54 IMU, its batteries and weatherproofed fans for cooling the electronics. On the front of the body is a RGBD (red, green, blue and depth) camera, which provides several navigational functions, most importantly the detection of (and navigation towards) the system’s automated charging station. As a consequence, the lower front also features contacts for docking with it. Lastly, four wheels sit around the body, each driven by an in-wheel electric motor. Metal and fibreglass The RB-WATCHER’s outer body is made from fibreglass composite pieces, reinforced internally by an aluminium frame, which also serves as a chassis for mounting the internal subsystems on a plate. This aluminium plate also secures mechanically to the body at the rear for added rigidity. Aluminium was chosen for the interior structural material as a compromise between several key operating requirements. One is that it provides for effective heat extraction and dissipation, with the fans blowing air throughout the body to cool the metal as it conducts heat from the electronics. Another was weight, as a heavier robot consumes more battery energy and hence suffers from reduced operating endurance. The last requirement was stiffness, particularly to prevent any flexing or reverberation that could allow the upper inspection module to vibrate or sway; a key risk when operating outdoors where the system may periodically drive over gravel or sand. “As for fibreglass, that made more sense than carbon fibre as a body material, because we’re trying to offer a less pricey alternative to the very expensive UGV systems currently making the biggest movements into industrial inspection, like the four-legged robots you’ve seen before,” Millet explains. Using carbon instead of fibreglass might have doubled the price of RB-WATCHER. Additionally, fibreglass serves as a sufficiently safe and robust material in many environments, including those with electrostatic and chemical risks, which some carbon fibres might not have guaranteed. Navigation systems As with the structural materials, the choice of 3D Lidar (from a few routinely used models) for sensing and avoiding obstacles depends on numerous factors. While these include perennial qualities such as price, the most important Lidar performance parameters are resolution and vertical FoV (all Lidar choices having a 360o horizontal FoV). Optimising the former means that the 614 mm-wide robot can move effectively between objects and around corners without needing cumbersomely wide paths to avoid collisions. Maximising the latter is critical to ensuring the UGV can sense the ground ahead in detail, including hazards that the RGBD camera may find hard to detect, such as potholes. Both Robosense’s Helios and Velodyne units have been used as the RB-WATCHER’s Lidar to fit these requirements. The RGBD is a stereo camera, with Intel RealSense systems being used as of writing, although Zed stereo cameras have also been used. Again, price is a key factor in component selection, but as a critical source of navigation inputs, operational stability was also vital. “The RGBD camera must be turned on and off many times over the robot’s lifespan, and in some camera designs this can provoke instability, but RealSense has proven quite stable so far where others failed. Its frame rate and FoV also worked very nicely for our needs,” Millet adds. RTK-GPS is used for centimetric accuracy in georeferencing the inspection data taken (where GPS signals are available), with the quality of corrections playing the biggest part in system selection. Meanwhile, the IMU was chosen for being a precise and autocalibrating system; a crucial requirement of the UGV’s autonomous 3D localisation working persistently. February/March 2025 | Uncrewed Systems Technology The RGBD camera is an Intel RealSense camera, chosen particularly for the stability of its performance over a lifespan of being turned on and off many times
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