A. L. Schwab

The influence of the biarticularity of the gastrocnemius muscle on vertical-jumping achievement

Hypotheses concerning the influence of changes in the design of the human musculoskeletal system on performance cannot be tested experimentally. Computer modelling and simulation provide a research methodology that does allow manipulation of the systems design. In the present study this methodology was used to test a recently formulated hypothesis concerning the role of the biarticularity of the gastrocnemius muscle (GAS) in vertical jumping [Bobbert and van Ingen Schenau, J. Biomechanics 21, 249-262 (1988)]. This was done by comparing maximal jump heights for a model equipped with biarticular GAS with a model equipped with a monoarticular GAS. It was found that jump height decreased by 10 mm when GAS was changed into a monoarticular muscle. Thus, the hypothesis formulated by Bobbert was substantiated, although quantitatively the effect is small. Our result differs from that of Pandy and Zajac [J. Biomechanics 24, 1-10 (1991)], who performed similar model calculations. It is shown that the results described by these authors can be explained from the moment-arm-joint-angle relation of GAS at the knee in their model.

Linearized dynamics equations for the balance and steer of a bicycle: a benchmark and review

We present canonical linearized equations of motion for the Whipple bicycle model consisting of four rigid laterally symmetric ideally hinged parts: two wheels, a frame and a front assembly. The wheels are also axisymmetric and make ideal knife-edge rolling point contact with the ground level. The mass distribution and geometry are otherwise arbitrary. This conservative non-holonomic system has a seven-dimensional accessible configuration space and three velocity degrees of freedom parametrized by rates of frame lean, steer angle and rear wheel rotation. We construct the terms in the governing equations methodically for easy implementation. The equations are suitable for e.g. the study of bicycle self-stability. We derived these equations by hand in two ways and also checked them against two nonlinear dynamics simulations. In the century-old literature, several sets of equations fully agree with those here and several do not. Two benchmarks provide test cases for checking alternative formulations of the equations of motion or alternative numerical solutions. Further, the results here can also serve as a check for general purpose dynamic programs. For the benchmark bicycles, we accurately calculate the eigenvalues (the roots of the characteristic equation) and the speeds at which bicycle lean and steer are self-stable, confirming the century-old result that this conservative system can have asymptotic stability.

Passive dynamic walking model with upper body

This paper presents the simplest walking model with an upper body. The model is a passive dynamic walker, i.e. it walks down a slope without motor input or control. The upper body is confined to the midway angle of the two legs. With this kinematic constraint, the model has only two degrees of freedom. The model achieves surprisingly successful walking results: it can handle disturbances of 8% of the initial conditions and it has a specific resistance of only 0.0725(−).

Adding an Upper Body to Passive Dynamic Walking Robots by Means of a Bisecting Hip Mechanism

Passive dynamic walking is a promising idea for the development of simple and efficient two-legged walking robots. One of the difficulties with this concept is the addition of a stable upper body; on the one hand, a passive swing leg motion must be possible, whereas on the other hand, the upper body (an inverted pendulum) must be stabilized via the stance leg. This paper presents a solution to the problem in the form of a bisecting hip mechanism. The mechanism is studied with a simulation model and a prototype based on the concept of passive dynamic walking. The successful walking results of the prototype show that the bisecting hip mechanism forms a powerful ingredient for stable, simple, and efficient bipeds

A Bicycle Can Be Self-Stable Without Gyroscopic or Caster Effects

A new bicycle design points to the importance of mass distribution for stability. A riderless bicycle can automatically steer itself so as to recover from falls. The common view is that this self-steering is caused by gyroscopic precession of the front wheel, or by the wheel contact trailing like a caster behind the steer axis. We show that neither effect is necessary for self-stability. Using linearized stability calculations as a guide, we built a bicycle with extra counter-rotating wheels (canceling the wheel spin angular momentum) and with its front-wheel ground-contact forward of the steer axis (making the trailing distance negative). When laterally disturbed from rolling straight, this bicycle automatically recovers to upright travel. Our results show that various design variables, like the front mass location and the steer axis tilt, contribute to stability in complex interacting ways.

Benchmark results on the linearized equations of motion of an uncontrolled bicycle

In this paper we present the linearized equations of motion for a bicycle as, a benchmark The results obtained by pencil-and-paper and two programs are compaied The bicycle model we consider here consists of four rigid bodies, viz a rear frame, a front frame being the front fork and handlebar assembly, a rear wheel and a fiont wheel, which are connected by revolute joints The contact between the knife-edge wheels and the flat level surface is modelled by holonomic constiaints in the normal direction and by non-holonomic constraints in the longitudinal and lateral direction The rider is rigidly attached to the rear frame with hands free from the handlebar This system has three degrees of freedom, the roll, the steer, and the forward speed For the benchmark we consider the linearized equations for small perturbations of the upright steady forward motion The entries of the matrices of these equations form the basis for comparison Three diffrent kinds of methods to obtain the results are compared pencil-and-paper, the numeric multibody dynamics program SPACAR, and the symbolic software system AutoSim Because the results of the three methods are the same within the machine round-off error, we assume that the results are correct and can be used as a bicycle dynamics benchmark

The safety of electrically assisted bicycles compared to classic bicycles.

Use of electrically assisted bicycles with a maximum speed of 25 km/h is rapidly increasing. This growth has been particularly rapid in the Netherlands, yet very little research has been conducted to assess the road safety implications. This case-control study compares the likelihood of crashes for which treatment at an emergency department is needed and injury consequences for electric bicycles to classic bicycles in the Netherlands among users of 16 years and older. Data were gathered through a survey of victims treated at emergency departments. Additionally, a survey of cyclists without any known crash experience, drawn from a panel of the Dutch population acted as a control sample. Logistic regression analysis is used to compare the risk of crashes with electric and classical bicycles requiring treatment at an emergency department. Among the victims treated at an emergency department we compared those being hospitalized to those being send home after the treatment at the emergency department to compare the injury consequences between electric and classical bicycle victims. The results suggest that, after controlling for age, gender and amount of bicycle use, electric bicycle users are more likely to be involved in a crash that requires treatment at an emergency department due to a crash. Crashes with electric bicycles are about equally severe as crashes with classic bicycles. We advise further research to develop policies to minimize the risk and maximize the health benefits for users of electric bicycles.

COMPARISON OF THREE-DIMENSIONAL FLEXIBLE BEAM ELEMENTS FOR DYNAMIC ANALYSIS: FINITE ELEMENT METHOD AND ABSOLUTE NODAL COORDINATE FORMULATION

Three formulations for a flexible spatial beam element for dynamic analysis are compared: a finite element method (FEM) formulation, an absolute nodal coordinate (ANC) formulation with a continuum mechanics approach and an ANC formulation with an elastic line concept where the shear locking of the asymmetric bending mode is suppressed by the application of the Hellinger–Reissner principle. The comparison is made by means of an eigenfrequency analysis on two stylized problems. It is shown that the ANC continuum approach yields too large torsional and flexural rigidity and that shear locking suppresses the asymmetric bending mode. The presented ANC formulation with the elastic line concept resolves most of these problems.Copyright

Comparison of Three-Dimensional Flexible Beam Elements for Dynamic Analysis: Classical Finite Element Formulation and Absolute Nodal Coordinate Formulation

Three formulations for a flexible spatial beam element for dynamic analysis are compared: a Timoshenko beam with large displacements and rotations, a fully parametrized element according to the absolute nodal coordinate formulation (ANCF), and an ANCF element based on an elastic line approach. In the last formulation, the shear locking of the antisymmetric bending mode is avoided by the application of either the two-field Hellinger‐Reissner or the three-field Hu‐Washizu variational principle. The comparison is made by means of linear static deflection and eigenfrequency analyses on stylized problems. It is shown that the ANCF fully parametrized element yields too large torsional and flexural rigidities, and shear locking effectively suppresses the antisymmetric bending mode. The presented ANCF formulation with the elastic line approach resolves most of these problems. DOI: 10.1115/1.4000320

Skateboards, Bicycles, and Three-dimensional Biped Walking Machines: Velocity-dependent Stability by Means of Lean-to-yaw Coupling

One of the great challenges in the development of passive dynamic walking robots (useful for an understanding of human gait and for future applications in entertainment and the like) is the stabilization of three-dimensional motions. This is a difficult problem due to the inherent interaction between fore-aft motions and sideways motions. In this paper we propose a simple solution. Conceptually, one can avert a sideways fall by steering in that direction, similar to skateboards and bicycles. We propose to implement this concept for walking robots by the introduction of an ankle joint that kinematically couples lean to yaw. The ankle joint has an unusual orientation; its axis points forward and downward, without any left-right component. The effect of the ankle joint is investigated in a simple three-dimensional model with three internal degrees of freedom: one at the hip and two at the ankles. It has cylindric feet and an actuator at the hip joint, which quickly moves the swing leg to a preset forward position. The simulations show that it is easy to find a stable configuration, and that the resultant walking motion is highly robust to disturbances. Similar to skateboards and bicycles, there exists a critical velocity (as a function of the parameters) above which stable walking motions occur. The critical velocity can be lower for a more vertical ankle axis orientation. As an additional benefit, the ankle joint allows a straightforward implementation for steering; a simple sideways offset of the mass distribution will cause the model to gently steer in that direction. The results show great potential for the construction of a real-world prototype with the proposed ankle joint.