Mechanical & Fluid Systems

Gear Bearings and Gear-Bearing Transmissions

Planetary transmissions could be simpler, cheaper, and more rigid. Gear bearings are conceptual mechanical components so named because they function as gears and as roller and/or thrust bearings. Gear bearings will be essential components of the next generation of compact, large-mechanical- advantage gear drives.

Posted in: Briefs, TSP, Mechanical Components

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Linear Dynamometer With Variable Stroke and Frequency

Stroke length and frequency can be adjusted continuously during operation. An improved linear dynamometer has been developed for testing linear alternators that are to be used to convert mechanical power to electrical power in free-piston Stirlingcycle engines. Both the frequency and the length of the stroke of this dynamometer can be varied continuously, even during operation; consequently, the dynamometer can be used to fully map the capabilities of a linear alternator throughout its service envelope (its operational range as defined on a plot of limiting stroke length versus frequency) in a single test.

Posted in: Briefs, TSP, Mechanical Components

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Study of Turbulent Boundary Layer on the F-15B Airplane

Automated hot-wire anemometry has been demonstrated in flight tests. NASA’s F-15B #836 is a two-seat version of the F-15, which is a high-performance, supersonic, all-weather fighter airplane. The F-15B is used as a test-bed aircraft for a wide variety of flight experiments. In support of this use, a flight-test fixture (FTF) was developed to provide a space for flight experiments in a region with known aerodynamic conditions. The FTF is a fully instrumented test article mounted on the center line of the bottom of the fuselage of an F-15B airplane. The FTF includes an interchangeable experiment panel and is 107 in. (2.72 m) long, 32 in. (0.81 m) high, and 8 in.(20.3 cm) wide, with a 12-in. (30.5-cm) elliptical nose section. The FTF has been used in many flight experiments during the past several years and can be modified to satisfy a variety of research requirements.

Posted in: Briefs, TSP, Mechanical Components

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Improved Alignment Mechanism for Robotic Drilling

The improved design prevents jamming of an alignment key in an incorrect position. An improved alignment mechanism and mating procedure have been devised for a robotic drilling system in which there is a need to assemble drill stem rods for sampling soils and rocks on a distant planet or asteroid. This mechanism is applicable to systems requiring positive axial alignment between segments. Similar mechanisms could be used on Earth, not only for assembling long drills but also for any system where a series of rods must be robotically assembled, such as in truss construction.

Posted in: Briefs, TSP, Mechanical Components

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Measuring Volume of Incompressible Liquid in a Rigid Tank

The measurement is unaffected by the shape of the liquid or tank. A technique for measuring the volume of an incompressible liquid in a rigid tank involves measurement of the total volume of gas in those parts of the tank not occupied by the liquid. The volume of liquid is then computed by subtracting V from the total volume of the tank and the associated plumbing.

Posted in: Briefs, TSP, Mechanical Components

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Vision-Based Maneuvering and Manipulation by a Mobile Robot

Mobility is used to augment limited dexterity. A small mobile robot equipped with a stereoscopic machine vision system and two manipulator arms that have limited degrees of freedom has been given the ability to perform moderately dexterous manipulation autonomously, under control by an onboard computer. The approach taken in this development has been one of formulating vision-based control software to utilize the mobility of the vehicle to compensate for the limitation on the dexterity of the manipulator arms. Although the goal was selected visually, it is tracked onboard using information about its shape; in particular, the target is assumed to be a local elevation maximum (i.e., the highest point within a small patch of area).

Posted in: Briefs, TSP, Mechanical Components

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Algorithms for Collision Avoidant Formation Flying

A report discusses algorithms for realtime planning of translation paths of multiple spacecraft flying in formation. The algorithm takes account of requirements to avoid collisions while operating within resource constraints (e.g., not calling for an acceleration greater than maximum possible) and striving for optimality (e.g., completing a change of formation in minimum time or at minimum energy cost). The optimality/collision- avoidance problem is formulated as a parameter-optimization problem, in which the translation path of each spacecraft is parameterized by polynomial functions of time. It is shown that this parameterization is the key to the solution of the parameter-optimization problem in that it enables decoupling of the collision-avoidance and accelerationlimit constraints, thereby making it possible to solve the problem in two stages. In the first stage, one constructs feasible paths that satisfy only the collision-avoidance constraints subject to certain optimality criteria. It is shown that the acceleration- limit constraints can be imposed a posteriori to compute the required maneuver duration such that at least one acceleration component is saturated. This also enables construction of paths that require minimum time in the class of solutions being considered.

Posted in: Briefs, TSP, Mechanical Components

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