A challenge for greyhound racing is optimizing the tracks to minimize the risk of injuries. The effects of different track design variables on greyhound injury rates has not been explored sufficiently. The purpose of this paper is to present some preliminary findings on the effect of greyhound racetrack design variables such as the track curvature and lure alignment. An analysis was carried out of two years of greyhound racing injury data from three different tracks in New South Wales, Australia. The data from before and after an intervention was introduced were compared. Variables in the study, which may affect\ the analysis were investigated to minimize the errors. The analysis showed that there is a reduction in injury rates for a longer lure arm in the tracks with short or no straight section. To verify the effect of track design variables on the greyhound dynamics a kinematic simulation of greyhound center of gravity was created. The simulation considered fundamental variables correlating directly with kinematics between the greyhound and the track. The simulation data showed that the rate of change in the rotation of the greyhound heading direction decreases when the track running path has a more gradual curvature. The result of the simulation showed excellent agreement with that of injury data analysis.

A simplified roll-plane model is proposed to assess the effect of the vertical position of the center of gravity of the body-cargo system, on the rail fatigue life. A set of assumptions are made to simplify the analysis, including neglecting the bogie’s dynamic contribution to the wheel-rail forces. Three performance measures are defined to assess the effect of different dedicated railway cars on the rail fatigue life, including the fourth-power law, the load dispersion, and the rail fatigue. The simulation results suggest that the vertical position of the center of gravity of the body-cargo set, severely affects the fatigue life of the railway material, with the two-stack car being the most aggressive. For example, twice as aggressive as the gondola car.

For rigid-body systems subjected to non-holonomic constraints, a streamlined method is presented to derive a minimum number of analytical equations of motion. To illustrate the method, a rolling disk problem is considered. In kinematics, an orthonormal coordinate system is attached to the center of mass together with additional coordinate systems introduced to define the connection path. For each coordinate system, a moving frame is defined by explicitly writing the coordinate vector basis and the position vector of the origin, whereby the attitude of the coordinate vector basis and the coordinates of the origin are compactly stored in a 4 × 4 frame connection matrix of the special Euclidean group , SE(3). Contact velocity constraints are transformed to pfaffians to obtain the associated variational constraints. In kinetics, the principle of virtual work is employed. The desired equations of motion are obtained by expressing the translational and angular velocities at the center of mass as the linear functions of the generalized velocities with the coefficients stored in [B]-matrix, and reducing it to [B*]-matrix after incorporating the contact constraints. The method can be easily extended to multi-body systems with both holonomic and non-holonomic constraints.

This work presents a new systematic solution to identify the vehicle inertia parameters which are essential inputs for vehicle simulation and vehicle safety research. In conceptual design phase of this work, a virtual three Degree-of-Freedom (DoF) test bench/ parallel manipulator (PM) whose moving platform is used to clamp vehicle under test is developed. In order to realize the kinematic characteristics of the proposed PM, the kinematic analysis consists of inverse kinematic and singularity architecture is carried out. Aiming at obtaining all ten vehicle inertia parameters (i.e., mass, center of gravity and inertia tensor), the observation matrix for parameter identification is derived from the dynamic model of PM. To get the dynamic model, the Euler’s equation and Lagrange approach are applied to implement the dynamic analysis for PM’s moving platform and actuators, respectively. It is beneficial to reduce the complexity of dynamic model and load of numerical computation. In the following section, to minimize the sensitivity of parameter identification to measurement noise, an optimization process of searching for the optimal movement trajectory of PM is proposed. For this purpose, the parameterized finite-Fourier-series are used to definite the general movement trajectory of PM firstly. Subsequently, the parameters of general trajectory are optimized by employing a nonlinear iterative algorithm. Objective of this algorithm is to obtain the minimal condition number of observation matrix and meanwhile to ensure the PM still works in the achievable working space during the test. The results show that the vehicle inertial parameters can be effectively identified by executing the single optimal movement trajectory on the PM. It is expected that the proposed systematic solution could be an important approach to improve the identification efficiency and identification accuracy of vehicle inertial parameters.

The effect of all-inclusive generic offset payload characteristics on the modes of vibration and nonlinear characteristics of a rotating flexible manipulator with a revolute pair has been accomplished in the present article. A brief dynamic modelling and free vibration analysis to obtain the eigenspectrums of the system, whereafter nonlinear analysis of a manipulator with a general offset payload undergoing overall motion has been accomplished. Dynamic equation of motion and associated boundary conditions have been developed where the payload is considered as a mass whose center of gravity doesn’t coincide with the point of attachment with the manipulator. The effect of various system parameters such as offset mass, offset inertia, offset length, hub mass, actuated inertia and hub stiffness on eigenfrequency is well tabulated and the same effect on eigenspectrums is presented graphically. Further, MMS is employed to investigate the effect of parametric variation on the nonlinear behaviour and associated bifurcation of the rotating single-link flexible manipulator being harmonically driven at the joint under primary resonance considering the centrifugal forces acting on the link and payload as well. The present analysis indicated the pronounced effect of system mass, inertia, stiffness and rotating speed on the eigencharacteristics and bifurcations of a flexible manipulator with a rotating joint.

Humanoid robots have the potential to help or even take the place of humans working in extreme or undesirable environments. Wheeled humanoids are robots that combine the mobility of mobile platforms, and the dexterity of an articulated body with two robotic arms. To perform like a human being, these robots normally are designed with a high center of mass, which makes it challenging to maintain stability while achieving high performance on complex and unpredictable terrain. Inspired from how humans react to balance themselves, a compliance control method is studied to help the wheeled humanoid robot developed at the Robotics Laboratory at Cal State LA achieve high dynamic performance while scouting over uneven terrain. Lagrange-Euler method is used to obtain the dynamic model of the humanoid robot. Then a nonlinear sliding mode compliance controller is derived and proven to ensure asymptotic stability of the humanoid robot while tracking desired reference trajectories. Finally, the performance of the proposed compliance control system is demonstrated using simulation. The results show that the robot successfully tracks a given input while maintaining balance based on the proposed tip-over avoidance algorithm.

The presence of architectural barriers in public or private buildings represents an important limit for the mobility of wheelchair users. Although norms promote barriers removal, often a complete accessibility cannot be guaranteed due to economic or technical reasons. In such cases, it is necessary to provide disable people with devices able to autonomously climb architectural barriers or obstacles. Referring to user needs, some requirements for the wheelchair can be defined. Firstly, the user must use it autonomously. Secondly, it should be easy to use, simple in the mechanical and control systems and with limited weight, dimensions, and cost. Finally, also the appearance of the wheelchair must be adequate to guarantee the user acceptability. In literature, several solutions of stair-climbing wheelchair are proposed. However, none of these completely satisfies the identified requirements. In this paper, the Wheelchair.q05, an innovative concept for a stair-climbing wheelchair, is presented. This idea has been developed through several years of researches and functional designs. In detail, this work presents the final design for a constructive and real scale prototype. The proposed wheelchair, thanks to a smart and hybrid locomotion system, is able to move on flat ground and to climb stairs and sidewalks. A triangular shaped frame with a wheel on each corner, connected through an internal epicyclical transmission system, constitutes the locomotion unit. This system provides the traction both for flat ground and stair motion. Moreover, the wheelchair has an idle track that represents the rear contact point during stair-climbing and guarantees only a stable and regular climbing motion. The wheelchair structure is thus constituted by the following functional elements: two locomotion units, the track, the seat and a couple of pivoting wheels connected to floating arms that represents the rear support during flat ground motion and during sidewalks overcoming. Through a kinematic synthesis, the optimal layout has been defined and the mechanisms that connect the functional elements with the frame have been designed. These mechanisms allow controlling the wheelchair reconfiguration that is necessary to adapt the vehicle to different working conditions. Moreover, attention has been paid to the user comfort. Thanks to the introduction of a mechanism that controls the seat orientation, the oscillations generated by the motion on stair are compensated and a regular trajectory is guaranteed for the user center of mass.

A realization of how specific exercises relate to balance performance is important for a wide demographic of individuals. Maintaining active and healthy living is particularly important for balance-impaired individuals (e.g., otherwise healthy individuals recovering from injury, fall-prone elderly, and stroke survivors) whom are interested in improving their balance for function in daily life. However, balance performance is also important for persons that are unimpaired (e.g., athletes). How balance performance may be improved as a result of, and in relation to, various athletic activities and exercises is a common question. Further, how certain activities can be used to prevent injury is an ultimate goal. Our objective was to compare standing balance in 3 unimpaired groups (i.e., female track & female tennis collegiate athletes and female non-athletes). To assess static balance, participants performed stance variations increasing in difficulty-level, utilizing a wide or tandem stance (increasing or decreasing support base) and eyes-open or eyes-closed (limiting or providing visual cues), while standing on a forceplate walkway. Through the recorded ground reaction forceplate-based, center-of-pressure (COP) position time series, we extracted velocity and displacement parameters that aided in identifying differences between the above groups. Our general findings were that anterior-posterior (AP, or front-to-back) COP displacement and velocity measures for female track athletes were unchanged relative to the (baseline) female non-athletes. However, mediolateral (ML, or side-to-side) measures, which have previously been shown to be associated with fall-risk, showed observable differences in displacement and velocity parameters, particularly for the female track athletes. Specifically, the female track athletes were better able to control their ML COP velocity in eyes-closed, wide, and eyes-open tandem conditions compared to non-athletes. However, tennis athletes had difficulty balancing in situations where eyes were closed (vision eliminated) and feet were tandem (base-of-support decreased) which was made apparent by the increases in all AP and ML COP-derived parameters. We interpreted this finding as the female tennis athletes were trained to rely heavily on visual cues (e.g., hand-eye or eye-body coordination), and also their balance may be more focused on maintaining their center-of-mass stability and body orientation, as opposed to COP per se. Our study lends new insights as to how various types of athletic activities, and reliance on vision in athletes, impacts balance performance in un-impaired females.

Taking into account a multitude of experimental and theoretical studies reported in the literature, the braking efficiency of road tankers can be affected by the sloshing forces developed by the carried liquid during such maneuvers, as a result of the dynamic pressures exerted by the sloshing liquid on the vehicle containers walls, and of the shifting of the liquid center of gravity. However, such studies have not involved a full scale experiment. In this paper, a simplified model is proposed to study the effect of the sloshing dynamics on a road tanker braking efficiency. Results from this simplified approach, are compared with data from full scale testing, revealing that the simplified model is good to predict the maximum pressure that the sloshing liquid exerts on one of the vehicle chambers. The simplified model considers a straight truck and a pendulum analogy for the sloshing liquid, whose parameters are derived from a validated methodology to predict the sloshing frequency of the fluid within its container. Simulation of non-sloshing cargo further suggests that the stopping time can be increased by 7 % due to the sloshing cargo.

Multirotor Unmanned Aerial Systems (UAS) are highly mobile in flight and possess stable hovering capabilities. Because of their unique flight characteristics, the utilization of the platform for active tasks such as aerial manipulation is highly attractive. Much work has been done in recent years towards the implementation of multirotor for aerial manipulation, however, progress in the field has been slow due to the many challenges involved in the implementation of robust rotor control. In an attempt to reduce the effects of the manipulator, a technique for disturbance rejection using a novel balancing mechanism is proposed. In this paper, the dynamic equations of a coupled multirotor and manipulator are analyzed as a single body for use in the attitude control of the platform. By mounting the mechanism, the platform effectively gains marginal control over the positioning of its center of gravity relative to a body fixed frame. It can be shown that the increased mobility can be utilized to reduce rotor saturation for any given flight condition and improve the effectiveness of previously developed rotor control methods.

One of the most critical testing procedures for an airplane certification is Ground Vibration Testing (GVT). With proper GVT analysts can determine the stiffness distribution, natural frequencies, mode shapes and structural damping of each airplane components, which are needed for flutter and dynamic loads analyses. Hence, the results from GVT are crucial. The problem identified in this study is focused on structural design, which can lead to catastrophic situations, if proper attention is not given to GVT results. In GVT, analysts attempt to instrument most of the primary components of the airplane while often neglecting secondary structures such as bungees, gears, control surfaces, etc. These secondary structures must also be considered during GVT in identifying the in-phase and out-of-phase modes in order to achieve higher accuracy when tuning the stiffness of the primary structure. During the stiffness tuning process for the flutter analysis, tuning the primary structure stiffness to in-phase torsion mode can be considered as a conservative approach and will require design change. Conversely, if the stiffness of the primary structure is tuned to out-of-phase torsion mode, which is always higher, the analysis becomes unconservative. The goal of this study is to reconstruct the above-mentioned problem of in-phase and out-of-phase vibration modes of a cantilever plate with an attached secondary structure, replicating a simple model of aircraft wing structure. This includes performing the modal experiments and finite element analysis (FEA) of a cantilever plate (primary structure) with and without flexible links (secondary structure) attached to the plate and characterizing the in-phase and out-of-phase modes of the flexible links. A thorough study using frequency response functions (FRFs) is performed to characterize the modes using different accelerometer ‘raw data’ readings measured from different locations on the dynamic system. For GVT of the cantilever plate, natural frequencies associated with the respective mode shapes are identified and calculated and a comparison is made between the test results, the FEA results, and from an analytical approach. A parametric study is then conducted to evaluate and quantify the change in the frequencies of the in-phase and out-of-phase modes with the change in the chord-wise and span-wise location of the flexible attachment of the secondary structure to the primary structure, and due to the change in the compliant stiffness of the flexible link to the plate. Proper identification and correlation of the modes and natural frequencies of the cantilever plate with and without the secondary structure are presented. It is concluded that the in-phase and out-of-phase torsion frequencies increased with higher compliant stiffness. With the chord-wise change in location of the flexible link, both the in-phase and out-of-phase frequencies increased when the center of gravity of the link move towards the center of the chord from both leading and trailing edges of the plate. With the span-wise change in CG of the link, the in-phase frequency reduced with span (i.e., when the CG moves away from the constraint location of the plate) and the out-of-phase frequency increased.

In this paper, a joint simulat ion method based on nonlinear FEM and MBD is proposed. Firstly, the force-deformation character of single vehicle is analysed using nonlinear FEM software Dytran. Then, override simulations of two train units in frontal collision are carried out using multi-body dynamics. Simulation results indicate that the pitching motion of vehicles has great effect to the overriding phenomenon. It also depends on several factors, such as collision mass, pitching frequency, height of the center of mass above the rail level. Besides that, it is shown in this paper the overriding phenomenon is more sensitive to variations in pitching frequency and height of the center of mass, compared to the factor of collision mass.

In today’s society, those who do not take advantage of public transportation services typically drive personal vehicles to school, work, and other locations of interest. Due to the required amount of physical exertion, walking or riding a bike is often avoided. This is concerning given that a large percentage of carbon and hazardous emissions emanate from motor vehicles. This creates a need for an alternative means of travel for shorter commutes with electric bikes (e-bikes) one potential solution. They have zero tailpipe emissions and significantly lower overall emissions relative to motorized vehicles; however, their cost often prevents them from being readily marketable. In order to address this issue, two undergraduate capstone design teams have constructed e-bikes using recycled and donated parts over the past two years. In the first year, the runner from a pickup truck was scavenged from a junkyard and employed as the frame to provide for the greatest environmental benefit. However, this resulted in an odd bicycle shape because of limited material availability. As a result, the second years team decided to use a donated chrome moly tube as the frame while focusing on ergonomics and aesthetics. This second bike was designed so that a male rider of average height (5′10″ – 1.78 m) could complete commutes of several miles in relative comfort. Both e-bikes employ a direct drive motor (first year – front wheel; second year – back wheel) to provide assistance when needed, leaving the rider less fatigued. To promote further development in electric bike design, each team has made a considerable effort to record the design process with highlights presented in this effort. Furthermore, e-bike testing results are presented including center of mass calculations, braking distances, turning radii, and overall efficiencies quantified by the miles traveled using the same battery pack. This information will be used to compare the bikes against each other in order to illustrate bike attributes that are desired when an electric motor is employed. The result is an appealing, cost-effective, and efficient electrical bike that will greatly reduce traffic related emissions should it become widely implemented. Given the issues related to transportation at a university (e.g., available parking) including the reticence of students to traverse long distances across campus to attend classes, it is believed that this effort can serve as a model example to other universities who might see e-bikes as a potential solution to reducing congestion and improving student attendance.

This paper presents a four-pendulum design for an omnidirectional spherical robot. The robot moves by the rotation of tetrahedrally-located pendulums to change the center of mass, and can do so instantaneously in any direction. In that respect, it is omnidirectional unlike the more common single-pendulum designs. In the paper, the theoretical design is discussed and contrasted to existing theoretical center-of-mass designs in terms of directionality, torque arm, eccentricity, and radius of gyration. The torque arm comparison is based on the envelope of the dynamically-controlled mass (i.e., how far in any direction can the center of mass be moved), while the eccentricity and gyration criteria are based on homogeneity and size of the mass moment of inertia (i.e., how much does the design “wobble” while rolling; how much inertia does it have). In these regards, the four-pendulum architecture is better than some in one respect, better than many in other respects. A prototype has been built and tested to successfully implement the four-pendulum propulsion. Significance of the proposed system is presented through a comparison of results with previous work.

In this paper, the problem of vehicle stability control using model predictive technique is addressed. The vehicle under consideration is an electric vehicle with an electric motor driving each wheel independently. For the purpose of stability control, it is required that the vehicle tracks a desired yaw rate at all times therefore, extending the linear range of the vehicle dynamics. The desired yaw rate is defined based on vehicle speed, steering wheel angle and road surface friction. The vehicle stability control system considered in this paper consists of a high-level controller that compares the current states of the vehicle with its desired states to determine the required forces and moments at the center of mass, and a low-level controller to track those C.G. forces and moments by adjusting the motor torques on each wheel. It will be shown that a non-predictive low-level controller can have a closed form solution. In order to avoid saturation of the tires, the low-level controller has a penalty function that increases exponentially when the tire forces are close to the limits of saturation to reduce tire forces to keep them within the tires force capacity. In this paper, a model predictive controller is designed as the low-level controller to predict the tire forces and the yaw moment at the C.G. to minimize the tracking error of desired C.G. forces and moments. To keep the tire forces within the tires capacity limit, a penalty function is used at each sample time to penalize control actions that result in excessive tire forces. This adds a level of anticipation to the low-level controller to detect in advance when tires are about to saturate and to choose control actions to prevent that from happening. Since tire capacity limit is treated with an analytical penalty function, it is still possible to find a closed form solution for the model predictive low-level controller. The proposed controller is tested with simulations and the results are compared with a similar non-predictive controller.

To meet new Corporate Average Fuel Economy (CAFE) standards, future vehicles are expected to be more environmentally friendly and fuel efficient. In addition to introducing innovative manufacturing methods and structural modifications, automobile manufacturers are primarily adopting lightweighting technologies to meet the demands for more fuel efficient vehicles. It is seen from prior research that by focusing on lightweight (LW) designs alone, the average new vehicle could weigh 28% less in 2016 than it does today. Using LW designs is not without its challenges though. These designs represent significantly different dynamic characteristics and crashworthiness response when compared against original designs. Accordingly, it is necessary to evaluate the safety implications of these LW vehicles under impact scenarios with various roadside infrastructures. It is also necessary to ensure that the existing infrastructure can satisfy required safety standards in protecting the occupants under different crash conditions. In this paper, we adopt Finite Element Method (FEM) for modeling and simulating different crash scenarios in order to evaluate the safety implications of future LW vehicle designs. Baseline (BL) models for three vehicles — Toyota Yaris, Ford Taurus and Chevy Silverado are appropriately LW modeled with 15% (LW15) and 25% (LW25) reduction in weight, whilst maintaining structural stiffness and Center of Gravity. Numerical simulations are then performed for a 25° impact angle against three common roadside infrastructures — Concrete median barrier, Strong post W-beam guardrail and W-beam transition barrier at three different speeds — 50, 70 and 100 km/hr. The goal is to conduct a matrix of simulations in order to provide comprehensive and relative safety assessment. Barrier performance is then gauged in accordance to the MASH (Manual for Assessing Safety Hardware) [1] criteria wherein the metrics take into account evaluation factors such as structural adequacy and occupant risk.

The determination of head and neck biomechanics is one of the keys for deep understanding of impairments in neck function and cervical spine pathologies. Finite element models are a valuable tool to perform parametric studies. In this study, we aim to investigate the effect of a 40N head weight on the biomechanics of the head and neck complex under flexion-extension moments. The loading is applied to the centre of mass of the head and the first thoracic vertebra is fixed. Our predictions show that the kinematics and the load distribution at the facet joints were altered significantly with considering of the head weight under the flexion and extension movements. Our investigations indicate the substantial role of the head weight on the biomechanical behavior of the cervical spine and suggest its consideration in comparing the models predictions with the measurements.

In this paper the kinematics and dynamics of a uniball robot is demonstrated. The motion of a uniball robot is derived from the dynamics of a sphere rolling on a surface which is considered as a motion about a fixed point. The equations of motion are derived using Newton-Euler method incorporating the geometrical features of the surface. A uniball-robot can be considered as a Routh’s sphere whose center of mass is not at the geometrical center and have equal principal moments of inertia in the plane perpendicular to the axis connecting the center of mass and the geometrical center. The Euler angles are obtained using the Meusnier’s theorem which deals with the evolution of the surface as the robot moves along.

In this paper, the nonlinear model of an asymmetric micro-bridge resonator with an attached eccentric mass is investigated. The resonator is treated using the Euler-Bernoulli beam theory. The attached mass represents the electrostatic comb-drive actuator in micro-electromechanical applications. The center of mass of the actuator is assumed to be off the neutral axis of the beam. The governing equations of motion are derived assuming that a concentrated harmonic force is applied to the attached mass. The nonlinear forced vibration of the system is studied using the method of multiple scales. It has been demonstrated that the eccentricity of the mass may lead to different types of nonlinear resonance, e.g., superharmonic and internal resonance. The end application of the structure under investigation is in resonant sensing and energy harvesting applications.

Hobie Cat is one of the most popular sailboat production companies to ever exist, and the Hobie 16 is the most popular boat in the Hobie Cat line-up. The key to Hobie’s success was largely in part to advancements in strong and lightweight materials. This advancement allowed Hobie to achieve record breaking performance in their particular class of boat. The mast of the Hobie 16 is one of the heavier pieces of the craft. The overall mass and center of mass is greatly affected by this component, which begs to question if there may possibly be room for improvement. A sailboat mast is defined as a tall vertical spar, sometimes sectioned, that rises from the keel or deck of a sailing vessel to support the sails and the standing and running rigging. Sailboat masts are long, slender structures. They must be designed to be able to hold the thrust loads that are acting on them from the sails which will differ based on wind conditions. A mast must also be made of a material that will allow it to go through the varying environmental conditions without fatiguing. When designing a sailboat mast a few of the main goals are to have a low center of gravity, be light weight, and also aerodynamically efficient. During this research a Hobie 16 mast design was taken as a baseline design for testing. The current mast on the market weighs between 50–60 lbs. While this is not extremely heavy, the center of gravity is approximately 13.5 feet from the end of the mast. This high center of gravity makes it tough to raise and lower the mast when launching the boat. One important objective in this work is to create a mast that will be easier for the user to raise and lower without sacrificing the structural integrity of the mast. Three masts have been created in solid modeling software, and their performance characteristics have been tested using finite element analysis software ANSYS. Two of the designs are original works, while one is a copy of the original Hobie Cat design. The original design was analyzed, providing baseline data for which to compare the new designs with. In addition to the new designs, all designs have been constructed from three different materials as Aluminum Alloy 6061, Aluminum Alloy 7075 and Acrylic. This allows for comparison of designs and possible new materials. After an in depth analysis of all masts, the recommendation is made that Hobie 16 users would benefit greatly from the use of a tapered mast made of aluminum alloy 7075.