Engineers at EPFL have built a motor shaped like a thread, and it turns electrical energy directly into movement. It measures 1 to 3 mm across and is made of two hollow fibres, one nested tightly inside the other. The Swiss team works in the Soft Transducers Laboratory, part of the university's School of Engineering, and it has published the design in the journal Advanced Materials.

Each fibre is coiled with insulated copper wire electrodes that are only slightly thicker than a human hair. When a voltage is applied across those electrodes, electrostatic forces repeatedly pull the fibres into alignment. That makes the inner fibre slide inside the outer one, in a smooth motion much like the extension of a telescope.

The motor produces linear movement directly, without gears or transmissions. And that absence of rigid parts is the point, because it leaves the device silent, flexible and bidirectional. It is also backdriveable, so an opposing force slides the fibres past each other instead of locking them up.

Its travel is set only by the length of the fibres. Artificial muscles, by contrast, are limited by how far their materials can stretch, contract or bend. That gives the EPFL design a far longer working stroke than the soft actuators it is meant to replace in wearable systems.

The laboratory demonstrations were modest but specific. A single FiberMotor held stationary loads of roughly 75 grams. Four bundled motors produced enough force to lift a 46 gram chocolate bar and to bend a robotic finger that was worked by a tendon.

The team also fitted the motors into a prototype garment shaped around a knee. But the researchers describe these as laboratory results, not a finished product. The figures for 75 grams and 46 grams come from EPFL's own tests, and they have not been independently reproduced by another laboratory.

Herbert Shea, who heads the Soft Transducers Laboratory, said the device is the first sliding motor in a fibre format. He said it produces enough force to drive devices for soft robotics while staying silent, flexible and bidirectional. According to Interesting Engineering, which reported the work, the motor is being developed for soft exosuits, wearable haptic systems and lightweight prosthetics.

The work builds on earlier research from the same laboratory. Its team presented a pump in the form of a fibre in 2023, a predecessor that could be sewn into smart textiles to move fluids. The new motor takes that idea from moving fluids to producing motion.

Durability remains the open question. The team says it wants to improve the motor's performance and lifespan through thinner electrodes and better materials before the technology can power soft assistive clothing for daily use. So the path from these demonstrations to a wearable exosuit is longer than the video clips suggest.

No price has been disclosed for the FiberMotor. The electrodes are still being refined, and the researchers see the next stage as feedback that reads a wearer's position and movement so the motor can adapt in real time to their intention.

• EPFL's Soft Transducers Laboratory built FiberMotor, a motor shaped like a thread and 1 to 3 mm in diameter.

• Voltage drives electrostatic forces that pull two coiled fibres into alignment, sliding the inner fibre like a telescope.

• A single motor held about 75 grams, and four bundled motors lifted a 46 gram chocolate bar and bent a robotic finger.

• The motor is silent, flexible, bidirectional and backdriveable because it has no gears or transmissions.

• These are laboratory demonstrations, durability is still being improved, and no price has been disclosed.

Source: Interesting Engineering