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Feb 10, 2017, 12:00 AM
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robot legs


After years of searching for robot dogs, putting "robot legs" into the search box turned up more intriguing results. This one was closer to the ultimate goal than any previous ones:

http://spectrum.ieee.org/automaton/r...losive-jumping

http://www.ri.cmu.edu/pub_files/2016...ucheThesis.pdf

Introducing GOAT: A Legged Robot with 3D Agility & Virtual Compliance (3 min 42 sec)



The key was the use of direct drive, brushless motors with stock windings to achieve high jumping. Jumping is the key to any robot running. It wasn't obvious in his thesis, but after extensively testing $75 gearboxes, he didn't use any gearboxes for the jumping. Pulsing the motors allowed the briefly high torque for jumping. More surprising was the holding torque they could provide.


They were the t-motor U10's at $330. The windings were only 95mOhm. A rewound motor for higher torque would have 14Ohms. The mane question is whether similar motors can be had for less money or if the robot can be scaled down for an after-tax budget. Maybe there could be a cheap motor for directional control & an expensive motor for the thrust. Maybe a servo could provide a degree of freedom.


The other note was how instead of 1 knee & 2 hip motors, he used 3 identical hip motors with freewheeling knee joints to achieve the same degrees of freedom. If it was passively stable in 1 direction, the leg could get by with 2 motors. To be passively stable in 1 direction, the CG has to be closer to the ground. That requires using jumping to overcome obstacles instead of leg clearance.


Unlike the quest for autonomous cars, virtual reality, & 3D TV's, there's going to be a single blog post someday about a commercially viable robot leg & it's instantly going to change the world. We've never had a commercially viable robot leg, so no machine has ever been able to get around terrain with the ease of an animal.
Last edited by Jack Crossfire; Feb 10, 2017 at 01:41 AM.
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