Unmanned Systems Technology 028 | ecoSUB Robotics AUVs I ECUs focus I Space vehicles insight I AMZ Driverless gotthard I InterDrone 2019 report I ATI WAM 167-BB I Video systems focus I Aerdron HL4 Herculift

59 AMZ Driverless gotthard | Digest and thus recuperate energy through regenerative braking. “While driving normally, we hold off on the brake and just decelerate – and recuperate energy – with our motors,” Valls says. “In an emergency we actuate the emergency braking system, which is behind the braking pedal.” For the 2018 season the team redesigned its in-house accumulator to reduce its voltage and energy density, to 420 V and 2.7 kWh. That was to optimise the packaging and to better suit a change in the competition that reduced the length of the longest course it had to drive to 5 km. The accumulators in the competition are generally designed for high specific energy; AMZ’s are about 190 Wh/kg. The charge/discharge rate – which is key for rapidly recuperating energy during braking – was extensively tested to ensure it did not degrade the lifecycles of the battery cells. Under the front axle is an actuator for steering. That enables the vehicle to steer from full right to full left in 0.9 s. This, along with the drag reduction system actuator and the gearbox, is supplied by Maxon Motor. “The four wheel-hub motors were built in-house,” Hendrikx says. “We’re up to our ninth generation of the motors now, and because of the very specific design and performance requirements of Formula Student, ours have among the highest power-to-weight ratios of any ever built.” Each motor weighs 3.4 kg, has an electrical frequency of 1.6 kHz, and is capable of a power output of up to 40 kW. They are permanent magnet synchronous motors, featuring an inrunner (internal rotor) design with 12 magnets made from a proprietary type of neodymium, and five pole pairs on each stator. “Our inverter has a 16 kHz switching frequency to make sure we have stable control over those motors,” Valls adds. AMZ has also recently designed and produced its own motor controllers, in order to increase the switching frequency towards the limits of what their inverter allows. “For our old COTS motor controller we replaced the cooling system with our own cooling plate, which was lighter and better optimised for our specific cooling requirements,” Valls notes. “We also use an active cooling system of fans and radiators throughout the powertrain, to keep the motor temperature below 80 C.” Doing that was critical to preventing the magnets from degrading due to the heat, he adds. Buhler says, “There aren’t a lot of motor controllers configured for Formula Student requirements. It’s something of a niche, as you can imagine, and using COTS motor controllers means a lot of compromises, so we developed our own to overcome those. We’re now working on the second generation of them to reduce their weight.” AMZ also used a liquid-cooling system for the inverter and an air-cooling system for the accumulator. The temperature field between the two components was very different – for one, the accumulator stops working at just 60 C, as per the rules, compared with the 80 C maximum for the inverter, so the thermal management systems had to be different too. The maximum powertrain voltage allowed by the competition is 600 V, and within such constraints the team plans to optimise cooling and reduce the size and weight of the inverter to help with thermal management and lower weight. At the time of writing, the 2019 season of Formula Student’s driverless races had finished, and AMZ Driverless had won again, with its new ‘pilatus’ car. It has the same overall architecture as the gotthard but incorporates iterations of its technologies. Unmanned Systems Technology | October/November 2019 4WD all-electric, open-cockpit Empty vehicle weight: 175 kg Operating weight: 192 kg Dimensions: 2943 x 1425 x 1159 mm Maximum speed: 117 kph Maximum acceleration: 14.62 m/s 2 Endurance: About 5 minutes (typical track time), 20 minutes (maximum) Some key suppliers Battery: Melasta Navigation: Advanced Navigation Lidar: Velodyne Camera: Basler Composites manufacturing: Connova Steering motor: Maxon Motor Reduction motor: Maxon Motor Gearbox: Maxon Motor Processors: MPL Processors: Nvidia Specifications Being a four-wheel-drive car, each wheel has a motor- gearbox pairing. The wheel- hub permanent magnet synchronous motor was designed and built in-house