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Saturday, December 6, 2014

Maglev Hover Racer

Oh boy, this is going to be a long one....

Let's start with some inspiration. You've probably seen this: Hendo Hoverboard . The first time I saw it, I thought it was total BS. If you have any sort of engineering or electronics background, you know that magnetic levitation is extremely energy intensive: you either need a ton of power to drive the electromagnets or you need them to be superconducting (or maybe both). There is no way that that board has cryogens on board (for superconducting) nor has 10's of kW's. Even though the videos they posted wouldn't be hard to fake, I noticed a lot of reviews saying that it actually works. What gives? So a guy from my lab looks up his patents. Turns out he's using large rare-earth permanent magnet Halbach arrays arranged on a disk and spinning them at many 1000's RPM over non-ferrous conducting surfaces, e.g. copper (like in their videos) or aluminum. The varying magnetic fields in the conducting surface create eddy currents in the conducting surface, which generate magnetic fields to oppose the applied magnetic fields. Thus, you get lift (and drag torque). Arrange four of those "hover engine" pods in a fashion similar to quadcopter to cancel the torques, and presto: hover board.

There are a few catches though. While power isn't being used to generate the applied magnetic field (permanent magnets), a large amount of power must be used to spin the disks and overcome the power being dissipated by the eddy currents. The motors used must also be efficient and light weight. Judging by the use of RC style wires and connectors, I can almost guarantee that each of the pods on their board has a ~1.5kW brushless outrunner hobby motor. The central compartment probably contains the four hobby ESC's and about (judging by the size of the compartment) 300Whrs of high discharge rate hobby LiPo packs. That gives the 3 minutes of runtime reported by some people who've ridden the board. Also, while they don't have sound in the kickstarter videos, this thing is LOUD. Look up some of the other videos of it on youtube. Four large rotors spinning very fast are going to make a lot of noise if they aren't *perfectly* balanced.

They are also selling a developer kit that has four smaller versions of their "hover engines" for $900. I'm betting these are just scaled down from the big ones: hobby motors, controllers, and smaller permanent magnet halbach arrays. That got me thinking....I could make a better one for less.

Turns out I wasn't the first to think of this concept...turns out Hendo wasn't either! A pair of Brits showed off a small quadcopter-style hover-er at a maker-faire about a month before Hendo went public. Here's the link on Hackaday. Check out the videos at the bottom. (I think that shows prior-art, so I'm not sure how the Hendo patents will get approved, but I'm not an expert in patent law...) . Very cool. 3D-printed rotors hold the magnets. A minimal chassis holds the large battery and the ESC's. This is totally do-able.

So what did I do? I started a lab-wide competition. "The First (and probably last) Great FIT Hover Race"! FIT=Florida Institute of Technology by the way...apparently my grad school isn't well known. Currently there are 4 teams, one of which is me all by me-self (because I want to use it as my Mechatronics class final project). The competition consists of a hover race around a 1/4" thick aluminum track, weight lifting, and a tug-of-war. The rules are: 1. All lift force must come from magnetic levitation. 2. No part of the vehicle may touch the ground at any time. 3. Onboard batteries must be used for power. No external power sources. 4. Thrust/steering may be from any source (as long as it is not in violation of rules 1-3). 5. Maximum vehicle dimensions are 12"x12"x12" (because we can't afford giant slabs of aluminum). 6. Must look cool (no boring white boxes like Hendo's).

Sound fun?

I decided to split up this post. Next: My design.


  1. Well this looks like an awesome idea. Are you making it FIT only or accepting outsiders? Not that we'd be that likely to be able to get over to Florida... Also stick a comment on if you want any tips from our work. We'd be happy to help out:)

  2. Sure. No idea when race will actually be though.

  3. Dear Jed, thank you for sharing, I wish I had seen your blog earlier! Great work, I am delighted to see that it does work..... Most of the steps I've just gone through, you already had solutions..... Unbalanced 3D printed rotors circulating at about 6000 rpm is freaking scary, now I have them machined Aluminum, only to learn some days ago about a so called Halbach effect.... which is difficult to reach with cylindrical magnets..... Did you already race, or is the event still to be planned?

    1. Thanks!

      Unfortunately, the other teams lost interest, so it never happened. I also haven't had time to work on the next version.

  4. Brilliant work, Jed. May I suggest a non-contact instant response thruster? Use two flat vertical axis coils to produce eddy currents in the aluminum base plate. These will interact to produce lateral force. Like in an old-fashioned induction type electrical power meter. All the best for your future work, mike