Issue 37 Unmanned Systems Technology April/May 2021 Einride next-gen Pod l Battery technology l Dive Technologies AUV-Kit l UGVs insight l Vanguard EFI/ETC vee twins l Icarus Swarms l Transponders l Sonobot 5 l IDEX 2021 report

12 Researchers have developed a micro-aerial vehicle (MAV) weighing less than 1 g using soft, flexible materials (writes Nick Flaherty). Current state-of-the-art sub-gram MAVs are powered predominately by rigid actuators such as piezoelectric ceramics, but they have a low fracture strength (120 MPa) and failure strain (0.3%). The team, at the Massachusetts Institute of Technology, has developed a 665 mg aerial robot however that is powered by novel dielectric elastomer actuators (DEAs). They have a high power density (1.2 kW/kg) and a relatively high transduction efficiency (37%). The insect- scale UAV has a lift-to-weight ratio of 2.2:1 and achieves an ascending speed of 70 cm/s. In addition to demonstrating controlled hovering flight, it can recover from an in- flight collision and perform a somersault within 0.16 s. This demonstrates that soft aerial robots can achieve insect-like flight capabilities that are absent in ‘rigid’ MAVs, creating a new class of hybrid soft-rigid UAV. The key is the DEA, which contracts when a voltage is applied, according to Kevin Yufeng Chen, a researcher at the Department of Electrical Engineering and Computer Science at MIT.  The DEA consists of a multi-layered Elastosil P7670 elastomer sheet that is rolled into a cylinder 8 mm long, 50 mm wide and with a wall thickness of 210 µm. After it has been rolled, carbon fibre caps are attached to each end to serve as both the electrical and mechanical connections. The elastomer’s dielectric strength is 65 V/µm at frequencies above 300 Hz. Its thickness, of about 30 µm, gives a maximum DEA voltage of 2 kV, which is varied at 480 Hz to contract and expand the tube to allow the UAV’s wings to ‘flap’. The wings have been tested on a tether supplying the voltage, with the wings flapping at 240 times a second. Soft slant on micro-UAV... Airborne vehicles April/May 2021 | Unmanned Systems Technology The MIT craft uses dielectric elastomer actuators to flap its wings A silicone underwater vehicle with distributed electronics has been tested in the Mariana Trench, the deepest part of the world’s oceans (writes Nick Flaherty). The test was conducted by researchers from the Laboratory of Fluid Power and Mechatronic Systems at Zhejiang University in China. Conventional underwater vehicles need watertight enclosures made of metallic materials to withstand the high pressures at extreme depths. Instead, Prof Guorui Li and colleagues used soft silicone and a distributed electronic control system to drive fins of dielectric elastomer. This approach allowed the UUV to move at a rate of 5.19 cm/s at a depth of 3224 m in the South China Sea. This compares to a speed of 3.16 cm/s when tested at a depth of 70 m. The system was also tested in the Mariana Trench, at a depth of 10,900 m but it was attached to a conventional underwater robot. ... as well as deep-sea UUV Underwater vehicles Zhejiang University’s robot uses a distributed control system and dielectric elastomers to drive its fins