Designfax weekly eMagazine

Subscribe Today!

Archives

View Archives

Partners

Manufacturing Center
Product Spotlight

Modern Applications News
Metalworking Ideas For
Today's Job Shops

Tooling and Production
Strategies for large
metalworking plants

Working electric motor made with non-metal coils!

Dr. Dae-Yoon Kim and his team at the Korea Institute of Science and Technology (KIST) Composite Materials Research Institute have succeeded in constructing the coil of an electric motor using only carbon nanotubes (CNTs) without any metals -- and realizing the device to the point where it can actually run.

The team conducted experiments by applying the coil made of CNTs to the motor and found that the revolutions per minute (RPM) of the motor could be stably controlled according to the input voltage. This demonstrates that the basic operation of a motor, which converts electrical energy into mechanical rotational force, can be accomplished without metal windings. Until now, metals such as copper have been used as the main material for coils due to their high electrical conductivity, but it has been consistently pointed out that they have various limitations, such as difficulty in securing resources, price volatility, and weight problems due to high density.

CNTs are one-dimensional, tube-shaped nanomaterials with carbon atoms arranged in a hexagonal honeycomb structure. They are known to be much lighter than ordinary metals, while at the same time possessing excellent electrical conductivity, mechanical strength, and thermal conductivity. These properties have long attracted attention as a next-generation material, but CNTs have faced a number of barriers to real-world industrial applications.

One of the technical obstacles with CNTs is the residue of catalyst metals used during the manufacturing process. This residue remains as metallic particles on the surface of CNTs, degrading their electrical properties, which are directly related to motor performance, making it difficult to utilize CNTs in high-performance components.

The KIST team has made a real breakthrough by developing a new CNT purification process that utilizes the alignment principle of liquid crystals, a "fourth state of matter" known as the intermediate state between liquid and solid. The process naturally resolves strong aggregation during the alignment of CNTs, effectively removing metallic particles that remain on the surface.

Most importantly, the new process is able to selectively remove impurities without damaging the nanostructure of the CNTs, making it distinctly different from existing liquid- and gas-phase-based purification methods. The purified CNTs show a significant improvement in conductivity, which can be brought to a level that can be applied to uses such as in electric motors.

The CNT motor made by the researchers was able to run a small toy car. A paper describing the technology was published in Springer Nature. The paper states the rotor was filled with coils wound from nine parallel 30-cm-long core-sheath composite electric cables (CSCECs), with each winding consisting of 10 turns. The rotor was "assembled together with brush, commutator, and stator. This metal-free motor was directly contacted with the digital tachometer under no-load conditions, and the rotational velocity was recorded in revolutions per minute (RPM) by varying the voltage."

The researchers increased the RPM of the metal-free motor from 540 to 3,420 within the range of 2 to 3 V. According to the paper, "The metal-free motor with CSCECs maintained a consistent RPM at least 60 min. of operation, when 2.0 W, 2.5 W, 3.0 W, and 3.5 W of electric power were applied." The researchers said the same size electric motor was tested that used copper windings (3 parallel 30-cm-long copper wires ), and it topped out at 18,120 RPM at 3 V -- much more powerful than the motor that used carbon nanotubes. However, the copper-based motor was also much heavier (about five times as heavy), so you can quickly see the tradeoffs. The electrical conductivity of the copper-based cables was reported as "7.4 times higher than that of CSCECs," with the little test car reaching a speed of 1.35 m s^-1 powered by a 3-V battery. Using the motor with the carbon nanotube windings, the car speed was 0.52 m s^-1 powered at 3 V.

The researchers also tested their CNT motor windings using their new purification process vs. CNT cables made without the process, with the new technology the clear winner. The new process increased the electrical conductivity of CNT wires by 133%.

The researchers posed an important question in their paper when they asked, "Will CNTs ever be able to compete with metallic materials for next-generation advanced cables?" From a density perspective, they say the use of CNTs has a lot of advantages. The weight of the CNT wires (78.75 mg) was about one-fifth that of the copper wires (379.08 mg). The researchers conclude, "Therefore, the difference in specific rotational velocity is only 1.06-fold, from 43.4 RPM mg^-1 for electric motors made with CNT wires to 47.8 RPM mg^-1 for those made with copper."

So, if the electrical conductivity for the CNT motor can be increased, this type of motor could well have some serious advantages, since a common technical challenge for future transportation is lightweighting, whether that be for electric vehicles, drones, or even spacecraft. Electric motors in particular are an essential component of most electric mobility vehicles, and coils account for a large proportion of the total weight of the motor.

"Based on the innovation of CNT materials, we will take the lead in localizing materials such as conductive materials for batteries, pellicles for semiconductors, and cables for robots," said Dr. Dae-Yoon Kim of KIST.

We encourage you to check out the researchers' paper here to review all of their results.

Source: Korea Institute of Science and Technology

Published June 2025

Rate this article