Unmanned Systems Technology 014 | Quantum Tron | Radio links and telemetry | Unmanned Aerial Vehicles | Protonex fuel cell | Ancillary systems | AUVSI 2017 Show report

19 to pneumatic harpoons to skewer them. “What we are using now though is a low- voltage electrical pulse to stun the fish, and an impellor to create a low-speed water current to suck the lionfish into a capture chamber,” Hoffman says. Although the first version of the ROV, the Guardian LF1, is unmanned, it still needs some human input, he says. “We are trying to make a robot that local fishermen can use, and we aim to keep the lionfish alive for the fishermen and biologists, who are tracking their DNA and stomach contents. “We also wanted a system that is as safe as possible – the high-voltage strategies are not so user-friendly. As a result, we have done something pretty unexpected – electro-fishing in freshwater is well-established but people haven’t done it in salt water.” The pulse is delivered by a series of 14 probes on the front of the ROV, which are set about 10 in apart and provide a pulse lasting 15 s. During development, the team discovered that a lionfish will regard the probes as non-threatening, as they look like coral fans, but will swim away if the ROV approaches straight from ahead or behind. The best way to approach the fish is therefore to come in at an angle from above, so the probes and collection tube are at an angle pointing downwards to acquire the fish. “There have been an amazing number of trade-offs to balance the biology of capturing live fish with the robot development,” Hoffman says. This includes the size of the collection tube, the width of the aperture and the length and number of the probes. The ROV is propelled by eight off- the-shelf thrusters from Blue Robotics, which makes it highly manoeuvrable and enables it to get into the water and capture lionfish quickly. “We are building the system to capture ten to 20 lionfish at a time,” says Hoffman. “They are all over the reef, so if we can drop the robot down for half-an-hour we should be able to achieve that.” A camera on the ROV feeds back to the support boat a display that combines the pitch, heading telemetry status and battery life. It is powered from the surface to extend the operating time, as larger marine batteries can be used on the support boat. That was a deliberate choice over using customised lithium-ion batteries, says Hoffman, as the marine types are easily available throughout the area and cheap to replace, rather than having to ship custom batteries from a manufacturer. “It’s a highly specialised robot but it also needs to be easy to use, and the maintenance needs to be minor,” he says. Control system That also applies to the control system, which is based on a games console controller. “The system is controlled using a PlayStation-type joystick. Unlike other systems that are controlled thruster by thruster, we have designed the autopilot to give forward, back, roll and pitch control with simple commands from the handset as well as macros,” he says. The macros include automatic diving and surfacing as well as positioning for an approach to a lionfish. That is a key part of meeting the aim of reducing the training time to less than an hour. The macros come from existing research into video game interfaces, and simplify the control of the ROV. “There’s a huge body of work out there on the user interface so we don’t want to reinvent the wheel,” Hoffman says. There are also trade-offs with the ROV’s carrying capacity. “We want to fit as many fish into the collection tube as possible, and make that as wide as possible, so the trade-off is the ROV’s dynamic manoeuvrability,” he says. Orin Hoffman | In conversation Unmanned Systems Technology | June/July 2017 Volunteers from the Robots in Service of the Environment team put the Guardian LF1 through its paces