The Technology Behind The Segway
December 12, 2001

For all of its hype, the Segway Human Transporter superscooter is a remarkable piece of engineering.

In an interview Tuesday, executives at Segway LLC, Manchester, N.H., described the technology behind the device code-named "Ginger", a personal transportation machine that uses a complex series of sensors and gyroscopes to balance a human passenger on a pair of wheels.

Dean Kamen, the Segway's inventor, unveiled the machine after almost a year of fevered speculation last week; instead of a personal levitation device, the Segway is actually an innovative two-wheel scooter seen as a replacement for automobiles in urban environments. The device resembles a push mower; the user stands on a platform between two wheels set side by side.

The Segway will ship in two models, according to Tobe Cohen, director of brand strategy and marketing for the Segway. A p-series machine will be sold to consumers as a "personal" model, a smaller, lighter model designed with a slimmer wheelbase. Segway is also marketing an industrial "i-series" model designed for the U.S. Post Office, police officers, and other individuals that will need a sturdier model capable of a longer range. Segway hopes to have both on the market in volume by the end of 2002.

"With the i-series we'll be offering a family of accessories, such as a series of bags, which can be mounted on a variety of points on the vehicle," Cohen said. Currently, the Segways will cost between $8,000 and $10,000, with the goal to reduce the cost to about $3,000 over time.

Like a computer, the Segway has been designed as a platform for Segway and other manufacturers to add to with additional capabilities, Cohen said. For example, Cohen said that Segway is evaluating two types of trailers that could be mounted on the "i-series" Segway: a traditional unpowered passive trailer, and an "active" powered model that would intelligently follow the master Segway around obstacles and corners.

The p-series is designed for "dense" urban environments, where crowds of people make cars an inconvenience. The wheelbase is tighter°X21 inches versus the 25 inches used for the industrial model°Xand the wheels are smaller, only 14 inches. Legally, the Segway is not a motor vehicle and can run on sidewalks at speeds up to 12.5 mph for the industrial model and 10 mph for the personal model.

"We're working with local governments to make sure they understand this," Cohen said.

The industrial model lifts the user 8 inches off of the ground, while the personal Segway's height is a bit smaller, thanks to the smaller and thinner wheels. Both Segway models boast small fenders to prevent flying gravel and mud, and each has rubber tires similar to a gas-powered scooter. The industrial model weighs 80 pounds, while the smaller, personal Segway is 65 pounds.

Each Segway comes equipped with a 64-bit encrypted magnetic key to prevent theft. The key can also be used to ask the Segway to conform to a profile that governs speed, turning radius, and battery life. For example, a "new user" profile will limit the speed of the Segway until the rider feels comfortable to unlock its full capabilities.

Segway's revolutionary balance-control system works in tandem with a pair of electric motors, one powering each wheel. The principle is simple: as the rider shifts his or her balance, the Segway adjusts itself to keep from tipping over. The same algorithm governs the turning radius at various speeds, preventing the driver from tipping over while cornering.

That motion-control algorithm, which requires input from four sensors under the riders' feet and five solid-state gyroscopes, is the soul of the Segway, explained J. Douglas Field, vice-president of product development at the company.

"If I ask you to hold a pen in your hand and balance it, it's quite difficult," Field said. "But if I ask you to do the same thing with a broom in your hand, it's relatively simple. The reason is that's there's more time to compensate. For that reason it's actually easier the higher you are off the ground. But standing on a stepladder (on a Segway) is not recommended."

For safety's sake, the Segway's control mechanisms were designed to be redundant. Each component has either two or three backup devices in case the primary fails, Field said. In a case where a failing component might generate inaccurate data that might endanger the rider, the third component is in place to "vote" the faulty component out if the output fails to match that of the other systems. The motion control algorithms are run on a DSP designed by Texas Instruments, using a variety of embedded control and data buses like I2C, SPI, and SCI.
Inside the Segway: Top view
click on image for full view
Inside the Segway: Top view (angled)
click on image for full view

The Segway contains two motors, each with a set of windings, but with a common shaft. Since the motors can apply opposite torque, the machine can turn in place with no additional turning radius. "Mechanically, the Segway contains one motor, but electrically it contains two," Field said.
Inside the Segway: Close-Up
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At idle, the Segway can stand upright by itself, balancing on its internal gyros, and will do so for up to 34 hours, Field said. Segways will also ship with kickstands. According to the company, the maximum range of the i-series industrial Segway is 17 miles on a single charge, although the actual range will likely be 11 miles depending upon terrain and the machine's usage. The p-series personal Segways' range will be smaller, as the device uses a smaller version of the i-series' lithium-ion battery. However, the Segway does not need a fancy recharging system; the onboard charger uses a standard 110V/220V AC cord, with no "wall wart" or transformer needed.

"We wanted to make it simple, and for a user to use a monitor cord or other power cord in a pinch," Field said.

Like an electric car, the Segway returns power to the battery system during braking. During acceleration, priority is given to safety. "The Segway doesn't have a throttle, remember," Field said. "So if you're cruising around 8 miles per hour and hit a pothole, the Segway is going to apply enough torque to keep you safe and upright."

Even as the battery wears down, the Segway will apply up to its maximum 2-hp torque to keep the rider upright in the event of a pothole or other obstacle. Theoretically, Segway could improve the speed of the device

The Segway has been tested in up to 5 inches of water. Any more, and the operator's feet will get wet. "It's not designed to be immersed," Field said. "It's not a submarine."

While the Segway is not designed to be ridden up stairs, as other reports have said, the Segway can be used in a self-powered idle mode that allows the machine to be dragged behind a user at walking speed. The machine can climb a 30-degree grade, Field said.

Segway LLC has no plans to license the technology to any other company, Segway's Cohen said. Initially, the Segway will be marketed almost exclusively within the U.S. However, the president of Taipei, Taiwan visited Segway on Monday and requested a demonstration, Cohen said. "Dense urban environments are a global problem," he said.

The p-series personal Segway is designed to run for about as long as a car, or about ten years, Field said. An i-series Segway should last about half as long. Still, Field said the company is still trying to figure out how customers will use the new device, a key factor as it determines how long its warranty should last.

"We're still trying to determine how people will use this," Field said. "If it's just standing there, it's still putting hours on the machine."

Cohen declined to allow reporters to unlock the full potential of the Segway and ride at its fastest rated speeds. Meanwhile, however, inventor Kamen whizzed about, chatting with venture capitalists, San Francisco Chronicle editor Phil Bronstein and various reporters. When asked if anyone had learned to do any tricks with the Segway yet, Kamen chuckled.

"We're not into extreme sports yet," Kamen said, effortlessly pulling a standing 180-degree turn. "It's a productivity tool."

The Art of the Lean: Riding the Segway
December 12, 2001

The Art of the Lean

All this little scooter needs is a bit of Cavorite, the gravity-neutralizing coating from H.G. Wells' "The First Men in the Moon". Then the Segway would be a creation right out of "The Jetsons". As it is, the Segway is a charming, deceptively simple device. From the moment you see the little smile icon--eerily reminiscent of the smile icon on the Apple Macintosh, the Segway practically screams "Adore Me!". However, the cute face serves a serious purpose: changes in expression in the face allude to conditions within the Segway's innards.

Movies: Segway in Action
Segway Introduction Click Here
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Mark Hachman on Segway Click Here
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Loyd Case on Segway Click Here
Click Here
*Files available as Web downloads, not streaming video.

In fact, there's a lot of technology underneath the startlingly small hood. Start with the sensors, for example. In our discussions with Tobe Cohen (Director of Brand Strategy and Marketing for Segway) and J. Douglas Fields (VP of Product Development), we probed for as much detail about the internal workings of the Segway as possible, but they were reluctant to unveil much. With all the media attention, the last thing they want is for competitors to rush out and create duplicates. But we were able to glean some details.

There are five discrete, solid-state gyroscopic sensors. These sensors detect the Coriolis force generated by angular momentum, whether that momentum is generated by rotating wheels, planetary bodies, sharp turns or other rotational forces. One example of this type of sensor can be found here. These sensors feed data into the onboard network on the Segway at 100 samples per second. There are a number of different processors built into the Segway's electronics, but the network is continually monitored by the TI TMS320 digital signal processor.

Although Fields was reluctant to divulge details of the control software, the behavior of the software as described seems to resemble process control software used in industrial applications. There's a control loop that polls the network of sensors, but the capability exists for an interrupt to quickly get attention from the master DSP. All of the software is written in-house, and no commercial real-time operating system kernel is used.
Inside the Segway: Top view
click on image for full view

The motors themselves are electrically redundant. In other words, there are two motors that drive the Segway's solid wheels. Each motor has two discrete sets of windings, so if one fails electrically, the other set picks up the slack. Battery life is anywhere from 11 to 17 miles, depending on usage. The battery recharges whenever braking occurs (including when traveling downhill). The Segway can plug into any standard wall outlet, and even uses the standard 3-wire power cord that's familiar to all PC users, so finding a charging outlet will rarely be a problem.
Inside the Segway: Close-Up
click on image for full view

Adult Preconceptions
What's really cool about the Segway, though, is the incredible degree of simplicity from the user perspective. There's a vast array of compute power built into the compact, redundant circuit boards, and all of it goes to make the Segway easy and intuitive to use. For example, imagine what happens when the Segway is powered up: it stands there. That sounds simple, but in fact, the sensors, processors and motors are all working to keep the unit upright and balanced.

When you stand on the Segway, there's a temptation to try to balance yourself on an unstable platform. All our grown-up experience tells us that this thing can't possibly stand on its own. Once you relax and let the Segway do its thing, it still just stands there--but with you on it. Tobe Cohen noted that kids and teenagers tend to have no problems just getting on the Segway and assuming it will work. It's grown-ups that have the biggest problems adjusting.

However, for this grown-up, the adjustment period was relatively small--although our test rides were restricted to flat, level surfaces. In fact, when Mark Hachman tried to go up an inclined platform, Cohen immediately stopped him. There is a learning curve, as with any device, although unlike other mechanical gadgets, much of that learning curve is forgetting what you already "know".
ExtremeTech's Mark Hachman giving the Segway a trial run
ExtremeTech's Mark Hachman giving the Segway a trial run

Driving the Segway is as simple as leaning forward--just as you lean slightly forward when you begin to walk. As soon as you start to lean, the Segway begins to move. The further you lean, the faster it goes, up to its governed speed. You stop the Segway by leaning back. It's easy to talk about, but difficult to describe.

Turning is a bit different, and does require some conscious thought. There's a grip on the left handlebar, similar to the twist grip gearshift on modern bicycles. Rotating the grip towards you (which is to the left) initiates a left turn; twisting the grip the opposite direction will enable a turn to the right. Note that the grip is small--perhaps three centimeters wide--and doesn't take up the entire left handlebar grip. It's quite easy to rotate with just a thumb and forefinger.

In our brief time with the Segway, we became facile in maneuvering (slowly) around the flat floor of the conference center. It's clear that it will take some practice to begin zooming around inclines and bumpy roads, but probably not nearly as much time as it took any of us to learn to ride bicycles.

Real Applications
So the Segway is great fun to ride around in, and even reasonably practical for a single person.

While Dean Kamen has waxed lyrical about vast numbers of Segways populating the sidewalks of metropolitan cities, it's unlikely that this will happen in the foreseeable future. However, there are very serious industrial applications. The first announced customer is the US Postal Service, and it's easy to see how the Segway could work as a mailman's vehicle (when the weather isn't too inclement, anyway).

Another potential use is large factory floor or light industrial environments. The Segway could function as a simple transportation device, or as a delivery vehicle for light industrial inventory. In fact, the Segway is designed to tow carts--but the carts envisioned by the company are not simply dumb wagons. Instead, each cart will be a sort of mini-Segway that can intelligently follow the towing vehicle's path, so carts will never get hung up on sharp corners. You could even envision carts that aren't physically connected, but instead "imprint" on a "parent" Segway and follow it around like a gaggle of baby geese.

Most of America's urban environment is probably ill-suited for the Segway, though it could be quite popular on college campuses (if you ignore the high price). However, passenger Segways may be more popular overseas than in the US. I can still recall veritable hordes of small motor scooters rodding around the streets of Taipei, spewing out plumes of blue hydrocarbon exhaust. Substituting Segways will at least move the pollution problem to the power generation plant.

In the end, the Segway may be more of a precursor device, than anything that will change the urban landscape in and of itself. Like the early personal computers, there will no doubt be many engineers who are looking at the Segway and scratching their heads, thinking, "what if I..."
J. Douglas Fields
J. Douglas Fields (VP of Product Development) explaining Segway

Photos: Front & Back

Segway, in all its glory
View from back side
View from back side
Second back shot

Photos: Side views

Side view
Side view
Angled side view
Angled side view

Photos: Close-ups

Segway Platform
Segway Platform
Power plug
Power plug
Segway Dashboard
Segway Dashboard Close-up

Photos: Riding the Segway

Key to Segway
Key to Segway
Mark Hachman getting onboard
Mark Hachman getting onboard
Mark on the Segway
Mark on the Segway

Copyright (c) 2003 Ziff Davis Media Inc. All Rights Reserved.