The sensor system is made up of delicate gyroscopes, or spinning wheels built into a frame. Using applied force to move the object itself, the spinning wheel maintains its position relative to the ground, even when it is tilted. By noting the position of the gyro’s spinning wheel in relation to the position of the frame, a sensor can identify the ‘pitch’ of an object, or how far it is tilting away from an upright position, and also the ‘pitch rate,’ or how quickly it is tilting. This complex system keeps the Segway’s wheels from spinning out from under the rider, just as it keeps your feet from flying out from under you when you walk, and also allows it to maintain a standing position even while the rider is away.
The solid-state, silicon gyroscope system is able to record the change in vibration during a ride and it passes this information on to an onboard computer, so the Segway can tell when it is rotating on a particular axis. The Segway is built with five gyroscopic sensors. It requires only three of these to detect “roll,” or forward and backward pitch combined with side to side movement. The remaining sensors are to ensure redundancy and make the vehicle operate more reliably for a longer period of time. And much like the human body, two tilt sensors inside the Segway are filled with electrolyte fluid so the machine always knows its own position on the ground from the tilt of the fluids.
This and other information on tilt is passed onto the vehicle’s ‘brain,’ where two control circuit boards hold a series of 10 microprocessors, or three times the power of a typical personal computer. Typically, both circuit boards work together, but if one goes out the other can carry the entire load in order to notify the user of the failure and shut down gradually rather than ‘seizing up’ in mid-motion. This incredible use of ‘brain power’ allows the Segway to make difficult choices and adjustments easily and automatically, without the rider having to do anything at all except enjoy! Meanwhile, the controller boards keep busy by checking the position sensors approximately 100 times per second and the microprocessors run software that monitors stability information and adjusts the speed of on-board electric motors, which are powered by rechargeable nickel metal hydride (NIMH) batteries.
As the rider leans forward, the motors spin the two main wheels in the same direction to stay upright, and the same goes for backward motion. When the operator turns the handlebar controls left or right, the motors spin one wheel faster than the other or in the opposite direction to rotate the Segway.
This may help one understand why some people refer to the Segway as “the most advanced vehicle in the world.”