Novel motor propels the `human transporter`

High-performance servomotors and a British-made gyroscopic sensing system are key components in the pioneering Segway Human Transporter (HT) that was unveiled in the US recently in a blaze of publicity.

Some enthusiasts have described the self-balancing, battery powered HT as being a more important development than the Internet and have predicted that it will change the way we move around cities.

The HT is a two-wheeled, one-passenger vehicle that senses when the rider leans forwards to go faster or backwards to slow down, and responds accordingly. It balances itself automatically and can reach speeds of 27 km/h.

The brushless servo motors that drive each wheel - and recover energy during braking - were designed for the HT by Danaher Corporation`s Pacific Scientific company. A patented, hemispherically wound stator contains redundant windings, effectively providing two functional motors in one shell. If one set of windings fails, the motor can continue to run.

Key parts of the permanent magnet motor are created using an injection moulding process that also encapsulates the windings in a single step, simplifying the manufacturing process. The motor is said to produce 40% more torque per unit volume than similar sized conventional motors.

Another novel aspect of the HT`s motors is a new sensor design that provides precision feedback to the drive electronics without needing a conventional encoder or resolver. Tom Gross, Danaher`s group executive, describes the HT motor as "a breakthrough technology for our company".

Silicon Sensing Systems, based in Plymouth in the UK, is supplying another key HT technology - the gyroscopic and tilt sensors that determine the position of the vehicle and its passenger. This information is used to control the balance and the movement of the transporter. SSS has also developed the inertial algorithms that stabilise the vehicle and will build the "Commercial Sensor Assembly" (CSA) incorporating a smart array of silicon gyros that provide redundant safety features on the critical axes.

The HT is undergoing trials in the US with commercial organisations including the US Postal Service and Amazon.com. It is due to go on sale later this year at a price of around £3,000.