Giant wheel used to test a linear motor

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Giant wheel used to test a linear motor

Summer series - Master’s project (10). Jérémie Pochon has built a test bench for evaluating the type of motor that could one day drive the Hyperloop transportation system.

The Hyperloop holds the promise of low-carbon transportation that’s fast, efficient and affordable. But before passengers can be enclosed inside a pod and propelled along a vacuum tube at mind-boggling speeds, there’s a lot of modeling, simulation, testing and validation work to be done - starting at a pilot scale. That’s the work being done by engineers at EPFL’s Distributed Electrical Systems Laboratory (DESL), as they seek to further research in the field.

Two PhD students at DESL are currently working on Hyperloop-related technology. One of them is looking specifically at a key component of the system: the linear induction motor (LIM). In broad terms, this type of motor consists of a series of coils carrying an electric current. LIMs are capable of propelling a vehicle forward, while the magnetic field created inside the motor also generates a levitation force. "A linear induction motor wants to do just one thing: move," explains Jérémie Pochon, who’s completing a Master’s degree in Energy Science and Technology. "So testing one is a real challenge." The problem, of course, is that the technology must be tested before it can be validated for wider use.

Moving the rail instead of the motor

How, then, can engineers measure the properties of something so hard to pin down? One option is to build sections of tube dozens of kilometers long and propel the LIM along a rail. Another is to use the purpose-built Hyperloop test track on EPFL’s Lausanne campus. "The problem is that, in order to test an LIM, you need the whole system: the frame, the batteries, the connectors and so on," says Pochon. His answer was to flip the problem on its head, keeping the LIM and measurement devices static while moving the rail by mounting it on a wheel.

For his Master’s project, Pochon built a giant aluminum wheel - some 1.4 m’in diameter - equipped with spokes and a 2 mm rail in place of the rim. The wheel is encased in a rectangular structure measuring 1.9 m’high. "We ran simulations to check that the curvature of the rail wouldn’t compromise our test results," he explains. "Our design also makes it easy to run several tests in succession, since everything barring the rail is static."

In Pochon’s test bench, the LIM is firmly anchored to a base and closes around both sides of the rail like a jaw. But it never actually touches the rail, maintaining a distance of 2 mm at all times. The forces generated between the LIM and the wheel are measured with sensors. Engineers can use this rotating rail to test the LIM in two sections. But the test bench can also be employed to run experiments on the levitation forces produced by the induction motor. In this case, the LIM would sit inside the rail, which would be reinforced with a layer of iron to keep the magnetic field from dissipating. Two kinds of tests will be run on Pochon’s test bench. The first will be conducted at constant speed, so that engineers can characterize the LIM and understand its properties. The second will simulate a real application of the LIM where it has to drive a mass equivalent to a pod. This inertia will then be reproduced by the second motor.

Taking the research to the next level

"Our goal is to have the wheel rotate at a speed equivalent to the rail moving at around 400 km/h," says Pochon. "But that’s nowhere near the kinds of speeds the Hyperloop could achieve. For now we’re working at a pilot scale in order to characterize the LIM and make sure our models are correct. Once we’ve validated the LIM in miniature, we can proceed to full-scale testing."

The aim of Pochon’s Master’s project was to design, build and assemble the test bench. That’s now been done - but it’d be a shame to stop there! Once he’s completed his Master’s degree, Pochon plans to continue working with DESL for a few more months. "I want to solve some unanswered problems - and, more importantly, use the test bench to take some concrete measurements," he adds with a touch of pride.