Design limits of electric motors?



grateful
Have a look at the spindle motors on the lpkf PCB prototyping machines. The fastest of these go to 100,000RPM, and are speed controlled brushless DC motors. Brush designs, are generally rare beyond perhaps 25,000RPM, but brushless designs are remarkably common at these speeds. Also look at: http://www.coercive.com/dcmotor.htm
Best Wishes
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GEARED down?I have seen a WWII airplane engine, and the crankshaft is directly coupled to the propeller.The jet engines are ~2500 hp, so it's impossible to gear.The pilot controls only the fuel supply.
-- Dimitris Tzortzakakis,Iraklion Crete,Greece Analogue technology rules-digital sucks http://www.patriko-kreta.com dimtzort AT otenet DOT gr the return adress is corrupted Warning:all offending emails will be deleted, and the offender/spammer will be put on my personal "black list".

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On Tue, 8 Jun 2004 14:31:09 +0300, "Tzortzakakis Dimitrios"

--
Suggest you look at propjet engines. Check out

http://www.garrettaviation.com /
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On Tue, 8 Jun 2004 14:31:09 +0300, "Tzortzakakis Dimitrios"

The single-engine VTOL Joint Strike Fighter runs a shaft fore-aft, from the engine to the front lift fan, which blows down. There is right-angle gearing at the fan casing. They shoot 32,000 horsepower down this shaft; there's a clutch somewhere, too. They're using my VME arbitrary waveform generators to simulate all the sensor inputs (shaft speed, torque, displacements) into the control computers now being designed.
Most jet engines have internal gearing. Jet helicopters obviously have gears.
John
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John Larkin wrote...

What happens when a tooth breaks? I suppose there's a mandatory replacement schedule. What's a typical mandated gear life?
Thanks, - Win
(email: use hill_at_rowland-dot-org for now)
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On 8 Jun 2004 10:45:08 -0700, Winfield Hill

Gosh, I don't know. I'd imagine the stress levels are pretty high. Helicopters in particular are suicide machines. I've seen some of the big fanjets disassembled, and they have a 4-foot wide, several inch thick wrapping of epoxy-kevlar around the main (12 foot diameter) fan blades to catch them if the rotor disintegrates. They actually test this, and I'd love to see one of those tests.
This aerospace stuff looks like fun, and it is if you get to see it but don't have to actually do it. My son-in-law works for Sandia, and does some explosives stuff. I commented that it must be fun, and he said, no, after all the management and paperwork and safety measures and planning and stuff, it's not fun any more.
John
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On 8 Jun 2004 10:45:08 -0700, Winfield Hill

They take sonic signatures with built-in transducers of the new installations. They then listen periodically to see what has changed. An FFT will reveal where in the gear chain the wear is happening, and with some experience on the part of the operator, how bad it is. The parts are changed on the basis of the results.
For carbon fibre parts the situation is different. The parts are stressed severely to a degree that uses about one third of their useful life. The remaining two thirds are then very accurately predictable, and bits don't get changed until they really need to.
d Pearce Consulting http://www.pearce.uk.com
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crankshaft
hp,
supply.
horsepower
inputs
now
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
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On Wed, 9 Jun 2004 09:45:32 +0100, "Ian Buckner"

A _really_ short day.
John
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If you read _Surely You're Joking Mr Feynman_, you will find most of a chapter devoted to how he sold his patent for a nuclear- powered airplane for the sum of $1.
Tim.
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No.The thrust of a jet engine is not created solebly by the high rpm, but also from the high speed of the exhaust gases, coming from the back of the engine.The jet engine intakes air, compresses it, the fuel is ignited in the combustion chamber, and the gases simultaneously rotate the turbine and propel the plane.
-- Dimitris Tzortzakakis,Iraklion Crete,Greece Analogue technology rules-digital sucks http://www.patriko-kreta.com dimtzort AT otenet DOT gr the return adress is corrupted Warning:all offending emails will be deleted, and the offender/spammer will be put on my personal "black list".

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motors
engines
let's
there
----------------------------------- The problem is that a jet turbine has a better power/weight ratio than an electric motor. In an aircraft this is considered to be important.
--
Don Kelly
snipped-for-privacy@peeshaw.ca
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DaveC wrote:

Really, the electromagnetic part of such a motor is no biggie. The mechanical part, especially related to first critical speed of high speed rotating machinery, is the part that requires the most attention to detail. If the motor is ever operated at the speed where the natural frequency of the first bending moment matches the rotational frequency, the vibrations tend to build to enormous magnitude in just a few revolutions. Very stiff structures can tolerate a rapid acceleration through the first critical speed, and then operate safely above that speed. But, getting a machine to tolerate that speed, even for a moment, is quite tricky. The other problem is ball bearings, for the most part, can't handle 100,000 + RPM. At the least, they need continuous oil mist cooling to remove the heat. Conventional journal bearings would need a continuous flow of cool oil to survive. Air bearings are a good choice, and are used in a lot of high-speed drilling and machining spindles, like Westwind. I'm pretty sure these run above first critical speed, just to look at the structure of them. The induction motor rotor, bearings, etc. are all the same diameter, about 1/2 to 3/4" diameter, with a flange at one end to act as a thrust bearing.
Jon
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On Mon, 7 Jun 2004 15:08:58 -0700, Jon Elson wrote

But what about conventional (fuel) turbine engines. Surely they turn in the 100,000 rpm range, and use ball bearings.
--
DaveC
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speed.
quite
handle
the
Actually, I think you'll find the high speed shafts are in journal bearings. And they have a continuous supply of oil, pumped by an oil pump driven from an auxilary shaft. The aux shaft is at right-angle to the main shaft and driven by bevel gearing at a slower speed.
daestrom
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Big commercial jets are in the 12K RPM range, and I think some of the military engine parts spin up to maybe 18K. There are some tiny jet engines (coke-can size, or smaller) that run around 100K or more. Research microturbines are pushing something like 500K.
Some steam turbines run in the teens, and they use plain pressurized-oil bearings, not ball bearings.
John
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DaveC wrote:

----------------- Dental drills.
-Steve
--
-Steve Walz snipped-for-privacy@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
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wrote:

Those are mostly air turbines nowadays. They can go very fast, and are nicely self-cooling. Some NMR experiments benefit from spinning the sample, which they do with air motors at speeds like 40 KHz: 2.4 million RPM.
http://nmr.magnet.fsu.edu/rf/830-X-MAS2.htm
http://www.varianinc.com/cgi-bin/nav?products/nmr/probes/solids/index&cid=KNHPHNJFK
John
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Are you joking?GEARED?Steam turbine?They are on a single-cast shaft.THAT shaft is expensive, thus it connects the turbine and generator.Imagine a gear for 2,500,000 hp (usual power of a nuclear plant generator).The generator and turbine are designed to run at the same speed.Even train locomotives use diesel-electric transmission, and the traction motors are directly coupled on the wheels.So must be happening at the ships, too.
-- Dimitris Tzortzakakis,Iraklion Crete,Greece Analogue technology rules-digital sucks http://www.patriko-kreta.com dimtzort AT otenet DOT gr the return adress is corrupted Warning:all offending emails will be deleted, and the offender/spammer will be put on my personal "black list".
?????? wrote:

Mary
built.
ship at

necessarily
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On Tue, 8 Jun 2004 14:24:49 +0300, "Tzortzakakis Dimitrios"

I was referring to a steamship. Prop RPMs are in the 100 range, the small high-pressure turbine spins maybe 12 grand - it makes 80% of the power - and the huge LP turbine runs roughly three or four. The main bull gear is typically about 30 feet in diameter or so... I saw one being ground at DeLaval, and I designed a number of steamship throttle control systems. The LASH ships I worked on made 32,000 shaft horsepower at 120 RPM. If the prop falls off, there's a good chance the turbine will disintegrate.
Direct-coupled reversing diesels are popular in ships nowadays because they are simpler and more compact than a high-efficiency steam plant. I think the steam plants are still more efficient, and the stuff they burn - essentially asphalt - is nasty and dirt cheap.
John
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