A rapidly developing trend based on high-performance digital signal processors commanding a mix of sensors and electromechanical actuators is set to propel civilization into a new era of scaled-down "personal transportation." Low-cost electric scooters, scaled-down electric cars and Segway LLC's novel "human transporter," a self-balancing two-wheeled vehicle offering an intuitive, smooth and spontaneous sense of motion, are being marketed by entrepreneurs eyeing the ground floor of a significant market.

Although personal transportation vehicles might appear to be simply an amusement, they might well turn out to be as disruptive as the personal computer. Like desktop systems, these vehicles are far more limited than entrenched technologies like the automobile. But once established as a consumer item like the PC, they could rapidly evolve into a powerful force in the industry.

A number of developments, including lightweight composite materials, highly efficient electric motors and actuators, control systems that use advanced DSPs and better battery technology, are reducing the mass and price of such vehicles while propelling them with reliable and cheap electric motors. And although these toys are somewhat on the novelty end of transportation technology spectrum, they could turn out to be the answer to the traffic congestion dilemma plaguing the world's burgeoning population centers.

As with any new technology, however, economics will determine these vehicles' viability in the marketplace.

Automobile engineers have designed and demonstrated many new concepts enabled by electronic control, such as obstacle avoidance, object recognition for guiding cars automatically, active suspension and drive-by-wire controls.

"When you scale down to personal transportation systems, the complexity remains challenging. You basically have the same interconnect and real-time control issues, for example," said David Smith, chief scientist for Synopsys Inc.'s Saber design system. And personal transportation systems are putting more emphasis on instant response, energy efficiency and simplified control systems.

"Economics will determine which advanced features are built into future personal transportation systems. In principle, many interesting technologies exist, but making them available at an economic price is another matter," he said. One example Smith used was an experimental system that combines active suspension technology with image recognition.

Currently, high-end automobiles allow drivers to set the type of suspension response they want in the vehicle from the dashboard. Sensors detect the forces impinging on the suspension and a DSP computes the appropriate force response, which is implemented with electronically controlled hydraulic systems.

The latest concept is to equip the underside of a car with an object recognition system that analyzes the terrain and feeds the information to an active suspension system. That system can then adjust the ride in real-time, smoothing out the effects of bumps and potholes in the road.

Something along those lines might benefit smaller personal transportation systems, which typically must confront more varied terrain than automobiles. But economics can put a serious limitation on what can be realized in a mass-market product. "These new systems are being designed into cars costing $60,000 or more-far beyond the price levels of personal transportation products," said Smith.

Indeed, cost is already a big issue for scaled-down transportation systems. DaimlerChrysler introduced the GEM car, a small four-wheeled electric vehicle that achieves a top speed of 25 miles per hour, with an entry price of $6,995. That is much less than the price of a car, but the GEM car will not replace a conventional automobile. Thus, the question for consumers is whether they can justify adding an additional $6,877 to their transportation budget.

Personalized transportation systems could become an extension of existing mass transit, as illustrated by the Segway HT in this 'wheels-on-wheels' demonstration.

Segway's two-wheeled human transporter is even more closely tailored to crowded pedestrian situations. With a top speed of 11 miles per hour and a range of 12 miles, the human-scale vehicle does amplify the capabilities of the leg, but at a price of around $5,000, the consumer might wonder if the cost justifies the added value. Price may be one factor that dampened the initial response to a novel consumer product: Last year Segway revealed that only 6,000 transporters had been sold in the two years since its introduction in 2001. Segway is attacking the problem with a new, simplified model that sells for $2,995.

The Segway HT genuinely broke new ground in transportation technology with its unique ability to self-balance. Advanced DSPs, microelectromechanical systems-based gyroscopes and efficient, powerful electric motors allow the vehicle to remain upright under any conditions. That basic capability is extended to enable an intuitive motion control system that mirrors the human body's balancing system.

Motion sensors in the vehicle can instantly sense when a rider moves out of plumb, then send control signals to the wheels, providing motion that cancels it. Thus the rider can simply lean forward or backward to initiate motion. A fixed column with handlebars provides stability for the rider, and a control on the left handlebar is used for steering. DSPs drive the motors and perform all of the instantaneous computation needed to maintain a dynamic state of stable motion.

"The main DSP processor was selected because it had certain features that are particularly useful in the Segway HT, like brushless motor drive circuitry and the ability to lock access to the chip memory," said John Morrell, director of Systems Engineering at Segway. "With five different processors distributed around the system, each one was sized to accomplish a specific job, so there isn't much room left to add functions."

In terms of design evolution, the quasi-independent nature of the drive and control components would allow different or more powerful processors to be added. And with a wide variety of interesting electromechanical design possibilities, the Segway HT might become a platform for future personal transportation innovations.

The Segway HT remains upright via microelectromechanical systems-based gyroscopes, which sense the orientation of the vehicle, and brushless motor controllers, which use the information to counterbalance the vehicle via wheel movement.

Some improvements might address some of the vehicle's current limitations. The transporter has experienced a marketing barrier due to current laws regarding powered vehicles. Many cities make it illegal to operate powered vehicles in pedestrian areas, while other regulations forbid slow vehicles on roadways.

The GEM car, with a top speed of 25 miles per hour, can be driven on suburban side streets but is barred from arterials and freeways, which require a minimum speed of 35 miles per hour. The Segway HT can only achieve a top speed of 11 miles per hour.

No doubt the increasing popularity of scaled-down electric vehicles will begin to force changes in traffic laws and the construction of highways. The increasing use of bike lanes in urban areas is one example of personal transportation initiating road-engineering changes. But advanced designs might also ease the introduction of personal transportation by adapting the vehicles to current traffic conditions.

"I came back from a recent trip to China totally impressed with how Chinese cab drivers can instantly change lanes and maneuver on crowded roads," said Synopsys' Smith. He observed that China's citizens, who grow up in crowded urban areas, manage to blend foot traffic, bikes, motor scooters and cars in an overall traffic flow. He suggested that personal transportation systems could be equipped with object-avoidance systems-sensors and software that would reduce the skill required to maneuver in crowded traffic areas.

While agreeing that such systems would enhance the user-friendly aspects of a transporter, Segway's Morrell said that autonomous navigational elements are still not safe enough for consumer use.

DaimlerChrysler's GEM car, powered by batteries, is becoming popular in many industrial, government and suburban applications.

"Right now, autonomous sensing and control systems are not ready for unsupervised use anywhere except in the most benign environments or with the most docile of machines," he said. "Since the Segway HT is most useful in an environment populated by humans, it will be a while before any kind of avoidance algorithm is used.

"The most likely scenario is sensors that provide additional information to the operator but do not exert any control over the Segway HT. For example, warning an operator about a curb or a slippery surface or a GPS system that gives audible directions while gliding through a city," Morrell said "My sense is that the problem is not limited by DSP processing power but by the effectiveness of sensors and algorithms-it is often called the 'perception problem.' "

Another serious limitation is the inability of the transporter to navigate curbs or stairs, which are common in urban areas. A large potential application for the transporters would be commuters traveling between home and the subway. Typically, there are several long flights of stairs between the subway entrance and the train platform.

Current technology has the capability to solve the problem, but the solution would add cost and weight. "The real issue would become one of packaging-more degrees of freedom means more motors, more wires, more gears, etc. It drives the weight of the machine up, too," Morrell said. "It's questions like this that make one realize how sophisticated and elegant the human body is."

Stair climbing would mesh with the transporter's ability to maintain balance, and an articulated mechanism between the two wheels could offer a stair step motion. Morrell pointed out that a stair-climbing vehicle is already on the market. The Independence iBOT Mobility System developed by Johnson & Johnson is a wheelchair with an articulated hydraulic mechanism that allows it to travel up and down stairs. But there are several barriers to a mass market. A doctor's prescription is required along with mandatory training. And the price tag is prohibitive, putting it in the range of an SUV. But for the disabled, the vehicle offers a degree of freedom that cannot be realized in any other way.

A human-scale transporter that could navigate around obstacles, and smoothly travel over curbs and stairs, would be a genuinely new development in transportation. Robotic-legged automatons such as Honda's Asimo demonstrate that modern technology is capable of developing this kind of locomotion.

But the wheel seems to have a fundamental appeal that goes beyond mere utility. If personal transportation systems are to evolve, they must achieve a true blend of legged capability and the wheel. What is needed now is a successful first-generation platform that could support further innovation.

Morrell believes that active sensing and control will be the next developmental phase for personal transport.