What makes a segway work

Dean Kamen, the machine's inventor, held especially high hopes for the Segway. In an interview with Time Magazine, he claimed that his machine "will be to the car what the car was to the horse and buggy. Although the Segway hasn't quite lived up to its hype, it's most definitely an amazing machine. In this article, we'll find out what sets the Segway apart from earlier vehicles, and we'll see why its inventor thought it could change the world. Unlike a car , the Segway only has two wheels -- it looks something like an ordinary hand truck -- yet it manages to stay upright by itself.

To move forward or backward on the Segway, the rider just leans slightly forward or backward. To turn left or right, the rider turns the right handlebar forward or backward.

This balancing act is the most amazing thing about the Segway, and it is the key to its operation. To understand how this system works, it helps to consider Kamen's model for the device -- the human body. If you stand up and lean forward, so that you are out of balance, you probably won't fall on your face. Your brain knows you are out of balance, because fluid in your inner ear shifts, so it triggers you to put your leg forward and stop the fall.

Instead of falling, you walk forward, one step at a time. The Segway does pretty much the same thing, except it has wheels instead of legs, a motor instead of muscles , a collection of microprocessors instead of a brain and a set of sophisticated tilt sensors instead of an inner-ear balancing system.

Like your brain, the Segway knows when you are leaning forward. To maintain balance, it turns the wheels at just the right speed, so you move forward. On September 14, , Segway, Inc. Several riders have fallen off of their Segways and suffered injuries like broken teeth and a broken wrist. Segway is offering a free software upgrade that will fix the problem, which is available at Segway dealerships and service centers [ ref ].

At its most basic, the Segway is a combination of a series of sensors, a control system and a motor system. In this section, we'll look at each of these elements.

The primary sensor system is an assembly of gyroscopes. A basic gyroscope is a spinning wheel inside a stable frame. A spinning object resists changes to its axis of rotation, because an applied force moves along with the object itself. If you push on a point at the top of a spinning wheel, for example, that point moves around to the front of the wheel while it is still feeling the force you applied.

As the point of force keeps moving, it ends up applying force on opposite ends of the wheel -- the force balances itself out.

See How Gyroscopes Work to learn more. Because of its resistance to outside force, a gyroscope wheel will maintain its position in space relative to the ground , even if you tilt it. But the gyroscope's frame will move freely in space. By measuring the position of the gyroscope's spinning wheel relative to the frame, a precise sensor can tell the pitch of an object how much it is tilting away from an upright position as well as its pitch rate how quickly it is tilting.

A conventional gyroscope would be cumbersome and difficult to maintain in this sort of vehicle, so the Segway gets the same effect with a different sort of mechanism. Segways use a special solid-state angular rate sensor constructed using silicon. This sort of gyroscope determines an object's rotation using the Coriolis effect on a very small scale. Simply put, the Coriolis effect is the apparent turning of an object moving in relation to another rotating object.

For example, an airplane traveling in a straight line appears to turn because the Earth is rotating underneath it. A typical solid-state silicon gyroscope consists of a tiny silicon plate mounted on a support frame. The silicon particles are moved by an electrostatic current applied across the plate. The particles move in a particular way, which causes the plate to vibrate in a predictable manner.

But when the plate is rotated around its axis that is, when the Segway rotates in that particular plane , the particles suddenly shift in relation to the plate. This alters the vibration, and the change is in proportion to the degree of rotation. The gyroscope system measures the change in vibration, and passes this information on to the computer. In this way, the computer can figure out when the Segway is rotating along particular axes. Check out this site for more information on solid-state silicon gyroscopes.

The Segway HT has five gyroscopic sensors, though it only needs three to detect forward and backward pitch as well as leaning to the left or right termed "roll".

The extra sensors add redundancy, to make the vehicle more reliable. Additionally, the Segway has two tilt sensors filled with electrolyte fluid. Like your inner ear, this system figures out its own position relative to the ground based on the tilt of the fluid surface. All of the tilt information is passed on to the "brain" of the vehicle, two electronic controller circuit boards comprising a cluster of microprocessors. The Segway has a total of 10 onboard microprocessors, which boast, in total, about three times the power of a typical PC.

Normally, both boards work together, but if one board breaks down, the other will take over all functions so that the system can notify the rider of a failure and shut down gracefully.

The Segway requires this much brain power because it needs to make extremely precise adjustments to keep from falling over. In normal operation, the controller boards check the position sensors about times per second. The microprocessors run an advanced piece of software that monitors all of the stability information and adjusts the speed of several electric motors accordingly.

The electric motors, which are powered by a pair of rechargeable nickel metal hydride NIMH or Lithium-ion Li-ion batteries, can turn each of the wheels independently at variable speeds. The Segway is a two-wheeled, self-balancing, battery-powered electric vehicle that use c omputers, sensors, and electric motors in the base of the Segway keep the device upright when powered on with balancing enabled.

When you lean foward , the sensors activate the motors to get the wheels moving in order to keep you on your the center of gravity. The same way you put your feet foward to not fall when you walk. For instance, when you lean backwards you will move backwards until the center of gratvity is reached again, that is, when you stop leaning neither backwards or fowards. How does is stop? If you move forward, hence leaning forwards , you lean gently back until to point of gravity is reached again.

Segway hopes to have both on the market in volume by the end of Like a computer, the Segway has been designed as a platform for Segway and other manufacturers to add to with additional capabilities, Cohen said. Legally, the Segway is not a motor vehicle and can run on sidewalks at speeds up to 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 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. 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.

Douglas Field, vice-president of product development at the company. But standing on a stepladder on a Segway is not recommended. Each component has either two or three backup devices in case the primary fails, Field said.