Reverse Engineering Hoverboard Motor Drive

The must-have toy of the moment last winter was the “Hoverboard”. We all probably secretly wished them to be the boards from the Back to the Future series of films made real, but the more achievable reality is a self-balancing scooter somewhat akin to a miniature Segway. It seemed every child wanted one, schools banned them, and there was a media frenzy over some of the cheaper models that lacked protection circuitry for their li-ion batteries and thus had a tendency for self-incineration.

[Drew Dibble] is interested in the Power Racing Series (PRS), in which toy electric cars are souped up for competition. Casting around for a source of cheap and relatively powerful motors he lit upon the self-balancing scooters, and waited on Craigslist for the inevitable cast-offs. His resulting purchase had two 350W brushless hub motors and all the associated circuit boards for motor control, gyroscope, and oddly a Bluetooth speaker. The motor control board received an unknown two-wire digital feed from the scooter’s control board, so he set to work investigating its protocol. His write-up of how he did it is an interesting primer in logic line detective work.

Hooking up his logic analyzer he was quickly able to rule out the possibility of the control signal being PWM because all signals followed the same timing. Both lines had data so he was able to rule out I2C, for in that case one line would carry a clock. He was therefore left with a serial line, and taking the 38 microsecond timing interval, he was able to calculate that it had a rather unusual bitrate of 26315 BPS. Each packet had a multiple of 9 bits so he either had 9-bit or 8-bit with parity, and trying all possible parity schemes resulted in parity errors. Therefore the boards used a highly unusual 9-bit non-standard bitrate serial port. Some experimentation led him to an Arduino library, and he was able to get some movement from his motors. Some clever timing detective work later and he could make them move at will, success!

All his code for the project is on GitHub, for his 9-bit SoftwareSerial library and a motor control sketch.

If you want a real Back to the Future hoverboard then you may have to wait a while longer. We have featured a replica made as an unrideable floating artwork though, and a working board that is more of a personal hovercraft.

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Hoverboards are here – If You’re Crazy Enough to Try

A new video has been stirring questions on the internet this week. It shows a test of the Flyboard Air, a device that is somewhere between a Back to the Future Hoverboard and Green Goblin’s glider. The video depicts pilot [Frank Zapata] taking off, flying around, and landing an a platform not much larger than a milk crate. Plenty of folks are calling the video a fake. After a few back of the napkin calculations though, we’re coming out to say we think it’s real. Details are few and far between, so much of the information in this article is educated guessing based upon the video.

Here’s our hypothesis: Flyboard Air is a jet powered platform with little or no built-in intelligence. Balance, stability and control are all handled by the pilot. A hand controller simply provides throttle to adjust altitude, take off, and land.

jetfeetLet’s start with the jet powered part. During the video, [Frank] looks down at his board and the water below. Between his sneakers we can see two round openings – which look a lot like jet intakes. At the end of the video, [Frank] flies over the camera. stopping the action shows a split second where four exhaust holes are visible on the bottom of the board. These jets look quite a bit like model aircraft jet engines.

We don’t know exactly which engines [Frank] is using, but as an example, the Jet-Cat P 400 RX-G packs 88 lbs of thrust into a shell less than 6 inches in diameter, weighing less than 8 lbs. Four of those engines would provide 352 lbs of thrust. That’s plenty to lift [Frank], the board, and a few gallons of Jet-A strapped to his back.

Why no built-in intelligence? Even the smallest quadcopters have gyros, accellerometers, and PID loops keeping them upright. The problem boils down to the physics of jet engines. Active stability in a fixed pitch rotary blade system requires very fast throttle response. Quadcopters have this with their brushless motors. Turbines however, have throttle lag on the order of seconds. You can’t beat physics. Accelerating 3 or 4 pounds metal from 78,000 RPM (~70% throttle) to 98,000 RPM (~100 % throttle) takes time.

flyboard1Standing on a column of uncontrolled thrust would take quite a bit of skill on the part of the pilot. As it turns out, [Frank] is one of the world’s most experienced thrust riders. His previous invention, the Flyboard uses a personal watercraft to create a column of thrust which the rider stands on. These boards have become tremendously popular at vacation spots in the last few years. There are plenty of videos on [Frank’s] YouTube channel showing the amount of control a skilled ride has over the board. Loops, spins, and other aerobatics look easy.

With that much skill under his belt, [Frank] would have no problem keeping balanced on four jet engines.

Such a skilled rider means that control wouldn’t really be needed on the board. We’re betting that the only electronics are the remote throttle control and the Engine Control Computers (ECU) needed to keep the jets running and synchronized. The two electric ducted fans on the sides of the Flyboard Air appear to be running all the time, only shutting down when [Frank] lands the board.

One final thought – taking off and landing a jet vertically is difficult. Ground effects destabilize the craft. Engines can suck in their own exhaust, stalling them. These are problems faced by the harrier jump jet and the joint strike fighter. [Frank’s ] solution is not never get too close to the ground. If you watch closely, he takes off and lands from a perforated metal platform mounted off the back of a van. The metal doesn’t reflect enough thrust to cause the Flyboard to become unstable or stall.

So is the video real? We think so. This is an amazing achievement for [Frank Zapata]. Is it practical or safe? Heck no! Nor is it cheap – those engines cost €8,845.00 each.  That said, we’d love a chance to ride the Flyboard Air – after a few hours of training on the original Flyboard of course.

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Converting an Electric Scooter to Lithium Batteries and Disabling the Safeties

There’s a bunch of different electric scooters available nowadays, including those hoverboards that keep catching fire. [TK] had an older Razor E300 that uses lead acid batteries. After getting tired of the low speeds and 12 hour charge times, [TK] decided it was time to swap for lithium batteries.

The new batteries were sourced from a Ryobi drill. Each provides 18 V, giving 36 V in series. The original batteries only ran at 24 V, which caused some issues with the motor controller. It refused to start up with the higher voltage. The solution: disable the safety shutdown relay on the motor controller by bridging it with a wire.

With the voltage issue sorted out, it was time for the current limit to be modified. This motor controller uses a TI TL494 to generate the PWM waveforms that drive a MOSFET to provide variable power to the motor. Cutting the trace to the TL494’s current sense pin removed the current limit all together.

We’re not saying it’s advisable to disable all current and voltage limits on your scooter, but it seems to be working out for [TK]. The $200 scooter now does 28 km/h, up from 22 km/h and charges much faster. With gearing mods, he’s hoping to eke out some more performance.

After the break, the full conversion video.

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An Actual Working Hoverboard

What with 2015 being the apparent “year of the hoverboard”, we have a final contender before the year ends. It’s called the ArcaBoard from ArcaSpace, A private space company. And it doesn’t use magnets, or superconductors, or any smoke and mirrors — just a whole lot of ducted fans.

Thirty-six of them to be precise. The ArcaBoard uses 36 electric motors with an apparent 7.55HP each, powered by a massive bank of lithium ion batteries. Together, they produce 430 pounds of thrust, which allows most riders to float around quite easily. Even with that huge power drain, it apparently lasts for a whole 20 minutes, which is pretty impressive considering its size.

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The Inaccurate Predictions Of Back To The Future

Sometime this evening, after we haven’t rehydrated a pizza for dinner, all of the events portrayed in Back To The Future will have happened in the past. This is it. This is the day all your dreams die.

So, what’s so special about the technology in Back To The Future that we don’t have now? Hoverboards, obviously, but a lot of people have been doing their part to make sure we have something like a hoverboard on this important day. Last week, the record for the longest hoverboard flight was broken by a Canadian company making large multirotor platforms. While it’s called a hoverboard, it’s really not in the spirit of the device that would recreate the skateboard chase scene in front of Hill Valley’s courthouse. For that, you’ll need something that doesn’t use propellers, at least.

There’s a better way to construct a hoverboard than by strapping a few blenders to your feet. Last summer, Lexus built one with superconducting materials and magnets. Yes, it’s effectively the same demonstration you’ve always seen with superconducting materials, only this time it’s dressed up with pro skaters. There are tens of thousands of dollars worth of magnets in the Lexus hoverboard, making this entirely impractical for anyone who wants to build their own.

next-yearThere is another option if you want a hoverboard. This day, last year, Hendo Hoverboards launched a Kickstarter with the best media blitz we’ve ever seen. They built a hoverboard that is basically a quadcopter, but instead of propellers, they use magnets. These magnets produce eddy currents in the metallic, non-ferrous ‘hover surface’. The grand prize for this Kickstarter? Today, October 21, 2015, you’ll be invited to a VIP event where you will not only get to ride a hoverboard, you’ll get one to take home. Price: $10,000.

News Drones
News drones. People still read newspapers.

This company isn’t in the market of building hoverboards; they have a much, much more grandiose idea: the founder wants to use hoverboards as a stepping stone to an active earthquake mitigation strategy for buildings. Yes, buildings can hover inches above their foundation, just in case an earthquake strikes. You say the power might go out during an earthquake, causing the building to fall inches to the ground? I never said it was a good idea.

Lucky for us, the Hendo hoverboard did prove to be a proof of concept that a ‘spinning magnet’ hoverboard is capable of supporting the weight of a rider. We know a few people have been working on this technology before the Hendo hoverboard was announced, and replicating the Hendo hoverboard build shouldn’t cost more than about $1000 USD. We’re eventually going to have to do this, and we’re going to replicate the Pitbull hoverboard, bojo, because we want powah.

So, what else of Back to the Future Part II hasn’t become a reality? News drones. People don’t read newspapers anymore. Self-driving cars are more realistic than hovercar conversions. Pepsi Perfect exists, but only at a Comic Con. Nike Air Mags exist, but not with power laces. The world of Hill Valley still has fax machines, and I really want to rehydrate a pizza.

cubbiesIt’s alright, most of the technology of Back to the Future was just a joke; ‘Queen Diana’ would have never happened, and what exactly was the point of Gray’s Sports Almanac if you can look everything up on the Internet?

There was one possibly accurate prediction in Back to the Future: The Chicago Cubs may win the 2015 World Series. Let me repeat that, for effect. The most accurate prediction of the future given to us in Back to the Future was that the Chicago Cubs win the World Series. That’s how inaccurate Back To The Future was.

The French Built the Superconducting Hoverboard 4 Years Before Lexus

The internet only just got over Lexus’ real working hover board, but as it turns out, a team of researchers from the University of Paris Diderot already built one, over 4 years ago (machine translation)!

Using the same principles as the hover board Lexus build, the researchers built a very expensive neodymium magnet track to test the board on. Only difference here is that they didn’t hide the magnets. The hover board itself was machined out of wood, and houses a large sealed metal tray which contains the superconducting bricks.

Pour in some liquid nitrogen through the funnel, and you’re ready to witness some of the quantum properties of superconductors! The board floats a few centimeters above the magnetic rails, and in their tests was able to lift people over 100 kg in weight (hint for most Americans… there are 2.2 pounds to one kilogram).

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Secrets Of The Lexus Hoverboard Revealed

Auto site [Jalopnik] got some hands-on (or rather feet-on) time with the Lexus hoverboard that was built for an advert for the luxury car brand, and their video reveals a few secrets about how this interesting device works. It is definitely real: the Jalopnik writer got to ride it himself, and described it as “Unbelievably difficult yet at the same time unbelievably cool, both because you’re levitating and because the board is filled with magnets more than 300 degrees below zero“. But a look behind the scenes reveals that it is another tease.

The device looks like it is a real hoverboard, floating several inches above the surface and even traveling over water, a feat that Marty McFly couldn’t do. But, as usual, there is a little more going on than meets the eye. The device is built around superconducting magnets cooled by liquid nitrogen, so it only works for about 10 minutes. After that, you have to refill the device with liquid nitrogen. The surface that the board is floating over also has what the Jalopnik writer describes as having “several hundred thousand dollars worth of magnets built in“. Try this on a non-magnetic surface and you’ll come to a grinding halt. If you watch the video of the hoverboard serenely gliding over the water from another angle, you can see a magnetic track just under the surface. If you run off this track, you’ll end up with wet feet.

Is it a neat hack? Yes. Is it cool? Yes. Is it the future of transportation? No: it is a cool hack put together for a car advert with a big budget. Kudos to Lexus for spending the cash to do it properly, but once again, our dreams of hoverboards are dashed in the cold, hard light of reality. Darn.