34 node in a system, and those all have to be synched for timestamps,” Tome says. “That synchronisation requires triggering every node, all at once, all the time to recognise what messages they’re receiving and when. “But EtherCAT has one single message that travels to every node. It goes to one actuator, which writes it down, then it goes to the next, and that writes it down too, and so on until it loops through the entire bus, back to the control computer. You can’t do that at a high rate unless you have truly insane precision in how your protocol is built.” Power management A 48 V bus transmits battery power. Higher voltages would result in lower current losses in the servo motors, but also higher speed relative to torque, some of which would be lost through the gearbox in any case, making them unnecessary. “It’s even less necessary for our processors, as high voltages can also mean losses when transistor gates move, so we don’t stick with 48 V for everything,” Tome says. “Our principal electronics engineer, Nicolas Murguizur, has built some DC-DC converters in-house to meet our packaging needs. The sensors, computers and other electronics have their respective voltages below 48 V, but the ESCs and servo actuators do receive the 48 V output.” To guarantee electrical safety, a red emergency stop button sits at the back of the body, and an electronic emergency stop is also programmed in. This is a remote shutdown triggered through the power monitoring and distribution board, where voltages, power consumption and other healthcritical parameters are tracked. This is also where the DC-DCs are mounted, although Keybotic might simplify its power distribution board in the future, particularly if customer trials show that the amount of health data being tracked is surplus to requirements. “We’ve had to design some custom connectors to plug and disconnect each leg easily via a single cable, and to route power and data through that,” Tome says. “There are some great connector suppliers who will do excellent quality hybrid power-and-data connectors for you, but often they are designed for critical cases like aircraft, military vehicles or medical equipment. That would have driven up the price of the Keyper a lot.” Energy and recharging The battery contains 500 Wh and is assembled in a thin, longitudinal shape to match the body’s shape and for symmetrical weight distribution, as well as good balance for the centre of mass. “We interface with the BMS through a Modbus protocol; our supplier has been doing this for 30 years now and has a plethora of safety certifications,” Tome says. “We told them how many cells we wanted and the shape of the pack, and they soldered, packed and sealed it with the BMS inside, as well as putting in the Modbus and power connections.” The charging station on the robot’s underbelly works as a docking receptacle. A Keyper walks over a charging station, kneels and mates with the connector for recharging to begin. In the future however, Keybotic intends to switch to wireless charging. “The industrial environments where Keyper is expected to work are prone to high amounts of dust and other ambient contaminants,” Tome says. “To prevent ingress into the charging system, other walking robot chargers use mechanical trapdoor systems, but that just adds moving parts which are bound to fail eventually. “Wireless charging reduces the system to a receptor antenna and an emitter antenna, and everything’s fully sealed against dust. There are no mechanical parts that can fail, or any chance for dust to get into the trapdoor’s mechanism or any other part of the charging system.” Operator systems The Keyper’s 2.4 and 5.8 GHz wi-fi antennas are identical to those in consumer PCs, mounted topside in a gap in the aluminium to prevent transmissions being blocked or interfered with, as well as COTS 4G modems with builtin antennas for cellular comms, which Keybotic does not modify. “Our wi-fi can also be used in dual mode, so if a user has both a 2.4 and a 5.8 GHz network, it can connect to them separately. For instance, one can go to an independent October/November 2023 | Uncrewed Systems Technology Dossier | Keybotic Keyper Currently the Keyper docks and mates with a charging receptacle on the ground, but Keybotic is keen to switch to wireless charging in the future
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