[HN Gopher] C-Motive's electrostatic motors use printed circuit ...
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C-Motive's electrostatic motors use printed circuit boards instead
of magnets
Author : Jeff_Brown
Score : 60 points
Date : 2024-10-20 17:02 UTC (5 hours ago)
(HTM) web link (www.c-motive.com)
(TXT) w3m dump (www.c-motive.com)
| milesvp wrote:
| I've been doing pcb design around sensor coils for capacitive
| sensing. My engineering team has been playing with similar ideas
| around printing coils for other electro magnetic purposes. Motors
| are an obvious usecase. Good to see others doing similar stuff
| with printed circuit boards. It takes a way a lot of complexity
| and pcb processes have some pretty good precision these days.
| snek_case wrote:
| I'm fairly ignorant about motor design, but my immediate
| thought was "isn't this going to exert pulling forces on the
| PCB traces?". Seems like that would limit how much torque your
| motor can exert? Which I guess isn't necessarily a problem for
| many applications.
| skykooler wrote:
| The forces are pretty much shear forces in the plane of the
| PCB, which traces can handle reasonably well. Also, the
| amount of force per trace is very small - the motor only has
| significant torque because there are many traces per PCB
| multiplied by many PCBs.
| magicalhippo wrote:
| I recall watching Carl Brugeja on YouTube some years ago making
| tiny motors using PCB for the coils, like this[1] for example.
| Like you say idea is hardly groundbreaking, but there's a lot
| of details to optimize as with any non-trivial engineering
| project.
|
| [1]: https://www.youtube.com/watch?v=oa6sP-joAr8
| amelius wrote:
| Not a big fan of the dielectric fluid these motors have to be
| filled with.
| giantg2 wrote:
| Why?
| tonyarkles wrote:
| Not the person you asked but there's a few reasons off the
| top of my head:
|
| - weight
|
| - leaks: liquids are always a hassle in things that move. The
| liquid wants to escape and will do so at the first
| opportunity.
|
| - serviceability: if there is a leak and a significant loss
| of fluid, this doesn't sound like something I can just go
| pick up at the hardware store like motor oil or hydraulic
| oil. I'm curious what it is... they simultaneously call it a
| commodity fluid but also proprietary.
| giantg2 wrote:
| "- weight"
|
| They don't post any specs, but it's supposed to be smaller
| than traditional motors. If it only needs a small amount to
| fill small gaps between disks, it might still be lighter
| than traditional motors. This is especially true if the
| PCBs are significantly lighter than windings and magnets.
|
| "- leaks: liquids are always a hassle in things that move.
| The liquid wants to escape and will do so at the first
| opportunity."
|
| Sure, but this seems like a small concern when we consider
| that any mobile electric motors require batteries and most
| of those contain sealed liquid. Even things like bearings
| in cars are sealed these days.
|
| "- serviceability: if there is a leak and a significant
| loss of fluid, this doesn't sound like something I can just
| go pick up at the hardware store like motor oil or
| hydraulic oil. I'm curious what it is... they
| simultaneously call it a commodity fluid but also
| proprietary."
|
| Sure, if you have an oil leak in your ICE car today, you
| can't just go get oil, you first have to fix the leak.
| Don't forget that many transmissions for cars today get
| filled with "lifetime" fluid and are sealed. This, like the
| other concerns, is not likely to occur frequently and is
| consistent with existing paradigms.
|
| I'd be more concerned with what it is rather than it simply
| being there. Like is it flammable, acidic, caustic, or
| hazardous in some other way?
| bobim wrote:
| The dieletric oil in transformers is both toxic and
| flammable, causing a lot of damage when they start burning.
| If an alternative, safer fluid existed it would be a
| massive market.
| giantg2 wrote:
| I guess it depends on what dielectric constant they need
| and the serviceability. Even deionized water can be a
| dielectric. I think Novec makes multiple non-toxic non-
| flammable dielectric too.
| adrian_b wrote:
| Whatever they are using, it is absolutely necessary.
|
| The reason nobody has used high-power electrostatic motors is
| that they require high electric fields, which would cause the
| electric breakdown of air and of most fluids. In contrast, the
| normal electromagnetic motors use high magnetic fields, which
| do not cause the breakdown of air, so they do not need
| immersion in an insulating fluid.
|
| It is likely that the fluid used by them is some kind of
| fluorinated hydrocarbon, as those have high breakdown fields.
| Therefore leaks from such a motor are undesirable, so it would
| be interesting to know how do they prevent leaks between the
| rotating axle and its bearing. Rotating seals can never be
| perfect, as the users of Wankel motors must be aware. The main
| reliability problem of the Wankel motors has also been the
| rotating seals.
|
| I assume that nobody has tried before to make such motors
| because nobody has found a way to prevent the leaks until now.
|
| Perhaps the motors are intended to work only with the axle
| pointing upwards, in which case gravity would prevent the
| leaks.
| deepnotderp wrote:
| There are new dielectric refrigerants that aren't as
| polluting, but they're more expensive
| inciampati wrote:
| Extremely high value analysis! Probably why we aren't seeing
| an announcement for a motive product release.
| giantg2 wrote:
| "Rotating seals can never be perfect,"
|
| No seal is perfect, everything can deteriorate. Why would the
| seals need to rotate like a Wankel? I think this would be
| more like the end seals on traditional automotive
| transmissions. Leaks aren't really that common of a problem
| there.
|
| There seems to be a lot of different dielectric fluid
| options. It seems flourinared hydrocarbons are increasingly
| being replaced by other options. It's possible their
| proprietary fluid is something else. It would surprise me if
| their fluid is highly flammable.
| lbourdages wrote:
| Fishman has been doing these with guitar pickups for several
| years now. It's supposed to allow for greater consistency and
| also make it possible to do some stuff that couldn't be done with
| an actual coil of wire.
| Animats wrote:
| Electrostatic microphones have been a thing for a long time, so
| that's not unexpected. But it's not a power application.
| moffkalast wrote:
| What kind of stuff? Isn't just everything possible with FOC on
| BLDC motors?
| karlkloss wrote:
| A lot of blabla, no technical data. Suspicious.
| raphman wrote:
| Nice. I like the short paragraph on "Why hasn't anyone done this
| before?" at the bottom of the page.
|
| tl;dr: concept very old; C-Motive combined incremental
| improvements
| giantg2 wrote:
| I wish they had some examples of what RPM, torque, weight, and
| size specs were for a few possible applications. They seem to
| emphasize low RPM, but is that 200 RPM or 2000RPM? With other
| electric motors being capable of 10k-20k RPM, the "low" RPM
| mention is very vague.
|
| If it's capable of up to about 3000 RPM, and it doesn't weigh too
| much it could be interesting as an ultralight aircraft power
| plant.
| marcosdumay wrote:
| It's an electrostatic motor, so expect peak performance at
| close to 0 RPM. It probably won't work well at 1k RPM, but
| whether "too high frequency" for it is closer to 10 RPM or 100
| RPM isn't clear.
|
| There's a video with some waves in unlabeled axis. I didn't
| watch it.
|
| Anyway, it's almost certainly not aimed at aircraft propulsion
| or power generation. You may want something like it for
| robotics, but last time a paper from them circulated around
| here, they seemed to be focusing on instrument actuators and
| chip fabrication.
| mppm wrote:
| Their applications pages mentions wind turbines and
| automotive applications and promises increased efficiency vs
| conventional motors. That would require maintaining 90%+
| efficiency at well over 1k RPM. But no specs anywhere, so
| hard to tell whether this is real.
| giantg2 wrote:
| I don't think it was really for automotive applications. It
| said something like "low speed vehicles". Made me think of
| something like golf carts or maybe ATVs. Of course without
| a gearbox, the biggest factor would be what wheel diameters
| are used since that would be the main ratio with revs per
| mile.
| marcosdumay wrote:
| TBH, I didn't think about low rotational speed wind
| turbines. Yeah, it may be a big thing for those.
|
| "Electric drivetrains" can mean anything from an excavator
| moving at 5km/h with 3m large wheels in a frequency of less
| then 0.2Hz up to extreme race RC vehicles, at 100km/h with
| 5cm wheels at ~100Hz. A car wheels go barely over 1k RPM,
| but I don't really expect them to do anything useful for
| those.
| Animats wrote:
| The C-Motive guys have PR all over the web.
|
| Electrolytic capacitors can have far more capacitance than air
| capacitors. That's the basic concept here.
|
| Here's their patent.[1] Just scroll through the drawings and
| you'll see how it works.
|
| Here's the key concept: _" Numerous aspects of the present
| disclosure cooperate to increase the breakdown field strength
| 8406, and / or adjust (e.g. , flatten) the field strength
| trajectory such as : the permittivity of the dielectric fluid; a
| selection of fluid constituents to maintain a permittivity
| profile related to operating temperatures; protection of the
| dielectric fluid from impurities, presence of water, and / or
| presence of gases ; providing a surface smoothness of the
| electrodes 8402, 8404 (or portions thereof), related surfaces,
| and/ or a housing inner surface ; rinsing / removal of particles
| and / or impurities (e.g., from manufacturing residue, etc.);
| provision of a surface treatment on at least a portion of an
| electrode, and / or on a surface adjacent to the electrode,
| including varying surface treatments for different electrodes;
| provision of a coating on at least a portion of an electrode and
| / or on a surface adjacent to the electrode, including varying
| the coating for different electrodes; provision of a surface
| treatment and / or coating on a component at least selectively
| contacting the dielectric fluid (e.g., a housing inner surface, a
| packed bed, a side chamber, flow path, and / or eddy region );
| protection of composition integrity of the dielectric fluid
| (e.g., managing materials of bearings, seals , plates , etc. to
| avoid material breakdown and / or introduction of degradation
| constituents that negatively affect the performance of the
| dielectric fluid ); introduction of a field disrupting additive
| into the dielectric fluid ( e.g., a coated metal oxide, a nano-
| particle, and /or a conductive particle having a conductor that
| isolate the conductive particle from physical contact with the
| dielectric fluid ); introduction of an ion scavenging additive
| into the dielectric fluid ( e.g., BHT, antioxidants, etc. );
| management of gap distance (e.g., using bearings, magnetic
| separation, a separation assembly, etc.); and / or selected field
| weakening at certain operating conditions. The utilization of
| various field management aspects of the present disclosure allows
| for an increased average field strength in the gap, while
| maintaining a peak field strength below a breakdown threshold
| 8406, thereby increasing capacitive energy storage and consequent
| performance of the ESM 1002."_
|
| This thing is sort of like a high voltage electrolytic capacitor
| with moving parts. They go to a lot of trouble to deal with most
| of the problems that happen inside capacitors, plus the special
| problems from moving parts. They had to go all the way to a
| pumped fluid system with filters, to keep the dielectric fluid
| cool and clean. Many electric car motors have liquid cooling, so
| it's no worse than that. It does mean this is probably a
| technology for larger motors, because the motor requires some
| accessory systems.
|
| It's not clear that this is a win over magnetic motors, but it's
| reasonable engineering.
|
| [1]
| https://patentimages.storage.googleapis.com/cf/eb/f0/6d48f07...
| 01100011 wrote:
| I've long wondered if there's a possible application for
| something like this using 3d printing and electrets. Basically
| you can freeze an electric field inside of an insulator if you
| apply it as the material solidifies. I think you should be able
| to embed electrets inside of 3d prints simply by generating a
| strong electric field at the print head or slightly behind it.
| You can also vary the field and embed a 3d electret that can act
| as, say, a sensor or a hidden ID in the print.
| mNovak wrote:
| Some more technical content (literature review, but includes the
| university work this spun out of) if the sales page isn't doing
| it for you:
|
| https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=919...
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