Abstract

The measurement of dynamical parameters of moving objects is important in some activities like sport training, ballistic and aeronautics. The basic parameters required for these applications are the velocity, trajectory and spin. The latter is important because some of the main aerodynamic effects are present depending whether the object is spinning or not.

To measure these parameters different techniques are used. Aerodynamic coefficients are typically obtained on wind tunnels measuring the displayed forces on the object. Velocity, trajectory and spin are mainly obtained using techniques based on image processing. The use of wind tunnels is usually complicated and expensive while the image processing techniques, while providing good results in the measures, have a number of problems and conditions of use that limits its use. Furthermore, although the extent of spin is interesting because this parameter is responsible for a series of aerodynamic effects that change the trajectory, the aerodynamic coefficients are the key to reconstruct the entire trajectory of the object.

The aim of this work is the development and construction of a device for determining the aerodynamic coefficients of spherical objects in motion by an alternative method to image processing or to the use of wind tunnels. This procedure is based on the measurement of velocity fluctuations experienced by the object due to the presence of the forces involved in the movement. The velocity measurement is performed by using light barriers with large measurement area. A procedure for measuring the three components of instantaneous velocity using these devices has also been developed. Once the coefficients are known, the other parameters can be derived from them.

Test have been carried out using sport balls. Sport training is one of the most direct applications and has a size and velocity ranges that simplifies the development of a working device. Anyway, the method can be applied to any other kind of spherical or with revolution symmetry objects just adjusting some parameters coming from the aerodynamic model.

Keywords: Measurement system, aerodynamic coefficients, spin, velocity, electro-optical, aerodynamic, Magnus effect.