis
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