Issue 40 Unmanned Systems Technology October/November 2021 ANYbotics ANYmal D l AI systems focus l Aquatic Drones Phoenix 5 l Space vehicles insight l Sky Eye Rapier X-25 l FlyingBasket FB3 l GCS focus l AUVSI Xponential 2021

24 Dossier | ANYbotics ANYmal D co-founder Peter Fankhauser. “But the ALoF was purely direct drive: for each limb, a motor drove a gear for each leg, with essentially direct connections between each of those parts, so it walked a bit like a table, with very stiff and limited movements.” The team therefore designed series- elastic actuation (SEA) into their robots’ legs. This is a concept that introduces springs into the joints, the springs mimicking the elasticity of muscles and tendons. The springs allow the forces with which the legs are moving to be measured or modelled for precise force-based motion control, instead of being limited to position-based control. “Force control is how humans are able to traverse over ice or uneven rocks,” Fankhauser explains. “It’s less about the position we’re sending our foot towards as the force we’re putting into each step. “The kind of questions we’re asking ourselves instinctively when walking are, ‘How do I account for slip, and where is my centre of mass going?’ Those are the kind of questions our second prototype, the StarlETH, was capable of answering for itself, thanks to us going down the SEA route.” The StarlETH’s arrival in 2012 showed that the team’s robots could now jump, run and perform rapid 180 º turns. Being a largely open-frame design, however, the researchers soon set to work on a commercially viable version without visible (and therefore vulnerable) springs and electronics or protruding wire harnesses. That evolved into the ANYmal Alph in 2015, which also marked the decision to package the motors, springs, gears and essential electronics into a watertight module, which the team named the ANYdrive, hence the name of that first ANYmal and its subsequent iterations. “That had a main body, with 12 ANYdrives, three on each limb,” Fankhauser says. “Based on that overall concept, we were able to quickly develop and add new features and improvements. “That meant having a lot of autonomy and sensors – for localisation and terrain awareness at first – but we soon combined these new features into the ANYmal Beth in 2017, which was fully ruggedised and waterproof, and featured an inspection head for surveying. It was also intelligent enough to climb up and down pretty much any kind of staircase without issue.” The ANYmal C was unveiled in 2019, with improvements across the board as well as autonomous charging via a docking station. That removed what was essentially the only remaining point of human interaction still needed for its day-to-day operations, enabling a fully autonomous industrial inspection solution. “Now, with the recently launched ANYmal D, the product is certified, cost-optimised and ready for mass production,” Fankhauser says. Anatomy of the ANYmal As mentioned, the ANYmal D consists of a central body with four legs (as well as a dorsal inspection payload). Each leg consists of three SEAs, while the inspection payload is modularly configurable to hold different EO and IR cameras as well as microphones for audial inspections and LEDs for throwing light into darker areas. Dr Mario Mauerer, VP of hardware engineering, says, “The SEAs are integrated directly into each leg, with one forming a knee, another at the hip, and one more at the very top of the leg, hidden inside the body, which is disposed perpendicularly to the direction of the knee and hip joints so that the robot can sidestep when needed.” The main body is essentially an aluminium box for mounting and protecting the core subsystems. These include a battery pack near the bottom, and forward- and rear-facing sensors that provide perception, mapping, odometry, locomotion, balance and teleoperation. There is also a COTS Velodyne Lidar behind the payload for mapping and 360 º situational awareness (within a range of 100 m), and antennas for communication, typically over wi-fi (with a 400 MHz link as a back-up for remote operations) although 4G and LTE are available on request. Foam padding protects the sensitive electronics such as cameras October/November 2021 | Unmanned Systems Technology The four-legged design and embedded intelligence allows the robot to climb up and down stairs, and right itself if it’s been knocked over