Newsgroups: comp.robotics
Path: brunix!cat.cis.Brown.EDU!agate!howland.reston.ans.net!swrinde!sgiblab!sgigate.sgi.com!enews.sgi.com!wdl1!mail!cps233!dombrows
From: dombrows@lds.loral.com (Brian Dombrowski, 5424)
Subject: Underwater motors
Message-ID: <1994Jul12.173350.29777@lds.loral.com>
Sender: news@lds.loral.com
Reply-To: dombrows@lds.loral.com
Organization: Loral Data Systems
Date: Tue, 12 Jul 1994 17:33:50 GMT
Lines: 53


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

