The EU-funded MAGDRIVE project has taken this technology a huge step further, developing a prototype magnetic harmonic drive that can operate reliably at very low temperatures. A spin-off company is preparing the device for the market.

Space is a very hostile environment. Spacecraft, satellites and exploration rovers therefore need to be particularly hard-wearing – they need to operate in a vacuum and within a large temperature range.

Gears are needed for the deployment of antennas or other elements, for releasing instruments, or simply propelling wheels in sectors as diverse as aerospace, robotics, machine tools and medical devices. And it goes without saying that they must work properly. Harmonic drives are frequently used to set essential functions in motion, but they need lubrication and are susceptible to fatigue, wear and malfunction with temperatures below -150° C being particularly challenging.

“Nothing short of a breakthrough”

The MAGDRIVE project, which won first prize in the madrid+d awards in 2011 in recognition of its research efforts, overcame these challenges by developing a magnetic non-contact harmonic drive, in which none of the moving parts touch. “If you use a conventional harmonic drive in space and it jams, you cannot send anybody up there to change the gear or put some lubricant on it,” José Luis Pérez-Díaz points out – he coordinated the project on behalf of the Universidad Carlos III de Madrid. “We proposed something that was nothing short of a breakthrough: if pieces didn’t touch each other, there would be no wear, no friction, no need for a lubricant, and it would work at any kind of temperature. Instead of just pushing one piece towards another, we proposed that forces would be exerted by magnetic elements.”

The design is based on non-contact magnetic teeth: where in a traditional gear, teeth would mesh with another toothed part to transmit torque, the MAGDRIVE employs a combination of permanent magnets, soft magnetic materials and magnetic superconductor bearings, activated by a magnetic wave.

During the project, the consortium built two prototypes to cover different application scenarios: one operates at room temperature and could be used in a confined environment on Earth where contamination may be an issue; the other is able to operate at cryogenic temperatures and is suited to space applications. Both prototypes run smoothly. The cryogenic drive, however, is the greatest success.

Built-in jam protection

“We were able to demonstrate that it remains operational at -210° C, with the input axle reaching 3 000 rotations per minute (rpm),” Pérez-Díaz reports. “That is an absolute record for any kind of cryogenic mechanism. Any mechanism working under cryogenic conditions up to now only reached tens of rpm at most and would also suffer a lot of wear due to the cold. Our prototype was just running smoothly and gently at 3 000 rpm.”

And the innovative mechanism has another distinct advantage over the conventional technology: an anti-jamming property. If maximum torque is exceeded, the input axle does not jam, but simply slides, providing intrinsic protection for the mechanism. Traditional harmonic drives on the other hand may break down, resulting in catastrophic failure, and the mechanism would have to be changed.

A triumph in the battle for competitiveness

While the prototypes performed well during testing and worked smoothly under cryogenic conditions as well as in a vacuum, commercialising this innovative technology will still take time. Several of the project partners have founded the spin-off company MAG SOAR to press ahead and further improve the drive’s efficiency, optimise the manufacturing process and costs.

Pérez-Díaz is confident that the magnetic harmonic drive, which has many potential applications beyond aerospace, will soon be ready for market.

“Only a few groups worldwide are working in this field of magnetic research,” he says. “We are absolute pioneers. And I think we will also be pioneers when it comes to getting this technology on the market, a true triumph for Europe in the battle for competitiveness.”

Below picture of room temperature MAGDRIVE prototype

@ José Luis Pérez-Diaz

Video in Spanish: Desarrollan un engranaje magnético levitante