Made On Earth — DIY Segway

Craft & Design


Mechanical engineering student Charles Guan built a homemade Segway, called the Segfault, with some rather impressive geek cred. It uses absolutely no software, microprocessors, or other digital logic. He replicated the electric vehicle using a fully analog system made up of just op-amps and passive components. It’s no surprise — the MIT grad student has been building robots and other odd vehicles since he was 11 years old.

A classic inverted pendulum problem, the Segway system is naturally unstable — a point that was proven when, ironically, the company’s owner died test-driving a new all-terrain model. The system’s instability stems from having the mass located above its pivot point. This gives it two degrees of freedom — the pendulum’s angle and the horizontal freedom of the base.

“The job of the [Segway’s digital] controller is to keep the base under the center of gravity [you] at all times. Most Segway control code you will find does this if you analyze it in terms of discrete-time (digital) controls,” explains Guan.

The Segfault uses a gyroscope like the Segway — and even an accelerometer like that found in an iPhone — but it can’t yet compensate for the lean you experience at high speeds. So the vehicle tops out at around 8 miles per hour. That is, if you wish to not be thrown from the vehicle. Using a 35-cell lithium nanophosphate battery pack, the Segfault charges in about 10 minutes and has an operational time of about 2 hours.

Unfortunately, analog components are highly sensitive to ambient temperature and voltage noise, so obtaining one for a game of Segway polo is unlikely.

Segway, Analog-Style:

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