Danijel Gorupec

With 4-wire motor you must energize your motor windings in both polarities (bipolar). For example (wave drive): Step1: A1 is positive, A2 is negative, B1 & B2 are disconnected Step2: A1 & A2 are disconnected, B1 is positive, B2 is negative Step3: A1 is negative, A2 is positive, B1 & B2 are disconnected Step4: A1 & A2 are disconnected, B1 is negative, B2 is positive ... back to step1.... Full step drive is very similar, only both windings are always used simultaneously (for better torque). I don't know how to insert images so I cannot be of any better help.

Hard. Without a control circuit (unless your PLC has some special outputs) you will only obtain poor results. 4-wire stepper motors should be bipolar-driven. Does your PLC have transistor outputs? Open-collector or driven (push-pull) outputs? Does it have PWM capability? Does it have quadrature outputs? Also, what is you know about the motor - what size it is, what is winding resistance, are there any markings on it?

Today I read a short article about record-breaking maglev train... got me thinking if another kind of flywheel energy storage is possible: - a very large torus tube made of steel, well supported by concrete... say torus diameter 1000 - 2000 meters, tube diameter 2.5 - 4 meters (somewhat similar to a particle accelerator) - partial vacuum air or maybe hydrogen (just above air pressure) filled - passive maglev rails on the outer inner side of the torus ('inductrack') - ring-shaped (ringular, lol) heavyweight 'train' inside running at speeds of >150m/s... overall train mass, say, 10 - 50 million kg. The 'train' does not have to be a rigid ring. Any sense in this?

No dark mater? No sacramental bread?

Yes, I also think that maybe such setup would mostly heat the air. I asked this question because OP reminded me of my own dilemma I had some time ago - how to make sun heats water in a shallow pool faster... First idea was, of course, to make the pool interior black. But then I started thinking that maybe water surface is too reflective at certain angles, and thus making a thin non-glossy black foil cover could be a better solution. In any case, I don't know if in OP case there is direct sunlight at all...

"What if" question (for my personal interest): - What if the 'paddling pool' is very white and water is transparent - and the 'top cover' is black and not very insulating - and there is direct sunlight Would you still recommend removing the cover? That is, if there is direct sunlight, would you recommend covering the poll with some thin black non-insulating cover?

This Tesla car always confused me... It is considered both, a sports car and a green car. For me this is a funny contradiction. If a car is a sports car then it means it is not as economical as a car could be... To call something green, I suppose, it must be edged toward efficiency. (I might call Tesla a "green sports car" if you wish, but I would not use the more general "green car" term.) Should government pay people to buy electric sport cars? I suppose it depends on what is the intent... If the intent is fuel economy then the answer is "no". If the intent is to develop an alternate car technology then the answer is "yes". Hmm... Did you hear about this thing about light food... I read about it occasionally on various food-related internet portals: allegedly people tend to eat larger quantities of 'light'-designated food than ordinary food thinking that the light food is safe (but they overeat, taking in more calories than they would with ordinary food).... I am afraid such thing could happen with electric vehicles. Now we all buy sports cars - it is fine to have 600hp because it is green, isn't it? [unconnected to the above.... In my country government tend to pay a very large sum to a buyer of an electric/hybrid vehicle. But the overall fund is limited and so only a few lucky ones manage to get their car... I hate this... It would be much better if more people benefited for a smaller amount of money, but then the political-marketing effect would be much decreased, wouldn't it?]

A resistor connected to 120VAC will give you the same output power as the same resistor connected to 120VDC. This is how 120VAC is defined... The 120VAC has amplitude of about 170V.

I guess... if a creature doesn't have 'hands', it cannot build complex machines. And this is not (only) because it has no hands... IMO, a creature can be smart in various, not necesarily connected ways. Say, it can be good at communications and/or it can be good at technical stuff. But in any case, evolution must constantly have almost immediate feedback as it creates a complex brain. To successfully make a techical brain, evolution must develop hands in parallel. There is no much chance that evolution will remain on the technical-brain course if no positive feedback (benefit to that creature) was seen for one million years. So... my guess is that our dolphins will never be very good at working on a lathe.

How did you conclude/estimate this? (I am asking to learn).

Yes, what you are saying is all possible (but equaly speculative as is my post). (Note that the 'self-destructing' option is actually the A) option from my post.) I also think that there is possibility that maybe we are intentionally not contacted yet, but... If the intellignet life is so common then I speculate that there will be many fractions and opinions among them and hardly they would act in such disciplined way to successfully isolate us and mask their activity... On the other hand if the intelligent life is so rare, then we would be very very interesting to them - I guess they would actively seek for us (not because our WWW or other technological achivements, but because we are self aware intelligent creatures and this alone would then make us a rare gem)

I suppose, by 'intelligent' you mean human-level intelligence (which, BTW, I don't find easy to define). Because if you consider, say, dolphins 'intelligent' then there are many intelligent species even here on Earth. I see that some members doubt that human-level intelligence is rare in the universe - however, they speculate. IMO, if we stick to what we know, then I must agree with the OP statement: human-level intelligence is a rare thing, at least in the part of universe that we can probe. After all, if you encounter something only once in your lifetime, then it is a rare thing by definition. The rarity of human-level intelligence can be estimated from how long it took Earth's evolution to make one single example. While evolution re-invented many solutions many times during history, it was not the case with the human-level intelligence... (Compare this to the life itself - life was created almost 'immediately' after Earth was formed) The reason why human-level intelligence might be so rare is, IMO, because there is a wide gap where large and complex brains are just increased burden, but not yet powerful enough to effectively create helpful technology. It takes some serious luck for evolution to 'safely' walk this wide gap. You also ask about future of humanity (thanks, so I can continue to speculate)... I think there are three possibilities: A) We cease to exist, for any of many possible reasons. I tend to agree with claims that next <500 years might be criticial. B) A cyclical civilization - where at least several more cycles (ups and downs) will happen before either A) or C) C) We advance and spread through the universe - but possibly in very transformed form that many peopole today might not consider human civilization any more Regarding the C) option, here is how I see the future: - in less than 100 years we create artificially intellignet machines/computers that are both: capable to improve themselves and have 'a will to live'. - from then on, biological humans will not be able to follow, unless perhaps we somehow merge with our children-machines. - the 'evolution' moves to non-biological domain, zillions of different miniature machine 'spieces' are created (by machines) with different properties. Some intelligent, some maybe not (not having much intellignetce, but only a will to live).... The important thing is that this non-biological evolution happens at rate far faster than now. - in several decades these children-machines start spreading into universe virtally at the speed of light. So, where are they?

I just realized why Brits do not want to use metrics - it is because metrics is much more complex. Look at the following two diagrams: - simple version: http://en.wikipedia.org/wiki/File:Football_pitch_imperial.svg - complex version: http://en.wikipedia.org/wiki/Association_football#mediaviewer/File:Football_pitch_metric.svg But what stops Americans? (Warning: you too might be an American if you do not intuitively understand above diagrams)

I am wondering... If the thyroid cancer is 'easily' cured, does it mean that we can expect smaller-than-average number of death cases from thyroid cancer in the Fukushima region due to much better screening?

Thanks for referencing BIPM... a much more relevant source than Wikipedia. BIPM mentions newton meter and claims specifically it to be a compound unit: N m = kg m^2 / s^2. It is not easy for me to accept this, because if so then there is no difference between newton meter and joule: N m = J. In my mind, however, these are completely different things (For example, in vague terms... Joule is somehow 'integrative' - it does not exist in an infinitesimal small time scope, it is not a momentary value. Newton meter is somehow 'derivative', it is a momentary value.)... This brings me to your observation... I pondered on this... I can accept that if I write torque like T = 10 N m, I actually meant |T| = 10 N m. Thus, I can accept that units are always scalars. But this does not mean that newton meter, even if scalar, is equal to joule (for sure a scalar).... But notation, as suggested by BIPM, does not show this difference. I am not sure if BIPM claims 'N m' and 'J' are the same thing, or they just claim that we don't need to care about it while writing these units down (bacause it is a common understanding or something). Consider example: I make a value called 'specific toruqe'. This value tells what is the torque on each infinitesimally small portion across a hinged beam. The unit is Nm/m (newton meter per meter). Do you think this 'Nm/m' is the same as 'N'? I do not. But if one accepts BIPM notation, then it is confusing why we cannot shorten this m/m factor. Yes studiot, I understand this... and the question is why is this difference not reflected in BIPM notation (one newton meter is written as 'N m' or 'N*m' that suggests a dot product.) Yes, I would like Archimedes (although 'A' is already taken)

I have problem understanding Newton-metre unit (or should it be written in all-lowercase style: newton-metre? Or newton-meter perhaps?). I don't have the problem with the unit itself, but with the way the unit is written: N m (or even with a small central dot in between: N*m). According to Wikipedia, the newton-metre unit has a space between 'N' and 'm'. But this would indicate the 'dot product', wouldn't it? It seems to me that it would be better to write the Newton-meter unit all compact: Nm. This way 'Nm' is clearly a unique symbol, and not a compound unit. If you insist, I might accept: N x m (indicates vector product). Now, in my software (Math-o-mir) I implemented the newton-metre as a compound unit only because Wikipedia says so. But I am bothered with this and I am about to discard Wikipedia teaching. First I would like to hear what you can say about it. Thanks.

Yes. As far as I know, you are correct. a) Note: C = εA/d might not work for very big 'd' (relative to 'A'). Thus if you spread the plates to infinite distance you should not obtain infinite V and infinite E. b) What you say is true in first approximation. I however suspect that in a more detailed picture, the dielectric might heat up for just a little bit when inserted/removed. So if you keep inserting/removing it, a thousand times in a second, maybe you should count for some additional energy loss. BTW, your thinking is clear and I like it. I hope you will stay on the forum.

Yes, I was just thinking about it. I believe there is some sort of leveraging effect... Even a small difference in biological predispositions/interests will be highly intensified in our brains (people tend to segregate, put into niches, make stereotypes - I guess this is a way our brains simplify the world) and will then lead to large cultural differentiation.

I must admit that I tend to lean toward elfmotat side somewhat: lack of interest from female side. The magnitude of this difference is so big that I would be surprised (and sad) if it is only cultural... Because if it is only cultural, then our western society must be deeply rotten and dishonest (possibly not that much more 'civilized' than, say, fundamentalist Taliban society where such gender-role differences are openly forced). Anyone with some slight interest in science can join discussions here on SFN. Many posters here do not work in science field, but still consider this forum as a great way to spend some free time. However there are only very few female posters. The female crowd prefers other ways to spend free time... Okay, I know many of you will argue that women are "culturally convinced" that SFN is not a place for a decent lady. But this is a scary thought, don't you think? SFN is just an innocent thing - why would our society prevent women to join some innocent, unimportant discussion if interested in it? Therefore, this 'patriarchal conspiracy' theory does not seem like a likely explanation to me. It is just too complex, IMO. I see two other possible reasons: - women do not like to fight with men in fields where men are very passionate about. This is why women choose to just move away. - or, women just do not have that much interest in STEM as men do. In both cases, it seems to me, that the difference is, at least in part, biologically determined. (BTW, I noticed in my country, there is large increase in numbers of girls taking STEM courses in universities. This happened gradually over last 10 years. One might argue that finally our society is generating equal opportunities for both sexes and so finally girls are 'allowed' to study what are they really interested in... However I found no much increase in STEM-forums discussion by those STEM-girls. Makes me wonder what is the real reason so many girls join STEM courses - is it because this is what really interests them, or is it because of increased status, salary and probability to find a job.)

Oh, I think both of you made most excellent finds. Thanks.... When I was I kid I was thinking that Euler is maybe wearing a pajama. In the meantime I learned that portraits usually show the best outfit a person had.

Not a scientific one, but might still be hard to answer.... what is this head garment depicted on the 1753 Leonhard Euler portrait by Emanuel Handmann? http://en.wikipedia.org/wiki/Leonhard_Euler#mediaviewer/File:Leonhard_Euler.jpg I always wondered.

This might work, although probably very poorly (not efficiently) and possibly even dangerously to your equipment, as Acme said.... As you probably guess yourself, to make this simple diode-circuit idea work, both sources (turbine and solar) must be capable to provide higher voltage than that of the charged battery (if, as I understand, you want both sources to contribute simultaneously). Note that, while charged, a battery might increase its voltage above its nominal value, so it might happen that one of your sources will stay below this level and will not contribute. You will learn that charging batteries efficiently is not easy. Take datasheets of your equipment (solar, turbine and battery) and determine their optimal working/charging points/curves. You will see that these probably do not match to each other. Therefore you should build a charge controller that will keep all of your equipment happy, and at the same time the controller itself must be efficient. So... I would... take two diodes and try it ASAP

Is this about female parts, or am I in a wrong thread again?

No, what I meant is: A typical rotor of an induction motor has the highly conductive cage (that is, an array of closed loops). Strong currents are induced in the cage. Why then is so important to prevent eddy currents in the rotor - those eddy currents would simply add to the cage current. One might think that eddy currents are bad because they are flowing through a material (iron) that has higher resistance than the cage (copper/aluminum)... But it is not that obvious (at least not to me) - I know that, in first approximation, a higher resistance of the cage does not reduce the motor efficiency (it only makes it 'softer'). Therefore it is not obvious why would eddy currents in rotor decrease motor efficiency. It might be that, without a laminated rotor, eddy currents would not only be limited to travel in the same 'plane' as cage currents, but may also travel perpendicular to it (say, into the depth of the rotor) and that this is the part of eddy currents that needs to be eliminated.

You answered most of your questions... indeed, eddy currents are induced the same way as the current inside bar conductors - the iron is conductive (although not nearly as much as copper or aluminum) and some circular currents will be generated inside if iron is immersed into a changing magnetic field. Those currents will dissipate energy (heat) over the iron resistance... If instead of one large iron piece, you put together many small electrically isolated pieces of iron, the dissipated energy will be smaller despite the fact that the overall volume of iron is the same [The above can be shown by some easy math: consider one square wire loop 2x2 inches in a changeable magnetic field - the wire resistance is proportional to the wire length, and the EMF generated inside the wire is proportional to the loop surface area. The power dissipated by the loop is EMF^2/R... What if you replace this 2x2 loop with 4 loops of 1x1 inches? A single 1x1 wire loop has 2 times less length (resistance), but has 4 times less surface area (EMF) - this means that the power dissipated inside one 1x1 inch loop is 8 times smaller than in one 2x2 loop. Even if you combine power dissipation from all 4 small loops, the dissipation is still only half of the large loop.] Both stator and rotor of an induction motor are laminated. You might wonder why rotor needs lamination as it already has short-circuited loops around it. I must admit that I don't have the right answer. I know that we prefer motors with 'harder' torque curve. A motor that does not have a copper/aluminum cage, but only a solid-piece-iron rotor, would be ridiculously 'soft' (its speed would vary very much with load variation) - therefore we, in practice, must have the cage. It is possible that in combination with the cage a non-laminated rotor would decrease efficiency, but I never tried that math... Can anyone else help us on this? [Observe: it seems to me that in first approximation the increased cage resistance does not decrease induction motor efficiency - in fact, motors were once speed-controlled by varying its rotor 'winding' resistance. However, in a more detailed model of a motor, I guess, increased cage resistance would somewhat decrease motor efficiency and thus a solid-piece-iron rotor would be somewhat less efficient.]