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

33 behaviours we have programmed into the vehicle take into account the fact that you can’t go from ‘zero to hero’ in a millisecond, because the magnetic coupling has this characteristic.” The software monitors motor speed and current draw, along with the power demand from the control system, to figure out whether the propeller is turning as it should, without measuring its rpm directly. “If everything else is within limits then we know the prop speed exactly, because we are monitoring the shaft speed,” Sloane says. “One advantage of a magnetic coupling is that if the prop becomes fouled, we go into low-current mode as the drive disengages, whereas direct drive systems go into high-current mode and kill batteries or worse.” Energy storage and management The batteries in the pack are standard manganese alkaline D-cells, six in the smallest vehicle and 14 in the larger ones. However, ecoSUB Robotics will integrate lithium thionyl chloride batteries as an option, for customers who might need a very long, low-speed transit capability. While the batteries themselves might be fairly basic, the energy management system is very sophisticated and is designed to squeeze as much energy from them as possible to complete the mission, then to keep the vehicle ‘alive’ and communicating to ensure its recovery. One technique used when the batteries are nearly depleted and there is a risk of losing the ecoSUB is to effectively disconnect the batteries from all the loads for a period, which enables them to recover some charge. The power conditioning electronics enable the vehicle to run on supply voltages from 30 V down to 3.5 V. Generally, the system’s logic uses measurements of the batteries’ charge state to work out what to do. If it calculates that there is not enough energy remaining to complete the mission it will shut the sensors off but keep the motor, rudder and housekeeping functions running to eke out the endurance and get the vehicle as close to the planned recovery point as possible. As the energy continues to become depleted, the next decision the system makes is to shut the motor down and allow the ecoSUB to float to the surface, at which point the only systems remaining on line are the GNSS and the Iridium satcom modem. In this survival mode, Sloane explains, it can stay alive for about a week, occasionally transmitting an Iridium message, from once an hour to once every six hours. When a recovery team is nearby and the vehicle has enough energy left, they can send it a message telling it to broadcast its position more often to enable them to home in. Payloads and payload support Most payloads sit in the flooded nose cone outside the pressure case, ecoSUB Robotics AUVs | Dossier Unmanned Systems Technology | October/November 2019 The propeller and rudder on all ecoSUBs use magnetically coupled actuators, eliminating hull penetrations and shaft seals. The antenna is a potted component assembled in-house (Courtesy of ecoSUB Robotics) EcoSUBμ5 Length: 925 mm Diameter: 111 mm Weight: 4 kg Maximum depth: 500 m Maximum speed: 1 m/s Range: up to 72 km Endurance: up to 20 hours Propulsion: DC motor Propellers: one, with two blades Surface location: GPS, IR and visible light beacons Control: autonomous and remote control Comms: satcom, wi-fi, acoustic, 3G/4G, RS-232, Ethernet, I 2 C, USB Some key suppliers 3D printing: Digits to Widgets DC motor: Maxon Command, control and comms: in-house Sensors: Star Oddi Sensors: Valeport Sensors: National Oceanography Centre Acoustic modem: Newcastle University Satcom: Iridium Autopilot: Variscite Batteries: Varta Industrial GUI: in-house Underwater connectors and cables: STS Defence Datasheet