Re: [PSUBS-MAILIST] ETEK motor (speed controller for this?)

["Dan H." <jmachine@adelphia.net>]

Brian,

My motors run around 1800 RPMs top speed.  I have two 3/4 HP side thrusters
and one 3 HP rear thruster.  Slower then that would be better.

I think 3600 is quite high.  The people you want to talk to are the
engineers at a company like Michigan Wheel.  They make props for a living
and will help match you up with something.  Psub size props are on their
really small end but they'll help you crunch the numbers.

Not only is the Eket motor fast for a direct drive prop on a sub but it's so
much more power the you'd need and you'll hardly fit the required pile of
batteries in a Psub to use that much power for any length of time.

Now, if your calling a boat the size of Carsten's a Psub, you can use all
those horses.
Dan H.
----- Original Message ----- 
From: "Brian Cox" <ojaivalleybeefarm@dslextreme.com>
To: <personal_submersibles@psubs.org>
Sent: Wednesday, February 16, 2005 11:36 AM
Subject: Re: [PSUBS-MAILIST] ETEK motor (speed controller for this?)


> Dan,
>            What RPM do your motors run at?  And what are their specs?  Do
you think that Etek motor is too high an RPM then?    Maybe with a gear
reduction it would be good ,  but more complicated.
>
> There is a PDF file at the bottom of this page with the motor specs
> http://www.briggsandstratton.com/display/router.asp?DocID=68483
>
>
> Brian
> ----- Original Message ----- 
> From: "Dan H." <jmachine@adelphia.net>
> To: <personal_submersibles@psubs.org>
> Sent: Wednesday, February 16, 2005 6:43 AM
> Subject: Re: [PSUBS-MAILIST] ETEK motor (speed controller for this?)
>
>
> > Paul,
> > That's an impressive controller!
> >
> > I'm no expert at propulsion in water but if you look at it from a hands
on,
> > grass roots prospective, you'll see what I mean.
> >
> > Imagine a surfboard to represent a surface craft and a watermelon to
> > represent a sub.  Place one index finger on the tail of the surfboard
and
> > your other on the end of the watermelon.  Push them slowly through the
> > water.  They're about the same mass and take almost equal force to get
> > moving.  Now try the same thing at faster and faster speeds until your
> > finger gives out.  Which finger will give out first?  The one on the
melon!
> >
> > There are limits to this of course, but in the horsepower and speed your
> > talking about, five horsepower in a Psub, will move you along fine and
the
> > extra thirty won't make it go that many times faster, but in the surface
> > craft, you'll get a better return on the additional power you put into
it.
> >
> > If I can use my folksy water melon and surfboard comparison again I
could
> > explain the prop RPM.  Our surfboard and melon both have props on them
but
> > there only spinners like that of a pinwheel.  The faster you push the
faster
> > they revolve.
> >
> > This time you push with five pounds of force on the surfboard.  As the
> > surfboard is cruising along on the surface it's prop, being a screw,
screws
> > it way through the water at pretty high RPM's.  Push the melon with the
same
> > five pounds and of course as the melon doesn't travel as fast, it's prop
> > doesn't turn as fast.  Obviously to use props for propulsion, they have
to
> > turn faster then the water they are traveling through.  The surface
craft
> > needs a faster prop speed just to travel through the water and
additional
> > speed to produce thrust. The slower moving sub needs less prop speed to
> > screw through the water and additional speed to produce thrust.
> >
> > By now I'm sure most of you are thinking, but the surface boat uses a
> > different pitch prop.  True!  A faster moving boat uses a prop that has
a
> > long lead, more pitch.  For one turn of the prop it is designed to screw
> > farther through the water then a slower moving boats prop.  This is
taken
> > into consideration with propelling a sub.  Any slow moving craft has a
> > flatter prop then a fast moving craft.  If the pitch of the prop were
all
> > the same the fast boat wound need a zillion RPM and a subs props would
be
> > turning extremely slow.
> >
> > It's the combination of RPM, prop pitch, prop diameter and the speed of
the
> > craft through the water that have to be considered when sizing a prop.
A
> > big prop with a big bit will transfer more engine horse power per
revolution
> > into moving water.  But the point of diminishing return is reached
sooner
> > when powering a short plumpy sub then a sleek long surface craft.  A
fast
> > turning prop, slowly moving through the water (slow boat speed), will
> > cavitate sooner then a slow moving prop or a prop moving faster through
the
> > water (fast boat speed).
> >
> > I found the slowest motors I could find for my sub "Persistence",
matched
> > the props to them and later fine tuned the props monitoring the motors
> > amperage.
> >
> > A speed controller is a way of lowering the RPM but a 30 HP at 3600 RPM
> > motor turned down to half speed with a speed controller is no better the
a
> > 15HP at 1800 RPM.  If you need 1800 RPM then buy the smaller motor.  A
gear
> > reducer is another option but get cumbersome for a Psub.  A motor of
30HP
> > will still retain most of it's 30HP on the output of the gear reduction.
If
> > you half the speed with gears, you double the torque, minus that
converted
> > to heat by the gear reducer.  A gear box is clumsy and won't fit into a
pod
> > very easy but within the hull it's more useable.
> >
> > I think you got your battery assumptions correct.  You only store so
much
> > power,be it in a gasoline tank, diesel tank or battery.  In a Psub you
> > seldom travel for a long period of time.  It's mostly short bursts and
slow
> > speeds keeping the total power consumed in a hour of operation to far
less
> > then an hour in a surface craft.  Contact some battery people that do
the
> > calculations.  Figuring out how much operating time you have in a given
size
> > tank of electricity is just math.
> >
> > If you read to the end of this book and haven't read anything you didn't
> > already know, I apologize.  ;-)  Dan H.
> >
> >
> > ----- Original Message ----- 
> > From: <Deeperdowndude@aol.com>
> > To: <personal_submersibles@psubs.org>
> > Sent: Tuesday, February 15, 2005 8:19 PM
> > Subject: Re: [PSUBS-MAILIST] ETEK motor (speed controller for this?)
> >
> >
> > > Dan,
> > >
> > > Thanks for the advice and for the link.  Here's another controller
link I
> > got from the company that sells the motors.
> > >
> > >
http://www.evparts.com/shopping/product_details.php?id=271&product_id=3317
> > >
> > > Yes I am thinking of using it in a surface boat.  Some of your
comments
> > lead me to think about it from the standpoint of a sub, though.  Could I
ask
> > you a couple more questions about that?
> > >
> > > You said 34 horsepower was a lot for a sub and that 3600 rpm would be
fast
> > for the prop.  About that, wouldn't more horsepower simply mean the
ability
> > to go faster?  I understand the visibility-collision problem underwater,
but
> > other than that is there some reason why a fast psub isn't a good idea?
> > >
> > > About the prop RPM: I've also read that fast props are good for boats
and
> > subs do better with slow props.  Is it because the sub prop would
cavitate
> > at the higher RPM?  And if so, couldn't that problem be avoided with a
gear
> > reduction drive or by simply running at a slower power setting and RPM?
> > >
> > > But where you started me wondering was what you said about the
batteries,
> > though.  Unless I'm wrong, if I need 72 volts and 400 amps, and if I'm
using
> > 12-volt batteries wired together, that means I'd need at least six
batteries
> > rated for at least 66.6 amp-hours each?  So then, does your "starter"
> > comparison mean it's only going to run a very short time: in this case
less
> > than one hour?  Am I right so far?
> > >
> > > Paul
> > >
> > >
> > >
> > >
> > >
> > >
************************************************************************
> > >
************************************************************************
> > >
************************************************************************
> > > The personal submersibles mailing list complies with the US Federal
> > > CAN-SPAM Act of 2003.  Your email address appears in our database
> > > because either you, or someone you know, requested you receive
messages
> > > from our organization.
> > >
> > > If you want to be removed from this mailing list simply click on the
> > > link below or send a blank email message to:
> > > removeme-personal_submersibles@psubs.org
> > >
> > > Removal of your email address from this mailing list occurs by an
> > > automated process and should be complete within five minutes of
> > > our server receiving your request.
> > >
> > > PSUBS.ORG
> > > PO Box 311
> > > Weare, NH  03281
> > > 603-529-1100
> > >
************************************************************************
> > >
************************************************************************
> > >
************************************************************************
> > >
> > >
> >
> >
> >
> >
> >
> > ************************************************************************
> > ************************************************************************
> > ************************************************************************
> > The personal submersibles mailing list complies with the US Federal
> > CAN-SPAM Act of 2003.  Your email address appears in our database
> > because either you, or someone you know, requested you receive messages
> > from our organization.
> >
> > If you want to be removed from this mailing list simply click on the
> > link below or send a blank email message to:
> > removeme-personal_submersibles@psubs.org
> >
> > Removal of your email address from this mailing list occurs by an
> > automated process and should be complete within five minutes of
> > our server receiving your request.
> >
> > PSUBS.ORG
> > PO Box 311
> > Weare, NH  03281
> > 603-529-1100
> > ************************************************************************
> > ************************************************************************
> > ************************************************************************
> >
> >
> >
>
>
>
>
> ************************************************************************
> ************************************************************************
> ************************************************************************
> The personal submersibles mailing list complies with the US Federal
> CAN-SPAM Act of 2003.  Your email address appears in our database
> because either you, or someone you know, requested you receive messages
> from our organization.
>
> If you want to be removed from this mailing list simply click on the
> link below or send a blank email message to:
> removeme-personal_submersibles@psubs.org
>
> Removal of your email address from this mailing list occurs by an
> automated process and should be complete within five minutes of
> our server receiving your request.
>
> PSUBS.ORG
> PO Box 311
> Weare, NH  03281
> 603-529-1100
> ************************************************************************
> ************************************************************************
> ************************************************************************
>
>





************************************************************************
************************************************************************
************************************************************************
The personal submersibles mailing list complies with the US Federal
CAN-SPAM Act of 2003.  Your email address appears in our database
because either you, or someone you know, requested you receive messages
from our organization.

If you want to be removed from this mailing list simply click on the
link below or send a blank email message to:
	removeme-personal_submersibles@psubs.org

Removal of your email address from this mailing list occurs by an
automated process and should be complete within five minutes of
our server receiving your request.

PSUBS.ORG
PO Box 311
Weare, NH  03281
603-529-1100
************************************************************************
************************************************************************
************************************************************************