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10 Platform one Volz has launched its largest and most powerful electromechanical servo actuator so far, the DA 58-D Duplex (writes Rory Jackson). The 200 Nm DA 58-D (80 Nm continuous torque) weighs about 5.6 kg and measures 307 x 240 x 58 mm in its IP67-rated aluminium enclosure. It has been designed and tested to Mil-Std 810G with temperature tolerances from -55 C to +70 C. “The DA 58-Duplex came about from a customer request for a fully redundant actuator, built with two motors, two controllers, two geartrains, two connectors and two comms interfaces,” said Mark Juhrig, CTO at Volz. “Both motors can work together in an active-active configuration for maximum torque output as commanded by the flight computer.” Engineering the actuator meant learning a lot of new lessons, however, with much of the methodology being unfamiliar territory for the company. For instance, the degree of torque required for the new servo prompted working with the transmission branch of the Mahle Group, which performed key services including CAD, FEM analysis and reliability studies to ensure the all- new geartrain could successfully translate the speed of the motors into torque at the output shaft. “The motor design is based on the ones we’ve used in our existing servos,” Juhrig said. “It’s the same radial flux permanent magnet configuration as in our DA 30-HT, with a 40 mm diameter and the same number of poles. It’s just around twice as long in order to generate more power and torque. “They’re also using fully integrated motor controllers to save volume, which can handle around 30 A – the highest- current controllers we’ve used to date.” With all this extra power throughput, Volz has also installed two actively switched shunt resistors in the DA 58-D. These serve to absorb excess power that can be generated by the brushless motors in certain circumstances, and would threaten to damage the internal electronics or other vehicle subsystems through overvoltage feedback. In addition, the two motors can absorb the backlash of the geartrain. Volz calls this the “anti-backlash option”, which is available for all of the company’s redundant actuators. Volz has also developed a new automated test stand capable of applying loads of 50-100 Nm to gauge the tolerances of the new servo’s gears, bearings and other parts. It can also be programmed with customer-provided load profiles based on their operating envelopes. Test methods include alternating between using one motor as a load and the other as a driver. By driving one motor using the other, each half of the DA 58-D could be exposed to a range of different load cases. The first prototype DA 58-Ds were shipped in May last year to enable the customer to begin qualifying them in their platform, while in the meantime Volz continued development largely on the interfacing, to suit some specific requests the customer had for the comms protocol. The connections to the servo include two serial RS-485 interfaces (half-duplex or full duplex), or two CAN interfaces, or a combination of one RS-485 and one CAN can be configured if a customer prefers diversity over identical dual redundant comms protocols. These enable live diagnostics feedback before, during and after flights, similar to Volz’s other servos, but they also come with some new features. For example, the new driver chips for the new motors enable diagnostics while the motors are running; previously this was only possible when the motor was stopped. “One last thing we have developed with the customer is a notch filter in the servo, to prevent issues from specific frequencies arising from the rotary-wing platform they’re building,” Juhrig added. “For example, if the rotor spins at 600 rpm you’ll get a 10 Hz frequency from the rotor head, which could otherwise interfere with the servo’s operations. “Overall, we anticipate this servo being well-suited to the new classes of vehicles weighing more than a tonne, in urban air mobility and very heavy aerial logistics, as well as helicopters where redundancy in the swashplate actuators can be a huge safety benefit.” The company added that its electromagnetic clutch system is compatible with the DA 58-D’s architecture, for end-users needing OPV functionality alongside the high torque, diagnostics and redundancy. A ‘simplex’ version is also in the works. Servo sets new power level Servos June/July 2021 | Unmanned Systems Technology The Volz DA 58-D servo actuator delivers 80 Nm of torque and is fully redundant