There exists a class of two-legged machines for which walking is a natural dynamic mode. Once started on a shallow slope, a machine of this class will settle into a steady gait quite comparable to human walking, without active control or en ergy input. Interpretation and analysis of the physics are straightforward; the walking cycle, its stability, and its sensi tivity to parameter variations are easily calculated. Experi ments with a test machine verify that the passive walking effect can be readily exploited in practice. The dynamics are most clearly demonstrated by a machine powered only by gravity, but they can be combined easily with active energy input to produce efficient and dextrous walking over a broad range of terrain.
Human-like running is a natural dynamic mode of a simple mechanical biped. Such a machine consists of two telescoping legs with linear springs, connected by a hip joint with a torsional spring. It will run passively; no pattern of forcing is required to generate the gait. With careful design its energy consumption can approach zero, but in any case the passive cycle can be ‘pumped' by various means to sustain running over a range of speeds and slopes. Passive running can also be realized over a wide range of mechanical design parameters. Some parameter sets produce cycles that are inherently stable; otherwise the mode can be actively stabilized by a simple control law. Thus the passive running model offers an effective foundation for design of practical running machines, and also provides an insight into the physics of human locomotion.
Considerable interest in the use of autonomous aircraft for atmospheric measurements in remote and hazardous areas worldwide has arisen over recent years. Their application in tropical cyclone reconnaissance is under study by the World Meteorological Organization and the International Council for Scientific Unions under the United Nations International Decade for Natural Disaster Reduction. More diverse experiments, particularly for stratospheric operations, are being planned by agencies in the United States. The aerosonde can provide an economical and flexible element in these international initiatives. The concept is for a small aircraft (weighing less than 20 kg) with on-board meteorological sensors to provide radiosonde-quality observations at any location on the globe. Individual missions could span several thousand kilometers and several days' duration, using the Global Positioning System for autonomous navigation, and satellite relay for data return and flight-plan updates. With a supercharged engine, the aerosonde could make soundings from sea level to 100 hPa and back in a cycle of about 4 h. Aerosondes flying such profiles in routine wide-scale use are expected to achieve a per-sounding cost competitive with that of balloon-borne radiosondes, but with much greater flexibility of operation.
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