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

51 4Front Robotics Cricket | Digest Although most development is carried out in-house, many components are off-the-shelf items. These include DC motors from Faulhaber Drive Systems, the Hebi actuators, stepper motors from Maxon Precision motors, plus vision sensors and NUC (‘bare bones’ mini-PC) computers from Intel. At the moment, the electrical version of the robot uses smart, ruggedised LiGo batteries from Grin Technologies. Poses and locomotion The Cricket has a flat central body with a leg at each corner, and each leg has the equivalent of hip, knee and ankle joints, the track units pivoting off the ankle joints like feet. All the joints have wide ranges of motion, giving it the flexibility to arrange itself in a number of poses and to walk in a bipedal manner, as a tripod or a quadruped, to roll on its tracks and to climb via bipedal contact or multi-contact locomotion, Dr Ramirez-Serrano explains. By changing pose, it can walk or roll with its legs vertically under it like a mammal or out at the sides, more like those of a reptile. In the extreme expression of the latter, it can hold itself completely flat and still roll on its tracks. The Cricket can also make itself thinner by tilting its central body about its longitudinal axis and either roll or walk on one side to negotiate narrow passages. Different poses help it overcome a variety of locomotion challenges. It can hold its limbs out at different angles and different extensions, enabling it to climb over and through environments with surfaces at multiple angles, heights and over complex, non-coplanar terrain. To climb a large step, for example, it can stand on the tips of its rear tracks and place its ‘forelegs’ on top of the step, pulling itself up using the power of the actuators that move the joints as well as the tractive forces applied by the tracks. It can also hold its body level with the legs on either side at different elevations to move along the edge of a step or a slope, and it can climb a vertical ladder by hooking its tracked ‘feet’ over the rungs and pulling itself up. By pressing its tracks outwards against the walls, the Cricket can get enough traction to climb up and down inside a vertical pipe. “In theory at least, the robot can adopt hundreds of other configurations, enabling it to jump, twist, turn and even move inverted,” Dr Ramirez- Serrano says. Ongoing r&d is aimed at enabling the Cricket to run, along with the acrobatic manoeuvres needed for “aggressive locomotion”, in highly unstructured confined spaces and to increase its locomotion planning speed so that it can accomplish time-critical missions such as search & rescue operations faster. Control and autonomy Because of the Cricket’s many more degrees of freedom than wheeled, tracked and even most legged robots, the complexity of the control and manoeuvring scheme is significantly higher; there is always more than one unique solution to each manoeuvre performed by those simpler robots, Dr Ramirez-Serrano explains. While such robots might have two or four motors to drive it, the Cricket needs 20, to enable its multiple locomotion and reconfiguration capabilities, plus one more that moves a sensor head housing a depth camera at the front. Reconfiguration and movement decisions are based on sensor perception, the Cricket’s motion capabilities and the desired manoeuvre, plus data from the IMU, GPS (if available), cameras and joint encoders. The system determines the motion path for each leg, then reconfigures the Cricket. “To place a leg in a specific support position, one has to determine which of the hundreds of possible solutions is the most effective,” he says. “Finding such solutions is challenging, and selecting the one to use based on energy consumption, time, speed and so on leads to diverse possible – and not necessarily optimal – solutions. “In the real world, everything is always changing, so our robots do not seek optimal navigation and control solutions for example, but instead use the above tools to enable them to accomplish the task regardless of the conditions they face.” All the joints in the Cricket’s limbs are of the revolute type, with wide ranges Unmanned Systems Technology | December/January 2022 The ability to hold its tracks against the walls by pushing outwards with its limbs enables the Cricket to climb up and down inside vertical pipes