Newsgroups: comp.robotics
Path: brunix!sgiblab!zaphod.mps.ohio-state.edu!howland.reston.ans.net!darwin.sura.net!udel!bogus.sura.net!news-feed-1.peachnet.edu!umn.edu!staff.tc.umn.edu!rogers
From: rogers@staff.tc.umn.edu ()
Subject: Re: Position - how to know/keep? + found some "goodies"
Message-ID: <C6BM4t.FoI@news2.cis.umn.edu>
Sender: news@news2.cis.umn.edu (Usenet News Administration)
Nntp-Posting-Host: staff.tc.umn.edu
Organization: University of Minnesota
References: <10474@blue.cis.pitt.edu>
Date: Fri, 30 Apr 1993 23:45:25 GMT
Lines: 38

In article <10474@blue.cis.pitt.edu> fmg@alpha.smi.med.pitt.edu (Filip Gieszczykiewicz) writes:
>
>	Greetings. I was thinking about the position control of an
>	under/water (U/W for short) robot and have hit a wall: how
>	does a tethered robot know where it is? I came up with a
>	number of solutions (some doable now, some longterm)


>	Oh, perhaps my original plans for max depth of 250 feet were a bit
>	optimistic... is it just me or do Murphy's Laws apply to depth ->
>	It seems that pressure is expontially related to depth ;-)

   As for your depth problem, have you thought of filling your
U/W robot with a fluid?  If you filled up the robot with a fluid about the
density of water (hopefully non-conducting and non-corroding) you should
be able to go to very extreme depths and not worry about hull implosion.
Individual hermetically sealed components would pose a problem, but plastic
and ceramic parts (without a lid or window) would be quite happy.


   The Sonar is the way to go and I think all you really need is a nice
array of transducers you can read and write to well, and a DSP filled with
good code.   Analog Devices has a DSP book and they spend a chapter or
section on this problem.  (It is a hardcover book I got at an Analog Devices
DSP seminar.) (I can get the details of it if your interested, it is in my car).


  I have given up my sonar thoughts to concentrate on Lasers, Because at a
Linear Technology seminar they covered an inexpensive way to time events
with 100ps resolution.  (Light travels about an inch in 100ps)
Previously I didnt consider timing light echos to be an option, but this
picosecond resolution timer has given me lots of new Ideas. (It can be built
for Tens of dollars instead of Hundreds of dollars)


-- 
Brynn
        rogers@staff.tc.umn.edu    Varitronic Systems
