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Nanotube Structures Could Improve Electric Motors

Carbon nanotube commutator. Source: Rice University.  Click to enlarge.

Researchers from Rice University and the University of Oulu in Oulu, Finland, have found that carbon nanotubes could significantly improve the performance of electrical commutators that are common in electric motors and generators.

The research, which appeared online this month in the journal Advanced Materials, finds that brush contact pads made of carbon nanotubes had 10 times less resistance than did the carbon-copper composite brushes commonly used today. Brush contacts are an integral part of commutators, or spinning electrical switches, used in many battery-powered electrical devices, such as cordless drills.

The findings show that nanotubes have a great deal of practical relevance as brush contacts. The technology is widely used in industry, both in consumer gadgets as well as larger electrical machinery, so this could be a very interesting, near-term application for nanotubes.

—lead researcher Pulickel Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science

The combination of mechanical and electrical properties of nanotubes makes this possible.

The carbon nanotubes used in the study are hollow tubes of pure carbon that are about 30 nanometers in diameter. (By comparison, a human hair is about 100,000 nanometers in diameter.) Nanotubes are extremely lightweight and durable, and they are excellent conductors of heat and electricity.

Because of these properties, the researchers decided to test nanotubes as brush contacts. Brush contacts are conducting pads held against a spinning metal disc or rod by spring-loaded arms. Current is passed from the spinning disc through the brush contacts to other parts of the device.

To test the feasibility of using carbon nanotube brush contacts, the research team replaced the ordinary copper-carbon composite brushes of an electric motor with small blocks that contain millions of carbon nanotubes.

From Ajayan’s previous work, the team knew that these nanotube forests regain their shape very quickly after they are compressed.

This elasticity is something that’s not found in existing composites that are used for brush contacts, and that’s the essence of why the nanotube brush contacts perform better: They keep much more of their surface area in contact with the spinning disc.

—Robert Vajtai, faculty fellow at Rice

Vajtai worked on the study with Ajayan and a group of researchers in Finland led by University of Oulu Researcher Krisztian Kordas.

The team believes that the improved contact between the surface of the spinning disc and the brush accounts for the 90% reduction in lost energy.

Co-authors on the paper also included Geza Toth, Jani Mäklin, Niina Halonen, Jaakko Palosaari, Jari Juuti and Heli Jantunen, all of the University of Oulu, and Gregory Sawyer of the University of Florida.

Support for the research was provided by the Academy of Finland, the University of Oulu’s Micro and Nanotechnology Center, the Air Force Office of Scientific Research and the Semiconductor Research Corporation.


  • Geza Toth et al. (2009) Carbon-Nanotube-Based Electrical Brush Contacts. Advanced Materials Early View doi: 10.1002/adma.200802200



The big question is: How stable are the nanotubes under the arcing conditions found in a commutator? will the surface of the brushes remain nanotubes, or will they re-form as graphite?


Technological progress comes incrementally but inexorably.


What's wrong with brushless D.C. motors?

The cost of the electronics has been dropping steadily, the electrical noise much improved compared to brush commutators, and the reliability is excellent.


BDCM and 3 phase inductive are very useful for HEVs, PHEVs and EVs. Some applications like power steering and AC might be better done with a DC motor having a mechanical commutator. However, the main drive motor being done by multi phase inductive motors may be the future.


I was wondering the same thing SJC.

I doubt even power steering or AC would use brushes. I assume the reason starters, power seats and windows etc do NOT use brushless DC motors (BDCM) is because the low efficiency, and high wear do not matter for such low duty applications.

Maybe Lionel will benefit from these.


lol, I love it!


Maybe Lionel will benefit from these.

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