Design limits of electric motors?

requirement.

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

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

-- 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.

So they should just use pulleys and belts.

John

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

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

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

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

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.

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.

Muffin fans stink for that -- they're designed for reliability and quietness. Check out

for electric ducted fans that really work (except that they tend to be big, low velocity things).

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.

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

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

John

...

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

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 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

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

ARM

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

SioL

Don't go sit next to the engines in such a plane. Unless it is made of quite thick lead. Hmmm...

Thomas

Second try. Sorry about the HTML, Mozilla and I haven't come to terms yet. ARM

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

ARM

Project "Pluto" in the late '50s through '64. The engine (a ramjet, rather than turbo-jet) was intended to power ICBMs and was tested (statically) for the duration needed (7 minutes, IIRC). ISTR that it was also carried aboard a test B36, but un-powered, and perhaps even un-fueled.