How and Why We're Levitating the Hyperloop
By Casey Handmer, Levitation Engineer, Hyperloop One. (Our levitation team is pictured above with the "lev rig" (L-R) me, Elliot Owen, Jett Ferm, David DeHaan, James Coutre)
There are seven billion of us. Ranked by wealth, each successive billion has access to exponentially more energy-intensive transportation technology. The richest billion can travel, at least once in their life, by plane. The next billion, by car. The next, by bus, then train, then motorcycle, then bicycle, and then foot. If we want to lift the standard of living for all 7 billion through better transport options, while staying mindful of our ecological footprint, we’re going to need dramatic improvements in transportation efficiency.
Why move humans at all? Technologies that brings people together to share culture, information, and ideas are economic rocket fuel. The efflorescence of culture in the Upper Paleolithic era was driven not by agriculture, metal use, or telecoms, which came later, but by greater exchange of ideas through face to face interactions. This enabled the collection and preservation of knowledge that gradually led to the present heights of our technological civilization. This positive externality of synergistic technological and economic growth is what drives the public and private sectors to build new and massively expensive transportation infrastructure.
Hyperloop One’s mission is to short circuit the relationship between cost and speed: To push the tech down and to the right, well into the zone of opportunity; to bring useful, fast, cheap, reliable mass transportation to the billions who can’t afford more than a bus, or who must travel faster than private jet; to do for people and cargo what global fiber networks did for the internet--on demand, point to point transportation that’s at once banal and miraculous; to build a metro system that spans continents with a stop in every town.
How to make stuff slippery so you can move it around
A physicist in a previous life, I studied the fundamental mechanisms of warp drive, time travel, and teleportation. Fortunately, Hyperloop is much more energy efficient! It may seem like an incredible technology, but its basic principles are as mundane as the other transportation modes: It still has to take people or cargo from point A to point B, mediating relative movement between the stationary track and moving vehicle while providing a comfortable ride and countering the inevitable forces of gravity and curves.
There are five core trade-offs between the different transport mechanisms: Simplicity, weight, drag, compliance at the point of contact and, above all, cost. More than 5,000 years ago, one versatile solution was found: the wheel. Wheels are simple. They can bear many times their own weight. Modern wheel bearings have extremely low friction even under heavy loads. When rubber tires are combined with suspension, wheeled vehicles can traverse nearly all types of terrain. Effective and affordable, ubiquitous and indispensable, wheels are always in fashion.
Why, then, does Hyperloop One have a levitation engineering group? Speed. Hyperloop goes fast, disruptively fast! However fast wheels can go, by definition it is just not fast enough.
Drag is a drag
At lower speeds, wheels are attractive because of extremely low rolling friction. In trains, buses, trucks, and cars, however, the dominant source of drag is not from rolling, but from aerodynamics. The force of moving air molecules out of the way around a moving object irreversibly transfers momentum, leading to a loss of kinetic energy. In Hyperloop, we pull a vacuum in the tube, side stepping this inefficiency that afflicts all other methods of rapid surface transportation. We also levitate the pod just above the track, which avoids the need that a traditional rolling high-speed rail has for an absolutely smooth track.
That doesn’t mean our job is necessarily made easier. The levitation system has to work well at any speed, lift much more than its intrinsic weight, produce less drag than aerodynamic friction in a vacuum, and ideally do so with no moving parts at an affordable price. Taking these requirements together, it would appear the laws of physics crush our hopes and dreams, and that our levitation team is doomed from the start. Even Teflon has higher drag than we’d like.
Despair is premature – the universe requires innovation. If you arrange atoms carefully enough, they can do all sorts of surprising things. Superconductivity. The fractional quantum Hall effect. Life. Sand is, as far as matter goes, pretty generic. But slice and dice it just right and you can make silicon think. A good amount of atom rearrangement is underway inside the Hyperloop One levitation group.
Our take on levitation
Magnetic levitation (maglev) has been around for decades, usually never making it out of the test labs. Nor has maglev always developed with speed in mind. Sometimes in engineering it is obvious how a new kind of thing should be built, and sometimes it is not. The profusion of types of airplanes, rockets, cars, and even mobile phones during their early decades of development is testament to the experimental nature of the frontier. Among the very few high-speed maglev transport systems systems that have made it out of the labs are Germany’s Transrapid and Japan’s SCMaglev. Their differences underscore how divergent technology development can become.
Transrapid, after 35 years of development, was successfully deployed in 2004 in Shanghai. It links the airport to the city at up to 431 km per hour, a distance of 30.5 km in just over 7 minutes. This system uses electromagnets on the pod with an energized, computer-controlled track providing levitation control and propulsion. Transrapid’s choice of an active, powered track created a good deal of cost and complexity, something we are trying to minimize.
SCMaglev began its development in Japan in the 1970s. SCMaglev uses passive levitation, where only the propulsive parts of the track are powered, and holds the record for the fastest train ever tested, at more than 600 km per hour. A line from Tokyo to Osaka is currently under construction. On the lev team we view SCMaglev’s engineering with awe – its pod magnets are superconducting! But that mandates sub-optimal magnetic field geometry and colossal expense, while non-superconducting permanent magnets are much stronger now and easier to work with than they were in the 1970s. We are taking a different approach from theirs that we believe can achieve similar performance at a much lower cost.
Hyperloop One levitation uses pod-side permanent magnets repelling a carefully designed passive track. This system is very simple, stable, and the only input energy comes from the speed of the pod. When magnets and conductors play together, electrons in the conductor move around to try to cancel out any change of flux. In practice, this results in the generation of eddy currents, which dissipate energy as heat and are the operating principle behind induction stoves. In bulk conductors, eddy currents are tiny circular motions of current that aren’t particularly useful for efficient maglev. The trick with the Hyperloop One levitation system is to control the conductivity so that electricity flows more easily in some directions than in others. This way, the harmful eddy currents are reduced while bulk flows trace out shapes impossible in bulk conductors, repelling the pod magnets with very low drag. Metamaterials often exhibit bizarre, unintuitive behavior, such as the remarkable iridescence of a butterfly’s wings, a CD, or an opal. What biology does for light, we are doing for raw magnetism, in a deliberate approach to harness induced current flows through fine scale material manipulation.
The shower is a good place for thinking, so I keep a marker near the mirror. A new concept starts out as a sketch, then proceeds through steadily more sophisticated calculations. But one can’t build a complete system on a single analytic calculation, so we undertake detailed finite element simulations in full 3D for full theoretical validation. Then it’s time to don the safety glasses and step next door to the Test/Dev area, where our resident fabrication geniuses take our ideas and translate them to reality, building state of the art test rigs and collecting all the data we could ever want, and then some.
Data can disagree with the model. That’s life. Sometimes we know why, often we have to think. We pull in a few smart people from another team, tag up around a standing table, and throw ideas around. Pens squeak in protest, pads of paper go on back order. Iterated designs are pushed through the validation pipeline and, in a matter of weeks, our unit test is at version 2, which closes the gap between expectation and reality. Now all we have to do is integrate it with the rest of the system. We crack open the “team-building” refrigerator and push into the evening as ideas, food, and excellent cheer ebb and flow across the table.
When the atoms and currents are right, the levitation team puts Hyperloop One at the cutting edge of minimizing passive maglev drag at an affordable system cost. It may not be time travel, but levitating at airline speeds between cities for the cost of a bus ticket is the next best thing.