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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Sun, 23 Dec 2007 01:07:37 GMT
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Original-From:
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bigboss97 <bigboss97.geo@yahoo.comSPAMLESS>
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Viewed:
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5294 times
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Strangely, it slows down, i.e. it detects the further distance (less
reflection?) in the same angle.
I tried to put the US-sensor vertically. It still shows the same effect.
I also notice the closer it comes the larger angle it needs to get a
reaction. I observed...
When the vehicle hits the wall with a flat angle and I leave it running, it
keeps on pushing to the wall. I noticed that it only turns around when the
vehicle has been pushed to a position of almost 90 degree. The sensor is
almost covered by the all. The angle range is even smaller than if it comes
from a distance.
Brian Davis-3 wrote:
>
> 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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