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From: browen@aoc.nrao.edu (Bruce Rowen)
Subject: Re: Underwater motors
Message-ID: <1994Jul12.204502.3892@Mr-Hyde.aoc.nrao.edu>
Sender: news@Mr-Hyde.aoc.nrao.edu
Reply-To: browen@aoc.nrao.edu
Organization: National Radio Astronomy Observatory, Socorro NM
References: <1994Jul12.173350.29777@lds.loral.com>
Date: Tue, 12 Jul 94 20:45:02 GMT
Lines: 73


Both of these designs are common to aquarium pumps. The first one you mention 
seems to be the one most used on the higher quality pumps. The magnetic 
clutch design has the drawbacks you mentioned (slippage, low capacity) plus
it tends to demagnitize itself if the shaft remains locked for a length
of time.


>
>Hi:
>
>I'm brainstorming on how to use DC motors for underwater propulsion
>of an ROV.  The big problem is to keep water from getting inside
>of the ROV or motor.  For this reason I'd like to avoid a direct shaft
>from the motor to the prop.  I have a couple of ideas to bounce off
>the group.  If anyone has some experience in doing this I would
>appreciate relpies or comments.
>
>1)  BRUSHLESS MOTOR W/ INTEGRATED ARMATURE/PROP
>Pardon the ASCII drawing that follows.  The idea is to have an outer
>cylinder of PVC with motor windings around the outer circumference.
>The armature holds the permanent magnets and is within the cylinder.
>The radial supports of the armature are shaped to double as propeller
>blades.  The inside of the cylinder is open to water. 
>
>This is a side view...
>
>		     {WINDINGS}
>	PVC  ========================
>	             [MAGNETS]
>		         I		----->  flow
>	Shaft ---------------------
>		         I              ------>
>                     [MAGNETS]
>             ========================
>		     {WINDINGS}
>
>Are there any current motor designs that have the windings on the
>outside and the magnets on the armature besides a stepper motor?
>I'm not a motor person.
>
>2)  MAGNETIC COUPLING
>
>This seems simpler to do but I'm not sure it will hold up if
>the prop gets heavily loaded (slippage).  The idea is to have the motor
>sealed inside and a magnetic coupling connects the prop on the
>outside of the ROV.  
>
>		>       |--------------|
>		>      8|8    =======  |
>        Prop    -------8|8----(MOTOR)  |
>		<      8|8    =======  |
>		<       |--------------|
>
>The vertical bars of '8's are each side of the magnetic coupling.
>This is analogous to how those magnetic laboratory stirring 
>doohinkuses work.  Anybody ever use a magnetic mechanical coupling?
>Thanks
>
>Brian
>



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Bruce Rowen 				National Radio Astronomy Observatory
Scientific Programmer				Array Operations Center
browen@aoc.nrao.edu			  P.O. Box O  Socorro, NM   87801
(505)385-7329					     (505)385-7000
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