Issue 41 Unmanned Systems Technology December/January 2022 PteroDynamics X-P4 l Sense & avoid l 4Front Robotics Cricket l Autonomous transport l NWFC-1500 fuel cell l DroneX report l OceanScout I Composites I DSEI 2021 report

50 also grown in size and power in response to feedback from several industrial sectors and emergency services. While the Cricket has reached full operational capability, in that it is ready to be deployed inside confined spaces, he stresses that there is still a need to increase speed and reduce the computational requirements for real-time navigation planning. “The goal is to develop a robot capable of operating at speeds faster than a person working in similar conditions on the same tasks,” he says. This is where new compliant actuators, from Hebi Robotics, come in. They adapt to uncertainties in the terrain, the robot’s motion and any potential interaction the robot might have with human operators. Dr Ramirez-Serrano adds that a further identified need is for safe deployment in confined spaces with potentially explosive environments, which will require further development work. In terms of development challenges, he says, the whole-body locomotion system that takes the geometrical features of the environment as well as the robot’s motion and reconfiguration characteristics into account has been the most demanding, followed by the difficulties imposed by spaces that are hard for radio signals to penetrate. “The robot has to use alternative mechanisms to be able to locate itself within the environment with enough accuracy without GPS,” he explains. A question of size The Cricket’s overall dimensions vary with its pose, so 4Front Robotics quotes dimensions of key components and overall ones in its flat configuration with one pair of tracks pivoted away from the centre of the body in the fore and aft directions, and the other pivoted towards the centre. The current small, electrically powered version for example has a body 410 mm long and 360 mm wide, and tracks that are 60 mm deep and 250 mm long, for an overall length of 630 mm. Dr Ramirez-Serrano notes that the most important factors dictating its dimensions are the size and power of the actuator systems available on the market. The Cricket is designed to be scalable up or down, but that can only be achieved if there are motors available with enough power, torque and speed to drive all its movements and to carry the intended payload, he explains. The payload can include sensors, manipulator arms, fire extinguishers and other devices. The Cricket is made predominantly from aluminium, titanium and carbon fibre reinforced plastic, using a combination of CNC machining, moulding and 3D-printing, all selected to optimise weight, reduce cost and ease of manufacture. It was designed to be able to support its own weight with any two of its limbs in any configuration, freeing up the other two so that they can be repositioned as required. This placed significant strength demands on the frame structure and torque demands on the motors that actuate the leg joints and the tracks. A stepper motor paired with a customised gearbox actuates each joint in each leg independently. To provide a large gear reduction in a small volume, worm gears were selected for the final drive in each joint. A worm gear consists of a shaft with spiral thread running around it (the worm) that engages with a conventional gear wheel with curved teeth. As the worm will drive the gear but the gear won’t drive the worm, such set-ups present strong resistance to any tendency for external loads on the joints to drive them in reverse and stress the motors. For similar reasons, the track systems are actuated by DC motors paired with customised gearboxes with worm gears for the final reduction. In the latest design of the robot, such motor and gearbox configurations have been enhanced with compliant actuators. The core sensor systems housed in the body include a small time-of-flight laser sensor at the front for distance measurement, complemented by an IMU and an inclinometer in the centre. Also, each joint has its own position encoder, and the Hebi Robotics actuators include additional sensors that enhance mobility. December/January 2022 | Unmanned Systems Technology The Cricket’s geared and motorised shoulder joints are linked by a robust alloy structure to withstand the torque loads while supporting batteries and other ancillaries