7 ms·

Electrostatic motors reach the macro scale

128 points by namanyayg 2y ago

Animats 2y ago
"C-Motive team succeeded in producing an organic liquid dielectric with low viscosity and a relative permittivity in the low 20s." Nice.
- trebligdivad 2y ago
  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 2y ago
    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?
    - trebligdivad 2y ago
      I wasn't interested in the rotation speed; more the high voltage - I know there are vacuum variable caps for high voltage work, but don't know what the current state of other dielectrics at a few kV is.
- ta988 2y ago
  This will likely be a maintenance hell when the liquid ages and get particles in it.
- IsTom 2y ago
  Many organic liquids/solvents are cancer juice, I wonder if this is too.
imbusy111 2y ago
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 2y ago
  > What practical electric motor is even close to 30% efficient? This is laughably low. I think that means 30% over existing performance.
  - imbusy111 2y ago
    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 2y ago
      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 2y ago
        i wish people would just always use percentage points and never deviate from that.
doe_eyes 2y ago
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 2y ago
  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 2y ago
    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
    - throwway120385 2y ago
      Look it's a 1950's Craftsman I got from a guy who wired the hot and neutral backwards when he replaced the original motor. They did things differently back then.
  - SoftTalker 2y ago
    > Also how big is a "large?" motor? The motors discussed in the article were described as "fractional horsepower"
spankalee 2y ago
I wonder how well the dielectric fluid holds up if the motor is spinning at several thousand RPMs for dozens of hours?
- pragma_x 2y ago
  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 2y ago
  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 2y ago
    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 2y ago
      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 2y ago
"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 2y ago
  Related post on hackaday: https://hackaday.com/2017/10/03/ben-franklins-weak-motor-and-other-forgotten-locomotion/ https://hackaday.com/2017/10/03/ben-franklins-weak-motor-and...
  - ajb 2y ago
    Cool thanks!
- lawlessone 2y ago
  >He actually used the motor as a rotisserie to grill a turkey on a riverbank in Philadelphia Benjamins aeolipile?
PaulHoule 2y ago
This book describes a family of devices that work both as electrostatic generators and motors https://www.amazon.com/Electrostatics-Exploring-Controlling-Static-Electricity/dp/1885540043 https://www.amazon.com/Electrostatics-Exploring-Controlling-...
mikewarot 2y ago
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 2y ago
  static part of electrostatic! I'm curious about their leakage current though
  - DoctorOetker 2y ago
    To compare different dielectric liquids you would want to see the dielectric spectroscopy plots: https://en.wikipedia.org/wiki/Dielectric_spectroscopy https://en.wikipedia.org/wiki/Dielectric_spectroscopy And the different types of viscosity vs temperature plots.
- kazinator 2y ago
  Hydraulics can do this. Pump in the oil, close a valve. Mechanics: worm gears, ratchets. Static friction: e.g. tuning pegs in pianos (no gears).
buildsjets 2y ago
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.piezo-motor.net/ https://www.meddeviceonline.com/doc/what-are-canon-s-linear-ultrasonic-motors-all-about-0001 https://www.meddeviceonline.com/doc/what-are-canon-s-linear-...
- rcxdude 2y ago
  Those are pretty neat. Their main advantage is being able to move quickly and with extreme precision (think down to nanometers). They're not particularly strong or efficient.
  - Terr_ 2y ago
    I'm sure this has already been invented, but I don't know the proper terminology: Two or more motors with different characteristics that are somehow geared together, so that the X% errors in speed/position of a more-powerful motor get fixed by simultaneous activation of a finer motor (possibly in "reverse") and so on down the chain. I suppose it hits diminishing returns whenever the main source of error comes from all the connections or gears.
    - cdaringe 2y ago
      I wager the electric motors actually have a very low angular velocity error on average. However given the way they work, during a revolution you likely have non linear rotation of the shaft on a basic motor due to the classical physics of the rotational load accelerating between its push/pull magnetic poles. Theres some interesting work in the motor driver space trying to smooth out the curves in the motion profiles of the trusty stepper motor (see TMC2209 driver promo content) and surely similar work for other electric motors. I bet one of our peers here could speak more authoritatively than my conjecture above.
kazinator 2y ago
Who will buy a 0.5 hp motor whose parts must be bathed in an exotic dielectric fluid, and that needs a 2000V supply, and will they buy another one?
- natosaichek 2y ago
  The dielectric is internal, and the motor will presumably have a built-in driver to adapt from wall voltage to 2kv. Neither of those issues are at all an issue.
  - kazinator 2y ago
    "No user-serviceable parts inside", and nobody qualified to work on it within a 1000 mile radius.
    - Glyptodon 2y ago
      A big factor with this will be how inexpensive they are relative to something that's more maintenance friendly. If you can get five of them for the price of a similar traditional electric motor I imagine it might be worth planning to swap and never service yourself. Particularly the longer they tend to last.
      - kazinator 2y ago
        I get it now. These will be lighter and cheaper than induction motors, due to containing a lot more plastic and a lot less metal and wire. Nobody fixes fractional Watt induction motors. When a coil burns out (or whatever), it goes to the landfill (perhaps along with the whole appliance).
nomel 2y ago
And, for a simpler linear version that's used to drive air: electrostatic speakers [1]! [1] http://jazzman-esl-page.blogspot.com/2016/12/wire-stator-esls.html http://jazzman-esl-page.blogspot.com/2016/12/wire-stator-esl...
fnord77 2y ago
I counted at least 30 electric motors in my (non-EV) car. 3 in each mirror. 2 in the HUD. All of those will end up in a landfill/junk yard. Seems like a huge waste.
- audunw 2y ago
  The materials will probably be recycled
mikewarot 2y ago
This reminded me of the Propylene Carbonate on my Amazon wish list. A few years ago, I heard about HASEL actuators[1], which started out as zip lock bags with a dielectric fluid inside, aluminum foil, and high voltage power supply. The fluid turned out to be Propylene Carbonate. I don't know chemistry... so I figured I'd wait until I was actually ready to try things with it (having the power supplies figured out) before I got it in the house. I'm not there yet, but I understand 1700 volt transistors are a thing now. [1] https://www.artimusrobotics.com/ https://www.artimusrobotics.com/

128 points by namanyayg 2y ago

"C-Motive team succeeded in producing an organic liquid dielectric with low viscosity and a relative permittivity in the low 20s." Nice.

trebligdivad 2y ago
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 2y ago
  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?
  - trebligdivad 2y ago
    I wasn't interested in the rotation speed; more the high voltage - I know there are vacuum variable caps for high voltage work, but don't know what the current state of other dielectrics at a few kV is.
ta988 2y ago
This will likely be a maintenance hell when the liquid ages and get particles in it.
IsTom 2y ago
Many organic liquids/solvents are cancer juice, I wonder if this is too.

imbusy111 2y ago

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 2y ago
> What practical electric motor is even close to 30% efficient? This is laughably low. I think that means 30% over existing performance.
- imbusy111 2y ago
  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 2y ago
    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 2y ago
      i wish people would just always use percentage points and never deviate from that.

doe_eyes 2y ago

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 2y ago
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 2y ago
  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
  - throwway120385 2y ago
    Look it's a 1950's Craftsman I got from a guy who wired the hot and neutral backwards when he replaced the original motor. They did things differently back then.
- SoftTalker 2y ago
  > Also how big is a "large?" motor? The motors discussed in the article were described as "fractional horsepower"

spankalee 2y ago

I wonder how well the dielectric fluid holds up if the motor is spinning at several thousand RPMs for dozens of hours?

pragma_x 2y ago
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 2y ago
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 2y ago
  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 2y ago
    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 2y ago

"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 2y ago
Related post on hackaday: https://hackaday.com/2017/10/03/ben-franklins-weak-motor-and-other-forgotten-locomotion/ https://hackaday.com/2017/10/03/ben-franklins-weak-motor-and...
- ajb 2y ago
  Cool thanks!
lawlessone 2y ago
>He actually used the motor as a rotisserie to grill a turkey on a riverbank in Philadelphia Benjamins aeolipile?

PaulHoule 2y ago

This book describes a family of devices that work both as electrostatic generators and motors https://www.amazon.com/Electrostatics-Exploring-Controlling-Static-Electricity/dp/1885540043 https://www.amazon.com/Electrostatics-Exploring-Controlling-...

mikewarot 2y ago

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 2y ago
static part of electrostatic! I'm curious about their leakage current though
- DoctorOetker 2y ago
  To compare different dielectric liquids you would want to see the dielectric spectroscopy plots: https://en.wikipedia.org/wiki/Dielectric_spectroscopy https://en.wikipedia.org/wiki/Dielectric_spectroscopy And the different types of viscosity vs temperature plots.
kazinator 2y ago
Hydraulics can do this. Pump in the oil, close a valve. Mechanics: worm gears, ratchets. Static friction: e.g. tuning pegs in pianos (no gears).

buildsjets 2y ago

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.piezo-motor.net/ https://www.meddeviceonline.com/doc/what-are-canon-s-linear-ultrasonic-motors-all-about-0001 https://www.meddeviceonline.com/doc/what-are-canon-s-linear-...

rcxdude 2y ago
Those are pretty neat. Their main advantage is being able to move quickly and with extreme precision (think down to nanometers). They're not particularly strong or efficient.
- Terr_ 2y ago
  I'm sure this has already been invented, but I don't know the proper terminology: Two or more motors with different characteristics that are somehow geared together, so that the X% errors in speed/position of a more-powerful motor get fixed by simultaneous activation of a finer motor (possibly in "reverse") and so on down the chain. I suppose it hits diminishing returns whenever the main source of error comes from all the connections or gears.
  - cdaringe 2y ago
    I wager the electric motors actually have a very low angular velocity error on average. However given the way they work, during a revolution you likely have non linear rotation of the shaft on a basic motor due to the classical physics of the rotational load accelerating between its push/pull magnetic poles. Theres some interesting work in the motor driver space trying to smooth out the curves in the motion profiles of the trusty stepper motor (see TMC2209 driver promo content) and surely similar work for other electric motors. I bet one of our peers here could speak more authoritatively than my conjecture above.

kazinator 2y ago

Who will buy a 0.5 hp motor whose parts must be bathed in an exotic dielectric fluid, and that needs a 2000V supply, and will they buy another one?

natosaichek 2y ago
The dielectric is internal, and the motor will presumably have a built-in driver to adapt from wall voltage to 2kv. Neither of those issues are at all an issue.
- kazinator 2y ago
  "No user-serviceable parts inside", and nobody qualified to work on it within a 1000 mile radius.
  - Glyptodon 2y ago
    A big factor with this will be how inexpensive they are relative to something that's more maintenance friendly. If you can get five of them for the price of a similar traditional electric motor I imagine it might be worth planning to swap and never service yourself. Particularly the longer they tend to last.
    - kazinator 2y ago
      I get it now. These will be lighter and cheaper than induction motors, due to containing a lot more plastic and a lot less metal and wire. Nobody fixes fractional Watt induction motors. When a coil burns out (or whatever), it goes to the landfill (perhaps along with the whole appliance).

nomel 2y ago

And, for a simpler linear version that's used to drive air: electrostatic speakers [1]! [1] http://jazzman-esl-page.blogspot.com/2016/12/wire-stator-esls.html http://jazzman-esl-page.blogspot.com/2016/12/wire-stator-esl...

fnord77 2y ago

I counted at least 30 electric motors in my (non-EV) car. 3 in each mirror. 2 in the HUD. All of those will end up in a landfill/junk yard. Seems like a huge waste.

audunw 2y ago
The materials will probably be recycled

mikewarot 2y ago

This reminded me of the Propylene Carbonate on my Amazon wish list. A few years ago, I heard about HASEL actuators[1], which started out as zip lock bags with a dielectric fluid inside, aluminum foil, and high voltage power supply. The fluid turned out to be Propylene Carbonate. I don't know chemistry... so I figured I'd wait until I was actually ready to try things with it (having the power supplies figured out) before I got it in the house. I'm not there yet, but I understand 1700 volt transistors are a thing now. [1] https://www.artimusrobotics.com/ https://www.artimusrobotics.com/