Keybotic Keyper | Dossier The ESCs currently sit by the actuators, but in the final version of the Keyper they will be integrated inside them. That will help simplify the design by having the leg as a comprehensive, contained system, minimising wiring tasks during maintenance, and safeguarding motor control signal integrity by minimising wire lengths between each motor and its controller. “Each ESC needs five connections into the leg: three for the motor, two for the encoders for position feedback,” Tome notes. “We could eliminate a lot of wire by soldering the ESCs directly onto the motors and encoders. “We’re discussing who to use as our ESC supplier, the key thing being maximising the controller’s power-tosize ratio. RLS provides our encoders, and we’ve found their units are available across a wide range of precision levels. Encoder resolution correlates directly with price, which made it easy for us to choose the right solution for our needs.” Structural aspects Keybotic has chosen aluminium for every feasible structural need, as it is inexpensive, lightweight and easy to manufacture compared with composites and other metals. To further that, the Keyper’s engineers have stuck to a narrow range of aluminium alloy types and aluminium suppliers. 7075-T6 is predominant for its widespread availability. “When something structural bends in a robot, it’s either because of the material or the shape of your design, so we’ve focused on optimising key stressed areas of the structure to mitigate that,” Tome says. “The legs’ attachment points suffer the most severe loads, so we’ve designed reinforcements there with some very particular steels using FEA. Essentially, wherever there’s a stress problem, we reinforce it with a small amount of steel.” He adds that all FEA is performed in SolidWorks, for its ease of use and affordability. “FEA has evolved to the point that you can really trust it, particularly for things like large, reasonably stationary body panels,” Tome says. “In a system like ours though, there are so many moving parts, which means friction, backlash and other variables you can’t model, so you can’t be sure you’ve designed the right structure until you’ve built and tested it in different walking scenarios.” Walking intelligence The primary basis for the Keyper’s intelligence, walking stability as well as navigation, is an AHRS. An IMU alone would have fallen short of sensing requirements, as Keybotic needs the UGV to always understand where it faces, so attitude and heading are key, on top of acceleration and angular rate. “We chose Advanced Navigation’s Orientus as our AHRS,” Tome says. “We have many estimator algorithms embedded in the robot, and we could have 15MM CASE SERVO SG15BL SOUTH KOREA • Research & Development • Engineering & Manufacturing UNITED STATES • Research & Development • Distribution, Sales & Support PHILIPPINES • Manufacturing • Logistics MTTF DATA Compact Dimensions 31x15x50mm Wide Operating Voltage 9.0~15.0V Peak Torque 11kgf•cm North American Sales & Support San Diego, CA | www.HitecCS.com
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