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Gearset fabricated from molybdenum sulfide filled polyimide allows attention-free operation in vacuum and at extreme temperatures. Ring gear drives pinion gear on shaft in skewed-axis arrangement. Because loads are shared among multiple meshing teeth, self-lubricating material is strong enough to accomodate high gear ratio.
Space-compatible cryogenic valves are now required to operate between room and liquid helium temperatures. A remotely controllable cryogenic valve is described, which is made of bellows-type stainless steel and is operated by a miniature dc motor with integral gearset (485:1) at a nominal voltage of 28 Vdc. The power transmission provides a further reduction of 7.2:1 to give an overall gear ratio of nearly 3500:1, assuring reliability of operation at low temperatures. Valve performance (leak rate) data are presented at LN2, LHe, and SfHe temperatures at delivered torques of 18, 27, 31, and 35 N-m. At a closing torque of 31 N-m, a leak rate of 0.028 scc/sec was achieved at 2 K, while at a torque of 18 N-m the leak rate at 300 K was less than 3 x 10 to the -9th scc/sec.
Low-cost modification of Sun tracker automatically compensates equation of time and seasonal variations in declination of Sun. Output of Scotch Yoke drive mechanism adjusted through proper sizing of crank, yoke and other components and through choice of gear ratios to approximate seasonal northand south motion of Sun. Used for industrial solar-energy monitoring and in remote meteorological stations.
The penetration depth onto the tooth flank of a jet of oil at different velocities pointed at the pitch line on the outgoing side of mesh was determined. The analysis determines the impingement depth for both the gear and the pinion. It includes the cases for speed increasers and decreasers as well as for one to one gear ratio. In some cases the jet will strike the loaded side of the teeth, and in others it will strike the unloaded side of the teeth. In nearly all cases the top land will be cooled regardless of the penetration depth, and postimpingement oil spray will usually provide adequate amounts of oil for lubrication but is marginal or inadequate for cooling.
The design concepts, performance capabilities, and projected applications of the Quiet Short-Haul Research Aircraft (QSRA) are discussed. The propulsive lift system of the QSRA provides the lift required for short field operations at low community noise levels. This system consists of four high bipass ratio, geared turbofan engines mounted so that the engine exhaust flows across the upper surface of the wing (upper surface blowing). Large specially shaped flaps behind each engine control the direction of the flow for each phase of flight. A 95 passenger short haul transport based on this technology could operate out of a 2500 foot runway with a combined takeoff and landing 90 EPNdB footprint area of 2.7 sq mi.
The effect of axial pinion displacement on gear meshing conditions during cutting and correction of the rolling chain gear ratio are analyzed. The so-called inverse problem-solving method is used.
This report describes the results of the evaluation of a novel torque converter concept. Features of the concept include: (1) automatic and rapid adjustment of effective gear ratio in response to changes in external torque (2) maintenance of output torque at zero output velocity without loading the input power source and (3) isolation of input power source from load. Two working models of the concept were fabricated and tested, and a theoretical analysis was performed to determine the limits of performance. It was found that the devices are apparently suited to certain types of tool driver applications, such as screwdrivers, nut drivers and valve actuators. However, quantiative information was insufficient to draw final conclusion as to robotic applications.
A teleoperator system consists of a manual controller, control hardware/software, and a remote manipulator. It was employed in either hazardous or unstructured, and/or remote environments. In teleoperation, the main-in-the-loop is the central concept that brings human intelligence to the teleoperator system. When teleoperation involves contact with an uncertain environment, providing the feeling of telepresence to the human operator is one of desired characteristics of the teleoperator system. Unfortunately, most available manual controllers in bilateral or force-reflecting teleoperator systems can be characterized by their bulky size, high costs, or lack of smoothness and transparency, and elementary architectures. To investigate other alternatives, a force-reflecting, 3 degree of freedom (dof) spherical manual controller is designed, analyzed, and implemented as a test bed demonstration in this research effort. To achieve an improved level of design to meet criteria such as compactness, portability, and a somewhat enhanced force-reflecting capability, the demonstration manual controller employs high gear-ratio reducers. To reduce the effects of the inertia and friction on the system, various force control strategies are applied and their performance investigated. The spherical manual controller uses a parallel geometry to minimize inertial and gravitational effects on its primary task of transparent information transfer. As an alternative to the spherical 3-dof manual controller, a new conceptual (or parallel) spherical 3-dof module is introduced with a full kinematic analysis. Also, the resulting kinematic properties are compared to those of other typical spherical 3-dof systems. The conceptual design of a parallel 6-dof manual controller and its kinematic analysis is presented. This 6-dof manual controller is similar to the Stewart Platform with the actuators located on the base to minimize the dynamic effects. Finally, a combination of the new 3-dof and 6-dof concepts is presented as a feasible test-bed for enhanced performance in a 9-dof system.
The effect of the joint drive system with gear reduction for a generic two-link system is studied. It is done by comparing the kinetic energy of such a system with that of a direct drive two-link system. The only difference are two terms involving the inertia of the motor rotor and gear ratio. Modifications of the equations of motion from a direct drive system are then developed and generalized to various cases encountered in robot manipulators.
A recursive formulation is presented for the calculation of the inverse and forward dynamics of rigid robot manipulators with gear systems on each joint. The complete effects of the gear ratios and the gyroscopic effects of the spinning motor/gear are included in the recursive formulation. The forward dynamics solution recursively calculates the joint accelerations when given motor torques, and the number of computations grows linearly with the number of links.
This paper presents a formulation for the modeling of a single-link flexible beam that is undergoing slewing motion at an actively controlled pinned end, where the other end of the beam is free. This pinned end, or slewing axis, is of fixed orientation such that the beam rotates in the horizontal plane. A geared dc electric motor is connected to the beam at the slewing axis. A position and a velocity sensor are placed at this hinged location, and their proportional feedback provides a position control system about the slewing axis. The motor characteristics, gear ratio, and the position feedback constant determine an equivalent rotational spring constant, often called the servo stiffness. This paper generalizes the structure's boundary conditions at the slewing axis to include the effects of the servo system. It is shown that the clamped-free beam assumption for the dynamics of the structure is a valid assumption if the ratio of the servo stiffness to beam flexibility is high. However, for moderate or low values of this ratio, the clamped-free beam leads to erroneous system models so that it becomes necessary to consider the effects of the driving servo on the dynamics of the flexible beam.
An implementation of a manual controller system is described in which a parallel 3-DOF spherical structure (for compactness and reduced weight) is combined with high-gear-ratio reducers using a force control algorithm to produce a 'power steering' effect for enhanced smoothness and transparency. The force control algorithm has the further benefit of minimizing the effect of the system friction and nonlinear inertia forces. The required analyses for a universal force-reflecting manual controller application are presented, as are test results for a prototype system.
The design and analysis of the electromechanical actuator (EMA) being developed for the NASA/Marshall Space Flight Center as part of the National Launch System (NLS) Propellant Control Effector Advanced Development Program (ADP) are addressed. The EMA design uses several proven technologies combined into a single modular package which includes single stage high ratio gear reduction, redundant electric motors mounted on a common drive shaft, redundant drive and control electronics, and digital technology for performing the closed loop position feedback, communication, and health monitoring functions. Results of tests aimed at evaluating both component characteristics and overall system performance demonstrated that the goal of low cost, reliable control in a cryogenic environment is feasible.
A joint helicopter transmission research program between NASA Lewis Research Center and the U.S. Army Research Lab has existed since 1970. Research goals are to reduce weight and noise while increasing life, reliability, and safety. These research goals are achieved by the NASA/Army Mechanical Systems Technology Branch through both in-house research and cooperative research projects with university and industry partners. Some recent significant technical accomplishments produced by this cooperative research are reviewed. The following research projects are reviewed: oil-off survivability of tapered roller bearings, design and evaluation of high contact ratio gearing, finite element analysis of spiral bevel gears, computer numerical control grinding of spiral bevel gears, gear dynamics code validation, computer program for life and reliability of helicopter transmissions, planetary gear train efficiency study, and the Advanced Rotorcraft Transmission (ART) program.
The main rotors of the NASA Large Civil Tilt-Rotor notional vehicle operate over a wide speed-range (100% at take-off to 54% at cruise). The variable-speed power turbine, when coupled to a fixed-gear-ratio transmission, offers one approach to accomplish this speed variation. The key aero-challenges of the variable-speed power turbine are related to high work factors at cruise, where the power turbine operates at 54% of take-off speed, wide incidence variations into the vane, blade, and exit-guide-vane rows associated with the power-turbine speed change, and the impact of low aft-stage Reynolds number (transitional flow) at 28 kft cruise. Meanline and 2-D Reynolds-Averaged Navier- Stokes analyses are used to characterize the variable-speed power-turbine aerodynamic challenges and to outline a conceptual design approach that accounts for multi-point operation. Identified technical challenges associated with the aerodynamics of high work factor, incidence-tolerant blading, and low Reynolds numbers pose research needs outlined in the paper
The vertical take-off and landing (VTOL) and high-speed cruise capability of the NASA Large Civil Tilt-Rotor (LCTR) notional vehicle is envisaged to enable increased throughput in the national airspace. A key challenge of the LCTR is the requirement to vary the main rotor speeds from 100% at take-off to near 50% at cruise as required to minimize mission fuel burn. The variable-speed power-turbine (VSPT), driving a fixed gear-ratio transmission, provides one approach for effecting this wide speed variation. The key aerodynamic and rotordynamic challenges of the VSPT were described in the FAP Conference presentation. The challenges include maintaining high turbine efficiency at high work factor, wide (60 deg.) of incidence variation in all blade rows due to the speed variation, and operation at low Reynolds numbers (with transitional flow). The PT -shaft of the VSPT must be designed for safe operation in the wide speed range required, and therefore poses challenges associated with rotordynamics. The technical challenges drive research activities underway at NASA. An overview of the NASA SRW VSPT research activities was provided. These activities included conceptual and preliminary aero and mechanical (rotordynamics) design of the VSPT for the LCTR application, experimental and computational research supporting the development of incidence tolerant blading, and steps toward component-level testing of a variable-speed power-turbine of relevance to the LCTR application.
The problem of trajectory optimization is important in all space missions. The solution of this problem enables one to specify the optimum thrust steering program which should be followed to achieve a specified mission objective, simultaneously satisfying the constraints.1 It is well known that whether or not the ascent trajectory is optimal can have a significant impact on propellant usage for a given payload, or on payload weight for the same gross vehicle weight.2 Consequently, ascent guidance commands are usually optimized in some fashion. Multi-stage vehicles add complexity to this analysis process as changes in vehicle properties in one stage propagate to the other stages through gear ratios and changes in the optimal trajectory. These effects can cause an increase in analysis time as more variables are added and convergence of the optimizer to system closure requires more analysis iterations. In this paper, an approach to simplifying this multi-stage problem through the creation of an upper stage capability boundary is presented. This work was completed as part of a larger study focused on trade space exploration for the advanced booster system that will eventually form a part of NASA s new Space Launch System.3 The approach developed leverages Design of Experiments and Surrogate Modeling4 techniques to create a predictive model of the SLS upper stage performance. The design of the SLS core stages is considered fixed for the purposes of this study, which results in trajectory parameters such as staging conditions being the only variables relevant to the upper stage. Through the creation of a surrogate model, which takes staging conditions as inputs and predicts the payload mass delivered by the SLS upper stage to a reference orbit as the response, it is possible to identify a "surface" of staging conditions which all satisfy the SLS requirement of placing 130 metric tons into low-Earth orbit (LEO).3 This identified surface represents the 130 metric ton capability boundary for the upper stage, such that if the combined first stage and boosters can achieve any one staging point on that surface, then the design is identified as feasible. With the surrogate model created, design and analysis of advanced booster concepts is streamlined, as optimization of the upper stage trajectory is no longer required in every design loop.
Venus, with a surface temperature of 450 C and an atmospheric pressure 90 times higher than that of the Earth, is a difficult target for exploration. However, high-temperature electronics and power systems now being developed make it possible that future missions may be able to operate in the Venus environment. Powering such a rover within the scope of a Discovery class mission will be difficult, but harnessing Venus' surface winds provides a possible way to keep a powered rover small and light. This project scopes out the feasibility of a wind-powered rover for Venus surface missions. Two rover concepts, a land-sailing rover and a wind-turbine-powered rover, were considered. The turbine-powered rover design is selected as being a low-risk and low-cost strategy. Turbine detailed analysis and design shows that the turbine can meet mission requirements across the desired range of wind speeds by utilizing three constant voltage generators at fixed gear ratios.