torque and electric motors (slightly OT)

For an academic, you seem loath to look anything up.

The cars are DC, of course, which makes all of that true.

Did you know that the locomotives and mine trucks are electric for that same reason?

Opportunities abound to expand your knowledge of what you see every day. Of course, to rework the old saying, if the student isn't willing a teacher is no avail.

Partially true. To obtain the desired performance, you often need a single reduction gearing between motor and wheel. While it's not a multi-speed transmission, it could be a gearbox.

This is a non-sequitor. Most any motor or engine can cause acceleration to be constant. And remember, when you are traveling down a flat stretch of road, at constant speed, and the wind isn't gusting, your acceleration is CONSTANT even though it happens to be zero at the moment, constant nonetheless.

You got that reveresed. It is internal combustion engines that do this. It is one of the main distinctions between motors and engines.

Dan

1. motor is not an AC Synchronous or vairable reluctance design - it is probably a polyphase motor with samarium cobalt magnets driven by a fairly elegant controller
2. a shunt wound DC motor produces max torque at stall

Ah c'mon George, lighten up a bit. Sure he could google it or go buy a set of Encyclopedia Britannicas or what not, but asking other folks is a time honored way to do research as well.

Shoot, this group exists so that people can ask questions and others can answer them. I doubt there's been a question asked here that couldn't be looked up in some dusty tome, but that's no fun. We're here because we like interacting with others and developing relationships with interesting people that we'd have virtually no chance of ever meeting otherwise. Picking each others brain is the whole point.

If you don't want to answer his queries, don't. But there's no need to castigate him...

...Kevin

: For an academic, you seem loath to look anything up.

And for a Usenet participant, you seem pompous and arrogant.

: Opportunities abound to expand your knowledge of what you see every day. Of : course, to rework the old saying, if the student isn't willing a teacher is : no avail.

You seem to have something of a problem with people asking questions on a discussion group. There's your reply to me, a really unpleasant one a couple of days ago to Bill in Detroit, and a number of others as I recall.

Oddly enough, the function of a discussion group is, well, discussion, part of which involves asking questions, and politely answering questions from others.

I don't know what you think Usenet is for, but you got the wrong idea. Perhaps you should do something else with your time? I'm sure I'm not the only one who wouldn't miss your snide and arrogant remarks.

-- Andy Barss

I'd have left off that first sentence if had had been anyone but you, Andy. You seem to have the sequence of events in error. Bill asked a question, which I answered, giving a reason for the answer and some additional information which would allow him to understand what general principle was in operation.

Then he came back with the "I'm (we're) not a chemist, dumb it down" reply. Not a request, but a complaint against the person making the only meaningful reply!!! Now I feel it's the responsibility of the person posing the question to go the extra Google if he doesn't know, not the person providing an answer and explanation. Since he had not shown willingness to understand what I had told him, I returned URLs along with my recommendation to stand up, reach up and pull up.

Then you were kind enough to chime in, implying that use of physical chemistry terms was "jargon" not merely appropriate vocabulary when discussing physical chemistry. Reminded me of nothing less than the HS whiners who used to complain about the "big words" even after I reminded them, and taught basic Greek and Latin at the outset. Exoskeleton and exothermic, geothermic, geographic ... you'd think it would have sunk in.

So I'll repeat what I told them for you and Bill. What you don't know, look up. That's information. What you don't understand, follow up. That's education.

As far as pretentions go, you've got me beat. Lighten up.

HEAR!!!!!! HEAR !!!!!!!!

Andrew Barss wrote:

snip...

Actually George, Andy asked a question about electric cars and torque - he was the originator of this thread. Specifically, he said he thought that electric motors have more torque at higher rpm, which is why we use pulleys and such and he wanted to know if that wasn't the case.

You responded:

====================================================================== "For an academic, you seem loath to look anything up.

The cars are DC, of course, which makes all of that true.

Did you know that the locomotives and mine trucks are electric for that same reason?

Opportunities abound to expand your knowledge of what you see every day. Of course, to rework the old saying, if the student isn't willing a teacher is no avail." ======================================================================

None of which actually answered his question at all...

...Kevin

Nope, you've read what you want, not what was there. The answer was and is that the cars are DC, which makes the claims made by the manufacturer correct.

"It's a review of a new, all-electric sports car. In it the performance on an electric engine is extolled, on the grounds that it produces constant torque at all RPMS, so there's no need for a transmission, and there's constant acceleration throughout the motor's RPM range.

Is this right? "

See how that works if you read what's printed?

Even included a tie to the familiar to help him internalize the new piece of knowledge, diesel/electric haul trucks and locomotives. They taught me in school that relating a new piece of information to familiar examples helped internalize it.

And saying the sky is blue is blue is correct too, but gives no clue as to why. All you told him was it was a DC motor which he probably surmised from the article.

Well, I see you left out a salient portion of what he wrote. To wit:

"I thought electric motors always produced more torque at higher RPMs than low ones (hence the use of pulleys, for example, to use a fast motor to get slow RPMs on a lathe). I'm quite ignorant in these matters, so clarification much appreciated."

You replied "The cars are DC, of course, which makes all of that true." But you didn't say all of what exactly is true. The fact that the cars had constant torque at all rpms, or that 'electric motors always produced more torque at higher RPMs'.

See how that works if you read what's asked?

The question was multifaceted and your reply was both virtually contentless for the aspect it attempted to address and ambiguous.

And I'm sure it does. Only thing is you didn't explain anything - just gave a couple more examples. So now poor Andy is wondering why cars, haul trucks & trains all have the same torque at varying rpms. And as far as I know, his understanding that the torque varies with rpm is still unanswered. My experience tells me that's so. I have a 1 hp DC motor on my Nova 3000. It seems to have a lot more power at speed than it does when I dial it down. Consequently, I use the belt/pulley system.

When the Nova DVR first came out I remember several discussions about how they were achieving high torque at low rpms. Obviously some DC motors have a way to deal with that, and apparently some don't.

Someone here may actually give a basic treatise on how these things work that those of us w/o an electrical engineering degree can understand. Or they'll hold their peace instead. What I can't grok is the demeaning tone you display while pretending to answer, yet actually contributing virtually nothing...

...Kevin

Kevin, Power isn't torque, which may be confusing you. Power is a unit of work. Torque is a force. Dan

Kevin Miller wrote in news:4570eaaf$1 @news.acsalaska.net:

manufacturer

Kevin, For a man who normally offers so much of his knowledge and experience to others, it's sad to see how he can make some feel like an asshole for asking a question. Hank

look guys, it is NOT a DC motor - there is no modern electric car with reasonable efficiency that uses a DC motor - while this is a wood turning group, and this whole thing is off topic, if you are going to flame someone, at least make sure the information is right. read Tesla Motor's site - and how they license the inverter used to drive the motor - read here about the inverter design and that it is an induction motor

Fish or fowl? What they call a "brushless DC motor" which is really confusing, because the current supplied by the complicated electronics is alternating current, but the motor features permanent-magnet technology, and thus the characteristics of a DC motor rather than a synchronous AC - only without the commutators. No sparks, no drag from the brushes, just black boxes to go bad. You don't vary the current like the simple brushed DC, rather the way it's supplied. Who really wins on this one, the Edison DC faction, or the GE Steinmetz/Tesla AC faction? Think it might just as well be poh-tay-to poh-tah-to? I call it DC, because it's a generator in reverse, not an alternator.

This is also the direction modern locomotives and haul trucks are taking, made possible by the marvels of silicon and ceramic magnet technology. More efficient, and most important, more reliable in the long term than the DC brush-type motors, without the need for heavy transmissions to gear a synchronous equivalent. Variable reluctance has a couple of drawbacks for traction applications.

To get things closer to home, you're probably sitting in front of a couple of those motors right now. They're cooling your CPU and power supply. Not a job that requires much torque, certainly, but my CPU fan is now controlled so that it doesn't make a racket at idle, but can get right on up there when I start playing with graphics and Mr. Intel gets as hot under his collar as ....

For those who don't care to speculate or expectorate on what motor does what or who gives an answer that they didn't want, there are a lot of resources available free on the net. One with good pictures for reinforcement can be found at

What's in a word? Does DC mean DC, on or off topic? Perhaps not. :)

Turn to Safety, Arch Fortiter

DC = "Doesn't Cut" --- on topic DC = Direct Current == possibly off topic DC - - a place in Virginia - Definately off topic

oh - by the way, in my terminology, only a motor that actually operates on DC is a DC motor - a "brushless DC motor" is NOT a DC motor, it's a polyphase PM AC motor with integrated electronics.

For those who are getting baffled by this - simple test - if it has brushes, it's a DC motor, or an AC/DC motor (will work with both, like the motor on an old singer sewing machine) - if there are no brushes, it is NOT a DC motor.

Oh. There's that jargon thing again. Being an electronic layman, what I was trying to say is that I can stall my lathe at slower speeds much easier than I can at high speeds. Power, torque, biscuits with gravy, call it whatever - I'll still get it fuddled up and I'll still need to swap the belt when I turn at low rpm.

The car doesn't seem to do that. Why, I think, is also the thrust of Andrews original question. As it turns out, Bill Noble explained in another post that it isn't a DC engine. So mystery solved.

Have a great weekend & keep the bevel rubbin'...

...Kevin

Oh. That explains the discrepancy, thanks.

Right. Humble apologies to the group. The thrust of my posts was less about the correctness of the information (which is mostly over my head anyway) than the tone of the responses. Plenty of room for polite disagreement or even for politely correcting someone else's misunderstanding or misinformation. Caustic denigration of other posters who did nothing wrong other than asking a question just sorta sticks in my craw though.

Hmmm. That doesn't make any sense to me, but I don't have an engineering background. Wonder if I could use that principle to convince my boss that I'm more productive if I sleep in? ;-)

S'later...

...Kevin

One wonders why they give it the name.

FWIW, if it has constant polarity, whether by permanent magnets or permanently energized fields, for those who will research the matter, rather than shifting, it's DC. That's why the torque is so great at one rpm. Constant force. Beats the problem of hysteresis in an economical fashion, too.

Of course universal motors have brushes, as do repulsion/induction types.