For all of its hype, the
Segway Human Transporter superscooter is a remarkable piece of
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
"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
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.
click on image for full
click on image for full
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.
click on image for full
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
"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
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
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
2001 By: Loyd Case
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.
*Files available as Web downloads, not
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
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.
click on image for full
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.
click on image for full
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
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
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
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
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
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 (VP of Product
Photos: Front & Back
Segway, in all its
View from back
Photos: Side views
Photos: Riding the Segway
Mark Hachman getting
Mark on the
Copyright (c) 2003 Ziff Davis Media Inc. All Rights