Subject:
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Re: Navigation using landmarks (Was: Re: lasers and RCX)
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 27 Jun 2002 06:55:34 GMT
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Original-From:
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Steve Baker <SJBAKER1@stopspammersAIRMAIL.NET>
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Reply-To:
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sjbaker1@!ihatespam!airmail.net
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Viewed:
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788 times
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PeterBalch wrote:
> This thread seems to have been going on for such a while I've forgotten
> where it started. Was the original question: how does my robot know where
> it is in a room?
>
> Has anyone suggested ultrasonic (or audio) "beacons" in each corner of the
> room?
>
> The (say) four beacons A, B, C, D produce squeaks at intervals - say A,
> 100mS, B, 100mS, C, 100mS, D, 1sec. The robot measures the time difference
> between successive squeaks.
So with the speed of sound being something like 300 meters/second, sounds
spaced 100mSec apart would travel about 30 meters before the next sound
started. That's a pretty reasonable distance. If you could measure the
arrival time to within (say) a millisecond, then you'd know were you were
to within about 30 centimeters. I guess that's do-able with ultrasound and
an RCX programmed in C or machine code using LegOS or something. If you used
NQC or something that's executing LEGO byte-code then you'd be lucky to
know where you were to within a meter or two...not good.
> If say the time difference between receipt of A and B is 98mS then the
> robot knows it is on a particular hyperbola. The time differences A-B, A-C,
> A-D, B-C, B-D and C-D each specify other hyperbolae. Where the hyperbolae
> intersect is where the robot is - approximately. There are problems with
> path lengths round furniture, etc. but it should be good enough.
I wonder how you estimate that error?
If you had the sound generation system emit an IR or radio pulse in time
with each 'squeak', you could possibly get all the information you need
with just two beacons.
How hard is it to reject sounds from sources other than the acoustic
emitters?
> (In the days before GPS I worked on radio navigation software that used a
> commercial system like this - I think it was called Hyperfix. We had to
> worry about path lengths through rain and fog.)
I work in flight simulation and we use acoustic head-tracking systems to
know where the pilot's head is within the simulator so that we can correct
the graphics so they are perspectively correct.
We have a devil of a time with these acoustic trackers when there is a
significant air conditioning blast (which you *need* here in Texas!) - it
seems that doppler effects and small changes in the speed of sound can
play havoc with these systems. However, something as simple as you propose
above ought to be much more robust than the high-end systems we have that
measure position in 3D and also head rotation around all three axes - reporting
back the position 60 times a second.
----------------------------- Steve Baker -------------------------------
Mail : <sjbaker1@airmail.net> WorkMail: <sjbaker@link.com>
URLs : http://www.sjbaker.org
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Message is in Reply To:
 | | Re: Navigation using landmarks (Was: Re: lasers and RCX)
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| This thread seems to have been going on for such a while I've forgotten where it started. Was the original question: how does my robot know where it is in a room? Has anyone suggested ultrasonic (or audio) "beacons" in each corner of the room? The (...) (22 years ago, 26-Jun-02, to lugnet.robotics)
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