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26 Dossier | 2getthere third-generation shuttle suspension that not only improved the ride substantially but also provided a self-levelling capability that prevented the pitching under braking that had confused the obstacle detection system. More progressive braking was another key requirement, which was met by introducing regenerative braking and disc brakes, backed up by a failsafe emergency air brake. The vehicles have carried 14 million passengers since 2006, six million at Rivium alone. Operational experience and the improvements in the second- generation machine have been carried over to the third generation, which features a new body, a more comprehensive sensor suite and more sophisticated autonomy software. Robust localisation and navigation are essential to reliable autonomy, and 2getthere’s software accepts multiple sources of information including GNSS and local landmarks, both natural and artificial. To serve as reference points, natural landmarks must be detected by sensors such as cameras or Lidar, which need a clear line of sight, whereas artificial ones such as transponders or magnets must be added to the environment in precisely surveyed positions as part of route preparation. The company notes that localisation based on natural landmarks is affected by weather conditions, and therefore provides 90% availability, but that based on artificial landmarks guarantees availability of more than 99%. Navigation relies on virtual routes constructed from set points that the vehicles follow using odometry and direction-of-travel information from steering angle sensors and gyros with reference to the localisation system. The combination is said to deliver centimetric accuracy at speeds of up to 60 kph. Third-generation requirements Chief technology officer Sjoerd van der Zwaan has a background in computer engineering and robotics, and held CTO positions in software companies before he joined 2getthere in 2015. By that time, development of the third-generation shuttle had been underway for about a year, he says. Its development was spurred by a long list of new requirements. These included reducing the system’s infrastructure footprint, by making the vehicle bidirectional to eliminate the need to turn around at either end of a route, for example, and incorporating four-wheel steering to improve manoeuvrability in tight spaces and ease docking at stops. Another key requirement was a long design life with a minimum of maintenance to fit the business models typical of bus operators. What emerged is a design life of 20 years with a major overhaul of the driveline and sensor systems at 10 years. The transition from the second to the third generation also brought a major change in the shuttle’s appearance. Keen to make novel technology seem more familiar, Connexxion had wanted the second-generation machine to be as bus-like as possible, but Masdar City specifically did not. Masdar wanted its PRT system – with smaller vehicles – to be futuristic and iconic, Lohmann says. “We now have a sleek family style common to the larger and smaller vehicles,” he says, adding that van Helsdingen was keen that they pay a lot of attention to how the vehicle would be perceived, meaning that the machinery had to fit into shapes and volumes dictated by the styling. “Carel says appearance comes first, so we need to make sure that, technically, we can cope with the spaces that are left for us, given that the styling takes the lead.” For the third-generation shuttle’s look, they turned to famed Italian automotive styling house Zagato. The result is a sleek fibreglass composite body with a steel frame to add extra strength and a large area of window glass that is also structural. This is bolted to the ladder frame chassis during assembly by manufacturing partner Altran. Passenger comfort is also a high priority, temperature in the cabin and airflow through it being crucial for a vehicle designed to operate in temperatures from well below freezing to more than 50 C. There was no off- the-shelf heating, ventilation and air conditioning (HVAC) system that was up to the job, van der Zwaan says, so 2getthere turned to DC Airco and NLR (the Royal Netherlands Aerospace Centre) to develop a bespoke solution that optimises the airflow and never lets the cabin temperature exceed 24 C. Like all HVAC systems though, October/November 2020 | Unmanned Systems Technology The battery pack seen from underneath the vehicle. The system is based on lithium nickel manganese cobalt oxide chemistry that supports high-rate opportunity charging and includes a BMS