# Step The Halbach From My Magnets

[Klaus Halbach] gets his name attached to these clever arrangements of permanent magnets but the effect was discovered by [John C. Mallinson]. Mallinson array sounds good too, but what’s in a name? A Halbach array consists of permanent magnets with their poles rotated relative to each other. Depending on how they’re rotated, you can create some useful patterns in the overall magnetic field.

Over at the K&J Magnetics blog, they dig into the effects and power of these arrays in the linear form and the circular form. The Halbach effect may not be a common topic over dinner, but the arrays are appearing in some of the best tech including maglev trains, hoverboards (that don’t ride on rubber wheels), and the particle accelerators they were designed for.

Once aligned, these arrays sculpt a magnetic field. The field can be one-sided, neutralized at one point, and metal filings are used to demonstrate the shape of these fields in a quick video. In the video after the break, a powerful magnetic field is built but when a rare earth magnet is placed in the center, rather than blasting into one of the nearby magnets, it wobbles lazily.

Be careful when working with powerful magnets, they can pinch and crush, but go ahead and build your own levitating flyer or if you came for hoverboards, check out this hoverboard built with gardening tools.

# Hovering Questions About Magnetic Levitation

Who doesn’t love magnets? They’re functional, mysterious, and at the heart of nearly every electric motor. They can make objects appear to defy gravity or move on their own. If you’re like us, when you first started grappling with the refrigerator magnets, you tried to make one hover motionlessly over another. We tried to position one magnet over another by pitting their repellent forces against each other but [K&J Magnetics] explains why this will never work and how levitation can be done with electromagnets. (YouTube, embedded below.)

In the video, there is a quick demonstration of their levitation rig and a brief explanation with some handy oscilloscope readings to show what’s happening on the control side. The most valuable part, is the explanation in the article where it walks us through the process, starting with the reason permanent magnets can’t be used which leads into why electromagnets can be successful.

[K&J Magnetics]’s posts about magnets are informative and well-written. They have a rich mix of high-level subjects without diluting them by glossing over the important parts. Of course, as a retailer, they want to sell their magnets but the knowledge they share can be used anywhere, possibly even the magnets you have in your home.

Simpler levitators can be built with a single electromagnet to get you on the fast-track to building your own levitation rig. Remember in the first paragraph when we said ‘nearly’ every electric motor used magnets, piezoelectric motors spin without magnets.

# Building A Magnetic Levitating Quadcopter

Three days ago on October 21, 2014 it was announced to the world the Back to the Future hoverboard was real. It’s a Kickstarter, of course, and it’s trending towards a \$5 Million dollar payday for the creator.  Surprisingly for a project with this much marketing genius, it’s a real, existing device and there’s even a patent. From the patent, we’re able to glean a few details of how this hoverboard/magnetic levitation device works, and in our post on the initial coverage, we said we’d be giving away some goodies to the first person who can clone this magnetic levitation device and put it up on hackaday.io.

[jellmeister] just won the prize. It’s somewhat cheating, as he’s had his prototype hoverboard working in July, and demoed a more advanced ‘upside-down quadcopter’ device at the Brighton Mini Maker Faire in September. Good on ‘ya [jelly]. You’re getting a gift card for the hackaday store.

Like the Kickstarter hoverboard, [jelly] is using an array of magnets rotating in a frame above a non-ferrous metal. For the initial test, eight neodymium magnets were arranged in a frame, suspended over 3/4″ aluminum plate, and spun up with a drill. With just this simple test, [jelly] was able to achieve 2kg of lift at 1cm and 1kg of lift at 1 inch of separation. This test also provided some valuable insight on what the magnets do to the aluminum or copper; the 3kg aluminum plate was nearly spinning, meaning if this device were to be used on small plates, counter-rotating pairs of magnetic lifters would need to be used.

The test rig then advanced to two pairs of rotors with standard hobby brushless motors, but stability was a problem; the magnetic rotors provided enough lift, but it would quickly fall over. To solve this problem, [jellmeister] took a standard quadcopter configuration, replaced the props with magnetic rotors, and successfully hovered it above a sheet of aluminum at the Brighton Maker Faire.

Since [jellmeister] has actually built one of these magnetically levitating hoverboards, he has a lot more data about how they work than an embargoed press release. The magnetic rotor hoverboard will work on aluminum as well as copper, but [jell] suspects the Kickstarter hoverboard may be operating right at the edge of its performance, necessitating the more efficient copper half pipe. The thickness of the non-ferrous plate also makes a difference, with better performance found using thicker plates. No, you bojo, hoverboards don’t work on salt water, even if you have pow-ah.

So there ‘ya go. That’s how you build a freakin’ hoverboard. [jellmeister]’s design is a little crude and using a Halbach array for the magnetic rotors should improve efficiency. Using a 3D printed rotor design is a stroke of genius, and we’ll expect a few more quad-magnetic-levitating-things to hit the tip line in short order.

Demos of [jellmeister]’s work below.

Oh. These things need a name. I humbly submit the term ‘Bojo’ to refer to any device that levitates though rotating magnets and eddy currents.

# The Hoverboard You Can Build At Home

Press embargoes lifted today, heralding the announcement of the world’s first hoverboard. Yes, the hovering skateboard from Back to the Future. It’s called the Hendo hoverboard, it’s apparently real, and you can buy one for \$10,000. If that’s too rich for your blood, you can spend \$900 for a ‘technology demonstrator’ – a remote-controlled hovering box powered by the same technology.

Of course the world’s first hoverboard is announced to the world as a crowd funding campaign, so before we get to how this thing is supposed to work, we’ll have to do our due diligence. The company behind this campaign, Arx Pax Labs, Inc, exists, as does the founder. All the relevant business registration, biographical information, and experience of the founder and employees of Arx Pax check out to my satisfaction. In fact, at least one employee has work experience with the innards of electric motors. At first glance, the company itself is actually legit.

The campaign is for a BttF-style hoverboard, but this is really only a marketing strategy for Arx Pax; the hoverboards themselves are admittedly loss leaders even at \$10,000 – the main goal of this Kickstarter is simply to get media attention to the magnetic levitation technology found in the hoverboard. All of this was carefully orchestrated, with a ‘huge event’ to be held exactly one year from today demonstrating a real, working hoverboard. What’s so special about demoing a hoverboard on October 21, 2015?

I defy anyone to come up with a better marketing campaign than this.

The meat of the story comes from what has until now been a scientific curiosity. Everyone reading this has no doubt seen superconductors levitated off a bed of magnets, and demonstrations of eddy currents are really just something cool you can do with a rare earth magnet and a copper pipe. What [Greg Henderson] and Arx Pax have done is take these phenomena and turned them into a platform for magnetic levitation.

According to the patent, the magnetic levitation system found in the Hendo hoverboard works like this:

• One or more electric motors spin a series of rotors consisting of an arrangement of strong permanent magnets.
• The magnets are arranged in a Halbach array that enhances the magnetic field on one side of the array, and cancels it on the other.
• By placing the rotors over a conductive, non-ferrous surface – a sheet of copper or aluminum, for example – eddy currents are induced in the conductive surface.
• These eddy currents create a magnetic field that opposes the magnetic field that created it, causing the entire device to levitate.

That’s it. That’s how you create a real, working hoverboard. Arx Pax has also developed a method to control a vehicle equipped with a few of these hover disks; the \$900 ‘Whitebox’ technology demonstrator includes a smart phone app as a remote control.

If you’re still sitting in a steaming pile of incredulity concerning this invention, you’re in good company. It’s a fine line between being blinded by brilliance and baffled by bullshit, so we’re leaving this one up to you: build one of these devices, put it up on hackaday.io, and we’ll make it worth your while. We’re giving away some gift cards to the Hackaday store for the first person to build one of these hoverboards, preferably with a cool body kit. The Star Wars landspeeder has already been done, but the snowspeeder hasn’t. Surprise us.

# Ethernet Connection Using Capacitive Coupling

Wanting to save space and weight on his project build [Florin] set out to find a way to add Ethernet connectivity without the magnetics. His ill-advised first try involved directly coupling two switches, frying both in the process. After some research he found that Ethernet hardware manufacturers have considered the need for devices without the magnetics and there are several application notes available on the subject. [Florin] followed the information that Realtek has for their devices and learned that they can be couple capacitively. After depopulating the magnetics from a second pair of switches he wired up some resistor-capacitor networks on a breadboard and got the connecting to work.