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?
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.
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.
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.
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.
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.
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.
The featured article is about electrostatic motors that provide less than one horsepower. Therefore any comparison to "large motors" is kind of off subject.
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
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.
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?