Mechanical & Fluid Systems

Thermal and Compressed-Air Storage System Provides Alternative to UPS Batteries

Three mature energy-storage technologies are combined in a new system to replace lead-acid batteries. Virtually all businesses and industries are vulnerable to electric power disturbances such as outages, sags, swells, and harmonics. These problems are less of an issue for data centers, protected behind their walls of Uninterruptible Power Supply (UPS) systems. But the typical battery-backed UPS is too fragile for use in less protected environments. UPS batteries must be maintained in a narrow temperature range and fail prematurely when subjected to a steady diet of step loads and motor drives. About six years ago, flywheel-based UPS products became commercially available. These devices store energy as rotational inertia, and are rugged enough to survive on the factory floor. However, flywheels have relatively short ride-through energy and are best-suited for use in locations with backup generators.

Posted in: Briefs, Mechanical Components, Mechanics, Energy storage systems, Flywheels, Reliability


Carbon-Fiber Brush Heat Exchangers

High thermal conductance between uneven surfaces could be achieved with low clamping force. Velvetlike and brushlike pads of carbon fibers have been proposed for use as mechanically compliant, highly thermally conductive interfaces for transferring heat. A pad of this type would be formed by attaching short carbon fibers to either or both of two objects that one desires to place in thermal contact with each other. The purpose of using a thermal-contact pad of this or any other type is to reduce the thermal resistance of an interface between a heat source (e.g., a module that contains electronic circuitry) and a heat sink (e.g., a common finned heat sink).

Posted in: Briefs, Mechanical Components, Mechanics, Heat exchangers, Conductivity, Fibers


Alternative Attitude Commanding and Control for Precise Spacecraft Landing

A report proposes an alternative method of control for precision landing on a remote planet. In the traditional method, the attitude of a spacecraft is required to track a commanded translational acceleration vector, which is generated at each time step by solving a two-point boundary value problem. No requirement of continuity is imposed on the acceleration. The translational acceleration does not necessarily vary smoothly. Tracking of a nonsmooth acceleration causes the vehicle attitude to exhibit undesirable transients and poor pointing stability behavior. In the alternative method, the two-point boundary value problem is not solved at each time step. A smooth reference position profile is computed. The profile is recomputed only when the control errors get sufficiently large. The nominal attitude is still required to track the smooth reference acceleration command. A steering logic is proposed that controls the position and velocity errors about the reference profile by perturbing the attitude slightly about the nominal attitude. The overall pointing behavior is therefore smooth, greatly reducing the degree of pointing instability.

Posted in: Briefs, TSP, Mechanical Components, Mechanics


Power Transmission for Motion Control

While technology has advanced and there are many new ways to accomplish useful motion within particular applications, electric motors and gearheads are still the preferred and most popular choices for power transmission throughout commercial, industrial, and automation applications. Motors are the components that convert electrical power to useful mechanical power. Gearheads transform the mechanical rotary power to the desired combination of speed and torque if the motor cannot do so directly. Benefits of this combination include low cost, simplicity, reliability, and versatility.

Posted in: Briefs, Mechanical Components, Mechanics, Electric power, Technical review, Electric motors


Miniature Linear Actuator for Small Spacecraft

A report discusses the development of a kit of mechanisms intended for use aboard future spacecraft having masses between 10 and 100 kg. The report focuses mostly on two prototypes of one of the mechanisms: a miniature linear actuator based on a shape-memory-alloy (SMA) wire. In this actuator, as in SMA-wire actuators described previously in NASA Tech Briefs, a spring biases a moving part toward one limit of its stroke and is restrained or pulled toward the other limit of the stroke by an SMA wire, which assumes a slightly lesser or greater "remembered" length, depending on whether or not an electric current is applied to the wire to heat it above a transition temperature. Topics addressed in the report include the need to develop mechanisms like these, the general approach to be taken in designing SMA actuators, tests of the two prototypes of the miniature linear actuators,and improvements in the second prototype over the first prototype resulting in reduced mass and increased stroke. The report also presents recommendations for future development, briefly discusses problems of tolerances and working with small parts, states a need for better understanding of behaviors of SMAs, and presents conclusions.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Sensors and actuators, Wiring, Smart materials, Spacecraft


Second-Generation Six-Limbed Experimental Robot

This robot is designed to be more agile and dexterous than its predecessor. The figure shows the LEMUR II—the second generation of the Limbed Excursion Mechanical Utility Robot (LEMUR), which was described in "Six-Legged Ex- perimental Robot " (NPO-20897), NASA Tech Briefs,Vol.25, No.12 (December 2001), page 58. The LEMUR II incorporates a number of improvements, including new features, that extend its capabilities beyond those of its predecessor, which is now denoted the LEMUR I.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Robotics


Development of Biomorphic Flyers

Autonomous flight control and navigation in small size is offered for planetary and terrestrial exploration applications. Biomorphic flyers have recently been demonstrated that utilize the approach described earlier in "Bio-Inspired Engineering of Exploration Systems" (NPO-21142), NASA Tech Briefs ,Vol.27, No.5 (May 2003), page 54, to distill the principles found in successful, nature-tested mechanisms of flight control. Two types of flyers are being built, corresponding to the imaging and shepherding flyers for a biomorphic mission described earlier in "Cooperative Lander-Surface/Aerial Microflyer Missions for Mars Exploration" (NPO-30286), NASA Tech Briefs, Vol.28, No.5 (May 2004), page 36. The common features of these two types of flyers are that both are delta-wing airplanes incorporating bio-inspired capabilities of control, navigation, and visual search for exploration. The delta-wing design is robust to ~40 G axial load and offers ease of stowing and packaging.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Flight control systems, Biological sciences


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