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The DFKI's EO2 microcar aims to fit in with cities of the future in many different ways. (DFKI GmbH, Timo Birnschein)

Flexible, modular robo-EV

Four years ago, when Germany announced that it planned to put 1 million electric cars on the nation’s autobahns and roads by 2020, government ministers turned to the public-private R&D partnership DFKI, the German Research Center for Artificial Intelligence, to develop a road platform to support e-mobility and autonomous driving experiments.

“When we saw the government’s ambitious e-mobility plan,” recalled Frank Kirchner, Director of the DFKI’s Robotics Innovation Center and chairman of the University of Bremen’s robotics department, “we said to ourselves, 'this is nothing new to us; after all, we build autonomous robots that move around on electric power. So an autonomous electric car is just a big robot to us.'” We took a chance and submitted a research proposal that we had literally scribbled down on a napkin.”

The robotic center’s team, which called their proposed car EO—Latin for “I go” (or “to there”)—received a $1.7-million grant for a 15-month program to develop their electric smart microcar. “The EO proof-of-concept vehicle turned out to be enough to convince the funding organization to provide another half-million Euros" to build a working prototype, the EO2, which was completed in late 2014, he said.

“Since we were basically a bunch of programming and engineering nerds who spent their time typing in front of computer screens,” Kirchner noted, “we had our own viewpoint. We wanted to design something that was totally different than the cars we saw on the road.” So EO was conceived as a reconfigurable robot—a highly flexible and fully modular vehicle that featured multiple degrees of freedom.

Maximum flexibility

The researchers opted for a distributed propulsion system comprising four in-wheel electric motors at the corners. “Distributed drive, together with a drive-by-wire system, enabled us to control the vehicle and distribute energy differently than most other cars,” he explained. The lack of a large engine and transmission amid the vehicle affords maximum design flexibility. EO2 can independently turn its wheels 90 degrees and so spin in place, drive diagonally, or sideways—abilities that can be useful when driving and parking in congested urban areas, especially in cities of the future with many autonomous vehicles that are less constrained by standard human driving patterns.

Another key aspect of the EO2’s design is modularity: “It lets us produce any component simpler and faster, more efficiently.” The Robotic Center’s team endowed the two-seat vehicle with the ability to reconfigure quickly and easily to carry more passengers or extra cargo, or to add range extenders simply by plugging rolling modules into the back of the car. They built a range-extender module to demonstrate the modular approach.

The concept’s modularity extends to the ability to connect multiple vehicles to form road trains. Platooning on highways can save energy and boost range by sharing electric power among the linked cars and cutting wind resistance.

The team developed a foldable docking interface that fits into the body of the car and allows easy connection of the charging cable and for connecting dedicated plug-in modules that carry seats, additional storage room, or a power supply—battery pack, fuel cell, or generator set. “We had previously developed something similar—compatible plug-and-play linkups—for the space program,” he said. The electromechanical docking interface features both inductive and direct electrical connections.

Yet another facet of the EO2 prototype’s reconfigurability was the capability to change shape and alter its footprint both to improve highway aerodynamics and better fit the tight spaces in cities, all while the passengers remain seated comfortably inside. The vehicle can squat down to reduce wind resistance at speed and also rise up into a smaller footprint for parking. It shrinks from 2 x 1.5 m (6.5 x 3.3 ft) to 1.5 x 1.5 m by shifting its rear axle toward the front and sliding the body up on a set of rails. “We wanted it to navigate in the confined spaces of urban scenarios to fit into smart cities of the future,” he said.

The 750-kg (1650-lb) EO2 prototype has a top speed of 40 mph (64 km/h), and can travel over 30 mi (48 km) on a single four-hour charge of its lithium-ion (LiFePO4) battery.

More street smarts

Finally, the design team wanted its car to have the sensors and street smarts to drive itself around town and on highways surely and safely. Its sensor suite includes stereo cameras at the front and back, a lidar laser rangefinder for 3D-scanning the environment, six time-of-flight 3D cameras for near field views, as well as internal Hall-effect and a string of potentiometer sensors for monitoring steering angle and make range measurements.

“Ever since we built the basic car, we’ve been working on the autonomy capabilities. We’re implementing a control system based on the sensors that look out on the environment and the existing drive-by-wire system,” Kirchner reported.

He described the design approach to the EO’s control system as very similar to the way they design their robots. “It’s ‘divide and conquer.’ First, we chop large problems up, then we develop a hierarchy of partial modular solutions that provide functionality with regard to each issue. Together, the layers add up to ever greater levels of control and safety.”

“Unfortunately, our funding has fallen off since we completed the car,” he said. “We’ve been trying to make do with internal and external funding to get to the next level—self-driving, automatic parking.” The EO2 can operate autonomously, but is currently “constrained to the Center’s grounds, since we have no allowance to drive on public roads.” A video about the car is available at:

When asked whether some of the Robotic Center’s corporate partners, BMW and Mercedes-Benz, might pony up some funds, Kirchner responded: “We collaborate with them on individual projects, but each has its own large autonomous driving program that they keep to themselves.”

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