It was around noon on Monday and I was working in my lab. I decided to take a short break and catch up on the latest news. There, blaring on my computer screen was the headline: “Jimi Heselden, owner of the Segway firm, dead.”
For years, I had used the Segway as a comedic muse. I even wrote about this obsession my sophomore year for The News-Letter’s April Fool’s edition. It was only natural that I wanted to read more about this tragic event.
It was at that moment I saw the cause of death: in a Segway accident, Heselden fell down a cliff and drowned. At the time, I appreciated the irony. Then I thought, this would be a great time to write an article explaining how a Segway works.
Some may say I am being very insensitive, that it is too soon. I do not intend to use this article to make fun of the tragic circumstances surrounding his death. If anything, I mean this article to be a celebration of Heselden’s life and work.
When Dean Kamen, inventor of Segway, unveiled his invention, he declared that it would revolutionize the way we get around. While that prediction has not panned out, the Segway is nonetheless an impressive machine. Modeled after the human body, the Segway reacts precisely to the slightest motion. A series of tilt-sensors act like the balancing system in the inner ear and the microprocessor acts like the human brain.
The primary sensor system consists of an assembly of gyroscopes. A basic gyroscope is made up of a spinning wheel inside a stable frame. The actual physics behind gyroscopes is very simple and is based on the conservation of angular momentum. When a force is applied to the gyroscope, an opposite force is produced by the spinning wheel. The forces end up balancing out.
A gyroscope wheel will maintain its position in space relative to the ground. However, the gyroscope’s frame will move freely in space. By measuring the position of the frame relative to the gyroscope wheel, you can determine the pitch of an object. In the Segway, the change in frame position is detected using sensors.
Because a traditional gyroscope would be too cumbersome and bulky, the Segway accomplishes the same effect using a different sort of mechanism. The Segway uses a special solid-state angular rate sensor, which functions using the principles of the Coriolis effect. The Coriolis effect is the apparent rotation we see in an object when it moves relative to a rotating body. This effect is most pronounced in large storm systems like hurricanes. The storm may be traveling in a straight line, but because the Earth itself is rotating, the storm appears to turn.
The solid-state angular sensor consists of a tiny silicon plate mounted on a support frame. The silicon particles move due to an electrostatic current applied across the surface of the plate. The movement of the silicon particles in turn causes the plate to vibrate. When the plate is rotated around a particular axis, there is a sudden shift in the position of the silicon particles relative to the plate. There is a change in vibration which is relative to the degree of rotation.
The tilt information is passed on from the sensors to the microprocessors, which act like the brain of the machine. The ten microprocessors onboard a Segway have a computing power greater than three PCs.
Such processing power is necessary in order to make precise adjustments and prevent anyone from falling over. The processor relays this information to a several electric motors, which can move each wheel independently.
If a processor fails, the other processors can temporarily compensate for the loss. The rider is typically notified and the Segway should come to a gentle stop.
While we may find it easy to make fun of Segways and their passengers, we can also appreciate the science and engineering that goes into building one of these unique machines.
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