Ball Drive Configurations and Kinematics for Holonomic Ground Mobility

Holonomic motion is desired for mobile ground robots and vehicles as it provides omnidirectional maneuvering capabilities, which can simplify the task of navigating around obstacles in confined spaces and unstructured environments. Mobility platforms that utilize spherical wheels are gaining popularity and interest due to the agile maneuvering and ground traversal capabilities they enable for mobility platforms. Ball-driven mobility platforms have a rich design space as various design parameters are available that can modify the physical and performance characteristics of the platforms. Various configurations for ball-driven mobility platforms are presented along with a generalized kinematic model that can be used for calculating motor velocities for a desired vehicle velocity. A naming convention is also presented in the paper for differentiating between configurations used for ball-driven mobility platforms. Metrics such as platform footprint, platform stability, and actuation force and efficiency are used to compare the configurations and to highlight some of the trade-offs associated with the selection of a configuration. Promising configurations are highlighted based on the metrics selected for the comparisons.

Numerical and Experimental Aerodynamic Evaluation of a Solar Vehicle

Solar car racing has created a competitive platform for research into alternative energy solutions and aids development in the green engineering space. The University of Johannesburg’s Solar Racing team developed a vehicle (Ilanga II) to compete in the 2014 South African Solar Car Challenge. This paper describes the numerical optimization of the vehicle’s body shape, utilizing Computational Fluid Dynamics (CFD) and finally compares the simulated results with the actual performance during the race. Motor control data is used to determine the aerodynamic drag coefficient of the vehicle. This work builds on the paper submitted in 2014 [1], which postulated the use of the Hermite cubic function in conjunction with the shape function analysis as a holistic design tool. By analyzing the motor control data it is possible to comment on the effectiveness of the shape function analysis technique. The final optimized design predicted a straight-line ACd 0.078. A yaw angle characterization study of ±25° degrees, in conjunction with historic weather data were used to fully characterize the vehicle with an average drag area coefficient of 0.119. The final comparative results of the simulated data and the race data show that the vehicle’s straight-line (Zero yaw) ACd was 11.2% higher than the simulated results, whereas the average aerodynamic characteristic ACd was 2.43% lower than the simulated results.

Cellulose Nanocrystals Assisted Preparation of Electrochemical Energy Storage Electrodes

Renewable energy sources demands sustainable energy storage technologies through the incorporation of low-cost and environment-friendly materials. In this regard, cellulose nanocrystals (CN), which are needle-shaped nanostructure derived from cellulose-rich resources, are extracted by sulfuric acid hydrolysis of biomass and used as both template and binder for the construction of electrochemical capacitors electrodes. A composite material is synthetized comprising CN and a conjugated electroactive polymer (CEP) to overcome the electrical insulating properties of cellulose as well as to exploit enhanced electrochemical activity by increased electrode surface-area. A one-step in-situ film synthesis protocol is evaluated by performing simultaneous polymerization and film deposition. The effect of proportion of starting components are evaluated through statistical Response Surface Methodology towards optimizing the electrochemical performance. Depending on the mass proportion of the starting components, a conducting network could be created by surface coating of the CEP on the whiskers during polymerization. Electrochemical measurements suggest an increase in specific surface area by at least a factor of two relative to bare CEP as a consequence of the template role of cellulose. Therefore, adjustment of the proposed one-step synthesis parameters allows tuning the material properties to meet specific application requirements regarding electrochemical performance.

Two-Stage Precession Type Gear: Design, Geometric and Kinematic Analysis

The paper presents the theoretical bases, design and the principle of operation of two-stage precession type transmission with face meshing. Description and the principle of forming the face meshing which is modified by the original method have been shown as well. Dimensional relations between particular components of the gears are established and the analysis of optimal gear ratio, depending on the number of teeth or magnets on the circumferences of meshing gear wheels is also provided in the paper. For further analysis four prototypes of mechanical precession transmission with face meshing were designed, built and investigated. Those prototypes present different sizes, reduction ratio and precession angle. Investigations, described in the paper, helped to determine the gear efficiency rate as well as the maximal torque that could be transferred for the given rotary speed. This paper presents also the conception of the design of a novel double stage precession magnetic gear with face neodymium magnets. The results of the initial studies are the background of the further research in the field of magnetic precession type transmission.

Creep Behavior of a Solder Paste With Bi Addition

A common failure mode of electronic PCB’s is the appearance of cold solder joints between the component and PCB, during product life. This phenomenon is related to solder joint fatigue and is attributed mainly to the mismatch of the coefficients of thermal expansion (CTE) of component-solder-PCB assembly. Although some experiments show that newer lead-free tin-silver-copper (Sn-Ag-Cu, or SAC) solders perform better than the older SnPb ones, with today’s solder joint thickness decreasing and increasing working temperatures, among others, the stresses and strains due to temperature changes are growing, leading to limited fatigue life of the products. As fatigue life decreases with increasing plastic strain, creep occurrence should have significant impact, especially during thermal cycles. In order to improve mechanical properties, but also as an attempt to reduce maximum reflow cycle temperatures due to component damage and production costs, various SAC solder alloying additives are being considered to use in industrial production facilities. Solder paste producers are proposing new products based on new solder paste formulations, but the real life effects on thermo-mechanical performance aren’t well known at the moment. In this paper a dynamic mechanical analyser (DMA) is used to study the influence of Bismuth (Bi) addition, up to 5 wt %, on SAC405 solder paste, in terms of creep behaviour. Creep tests were made on three-point-bending configuration, isothermally at 30 °C, 50 °C and 75 °C, and three different stresses of 3, 5 and 9 MPa. The results shown not only a significant Bi concentration influence on creep behaviour but also a noticeable temperature dependence.

Kinematic Analysis and Design of Eccentric Rolling Transmission

The paper shows an idea of a new type of mechanical gear — the eccentric rolling transmission. The main parts of that transmission are rolling bearings, mounted eccentrically on the input shaft which cooperate with the special-shaped cam wheels mounted on the output shaft. The number of rolling bearings is equal to the number of cam wheels. On the basis of kinematic analysis equations of the curve which describe a shape of cam wheels were determined for two different cases: in the first one the directions of shafts rotations were opposite, and in the second they were the same. Kinematic analysis of the novel transmission was carried out to determine maximum gear ratio depending on the adopted input parameters. As a result of analyses a design procedure of the eccentric rolling transmission and CAD model were prepared.

Review of Risk and Assessment of Safety for Powered Conveyor Systems

Conveyor systems are common mechanical handling equipment used throughout many industries to transport materials in various directions — horizontally, vertically, at an angle or around curves — and at various heights including floor-mounted and overhead systems. There are many types of conveyors including both powered and non-powered. Each type of conveyor presents its own unique sets of hazards. Although conveyors reduce injuries associated with manual material handling tasks, they can present a different set of hazards to those installing, operating or maintaining them. These hazards are typically associated with the powered mechanical motion of belts, shafts, sprockets, chains and various other subcomponents. Many industry standards are currently in use for conveyors, such as ASME B20.1, Safety Standard for Conveyors and Related Equipment. These industry standards address safe practices in the design, construction, installation, operation and maintenance of conveyor equipment. This paper will focus on identifying and defining the hazards associated with powered conveyor systems, reviewing workplace injury data for powered conveyors and comparing with data for nonpowered conveyors to better understand the trends, quantifying many of the risks associated with conveyors, and exploring and discussing the engineering and administrative controls currently available to address these hazards. A brief look at recent updates to some of the relevant standards will be presented to guide the discussion.

Analysis and Testing of Passenger Vehicle Bulkhead Fireworthiness

This paper presents a case study of an injury producing post-crash fire as well as testing methods to evaluate bulkhead pass through seal fire resistance and retention. In the subject crash, engine compartment fluids were released and ignited. The burning fluids entered the occupant compartment through a bulkhead pass through, resulting in rapid fire propagation and severe occupant injuries before extrication could be completed. A burn testing methodology was developed and used to evaluate the ability of the subject seal design to prevent flames and fluids from entering the occupant compartment. A retention testing methodology was also developed and used to evaluate a variety of seal designs.

Investigation of Structure-Property Relationships Between Crystal Orientation and Dielectric Behavior in Liquid Crystalline Polymers

Liquid crystalline polymers (LCP’s) make up a class of high performance materials, which derive favorable mechanical, chemical, and electrical characteristics from their long-range molecular order. The unique LCP microstructure gives rise to anisotropic bulk behavior and an understanding of the driving forces behind this morphology is essential to the design of manufacturing processes for isotropic material production. In this investigation, the crystalline orientation in injection molded LCP plaque samples was measured using 2D wide-angle x-ray scattering (WAXS). The direction of preferred alignment was observed from the WAXS scattering patterns and the degree of orientation in the material was quantified using an order parameter and an anisotropy factor. In addition, the dielectric constant was measured with respect to the mold direction (MD) and transverse direction (TD). To investigate the effects of processing on hierarchal structure in the material, and the resulting macroscopic properties, plaques of two different thicknesses were analyzed, both as-injection molded and with the skin layer mechanically removed. It is shown that preferred orientation along the shear direction in the LCP samples corresponds to dielectric anisotropy, and increasing sample thickness, or conversely, mechanically removing the shear aligned layer, results in a more isotropic dielectric response.

Scanning Kelvin Probe Microscopy Study of Mg-Zn-Ca Alloys

This study focused on understanding the interactions between alloying elements in a magnesium (Mg) matrix and the effect of the alloying elements on corrosion behavior of Mg-alloys. The development of atomic force microscope (AFM) techniques has enabled the evaluation of physical and chemical properties of surfaces at the sub-micron level. Scanning Kelvin probe force microscopy (SKPFM) is particularly useful for studying localized corrosion phenomena of alloys. SKPFM generates a map of the potential distribution across a sample with a resolution of probe tip radius, nowadays ranging from 5 to 30 nm. Furthermore, the open circuit potential of various pure metals in solution is linearly related to the Volta potential value measured in air immediately after exposure to corrosive media. SKPFM is a useful tool to practically assess the nobility of a surface. This technique has been applied to the heterogeneous microstructure of Mg-Zn-Ca-RE (RE = Zr, Nd, Ga) alloys and provided clear evidence regarding the shape, position, compositional inhomogeneities and local practical nobility of intermetallic particles. Correlation between the measured potential distribution and the reactivity of these particles has been shown. Atomic force lithography (AFL, scratching with the hard tip) is a controlled method for local disruption of the protective oxide film that naturally formed on an Mg-surface in air. Combining SKPFM and AFL, the stability of the passive film and the tendency for stabilization of localized corrosion can be monitored. In addition, the lateral imaging capabilities of the AFM provide an approach to study the role of different microstructural features such as grain boundaries and impurities in the process of inducing localized corrosion.