Newsgroups: comp.robotics
Path: brunix!uunet!centerline!noc.near.net!wpi.WPI.EDU!rkh
From: rkh@wpi.WPI.EDU (R Kurt Heinzmann)
Subject: Re: Underwater Motors
Message-ID: <1992Mar17.145351.27646@wpi.WPI.EDU>
Summary: Don't say It Can't Be Done
Organization: Worcester Polytechnic Institute
References: <1992Mar12.171941.25665@cs.UAlberta.CA> <1992Mar13.155322.14764@wpi.WPI.EDU> <16605@oasys.dt.navy.mil>
Date: Tue, 17 Mar 1992 14:53:51 GMT
Lines: 66

In Article 1986, tdsmith@oasys.dt.navy.mil (Timothy Smith) argued:

>In comp.robotics, rkh@wpi.WPI.EDU (R Kurt Heinzmann) writes:
>>In Article 1973, zhang@cs.UAlberta.CA (H Zhang) wrote:
>
>>>We are looking for submersible DC motors that can operate in shallow
>>>water (2-5 meters).  The motors will be used to propel a prototype of
>>>an underwater robot we are building.  We are aware of some...
>
>>I recommend buying a surplus motor with the desired feedback device
>>and putting it and your electronics and battery in a sealed box made
>>from acrylic sheet (Plexiglas).  Seal the cover with an O-ring.  For...

>    At 5m depth the box would be subject to 1/2 atmosphere of pressure,
>or about 7 psi.  Given a flat box side of 1 X 1.5 feet there would be...

    I already made a big assumption by guessing there is no tether.  What
makes you think a flat box of that size would be used?  What's wrong 
with using thick acrylic?  In 1957, Benthos Inc. (Falmouth, Mass., USA)
built an undersea camera case in exactly this manner and used it at
many atmospheres.

>...  Leak free seals on rotating shafts
>are expensive, and the o-ring idea is definately NOT leak free.

   O-rings, properly used (not recommended for poorly supported solid
rocket motor casings), are leak free.  Leak free.  (They don't leak.)

>    One solution is to maintain positive pressure inside the box with
>a regulator and compressed gas bottle.  Of course, submergence time
>and dive cycles would be restricted by the ammount of gas carried.

    Overcharge or short the battery and it will release enough gas  :-)

>    Another solution is to use expensive parts properly.  Of course this

... of course this is obvious.

>    The final solution is probably the cheapest (assuming you are serious
>and your time is valuable); anti up and buy a quality underwater motor.

    That solves the problem only if there is no other equipment to protect,
and only if the size of motor with the feedback device required is available. 
By the way, you didn't offer a source of such motors.  How about being helpful?

    Mr. Zhang, perhaps you would comment?


rkh@wpi.wpi.edu            ------ /////.
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