[HN Gopher] Electrostatic motors reach the macro scale
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Electrostatic motors reach the macro scale
Author : namanyayg
Score : 94 points
Date : 2024-08-21 11:43 UTC (11 hours ago)
(HTM) web link (spectrum.ieee.org)
(TXT) w3m dump (spectrum.ieee.org)
| imbusy111 wrote:
| I couldn't get past the first two paragraphs without the article
| losing all credibility.
|
| > And although there are many different kinds of electric motors,
| every single one of them, from the 200-kilowatt traction motor in
| your electric vehicle to the stepper motor in your quartz
| wristwatch, exploits the exact same physical phenomenon:
| electromagnetism.
|
| Well, basically your whole experience of the world is just
| electromagnetism, nothing more. And electrostatics is part of
| electromagnetism theory.
|
| > In some applications, these motors could offer an overall boost
| in efficiency ranging from 30 percent to close to 100 percent,
| according to experiment-based analysis.
|
| What practical electric motor is even close to 30% efficient?
| This is laughably low.
|
| Edit: it's BOOST over the current efficiency.
| mjhay wrote:
| > What practical electric motor is even close to 30% efficient?
| This is laughably low.
|
| I think that means 30% over existing performance.
| imbusy111 wrote:
| Got it, missed that part.
|
| Still, assuming efficiency can't get past 100%, 100% boost
| can be achieved only on something that already has only 50%
| efficiency.
| kraftman wrote:
| I assume that they are looking at in laymans terms, and
| saying that if an electromagnetic motor is 80% efficient,
| an electrostatic motor could increase efficiency of the
| remaining 20% by 30% to 100% (86-100% total efficiency).
| Not that it makes any sense, but I think that was their
| intention.
| exe34 wrote:
| i wish people would just always use percentage points and
| never deviate from that.
| DoctorOetker wrote:
| I wish people would just explicitly state they can't
| believe their eyes that 100% efficiency can be
| asymptotically reached, i.e. no known law of the universe
| prevents us from building electromotors that are 90%,
| 99%, 99.9% etc... absolute efficient.
|
| Then we could just remind them that Carnot efficiency
| does not apply to electrical / mechanical energy
| conversion.
| DoctorOetker wrote:
| This is absurd, detecting that a wrong interpretation is
| inconsistent (because it would result in overunity
| violation of energy conservation) and instead of rejecting
| the misinterpretation of the parent, concocting an even
| more convoluted interpretation.
|
| All because people refuse to believe 100% energy conversion
| between electromagnetic domain and mechanical domain is
| impossible?
|
| Turbosets have been doing this for a long time already, the
| Carnot efficiency limit does not apply to non-thermal
| energy conversions...
| DoctorOetker wrote:
| THey are in fact talking about absolute efficiency.
|
| Conventional electromotors are designed with high
| efficiency... at a certain range of RPM and torque. For lower
| RPM's permanent magnet electromotors suffer dramatic
| decreases in efficiency and torque, unless you use a gearbox,
| which also produce heat due to frictional loss.
|
| These electrostatic motors can achieve quasi reversible
| performance (i.e. asymptotically close to 100% efficient, not
| a violation of thermodynamics, since neither electrical nor
| mechanical energy are thermal forms of energy).
|
| Turbosets also reach nearly 100% conversion efficiency.
|
| Electrostatic motors started their niche with miniature
| motors, since they were more compact and it becomes
| progressively harder to miniaturize winding coils. Where a
| simple electrode surface would be more space efficient.
|
| Pay attention to Macroscale in the title, its these
| miniature-niche low RPM motors slowly capturing larger torque
| and higher RPM lebensraum from the gearboxed permanent magnet
| electromotors.
| aidenn0 wrote:
| Yeah, that was some poor quality for IEEE. I'm pretty sure they
| confused "electromagnets" and "electromagnetism."
|
| As far as the "boost in efficiency" sentence, I reread the
| paragraph around it several times and still have no clue WTF
| they are trying to say.
| plorg wrote:
| Spectrum is aimed at the general public and its articles are
| often university press release quality.
| DoctorOetker wrote:
| > I reread the paragraph around it several times and still
| have no clue WTF they are trying to say.
|
| some advice: next time you don't understand some article,
| consider the possibility that it is not a case of:
|
| > Yeah, that was some poor quality for IEEE. I'm pretty sure
| they confused "electromagnets" and "electromagnetism."
|
| but that the problem might be your lack of understanding that
| you already detected. it's a press article, it can't teach
| you an undergraduate course in physics condensed to a few
| paragraphs of text...
| aidenn0 wrote:
| I have taken several undergraduate courses in physics. If
| you have some clue what they are saying with:
|
| > In some applications, these motors could offer an overall
| boost in efficiency ranging from 30 percent to close to 100
| percent
|
| please illuminate. Brushless DC motors across a wide
| variety of applications already exceed 50% efficiency.
| Perhaps there are applications in which they cannot reach
| 50% efficiency, so a 100% boost in efficiency would be
| possible.
| maicro wrote:
| Also, piezoelectric motors are a thing - sure, they're super
| tiny and for specific purposes (very fine movement), but beyond
| the fact that they use electricity to generate the vibrations
| that they then use for movement, I don't think it would be
| considered "electromagnetic".
|
| Actually, in that same vein would be a Nitinol or similar
| "shape-memory alloy" motor - run power through it to have it
| change shape, then remove power to let it relax.
|
| So yeah, unless I'm misremembering or grossly misusing terms,
| "piezoelectric" and "thermoelectric" electric motors both
| exist...
| doe_eyes wrote:
| The sustainability angle is a bit suspect, although of course
| it's smart of them to make that pitch. Many large motors don't
| use permanent magnets, and even for the ones that do, neodymium
| isn't all that rare and is mined in the US. Most of our copper
| comes from friendly sources too (US, Chile, Peru, Mexico,
| Australia). When we talk about sustainability for EVs, I think
| the main concern is batteries, not motors.
|
| But the most interesting (and problematic!) part of their design
| is the use of a dielectric liquid to increase field strength.
| They don't give any specifics, but reliability and weight issues
| aside, I'd imagine that drag-related losses would get significant
| at high RPM. Maybe the point is to go slow?
| throwway120385 wrote:
| How many RPM is "high?" I have a router that can go up to
| 40,000 RPM, reciprocating sander that goes about 2000 RPM, et.
| al. But if I want to actually do good high-quality sanding,
| lower RPM with higher momentum is better.
|
| Also how big is a "large?" motor? Are we talking tens of
| horsepower, or single-digit horsepower? My drill press's motor
| is about 2 horsepower and my router is about 2.5 horsepower,
| for reference.
| tomcam wrote:
| Unfortunately your drill press is now manually driven. When I
| found out it was 2 horsepower I "borrowed" it from your shop
| and turned it into a tiny go-kart
| SoftTalker wrote:
| > Also how big is a "large?" motor?
|
| The motors discussed in the article were described as
| "fractional horsepower"
| DoctorOetker wrote:
| that question was obviously not directed to the authors of
| the article, but to doe_eyes:
|
| > Many large motors don't use permanent magnets, and even
| for the ones that do, neodymium isn't all that rare and is
| mined in the US.
|
| What doe_eyes is referring to are motors or generators
| where the magnetic fields are generated by currents through
| windings. Under certain conditions it is more LCO efficient
| to generate magnetic fields that are stronger than even
| Neodymium magnets can supply.
|
| Your dig about fractional horsepowers is thus misplaced.
| Panzer04 wrote:
| Most motors connected directly to AC power are likely to be
| induction motors, which require no special magnets. From
| fans, to fridges, to AC etc. Because they don't need drive
| electronics they can be very cheap compared to BLDC and the
| like, which would need power conversion from AC.
|
| Turbine generators typically use Synchronous motors, which
| often use DC to generate the opposing magnetic field
| ("exciters"), though they can also use permanent magnets for
| the same effect.
| skybrian wrote:
| They seem to be looking for low RPM, relatively higher torque
| applications. Maybe like a stepper motor? It's claimed that you
| don't need a gearbox.
|
| "Ability to hold a position with virtually no energy losses"
|
| https://www.c-motive.com/technology/
| Animats wrote:
| That could be useful for robotics. Gear trains in robots are
| a headache.
|
| The ability to hold a position without much power is a big
| win. Steppers need almost full power when stationary. But
| that's probably because these electrostatic motors are run as
| servomotors, with only as much power applied as is needed at
| the moment.
| xeonmc wrote:
| Could it also lower the cost of simracing direct drive
| wheels?
| skykooler wrote:
| While stepper motors produce torque based on the current
| flowing through them, electrostatic motors produce torque
| based on the voltage applied across them. As long as the
| motor is stationary, the voltage does not need to change,
| which means that there is no additional power needed to
| hold position even against an external force.
| DoctorOetker wrote:
| I am not correcting you since what you say is correct,
| but looking at other comments I thought it would help to
| expand a bit for the other readers.
|
| In your static torque situation, the electrostatic motor
| draws 0 current at your constant voltage. And thus 0
| power (instantaneous power is instantaneous voltage times
| instantaneous current).
|
| Whereas a conventional electromotor would be called
| stalled in such a situation, in which case the coils of
| the electromagnets in the motor behave like inductors.
|
| With the result that for a constant applied voltage the
| current increases linearly with time, until the parasitic
| winding resistance of the coil limits the current.
|
| This means a stalled electromotor will consume energy
| without performing mechanical work, and all this energy
| will be dissipated as heat developed over the winding
| resistance of the coils.
|
| If that heat cannot escape the electromotor fast enough,
| the insulation of the electromotor coil will be
| compromised, and you gradually loose loops of the coil as
| they short, further decreasing the total winding
| resistance (since the shortcut means a loop of single
| turn winding resistance less), which increases the
| current, and thus the power into the motor.
|
| This thermal runaway eventually destroys your motor.
|
| That is why you should immediately shut of electric
| motors as soon as you detect a stall condition (typically
| you will hear mains hum as the stalled motor is pounding
| whatever stalls the motor at twice the mains line
| frequency), and allow it to cool, while you resolve the
| cause of the stall condition.
|
| So next time you use your bar blender in the kitchen, and
| you notice its struggling, or worse blocked, immediately
| stop the motor / back off, or let it cool. Don't just
| press the "boost" button for prolonged durations unless
| you like buying blenders over and over.
| DoctorOetker wrote:
| They probably mean sustainability due to frictional heat losses
| in drive trains / gear boxes.
| spankalee wrote:
| I wonder how well the dielectric fluid holds up if the motor is
| spinning at several thousand RPMs for dozens of hours?
| pragma_x wrote:
| I suspect heat is a limiting factor here.
|
| Also, if the vanes of the rotor are spinning _in_ the fluid,
| doesn't this also make it a torque converter? If so, then
| suddenly stopping the motor could be catastrophic depending on
| how much kinetic energy is in the system at the time.
| marcosdumay wrote:
| From the context, I'd guess they want their motor to spin at
| single digit RPMs, not thousands of them.
|
| That's the stuff magnetic motors are bad at.
| imtringued wrote:
| Yeah, all you have to do to get a conventional motor to spin
| faster is to make it longer. When people show off their high
| speed motors they are actually showing off the easy part. It
| is much harder to get high torques, because you need to
| increase the number of poles and the diameter.
| DoctorOetker wrote:
| utter nonsense.
|
| small RPM but high torque electromotors are made by making
| them longer, make a motor axially longer by a factor L, and
| the torque will multiply by L, while the volume also
| increases by L.
|
| suppose we followed your advice and multiplied the diameter
| by the same factor L to get the same increase in torque,
| now the volume is multiplied by L squared!
| ajb wrote:
| "Benjamin Franklin built and demonstrated a macroscopic
| electrostatic motor in 1747," says Krein. "He actually used the
| motor as a rotisserie to grill a turkey on a riverbank in
| Philadelphia" "
|
| I want to know more about Ben Franklin's electrostatic turkey
| roaster
| riedel wrote:
| Related post on hackaday: https://hackaday.com/2017/10/03/ben-
| franklins-weak-motor-and...
| ajb wrote:
| Cool thanks!
| lawlessone wrote:
| >He actually used the motor as a rotisserie to grill a turkey
| on a riverbank in Philadelphia
|
| Benjamins aeolipile?
| PaulHoule wrote:
| This book describes a family of devices that work both as
| electrostatic generators _and_ motors
|
| https://www.amazon.com/Electrostatics-Exploring-Controlling-...
| Animats wrote:
| "C-Motive team succeeded in producing an organic liquid
| dielectric with low viscosity and a relative permittivity in the
| low 20s." Nice.
| trebligdivad wrote:
| I'm curious if that's any use in variable capacitors; heck the
| picture of the cross section looks like a variable capacitor.
| (Except I guess the discs are non-continuous)
| DoctorOetker wrote:
| a variable capacitor will present some mechanical resistance
| and thus conversion of mechanical energy into heat, at low
| speed this is negligible (unless you need the system to
| behave reversibly), but if you are going to rotate your
| variable capacitor at speeds where frictional heating becomes
| an issue (perhaps the generation of heat limits your
| application, or the loss of mechanical energy limits your
| application) then yes these types of dielectrics will be of
| interest to you.
|
| Otherwise, conventional dielectric can be more compact for
| the same maximum energy storage in the capacitor, since no
| simultaneous optimization on viscosity was performed in their
| selection, resulting in a wider range of dielectrics being
| viable.
|
| How fast do you plan to turn your variable capacitors?
| ta988 wrote:
| This will likely be a maintenance hell when the liquid ages and
| get particles in it.
| mikewarot wrote:
| The cool thing is that this motor shouldn't take any power to
| maintain a static force against something. (In the same sense
| that a table takes 0 watts to hold something above the floor)
|
| Only insulation resistance should be the loss at very low speeds.
| bgnn wrote:
| static part of electrostatic!
|
| I'm curious about their leakage current though
| DoctorOetker wrote:
| To compare different dielectric liquids you would want to see
| the dielectric spectroscopy plots:
|
| https://en.wikipedia.org/wiki/Dielectric_spectroscopy
|
| And the different types of viscosity vs temperature plots.
| buildsjets wrote:
| There are other types of motors that rely neither on magnetic
| fields nor electrostatic fields, for example the ultrasonic motor
| which is commonly used as a focusing actuator in high end camera
| lenses. They use the piezoelectric effect to cause a
| semiconductor material to physically deflect and "push" the
| rotating part around in circles... or in a line in the case of a
| linear USM.
|
| https://www.piezo-motor.net/
|
| https://www.meddeviceonline.com/doc/what-are-canon-s-linear-...
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