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Electrostatic motors come of age

Can static cling power the industrial processes of the future? A new startup called C-Motive Technologies says it has cracked the code using standard printed circuit boards (PCBs), a proprietary dielectric liquid, and some pretty crafty electrical and mechanical engineering all packaged together.

Ben Franklin made an electrostatic generator (or capacitor motor) all the way back in the mid 1700s, taking advantage of static forces to make a wheel turn. You can read about Franklin's machine, which included brass sewing thimbles attached to wheel, at the Smithsonian's National Museum of American History here.

The technology, in general, had its drawbacks -- not least of which was the high voltages required to do real work -- so its use was limited. Those drawbacks were eventually easily addressed by magnet-based motors, first produced in the 1820s.

C-Motive's motor tech differentiates itself from standard (magnet-based) electric motors by doing away with a gearbox, active cooling, or any oversizing -- and there are no magnets, of course. The end game is to have a more efficient machine -- fewer inefficiencies gets more work done directly using appropriately sized machines and better energy use. Torque should be increased too, comparing similarly sized traditional and C-Motive motors.

How does the C-Motive machine work?

According to C-Motive, within their machines "are sets of cascading and alternating rotor (moving) and stator (affixed) plates. These rotors and stators are made from standard printed circuit boards (PCBs) and have a highly optimized set of conductive metal traces (poles) that radiate out from the center hub on the plates. The machine's drive controls the voltages that determine the speed and torque output. These drives make C-Motive machines customizable for any application."

"In addition to these mechanical and electrical innovations, a proprietary dielectric liquid fills C-Motive's machines," which is safe and non-toxic.

Applying voltage to the machine causes the rotors to spin, while the stators remain in a fixed position (a 360-W motor has a half dozen each of rotors and stators, according to IEEE Spectrum). Each trace on a rotor is charged with alternating positive and negative voltages, which creates an electric field between the plates. The stator functions similarly, but with three phase A, B, and C voltages. The stator creates an electric field that pulls the rotor along. The number of rotors and stators determines the torque output of the machine.

C-Motive, based in Middleton, WI, says its machines "are naturally suited for low-speed operation and deliver low electrical losses."

C-Motive's CEO, Matt Maroon, told Designfax, "Our products are designed to replace 1-, 2-, and 3-hp gear motors that you would most commonly find in industrial applications. The electrostatic machine delivers full torque and efficiency at low speeds, so it is designed to replace both traditional motor and gearbox for the jobs where you only need 0 to 300 RPM."

According to an August 2024 IEEE Spectrum article, "In some applications, these motors could offer an overall boost in efficiency ranging from 30 percent to close to 100 percent."

The IEEE Spectrum article says C-Motive's current prototype motor, which needs 2,000 V to operate, "is capable of delivering torque as high as 18 newton meters and power at 360 watts (0.5 horsepower)," and the company "is now testing a 750-watt (1 hp) motor," with eyes on machines "in the range of 750 to 3,750 watts (1 to 5 hp)." Special 4.5-kilovolt insulated-gate bipolar transistors help get the job done.

C-Motive lists the benefits of its technology to include:

• Higher efficiency in both motor and generator applications;
• Torque generation at low speeds without a gearbox and without any active cooling requirements;
• Up to 10x the specific torque (Nm/kg) of traditional motors;
• Silent operation;
• Ability to hold a position with virtually no energy losses;
• Precise motion control with no torque ripple and smooth motion (no cogging torque);
• Can operate fully submerged in water;
• Scalable up to multi-megawatt size; and
• No rare earth metals or magnets necessary.

It is important to note that C-Motive motors do not work with standard, off-the-shelf drives. C-Motive makes its own, proprietary drives that "have equivalent efficiency as commercial drives, but are configured differently to deliver the high voltage needed by our machines."

Learn more about C-Motive technology at c-motive.com/.

Want to learn more about the first principles of C-Motive's electrostatic machines? Read the IEEE paper "Macroscale Electrostatic Rotating Machines and Drives: A Review and Multiplicative Gain Performance Strategy" authored by C-Motive employees.

Sources: C-Motive, IEEE Spectrum

Published October 2024

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