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  1. 09 Sep '14 14:41 / 5 edits
    http://phys.org/news/2014-09-tabletop-motor-principle.html

    "...."We have proven the concept of a new motor that uses electric fields rather than magnetic fields to transform electricity into a rotary force,"
    ....
    The distinction may sound minor, but it could solve a number of practical problems while saving money,

    Actually, the concept is not entirely new: Benjamin Franklin and others described and built motors based on electrostatic forces back in the 18th and 19th centuries, but none achieved practical operation. Since the widespread adoption of electric motors a century ago, magnetism has been the only practical source of rotation. Magnetism is easier to exploit than electrostatic fields due to the properties of naturally occurring materials and simple engineering techniques. However, new advances in materials, mechanical engineering and advanced manufacturing may enable electrostatic motors.

    In 2011, while Ludois was finishing a Ph.D. thesis at UW-Madison, he realized that instead of relying on magnetic fields, he could achieve a similar result by manipulating electric fields to create a motor based on electrostatic attraction. The new technique, he realized, could deliver major advantages in weight, material cost, operating efficiency and maintenance requirements.

    In the motor on display, nested stationary and rotating plates are held hairs-width apart by a unique air-cushioning strategy. An electric voltage delivered to the fixed plates creates an electrostatic field that attracts the rotating plates in a way that forces them to spin.

    The breakthrough relies on electronics that precisely control a high-voltage, high-frequency electric field and fluid mechanics to keep the surfaces close without touching. "Nothing is touching, because you are using electric fields to couple the stationary and rotating parts," Ludois says. "There is no contact, and no maintenance.

    Because motors and generators are essentially mirror images of each other, the invention may first meet the market in the form of a generator for wind turbines,
    ....
    By saving weight and materials, and boosting efficiency, the new design should give the company a bottom-line advantage. The new design avoids the use of precious "rare earth" metals and substitutes aluminum for the more expensive copper found in magnet windings of conventional motors and generators.
    ...
    ..."

    I had independently once thought roughly along the same lines but sadly didn't have the means to take the idea any further.

    I note that they mention "boosting efficiency" above but wonder if they can really boost energy efficiency by getting rid of the magnets because I happen to know that the most energy efficient electric motors and generators to date are a vary impressive 98% energy efficient which I assume would be rather hard to beat!? I know that often the main loses from conventional motors come from the resistance in the magnetic windings but, at the cost of reducing power density and also more manufacturing cost of the windings, it is simple enough to replace the windings with thicker ones that produce very little lose.
  2. Standard member sonhouse
    Fast and Curious
    11 Sep '14 11:18
    Originally posted by humy
    http://phys.org/news/2014-09-tabletop-motor-principle.html

    "...."We have proven the concept of a new motor that uses electric fields rather than magnetic fields to transform electricity into a rotary force,"
    ....
    The distinction may sound minor, but it could solve a number of practical problems while saving money,

    Actually, the concept is not entirely n ...[text shortened]... gs, it is simple enough to replace the windings with thicker ones that produce very little lose.
    And that doesn't even take into account superconducting motors which are now in use by the US navy, motors in the 100,000 HP area about 1/3 the size and weight of conventional electrics.

    I get the feeling that article was meant to attract venture capitalists and maybe the motor would even work for small hp ratings but I doubt it would work at the 1000 hp level.

    I also doubt the efficiency ratings, you will note they didn't give out any figures either on actual efficiency or power rating of that motor.

    I also wonder if it would need air to keep the parts separated, it might short out if used in a vacuum. Not sure though.
  3. Standard member DeepThought
    Losing the Thread
    12 Sep '14 00:43
    Originally posted by sonhouse
    And that doesn't even take into account superconducting motors which are now in use by the US navy, motors in the 100,000 HP area about 1/3 the size and weight of conventional electrics.

    I get the feeling that article was meant to attract venture capitalists and maybe the motor would even work for small hp ratings but I doubt it would work at the 1000 h ...[text shortened]... d need air to keep the parts separated, it might short out if used in a vacuum. Not sure though.
    Depends, it comes in a casing so the casing can hold the discs apart in which case a vacuum will be better. Niggles for me are that it requires a high frequency electric field and computer control. The great advantage of magnetic motors is the (relative) simplicity. A point though is that they are unlikely to be improved by superconductors, as they don't rely on a long cable repeatedly looped around some kind of core to make the magnetic field. If I'm right about that then if the theoretical (zero resistance) efficiency is the same as for a magnetic motor one should get the same effectiveness as a superconducting motor (generator) without the need for liquid nitrogen.
  4. Standard member sonhouse
    Fast and Curious
    12 Sep '14 07:28 / 2 edits
    Originally posted by DeepThought
    Depends, it comes in a casing so the casing can hold the discs apart in which case a vacuum will be better. Niggles for me are that it requires a high frequency electric field and computer control. The great advantage of magnetic motors is the (relative) simplicity. A point though is that they are unlikely to be improved by superconductors, as they do ...[text shortened]... same effectiveness as a superconducting motor (generator) without the need for liquid nitrogen.
    I didn't get the part about high frequency. What does that mean exactly? I think of 'high frequency' from my work in the RF field as something in the gigahertz range.

    They clearly are not going to use that high a frequency, I imagine the actual frequency the use to be (my guess, with no further explanation) of 30 or 40 Kilohertz.

    In terms of modern switching power supplies, that is now a low frequency, and the real ones are coming out using several hundred megahertz and bringing the size and weight of a power supply down to a few square cm where they were before say 100 X 50 X 100 cm or so.

    I can't imagine this kind of motor running even 100 megahertz much less the 300 mhz used in the latest switching power supplies.

    So the idea of a 'high frequency' field sounds like a misnomer to me.

    Magnetic motors like the 3 phase ones I deal with on a daily basis at work, get over 90% efficiency running just fine on 50 or 60 hertz.

    There are some magnetic motors running on 400 hertz, military stuff, that might get a bit more efficiency but like Humy said, some electric motors are approaching 100% efficiency already, within a couple of percent of that figure so to beat that you can't gain more than 2% and the talk about nothing touching, that already happens in magnetic motors, there is no longer a need for even the graphite brush to touch a commutator like in the old style motors, the only thing touching other parts now are the bearings holding the rotor in place and that won't go away just because this motor is running on electric fields rather than magnetic.

    I expect this kind of motor to be limited to a few horsepower at best and have only a niche use, maybe in spacecraft, underwater rigs, stuff that needs lighter weight than magnetics. The dude talks about no maintenance but I can say for certain the bearings holding the rotor will wear out eventually, NOTHING will make THAT part totally maintenance free, granted, they last for years but they still go out.

    The only maintenance free technique I know of is a rotor on a magnetic bearing in a vacuum where you can store energy in the kinetic energy inherent in a spinning rotor. THAT would be a much better shot at true zero maintenance than ANY motor needing bearings. Of course that is only an energy storage system and has limitations due to the thing flying apart at much higher than 100,000 RPM or so.

    Clearly in order to get higher power in some kind of electric field motor, you either get the parts closer together or use higher voltages.

    Both ways increases the local electric field strength and there is a limit as to how much insulating quality you can get from that concept.

    For instance, supercapacitors are exceeding farad ratings now, a significant amount of energy storage compared to 30 years ago. The only catch is they can't run over a couple of volts so in order to even run at car voltages, 14 volts or so, you need to stack 10 of these things in series but of course, there goes your farad rating. If it was 1 farad, now stacked in series, you get 1/10th of a farad at that 14 volt rating.

    So then in order to get back up to one farad, now you need ten of THOSE stacked side by side in parallel to get your one farad you needed for whatever project you were working on. So now that requires 100 separate capacitors to get that 14 volt at one farad. It gets out of hand pretty quickly.

    I saw one of these supercaps at walmart the other day, 1/2 farad at car voltages, it cost about 90 dollars just for that part.

    So if you needed 10 farads.....

    So they will run into the same kind of problems with this motor, I fear.