One leg balances in three dimensions
In a Carnegie Mellon Leg Laboratory report dated 13 December 1983, Marc Raibert, Benjamin Brown and Michael Chepponis described a machine on one springy leg that hops and runs on an open floor without any physical support. Control is split into three independent parts: hopping height, forward running velocity and body attitude. The machine hops in place, travels at a specified rate, follows simple paths and keeps its balance when disturbed; the top recorded running speed was 2.2 m/s (4.8 mph).
Why it matters
Until then walking machines were statically stable: four or six legs, at least three always on the ground, and low speed. Here the balance is active, the machine falling and catching itself with every hop, and three simple laws turned out to be enough for it. This is the start of the line of dynamic legged robots, to which the bipeds that walk with a natural gait also belong.
The document read is the report Dynamically Stable Legged Locomotion, Progress Report: October 1982 - October 1983, found in the CMU archive under the title of the journal paper; its section 2 is the paper Experiments with a 3D One-Legged Hopping Machine with the same authors and abstract, which appeared in The International Journal of Robotics Research, volume 3, issue 2, pages 75-92, in June 1984 by the Crossref record. The publisher's page was not read: it sits behind a Cloudflare challenge, which was not worked around. The 3D algorithms are, in the authors' words, direct generalisations of the 2D ones from the planar machine described earlier. What the record does not claim: the hopping height, the leg length, the mass of the machine or any figure beyond the 2.2 m/s, which the report states twice; the same report also describes a four-legged machine in design and planar models, which are not part of this record.