CGI Brought to Life
First popularized in Steven Spielberg’s Back to the Future franchise, hoverboards have endured a love-hate relationship with the public for the past three decades. There’s no denying that the concept of a personal, all-terrain hovercraft is incredibly enticing. However, the universal principles of gravity and electromagnetism have long relegated hoverboards to the imaginations of CGI artists and science fiction writers. That is, until now. Using the crowdfunding website kickstarter.com, technology start-up Hendo Hover has managed to raise half a million in funding for their hoverboard prototype. And while crowdfunding scams have recently become commonplace, public investors in Hendo Hover’s crowdfunding campaign need not worry: Hendo Hover recently released video footage of skateboard legend Tony Hawk effortlessly gliding over a specially designed “hoverboard park” perched atop an almost finalized prototype hoverboard.
There’s two major caveats to Hendo’s interpretation of the hoverboard: Unlike Marty in Back to the Future 2, you won’t be able to hover over water, concrete, grass, or any surface that isn’t a non-ferrous metal (copper and aluminum work best). On average, the Hendo Hoverboard allows around an inch of clearance for a 180 pound user, limiting performance to shallow gradients. A typical skateboard provides 3-4 inches of clearance, allowing the user to navigate the steep bowl-shaped surface common to many skate parks. Secondly, Hendo’s current prototype board does not have an internal propulsion system: the hoverboard rider pushes off the ground just like he or she would with an old-fashioned skateboard.
Tony Hawk: Hoverboard Beta Tester
Even considering it’s limitations, Hendo Hover’s prototype is an impressive achievement. In a publicity video released last month, skateboard legend Tony Hawk is seen expertly navigating the hoverboard at Hendo’s proprietary skate park. The visual affect is striking: With only air resistance to overcome, the hoverboard glides across the metallic surface at an eerily constant speed. But frictionless movement is a double-ended sword: near the end of the video, Tony Hawk, perched upon the board, overcompensates on a turn and the hoverboard spins out of control. Without any significant friction, angular momentum is conserved and the Hendo crew quickly jumps in to help Tony Hawk regain control.
The Science Behind the Magic
Hendo Hover provides their Kickstarter backers with a simple scientific explanation for their proprietary hoverboard mechanism:
“The magic behind the hoverboard lies in its four disc-shaped hover engines. These create a special magnetic field which literally pushes against itself, generating the lift which levitates our board off the ground.”
Fair enough–Newton’s third law supports the theoretical concept keeping the hoverboard in the air: Every action has an equal and opposite reaction. However, how does the hoverboard create a magnetic field that supports the entire area consistently? Magnetic repulsion is not a self-correcting mechanism: any initial differences in the magnitude of the magnetic repulsion across the surface area of the board will be magnified as the board tilts towards the ground. Earnshaw’s theorem, developed by British mathematician Samuel Earnshaw in 1842, states that any discrete collection of point charges cannot sustain a stable equilibrium solely using the electrostatic interaction of the charges.
The mathematics department at the University of California, Riverside campus proposes a few mechanisms that would allow stable magnetic levitation. Perhaps the simplest method is introducing rotation to the levitation object. By rapidly spinning a rotationally symmetric magnet, the magnetic repulsion field is adequately stable. A commercial toy company, FASCINATION DESIGNS, produces a “Levitron®” magnetic top that levitations above a fixed platform using this very principle. However, a hoverboard is neither rotationally symmetric nor allowed to be rapidly spun with a person aboard!
Using oscillating magnetic fields to create stability is a more versatile solution. While Hendo Hover doesn’t explicitly explain how their hoverboard maintains stability, I believe that oscillating magnetic field technology is the only currently viable method. By running an alternating current through the electromagnet, the conducting metallic surface behaves like a diamagnet. A diamagnet contains two perfectly opposed magnetic fields; one induced through the material, and one applied by the alternating current. Because a diamagnet’s stability is self-correcting rather than error-feedback multiplying, Earnshaw’s law does not apply.
Creating a hoverboard is like a game of whack-a-mole: The solution to one obstacle inevitably creates a new problem. Case in point: Using oscillating magnetic field technology requires a steady, powerful electric current. Wired’s Rhett Allain guesses that the Hendo Hoverboard consumes around 300 watts. To put this in perspective, an iPhone 5s battery holds a charge of 5.45 watt-hours–enough to power the Hendo Hover for a little over a minute. Hendo Hover states that current prototypes have a battery life of around 10 minutes, with recharge cycles taking almost two hours. With current lithium-ion battery technology, untethered hovercraft travel seems to be out of reach.
In the spirit of crowdfunding, Hendo Hover offers a litany of ways for a consumer to get involved with their project. A $100 pledge comes with a five-minute hoverboard ride at Hendo’s Silicon Valley headquarters. Various developer kits allow ambitious programmers to experiment with a single hover engine (to support a human, the actual Hoverboard requires four engines). At the pricier end of the scale, the sold-out $10,000 pledge option comes with “one of the world’s first 10 production hoverboards,” estimated to roll off the production line next October.
Kickstarter has recently endured criticism regarding their consumer protection policies–numerous project funders have accused project developers of misappropriating funds, or even completely fabricating projects. Critics often point to the infamous “Sound Band” debacle: A convincing pitch by “Hybra Advance Technology, Inc” for a wireless headset raised half a million dollars only for Hybra to fail to deliver a single functioning prototype. However, the Hendo Hover appears to be the real deal. Through ingenious publicity stunts, Hendo Hover has demonstrated their commitment to their project. While cynics may claim that hoverboards will never be commercially viable, Hendo Hover should be applauded for taking a risky first step.