Design limits of electric motors?

[John Beardmore]

In message <0kbbc0p2rg6ne2k8vpe2ahf5a54al51eds@4ax.com>, Tim Auton
<tim.auton@uton.[groupSexWithoutTheY]> writes

Love is a travelator

Meaningless is a sig ?


J/.
--
John Beardmore

 

[Tim Auton]

John Beardmore <wookie@wookie.demon.co.uk> wrote:

In message <0kbbc0p2rg6ne2k8vpe2ahf5a54al51eds@4ax.com>, Tim Auton
tim.auton@uton.[groupSexWithoutTheY]> writes

Love is a travelator

Meaningless is a sig ?

Correct.


Tim
--
Love is a travelator.

 

[John Larkin]

On Tue, 08 Jun 2004 21:03:37 GMT, "daestrom"
<daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:

Hate to burst your bubble, but they *do* make gearing for this kind of
power. Typical steamships use reduction gears between the IP/LP turbines
(in thousands of RPM) and the main shaft (hundreds of RPM). And smaller
gearing between the HP and IP turbines. Bull-gears, the final output gear
connected to the propeller shaft are large with double helix cut. Often use
double-reduction with 'quill' shafts between successive gear stages.

Saw more than one bull gear get some broken teeth ground out. Didn't
replace the teeth, just ground down the sharp edges so they wouldn't wear
into the low-speed pinions (some sailors didn't believe the rules about
FOD).

On the ships I saw, the access ports to the main gear were sealed with
huge padlocks, and only the Chief had the keys. The gears are just too
tempting a tagret for sabatoge.

John

 

[John Larkin]

On Wed, 9 Jun 2004 09:45:32 +0100, "Ian Buckner"
<Ian_Buckner@agilent.com> wrote:

I watched a programme on the development of the JSF. The comment
made was that the front lift fan is only used during vertical landing,
and if anything broke you were going to have "a _really_ bad day".

Regards
Ian

A _really_ short day.

John

 

[Terry Given]

"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:10cbn79t5bksjbd@corp.supernews.com...

DaveC wrote:

On Tue, 8 Jun 2004 06:40:33 -0700, DaveC wrote
(in article <0001HW.BCEB0FE10039AEFDF03055B0@news.individual.net&gt:


So, basically, turning a fan in a tube (spinning a turbojet engine
without
fuel) doesn't gain you much efficiency. If electrics are to power an
aircraft, it seems that an efficient propeller is the best that you can
do.


And then hi rpms isn't important any more. Indeed, since torque doesn't
increase with speed (I *do* have that fact right, don't I?), gearing
isn't
necessary and propellers have a relatively low maximum speed
requirement.

Your electric motor will probably be most efficient at speeds higher
than want to drive your prop -- so you'll still want to gear the motor
down to the prop.

wouldnt additional pole-pairs be a more efficient way of reducing motor top
speed?

And I disagree about the turbofan assertion -- assuming that you've got
the motor to do it, if you want to fly at jetliner speeds a propeller is
going to be horribly inefficient, which is why jetliners use turbofans
and not turboprops. Since only 20% or so of the thrust of a turbofan is
from the turbine I think you _could_ use a motor, keeping in mind that
it's going to be a _long_ time before this is a better solution than
just burning jet fuel in a turbine!

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[daestrom]

"John Larkin" <jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote in
message news:jkaec0tu69q5o3jsj9ijm0edpr4a95dl3u@4ax.com...

On Tue, 08 Jun 2004 21:03:37 GMT, "daestrom"
daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:



Hate to burst your bubble, but they *do* make gearing for this kind of
power. Typical steamships use reduction gears between the IP/LP turbines
(in thousands of RPM) and the main shaft (hundreds of RPM). And smaller
gearing between the HP and IP turbines. Bull-gears, the final output
gear
connected to the propeller shaft are large with double helix cut. Often
use
double-reduction with 'quill' shafts between successive gear stages.

Saw more than one bull gear get some broken teeth ground out. Didn't
replace the teeth, just ground down the sharp edges so they wouldn't wear
into the low-speed pinions (some sailors didn't believe the rules about
FOD).

On the ships I saw, the access ports to the main gear were sealed with
huge padlocks, and only the Chief had the keys. The gears are just too
tempting a tagret for sabatoge.

Yep. But when the sailor has a preventative maintenance procedure to go in
and take some measurements, if they aren't careful about restraining all the
things about their person, some genuine accidents do happen. And if the
sailor is too scared of the 'chief' to admit anything, then it gets left
inside. Eventually, with the motion of the ship and all, it gets ground up
in the gear. Leaving some damaged teeth behind.

daestrom

 

[Tim Wescott]

Terry Given wrote:

"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:10cbn79t5bksjbd@corp.supernews.com...

DaveC wrote:


On Tue, 8 Jun 2004 06:40:33 -0700, DaveC wrote
(in article <0001HW.BCEB0FE10039AEFDF03055B0@news.individual.net&gt:



So, basically, turning a fan in a tube (spinning a turbojet engine

without

fuel) doesn't gain you much efficiency. If electrics are to power an
aircraft, it seems that an efficient propeller is the best that you can

do.


And then hi rpms isn't important any more. Indeed, since torque doesn't
increase with speed (I *do* have that fact right, don't I?), gearing

isn't

necessary and propellers have a relatively low maximum speed

requirement.

Your electric motor will probably be most efficient at speeds higher
than want to drive your prop -- so you'll still want to gear the motor
down to the prop.


wouldnt additional pole-pairs be a more efficient way of reducing motor top
speed?


-- snip --

Not really -- motor torque as a function of power input has a lot to do
with the magnetic materials you use and how much of them you use. You
_may_ gain something by increasing the motor diameter and shortening it,
but I'm not sure. The motor torque doesn't have much to do with the
number of poles. DC Motor torque is generally limited by the amount of
current that you can push through it without warming it up too much or
demagnetizing it, so motor power is generally dependent on how fast you
can make the thing spin.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[John Larkin]

On Wed, 09 Jun 2004 20:38:45 GMT, "daestrom"
<daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:

"John Larkin" <jjlarkin@highlandSNIPtechTHISnologyPLEASE.com> wrote in
message news:jkaec0tu69q5o3jsj9ijm0edpr4a95dl3u@4ax.com...
On Tue, 08 Jun 2004 21:03:37 GMT, "daestrom"
daestrom@NO_SPAM_HEREtwcny.rr.com> wrote:



Hate to burst your bubble, but they *do* make gearing for this kind of
power. Typical steamships use reduction gears between the IP/LP turbines
(in thousands of RPM) and the main shaft (hundreds of RPM). And smaller
gearing between the HP and IP turbines. Bull-gears, the final output
gear
connected to the propeller shaft are large with double helix cut. Often
use
double-reduction with 'quill' shafts between successive gear stages.

Saw more than one bull gear get some broken teeth ground out. Didn't
replace the teeth, just ground down the sharp edges so they wouldn't wear
into the low-speed pinions (some sailors didn't believe the rules about
FOD).

On the ships I saw, the access ports to the main gear were sealed with
huge padlocks, and only the Chief had the keys. The gears are just too
tempting a tagret for sabatoge.

Yep. But when the sailor has a preventative maintenance procedure to go in
and take some measurements, if they aren't careful about restraining all the
things about their person, some genuine accidents do happen. And if the
sailor is too scared of the 'chief' to admit anything, then it gets left
inside. Eventually, with the motion of the ship and all, it gets ground up
in the gear. Leaving some damaged teeth behind.

daestrom

So they should just use pulleys and belts.

John

 

[Rich Grise]

"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:10cbmtdfmt29o76@corp.supernews.com...

Note that none of this applies to low-bypass engines, like the ones used
in older jet fighters and the concord: Those engines get _all_ of their
thrust directly from the hot, fast exhaust. It's great for supersonic
flight because the exhaust is going so very fast, but for slower travel
it's not good for fuel efficiency because a lot of air moving slowly
produces more thrust than a little bit of air moving fast.

What kind of "_-bypass" would you call the SR-71 engines? They have
a bypass system that when it's going way fast, bypasses almost the
whole engine - the only air they allow through the "compressor" is
subsonic - the rest of the intake, which has already been compressed
by the shock wave from the spike, goes through ducts, directly to
the afterburner.

Which is kinda the opposite of what you're looking for.

But I'd say, since your first given was infinite electric power,
would it be possible, given today's materials, to build an electric
ramjet? I'd think you'd just put a white-hot element in place of
the flame in the combustion chamber, or maybe a big-ass arc.

Cheers!
Rich

 

[Rich Grise]

"DaveC" <me@privacy.net> wrote in message
news:0001HW.BCEB11070039F3F1F03055B0@news.individual.net...

On Tue, 8 Jun 2004 06:40:33 -0700, DaveC wrote
(in article <0001HW.BCEB0FE10039AEFDF03055B0@news.individual.net&gt:

So, basically, turning a fan in a tube (spinning a turbojet engine
without
fuel) doesn't gain you much efficiency. If electrics are to power an
aircraft, it seems that an efficient propeller is the best that you can
do.

And then hi rpms isn't important any more. Indeed, since torque doesn't
increase with speed (I *do* have that fact right, don't I?), gearing isn't
necessary and propellers have a relatively low maximum speed requirement.
--

Look up "Muffin Fans." Imagine scaling one up big enough to fly an airplane.

Or imagine one right out of the catalog flying a small model plane. I think
it's pretty feasible, after all, given the dilithium-antimatter battery
pack.


Rich

 

[Rich Grise]

"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:10cf1055ih8qc8b@corp.supernews.com...

wouldnt additional pole-pairs be a more efficient way of reducing motor
top
speed?
-- snip --
Not really -- motor torque as a function of power input has a lot to do
with the magnetic materials you use and how much of them you use. You
_may_ gain something by increasing the motor diameter and shortening it,
but I'm not sure. The motor torque doesn't have much to do with the
number of poles. DC Motor torque is generally limited by the amount of
current that you can push through it without warming it up too much or
demagnetizing it, so motor power is generally dependent on how fast you
can make the thing spin.

It seems almost intuitive that if a 4-pole gets n rpm, then a 24-pole
would get n/6; is that incorrect? And I'd think the torque would change
proportionally, i.e. 6x as well, all with losses taken into account, of
course. (so not necessarily exactly 6, ...)

And wouldn't including superconductor magnets be cool? They do give
the most magnetism per pound that can be had, don't they?

Thanks,
Rich

 

[Tim Wescott]

Rich Grise wrote:

"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:10cbmtdfmt29o76@corp.supernews.com...


Note that none of this applies to low-bypass engines, like the ones used
in older jet fighters and the concord: Those engines get _all_ of their
thrust directly from the hot, fast exhaust. It's great for supersonic
flight because the exhaust is going so very fast, but for slower travel
it's not good for fuel efficiency because a lot of air moving slowly
produces more thrust than a little bit of air moving fast.


What kind of "_-bypass" would you call the SR-71 engines? They have
a bypass system that when it's going way fast, bypasses almost the
whole engine - the only air they allow through the "compressor" is
subsonic - the rest of the intake, which has already been compressed
by the shock wave from the spike, goes through ducts, directly to
the afterburner.

"Oddball". I was speaking, of course, of turbofans.

Which is kinda the opposite of what you're looking for.

But I'd say, since your first given was infinite electric power,
would it be possible, given today's materials, to build an electric
ramjet? I'd think you'd just put a white-hot element in place of
the flame in the combustion chamber, or maybe a big-ass arc.

Cheers!
Rich

They had atomic turbojets in the 50's (no kidding, and very scary if you
ever consider that airplanes do crash sometimes). Fortunately they
never flew them. _Any_ heat source can be used as long as it transfers
heat to the air quick enough, but I'm not sure if it'd work with a
ramjet because of the speed of the air.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Tim Wescott]

Rich Grise wrote:

"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:10cf1055ih8qc8b@corp.supernews.com...


wouldnt additional pole-pairs be a more efficient way of reducing motor

top

speed?

-- snip --
Not really -- motor torque as a function of power input has a lot to do
with the magnetic materials you use and how much of them you use. You
_may_ gain something by increasing the motor diameter and shortening it,
but I'm not sure. The motor torque doesn't have much to do with the
number of poles. DC Motor torque is generally limited by the amount of
current that you can push through it without warming it up too much or
demagnetizing it, so motor power is generally dependent on how fast you
can make the thing spin.


It seems almost intuitive that if a 4-pole gets n rpm, then a 24-pole
would get n/6; is that incorrect? And I'd think the torque would change
proportionally, i.e. 6x as well, all with losses taken into account, of
course. (so not necessarily exactly 6, ...)

And wouldn't including superconductor magnets be cool? They do give
the most magnetism per pound that can be had, don't they?

Thanks,
Rich

For a given drive frequency that's true, and it will be more difficult
to drive a multi-pole motor fast. As far as the torque goes your slots
get smaller when you have more poles, so you can't stuff as much copper
in there, so your torque per pole goes down as fast as the number of
poles goes up.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Tim Wescott]

Rich Grise wrote:

"DaveC" <me@privacy.net> wrote in message
news:0001HW.BCEB11070039F3F1F03055B0@news.individual.net...

On Tue, 8 Jun 2004 06:40:33 -0700, DaveC wrote
(in article <0001HW.BCEB0FE10039AEFDF03055B0@news.individual.net&gt:


So, basically, turning a fan in a tube (spinning a turbojet engine

without

fuel) doesn't gain you much efficiency. If electrics are to power an
aircraft, it seems that an efficient propeller is the best that you can

do.

And then hi rpms isn't important any more. Indeed, since torque doesn't
increase with speed (I *do* have that fact right, don't I?), gearing isn't
necessary and propellers have a relatively low maximum speed requirement.
--


Look up "Muffin Fans." Imagine scaling one up big enough to fly an airplane.

Or imagine one right out of the catalog flying a small model plane. I think
it's pretty feasible, after all, given the dilithium-antimatter battery
pack.


Rich

Muffin fans stink for that -- they're designed for reliability and
quietness. Check out http://www.hobby-lobby.com/ for electric ducted
fans that really work (except that they tend to be big, low velocity
things).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Clifford Heath]

John Larkin wrote:

The gears are just too tempting a tagret for sabatoge.

sabotage - the word has an interesting etymology.

A "sabot" is a wooden shoe, so named by the French peasants
who wore them. We know them as clogs, and tend to associate
them more with the Dutch. Anyhow... during the Industrial
Revolution, "saboteurs" became so-called from their practise
of throwing a sabot into the gears of the machinery, thereby
"clogging up the works" and often breaking the gears.

Irrelevant to electronics, but the kind of thing that geeks
and engineers like to know .

Clifford Heath.

 

[Rich Grise]

"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:10cfb0en0h9t455@corp.supernews.com...

Rich Grise wrote:

It seems almost intuitive that if a 4-pole gets n rpm, then a 24-pole
would get n/6; is that incorrect? And I'd think the torque would change
proportionally, i.e. 6x as well, all with losses taken into account, of
course. (so not necessarily exactly 6, ...)

And wouldn't including superconductor magnets be cool? They do give
the most magnetism per pound that can be had, don't they?

Thanks,
Rich



For a given drive frequency that's true, and it will be more difficult
to drive a multi-pole motor fast. As far as the torque goes your slots
get smaller when you have more poles, so you can't stuff as much copper
in there, so your torque per pole goes down as fast as the number of
poles goes up.

Well, yes - but is it proportional? If so, then the torque would be

constant, within a reasonable experimental error. ;-) Or so it looks
to me.

Thanks,
Rich

 

[John Larkin]

On Thu, 10 Jun 2004 10:46:03 +1000, Clifford Heath
<cjh-nospam@nospaManagesoft.com> wrote:

John Larkin wrote:
The gears are just too tempting a tagret for sabatoge.

sabotage - the word has an interesting etymology.

A "sabot" is a wooden shoe, so named by the French peasants
who wore them. We know them as clogs, and tend to associate
them more with the Dutch. Anyhow... during the Industrial
Revolution, "saboteurs" became so-called from their practise
of throwing a sabot into the gears of the machinery, thereby
"clogging up the works" and often breaking the gears.

Irrelevant to electronics, but the kind of thing that geeks
and engineers like to know .

Clifford Heath.

Isn't a sabot also the drop-away casing used on those hypervelocity
uranium tank-killer shells?

John

 

[Joel Kolstad]

Clifford Heath <cjh-nospam@nospaManagesoft.com> wrote:

sabotage - the word has an interesting etymology.
....
Irrelevant to electronics, but the kind of thing that geeks
and engineers like to know .

Yep, but surely most proper geeks and engineers would have learned it from
Star Trek... uh... VI, I think it was?

 

[Alan McClure]

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html;charset=UTF-7" http-equiv="Content-Type">
<title></title>
</head>
<body bgcolor="+ACM-ffffff" text="+ACM-000000">
daestrom wrote:<br>
&lt;blockquote cite="midpzKxc.63893+ACQ-j24.24493+AEA-twister.nyroc.rr.com"
type="cite"&gt;
<pre wrap="">"John Larkin" <a class="moz-txt-link-rfc2396E" href="mailto:jjlarkin+AEA-highlandSNIPtechTHISnologyPLEASE.com">+ACY-lt;jjlarkin+AEA-highlandSNIPtechTHISnologyPLEASE.com+ACY-gt;</a> wrote in
message <a class="moz-txt-link-freetext" href="news:jkaec0tu69q5o3jsj9ijm0edpr4a95dl3u+AEA-4ax.com">news:jkaec0tu69q5o3jsj9ijm0edpr4a95dl3u+AEA-4ax.com</a>...
</pre>
&lt;blockquote type="cite"&gt;
<pre wrap="">On Tue, 08 Jun 2004 21:03:37 GMT, "daestrom"
<a class="moz-txt-link-rfc2396E" href="mailto:daestrom+AEA-NO+AF8-SPAM+AF8-HEREtwcny.rr.com">+ACY-lt;daestrom+AEA-NO+AF8-SPAM+AF8-HEREtwcny.rr.com+ACY-gt;</a> wrote:


</pre>
&lt;blockquote type="cite"&gt;
<pre wrap="">Hate to burst your bubble, but they +ACo-do+ACo- make gearing for this kind of
power. Typical steamships use reduction gears between the IP/LP turbines
(in thousands of RPM) and the main shaft (hundreds of RPM). And smaller
gearing between the HP and IP turbines. Bull-gears, the final output
</pre>
&lt;/blockquote&gt;
&lt;/blockquote&gt;
<pre wrap="">&lt;!----&gt;gear
</pre>
&lt;blockquote type="cite"&gt;
&lt;blockquote type="cite"&gt;
<pre wrap="">connected to the propeller shaft are large with double helix cut. Often
</pre>
&lt;/blockquote&gt;
&lt;/blockquote&gt;
<pre wrap="">&lt;!----&gt;use
</pre>
&lt;blockquote type="cite"&gt;
&lt;blockquote type="cite"&gt;
<pre wrap="">double-reduction with 'quill' shafts between successive gear stages.

Saw more than one bull gear get some broken teeth ground out. Didn't
replace the teeth, just ground down the sharp edges so they wouldn't wear
into the low-speed pinions (some sailors didn't believe the rules about
FOD).
</pre>
&lt;/blockquote&gt;
<pre wrap="">On the ships I saw, the access ports to the main gear were sealed with
huge padlocks, and only the Chief had the keys. The gears are just too
tempting a tagret for sabatoge.
</pre>
&lt;/blockquote&gt;
<pre wrap="">&lt;!----&gt;
Yep. But when the sailor has a preventative maintenance procedure to go in
and take some measurements, if they aren't careful about restraining all the
things about their person, some genuine accidents do happen. And if the
sailor is too scared of the 'chief' to admit anything, then it gets left
inside. Eventually, with the motion of the ship and all, it gets ground up
in the gear. Leaving some damaged teeth behind.

daestrom


</pre>
&lt;/blockquote&gt;
&lt;tt&gt;In the US Navy I was in, ships reduction gears where not opened
except for very<br>
carefully planned evolutions.+AKA- All tools/parts/rags/etc. were logged in
and logged<br>
back out of a "clean" area around any open reduction gear cover. Any
time a cover <br>
was open an armed guard was placed on it to prevent any/all possibility
of damage<br>
to the gear. Opening up an red. gear was/is a very rare evolution and
is usually<br>
watched closely by the Engineer Officer, the M division officer, and
possibly the<br>
ships' Captain.<br>
In addition, the lube oil low pressure alarm for the reduction gear
energized a <br>
siren that could wake up the dead two area codes away, just to give an
indication<br>
serious even the possibility of damage to the gear is considered.<br>
It was easier for two missile techs to do PMs on a Polaris missile than
it was to<br>
get permission to open an inspection cover on the boats' reduction gear.<br>
ARM<br>
<br>
<br>
ARM<br>
<br>
&lt;/tt&gt;
&lt;/body&gt;
&lt;/html&gt;

 

[SioL]

"Alan McClure" &lt;mcclures@gwis.com&gt; wrote in message news:10ch2v87pmi0fff@corp.supernews.com...
daestrom wrote:

&lt;Snipped unreadable html crap&gt;

How light yellow on while background or perhaps even
dark brown on black?

SioL