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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Tue, 8 Aug 2000 01:56:58 GMT
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Viewed:
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831 times
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I thought of another possibility for robot coordinate recognition. It's
rather unorthodox, however, and requires some special equipment and setup to
make it work. Still, in the interest of creative discussion...
Building off the base station idea mentioned earlier, set up a single station
in the middle of the room/arena/whatever. This station incorporates an extra
RCX, two motors, two rotation sensors, and two laser pointers, one mounted on
the tower at ground level and one mounted about two feet high. The robot
itself sports a laser detection sensor.
Here's the tricky part... use polar coordinates. Suppose the robot wants to
know where it is relative to the tower. It stops, sends out an IR call for
help, and enables its laser detection sensor. The base station receives the
call, turns on the ground-level laser pointer, and starts rotating the tower.
As soon as the robot detects the ground-level laser it signals again, and the
tower stops rotating. Next the base station switches off the ground-level
laser and switches on the high-level laser. The high-level laser zeroes
itself perpendicular to the floor and starts sweeping upward towards
parallel. When the robot detects this laser, it signals again, and the tower-
based laser stops.
Now the base station records the orientation of the tower via the turntable
rotation sensor and the angle of the high-level laser via the laser rotation
sensor. The base RCX stores the turntable orientation provides the angle
reference. It then multiplies the height of the tower (two feet in this case)
by the tangent of the angle of the tower-based laser to get the distance from
the base station to the robot. Finally, it sends the ordered coordinate pair
to the robot, which updates its internal odometry and continues on its way.
In lugnet.robotics, Doug Weathers writes:
> [snip lots of interesting thoughts of Cartesian coordinate recognition]
> OK, let's look at the robot.
>
> [...]
>
> It may be possible to do good odometry with only a single angle sensor. Set
> up a Dorst adder/subtracter and hook the angle sensor to it. Normally this
> would be used to correct the robot's course while it's travelling in a
> straight line, but this loses information about how far it's traveled.
> However, you could adopt a policy of only running one motor at a time if you
> need to know how far you've moved - if you can live with your robot lurching
> along left/right/left/right. Of course if you don't care how far you're
> going you can run both motors and go straight, such as when you're following
> a line or headed for a landmark.
It *is* possible to use a single rotation sensor with an adder/subtractor, but
not quite like that. I have a robot driven by a differential transmission
(one motor fd/bk, one motor lt/rt) that has a rotation sensor attached to one
of the output shafts just before it drives the wheel. The transmission allows
precise maneuvering in any direction, and therefore eliminates uncertainty
about what the rotation sensor is saying.
For example - when the robot is moving straight, the rotation sensor is
recording the straight motion of one wheel. Since the transmission drives
both wheels equally, you can safely extend the sensor to the other wheel too.
When the robot is turning in place, the rotation sensor is recording the
turning of one wheel, which is an exact mirror image of the other wheel, again
eliminating the need to check the status of the other wheel. You can set up a
formula that relates the number of turns of the wheel (varies with wheel
diameter) to the number of degrees turned.
HTH,
Ian
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Message has 1 Reply:
 | | Re: Autonomous Robot
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| (...) Clever! ...Food for thought! The only snag I can see is that when the first laser is being acquired, both the tower and the robot have to spin. It might take a LOT of rotations for them both to happen to be pointing in the right direction for (...) (24 years ago, 8-Aug-00, to lugnet.robotics)
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Message is in Reply To:
| | Re: Autonomous Robot
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| in article 398D9DA5.300D416C@airmail.net, Steve Baker at lego-robotics@crynwr.com wrote on 8/6/00 10:17 AM: (...) <regretfully snipped excellent discussion of using line following to find bar codes for landmark recognition> It would be nifty if you (...) (24 years ago, 8-Aug-00, to lugnet.robotics)
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