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'[OT]: Underwater robots'
2001\07\30@162058 by Scott Beatty

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Doug

       I have some ideas for underwater robots that I would like to try.
So now that I know that there is someone on the list that has experience
with Underwater Robots, I have some questions.  What type of motors do you
use for propulsion?  How do you seal motors or points where wires protrude
from an enclosure from leakage or high water pressure or .  Can ultrasonic
signals be used to control robots underwater?


Thanks
Scott beatty

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2001\07\30@165401 by Douglas Butler

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This is the company that we buy thrusters from:
http://www.tecnadyne.com/business.htm
They aren't cheap but they are easy to use and have magnetic coupling
from the motor to the prop, so there are no rotating seals to leak.
If you want cheap motors look at electric trolling motors.  For hobby
use, seals or connectors rated "IP 68" or "NEMA 6P" are usually good to
at least twenty feet.

There was a thread here about three weeks ago titled [EE}: Underwater RF
about controlling a submerged model sub.  Basically ultrasonics is the
only way to go long distances like 100's of yards, but echoes make it
hard to use at close ranges.  "RC" rf controls work for short ranges in
fresh water, but not sea water.  In a nonmetallic tank or swimming pool
I would try putting an induction coil around the pool, but I have never
actually done this.

I think there was a group called the "Sub Committee" that had a neat
model sub website.  Unfortunatly that name is a bit hard to search
for...

If I didn't do this for a living I would have more time to do it for
fun.

Douglas Butler (aka Sherpa Doug)
Senior Engineer
Imetrix Inc.
1235 Route 28A
P.O. Box 152
Cataumet, MA 02534-0152
tel. (508) 564-6460
Fax (508) 564-6860
.....dbutlerKILLspamspam@spam@imetrix.com


> {Original Message removed}

2001\07\30@171453 by Tony Goetz

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Simply enough,   http://www.subcommittee.com/

A great site!

-Tony


<< I think there was a group called the "Sub Committee" that had a neat
model sub website.  Unfortunatly that name is a bit hard to search
for... >>

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2001\07\30@174400 by O'Reilly John E NORC

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Sub Committee:  http://www.subcommittee.com/

-----Original Message-----
From: Douglas Butler [.....dbutlerKILLspamspam.....IMETRIX.COM]
Sent: Monday, July 30, 2001 1:44 PM
To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
Subject: Re: [OT]: Underwater robots


This is the company that we buy thrusters from:
http://www.tecnadyne.com/business.htm
They aren't cheap but they are easy to use and have magnetic coupling
from the motor to the prop, so there are no rotating seals to leak.
If you want cheap motors look at electric trolling motors.  For hobby
use, seals or connectors rated "IP 68" or "NEMA 6P" are usually good to
at least twenty feet.

There was a thread here about three weeks ago titled [EE}: Underwater RF
about controlling a submerged model sub.  Basically ultrasonics is the
only way to go long distances like 100's of yards, but echoes make it
hard to use at close ranges.  "RC" rf controls work for short ranges in
fresh water, but not sea water.  In a nonmetallic tank or swimming pool
I would try putting an induction coil around the pool, but I have never
actually done this.

I think there was a group called the "Sub Committee" that had a neat
model sub website.  Unfortunatly that name is a bit hard to search
for...

If I didn't do this for a living I would have more time to do it for
fun.

Douglas Butler (aka Sherpa Doug)
Senior Engineer
Imetrix Inc.
1235 Route 28A
P.O. Box 152
Cataumet, MA 02534-0152
tel. (508) 564-6460
Fax (508) 564-6860
dbutlerspamspam_OUTimetrix.com


{Quote hidden}

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2001\07\31@060554 by Roman Black

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> >         I have some ideas for underwater robots that I would
> > like to try.
> > So now that I know that there is someone on the list that has
> > experience
> > with Underwater Robots, I have some questions.  What type of
> > motors do you
> > use for propulsion?  How do you seal motors or points where
> > wires protrude
> > from an enclosure from leakage or high water pressure or .


Hi Scott, if you can do some fabrication you
can get a pancake motor from any modern VCR
(capstan motor), these have a flat magnet
assembly and and a flat coil assembly.
Sometimes the bearing assembly is removable.
If you could rig the bearings up the electric
part could watertight with only the perm magnet
rotor and shaft in the water. :o)
-Roman

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2001\07\31@132104 by Eisermann, Phil [Ridg/CO]

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       Sort of like an aquarium powerhead? I think it's the same idea. Many
types of powerheads have a removeable shaft. The impeller is coupled to the
permanent magnet, and the whole thing spins about the shaft (but the shaft
itself does not rotate; it only serves to give the moving parts something to
rotate about). Powerheads are designed to be run submersed anyway. Maybe you
could adapt a propeller to it? The whole motor could then be mounted
externally to your robot. Plus, if it ever went bad, it would be easy to
swap out. Too bad they require AC. But that is easy enough to do by building
a simple 50% oscillator and powering a transformer in reverse.

Maybe this is one of those hair-brained ideas that's better shelved as an
intellectual exercise only :)


> {Original Message removed}

2001\07\31@134229 by Peter L. Peres

picon face
> seals

One of the easyier ways is to have normal (almost) capsulated motors
completely filled with light oil or safe freon. The water won't try to get
in as there will be no pressure differential and usual seals will be
enough. An equalizer membrane is usually necessary for thermal expansion
and such. The motors need to be run slower. In theory there is an
increased danger of explosion (not implosion) with this but if you go into
deep water you live dangerously anyway.

Peter

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2001\07\31@135629 by Douglas Butler

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For high power deep work they use hydraulic prop motors.  There is a
central hydraulic pump with an oil filled electric motor.  Those systems
are usually 10 to 1000 horsepower.
My company (Imetrix) uses electric 1/2hp to 1hp off-the-self
magnetically coupled thrusters.  They have an electric motor & gearbox
which spins permanent magnets in an air filled stainless steel cup.
Magnets outside the cup drive the prop.  If we had to custom build
something the pancake motor idea might work.  For a model the VCR motor
might be a place to start.

Sherpa Doug

> {Original Message removed}

2001\07\31@140524 by Roman Black

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Douglas Butler wrote:
>
> For high power deep work they use hydraulic prop motors.  There is a
> central hydraulic pump with an oil filled electric motor.  Those systems
> are usually 10 to 1000 horsepower.
> My company (Imetrix) uses electric 1/2hp to 1hp off-the-self
> magnetically coupled thrusters.  They have an electric motor & gearbox
> which spins permanent magnets in an air filled stainless steel cup.
> Magnets outside the cup drive the prop.  If we had to custom build
> something the pancake motor idea might work.  For a model the VCR motor
> might be a place to start.


What about using a rotorless system like in
the movie Red October?? If you apply electricity
to the water itself you can move it with a magnetic
field. There are a few experiments like this on
the net. Model "stealth" sub anyone?? ;o)
-Roman

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2001\07\31@143041 by Spehro Pefhany

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At 04:04 AM 8/1/01 +1000, you wrote:

>What about using a rotorless system like in
>the movie Red October?? If you apply electricity
>to the water itself you can move it with a magnetic
>field. There are a few experiments like this on
>the net. Model "stealth" sub anyone?? ;o)

Web search for magnetohydrodynamics (MHD) may turn something up.

I kinda suspect that with hobby materials it will be especially
stealthy because it won't move, but I'd love to be shown wrong
on that.

Best regards,

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2001\07\31@180538 by Mike Kendall

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I agree with your comment about filling with another compound.  For example
Shell Diala is a suitable non-conductive light oil that is used in electric
company transformers and will double as dummy load oil.  I found that it can
be purchased locally very easily for $27/gallon.  I found another compound
that is a natural for this type of work through my research.  A compound
called "Gelstar" is similiar to silicone grease but a fraction of the cost.
It is in the $20 per gallon price range.  This stuff is apparantly used to
inertly backfill fiber optics.  It can be used as a dielectric grease.
73,
Mike
----- Original Message -----
From: "Douglas Butler" <dbutlerEraseMEspam.....IMETRIX.COM>
To: <EraseMEPICLISTspamMITVMA.MIT.EDU>
Sent: Tuesday, July 31, 2001 5:48 PM
Subject: Re: [OT]: Underwater robots


{Quote hidden}

> > {Original Message removed}


'[OT]: Underwater robots'
2001\08\01@140430 by Peter L. Peres
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> I kinda suspect that with hobby materials it will be especially
> stealthy because it won't move, but I'd love to be shown wrong
> on that.

They'll see and hear the bubbles from 5 miles. But it won't move ;-).

Peter

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2001\08\01@140447 by Peter L. Peres

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> What about using a rotorless system like in
> the movie Red October?? If you apply electricity

If you apply electricity (DC) to anything in sea water the anything will
disappear very fast. Also the efficiency of a MHD thruster is directly
related to the conductivity of the liquid and the latter is very poor. You
will end up electrolyzing more water than what you can move (even with
ac).

The oil-filled small off the shelf motor has been used serveral times by
amateurs. It is not without problems but you can take almost any off the
shelf motor, seal it off properly, provide a membrane and O-ring seal on
the axle, and use it (within reason). The only trick is to use the motor
at slow rpm because the oil moving inside eats a lot of power at higher
rpms. This solution requires a lot of meintenance but amateurs have the
time ...

VCR motors seldomly reach 20W which is low power for a decent sized sub,
and they have very poor efficiency (due to the large magnetic circuit gap
and sheet steel pole under the stator). They deliberately do not reduce
eddy currents as this helps them run smooth in the intended application.

It is also very hard to over-energize them using a different coil set and
drivers as the magnets can't take the punishment and separate
mechanically.

However, I think that large size steppers could be promoted to submarine
thrusters. They have the necessary parts in them and the stator could be
potted. They could be oil filled as above or open to the sea.

One thing Steve Baldwin did not mention about their (Imetrix's)
magnetically coupled thrusters (great idea) is the slip clutch function of
the magnetic coupling. If something stops the prop the motor would stall.
With the magnetic clutch it does not.

Peter

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2001\08\01@141220 by David VanHorn

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>
>However, I think that large size steppers could be promoted to submarine
>thrusters. They have the necessary parts in them and the stator could be
>potted. They could be oil filled as above or open to the sea.

The rotors are also smooth, so they wouldn't suffer as much from the oil drag.
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2001\08\01@231338 by Mike Kendall

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I don't think the oil slowing down the motor may be that much of an issue.
I would use the Shell Diala as it is$27 for 5 gallons and it has the proper
inhibitors in it. If the stator is fixed and the permanent magnets are the
rotating element, then the curved magnets may have pieces of plastic
inserted between them.  The combination of the magnets and plastic would
make a continuos disk.  This "disk" would be mounted on the prop shaft
between two Delrin bushings (self lubricating in the water).  I have seen
some of the "supermagnets" made from ceramics/rare earth sold on ebay pretty
cheap.  They are recycled from computer disk drives and other electronics.
There is even a web page where a gentleman in Colorado built a brushless
wind generator turbine from them. The majority of the friction would be from
the laminar fluid flow but negligable on performance due to the low rpm and
the case of the u/w robot being shaped around the disk assembly.  I've got a
book written by a Alfred T. Forbes in new zealand called "the homebuilt
dynamo" that uses one of these designs. The NeFeB magnets have flux lines
that extend longer than traditional magnets and should extend through the
case between the magnets and the fixed stator windings. The u/w robot case
could have a molded section for the bushing to be pressed into it and molded
threaded holes that don't  penetrate through the case.  The second delrin
bushing could be then pressed into a crossarm, slid over the shaft and
secured into the threaded holes.  As I own a few fiberglass boat  molds, my
first choice for the case would be fiberglass. The part of the case that
forms the barrier between  the rotor magnet disc and the fixed stator
windings would have to be a different material that is thinner and attached
with a compression o-ring to the main case, probably the real reason for the
incompressible fluid inside the case as it allows for the thinner material
between the fixed stator and rotor disk containing the magnets.  The larger
the diameter of the disk the lower the rpm and higher the torque.  A dead
spot causing stalling is non-existant. Check out Hugh Piggot's web sites out
of Scotland for brake drum wind generators.  Everything down to his xerox
machine runs off of power from his homebuilt designs.  You have to be
careful about the oil.  For example, I have used the dummy load oil to cool
ferrite baluns before that have teflon dielectric windings.  The oil won't
bother ferrites or teflon, but will permeate powdered iron cores and change
their properties.  Also, you have to be certain that the correct potting
compounds and such are used.  I've seen mineral oil cause rubber insulated
wires turn "spongy" over time in sonar stuffing tubes for transmitters and
cause shorting.  I would even be tempted to look into encapsulating all my
circuit boards in potting compound.  If you don't have a vacuum machine to
pull the bubbles out of the epoxy potting compound, possibly a circuit board
potted with a spin casting machine?  Spin casting is some pretty cool stuff
and can be done in a garage setup. All said, I wonder if the disk could be
mounted 90degrees apposed to allow a better hydrodynamic shape?  Then, it
would require a delrin worm gear?
Regards,
Mike
{Original Message removed}

2001\08\02@035915 by Alan B. Pearce

face picon face
>However, I think that large size steppers could be promoted to submarine
>thrusters. They have the necessary parts in them and the stator could be
>potted. They could be oil filled as above or open to the sea.

How about using a Brushless DC Fan as used in PC Power Supplies? seal the
electronics unit and you already have a set of propeller blades on the
moving bit.

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2001\08\02@102130 by Roman Black

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Alan B. Pearce wrote:
>
> >However, I think that large size steppers could be promoted to submarine
> >thrusters. They have the necessary parts in them and the stator could be
> >potted. They could be oil filled as above or open to the sea.
>
> How about using a Brushless DC Fan as used in PC Power Supplies? seal the
> electronics unit and you already have a set of propeller blades on the
> moving bit.


That is one of the cleverest ideas yet, especially
if filled with waterproof grease or the like.
Those fans are pretty weak but you see more and
more brushless fans (DC) of higher power ratings,
and one might be an ideal drop-in for a small sub.
-Roman

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2001\08\02@103620 by Mike Kendall

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> That is one of the cleverest ideas yet, especially
> if filled with waterproof grease or the like.
> Those fans are pretty weak but you see more and
> more brushless fans (DC) of higher power ratings,
> and one might be an ideal drop-in for a small sub.

many/most types of grease are conductive. silicone grease is outragiously
expensive.  try a search for gelstar.  I bought a gallon of this stuff for
20something bucks (I can't remember the exact price) while on a quest for a
similiar product.  It is a polyofelin product that is suitable as a direct
replacement for grease in regular machinery fittings, food service, and
dielectric applications.  A kind of do-all grease that is cheap to boot.  It
is clear just like silicone grease.  Before finding this I even tried making
homemade petroleum jelly out of mineral oil and paraffin.  That  was a
smashing failure.  It does not have a stable temp. range as does this
gelstar stuff.
Mike


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2001\08\02@105234 by Roman Black

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Mike Kendall wrote:
>
> > That is one of the cleverest ideas yet, especially
> > if filled with waterproof grease or the like.
> > Those fans are pretty weak but you see more and
> > more brushless fans (DC) of higher power ratings,
> > and one might be an ideal drop-in for a small sub.
>
> many/most types of grease are conductive. silicone grease is outragiously
> expensive.  try a search for gelstar.  I bought a gallon of this stuff for
> 20something bucks (I can't remember the exact price) while on a quest for a
> similiar product.  It is a polyofelin product that is suitable as a direct
> replacement for grease in regular machinery fittings, food service, and
> dielectric applications.  A kind of do-all grease that is cheap to boot.  It
> is clear just like silicone grease.  Before finding this I even tried making
> homemade petroleum jelly out of mineral oil and paraffin.  That  was a
> smashing failure.  It does not have a stable temp. range as does this
> gelstar stuff.
> Mike


Hi Mike, so you are saying this Gelstar is cheap,
non-toxic, water resistant, etc?? How good a grease
is it, compared to some of the more expensive
super-slippery greases available?
-Roman

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2001\08\02@111205 by Mike Kendall

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Hi Roman,
   Here is the url for the stuff:  http://alim.com/commerc/gelstar.htm
they claim it outperforms petroleum based greases.  It is also available in
grease gun cartridges if you don't need it in 1 or 5 gallons.  What I meant
by "food service" is that you don't want any "moly" grease in let's say a
food packing plant machinery or Pizza Hut dough mixer because inevitably it
will leak out into the food.  I'm surprised the environmentalists have not
mandated this stuff in boat trailers/marine equipment.  Personally, I'd
recommend building your own mini-sub motor.  Did you see the info. I
included in the previous emails for the wind turbine stuff?  I'm a wind
turbine nut and have compiled a few books on making my own turbine.  If
you're interested, I could drop you my idea on what  would be  too cool for
building one of these.  I'm uncertain what size vehicle you are building or
it's charecteristics (speed/maneuverability) but you'd certainly get better
performance by alot of attention to detail on the piece/parts/construction
of the motor, prop, and shape of vehicle.  Check out the "Go-Devil" mud
motors.  The URL is http://www.godevil.com  They have some mpegs on the site
of the boats going through pure slop in the swamp with these engines. I get
a kick out of watching  them every time.  Are you looking for a really tiny
mini-sub?  If not, and looking for something cheap/off-the-shelf, why not
check out a trolling motor?  Possibly drilling and tapping a hole for a zirc
and then backfilling it with the dielectric grease would give you a greater
depth out of it (but probably lower performance)?  I have no idea of the
internal construction of  a trolling motor and still,  personally, would
want to build  my own for performance.
regards,
Mike
{Original Message removed}

2001\08\02@185624 by Peter L. Peres

picon face
Just keep in mind that most 'supermagnets' need a serious coat of paint
(better epoxy paint) because they are very allergic to water (even vapor)
and contain a lot of environment-unfriendly metals (environment-unfriendly
as in you-unfriendly when you are sloshin around the vehicle in the
water). I have never seen anything rust as fast as a supermagnet. It went
from dull gray surface to at least 1 mm deep rust in 45 minutes after the
paint was accidentally scrapped off (at 80% humidity and 30 degrees C).

Peter

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2001\08\02@210956 by Mike Kendall

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I agree, good point.  I was recommending the gelstar dielectric grease to be
in the section with the moving rotor containing the magnets.  The corrosion
would probably then be less of an issue. This set-up would be similiar to
mud motors that I was discussing have a rotating shaft with bushings (two
companies use bearings and one company uses bronze bushings).  The grease in
the mud motor (they use a moly type) is pumped in via zircs as a periodic
routine maintenance.  I don't know if the mud motor bushings are oil lite
(powdered bronze mixed with oil under high pressure that will self
lubricate) or solid bronze.  Delrin would probably be better for the u/w
robot.
Mike
{Original Message removed}

2001\08\03@040930 by Peter L. Peres

picon face
> many/most types of grease are conductive. silicone grease is
> outragiously expensive.  try a search for gelstar.  I bought a gallon
> of this stuff for 20something bucks (I can't remember the exact price)
> while on a quest for a similiar product.  It is a polyofelin product
> that is suitable as a direct replacement for grease in regular
> machinery fittings, food service, and dielectric applications.  A kind
> of do-all grease that is cheap to boot. It is clear just like silicone
> grease.  Before finding this I even tried making homemade petroleum
> jelly out of mineral oil and paraffin.  That was a smashing failure.
> It does not have a stable temp. range as does this gelstar stuff.

The oil I was suggesting for filling u/w motors is light transformer oil.
Light machine oil was also tried. The motors were window wiper motors on
12V dc with a modified case. Usually people who cared put a humidity
sensor in the oil, near the bottom of the casing (these thrusters were not
orientable). When water seeps in it goes down (when given a chance, as the
oil churns around in operation). There the sensor will sense it and
command the motor controller to shut down. Actually you have some time to
do things between when the water is sensed and when serious damage begins.
The motors used in this role were mounted with vertical axles with only
one seal (the lower one) and driving large pitch radial pumps in stator
cages made of PVC plates (both the stator and the rotor). (impeller drive
style). One of those (I forget the name) multi-blade drives with variable
pitch and direction could be tried. As sold by Graupner etc.

Considering that diesel subs often had external fuel tanks open to the sea
(diesel oil floats on water) there should be nothing wrong with this
method for amateur things. Maybe not only amateur.

Peter

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2001\08\03@061248 by John Walker

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I had to construct an experiment for our lab that required a magnet be
submerged in
water. I found a spray-on rubber coating material made by Plasti Dip, that
works
great. They also sell a liquid version that allows you to dip the item to
be coated.
In my case the spray version was much more desirable. Check it out.

At 01:34 AM 8/3/01 +0300, you wrote:
{Quote hidden}

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2001\08\03@062558 by Roman Black

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Peter L. Peres wrote:
>
> Just keep in mind that most 'supermagnets' need a serious coat of paint
> (better epoxy paint) because they are very allergic to water (even vapor)
> and contain a lot of environment-unfriendly metals (environment-unfriendly
> as in you-unfriendly when you are sloshin around the vehicle in the
> water). I have never seen anything rust as fast as a supermagnet. It went
> from dull gray surface to at least 1 mm deep rust in 45 minutes after the
> paint was accidentally scrapped off (at 80% humidity and 30 degrees C).


Hi Peter, thanks for the magnet tip. I had another
thought, what about a water pump?? More like a jetski
than a propeller sub. Any 12v water pump should
already be sealed between the motor and impeller,
or even a car engine water pump is sealed and has
a shaft ready to drive. I don't think they would
handle any real deep pressure, but its worth a
mention.
-Roman

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