Segway Inc. has changed direction. Or more precisely, it changed the way its riders change direction.
The company developed a new steering mechanism that makes its latest two-wheeled, self-balancing electric scooters easier to maneuver. Users simply lean in the direction they wish to go, and the machine matches the rider’s bank angle to a turn radius. “Lean left to go left, lean right to go right,” says Doug Field, Segway’s vice president of engineering and chief technology officer. “It’s something we all learned when we first learned how to walk.” The first version of the transporter, by contrast, had a less intuitive steering system that required users to operate a twist grip on the machine’s rigidly-mounted handlebars.
Called LeanSteer, the new steering system consists of new mechanical components, sensors and software. Mechanically, the system features handlebars that pivot as users lean into a turn. “A lot of work went into the pivot assembly,” says Field, who explains that the handlebar frame acts as a lever arm and exerts a tremendous force on the pivot. “The challenge here was developing a pivot assembly that would handle those forces and still feel smooth and friction-free to the user,” he says.
Much of that smooth pivot performance comes down to a conical rubber bushing that encircles a shaft connected to the handlebar assembly’s vertical frame. The rubber bushing deforms in shear as the handlebars pivot. As riders come out of a turn, the bushing springs back into shape, returning the handlebar assembly to its upright position. To come up with the ideal composition and shape for the rubber sleeve, Segway engineers worked with Anthony Best Dynamics Ltd., a suspension engineering firm that often works with Formula One racing teams.
From a control standpoint, the new LeanSteer system in some ways represents an outgrowth of the
that has always kept the Segway upright. While LeanSteer does have a new sensor to measure shaft position within the pivot assembly, this steering system gets most of its inputs from Segway’s existing balancing sensors - among them five gyros and two accelerometers that measure body angle and angular rate of change.
And like the original balancing system, whose control loops operate at 100 Hz, the new steering system translates those inertial sensor inputs into an appropriate motor torque. “But now the machine is turning and balancing laterally too,”Field says. So the torque applied to each wheel differs as the machine turns.
Another control challenge involves separating a rider’s intentional steering motions from motions caused by bumps or other obstacles. Segway engineers accomplished this task with software that considers only the inertial data relative to gravity while ignoring inertial data relative to the base of the machine.
The LeanSteer system can be found on the newest Segway Personal Transporter models - the i2, the x2 cross-country model as well as specially-outfitted versions of these machines for golfers, police and other specialized users. The same system also includes a new wireless controller built around a Zigbee chipset. Called InfoKey, it docks on the Segway, turning it on and off, controlling its security features and displaying real-time performance information.
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