The tyre-road interface is one of the most important research topics in the field of vehicle dynamics.
This is largely due to all the vehicle excitation forces (besides aerodynamic forces) being generated at
this interface. There are many parameters which govern the generation of tyre forces, of which the
side-slip angle is of utmost importance.
Vehicle side-slip angle can be used as a measure of vehicle stability. Stability control schemes require
side-slip angle and typically estimate this parameter instead of using a direct measurement. The
relationship between tyre lateral force and tyre side-slip allows the lateral force generated by the tyre
to be determined from the tyre side-slip angle. Therefore, real-time measurement of side-slip angle is
important in tyre research and vehicle stability. Solutions exist to measure the side-slip angle, however,
do not perform well at low speeds or over rough terrain and are prohibitively expensive.
In terramechanics, tyre soil deformation in the form of rut depth is a widely researched topic as it
can be used as a measure of the vehicle’s ability to traverse the terrain, estimate soil characteristics
and for vehicle environmental impact studies. Currently, these measurements are labour intensive and
are typically conducted by hand. Other solutions exist however they are developed for road use and
are prohibitively expensive. The research field would, therefore, benefit largely from online rut depth
Digital Image Correlation is the mathematical process of tracking changes in digital images. The development of robust algorithms and ease of implementation has allowed many fields to be adapt this
non-contact based, optical technique for application-specific measurements. Previous studies (Botha,
2015) have proved DIC to be a viable candidate for measuring the side-slip angle and rut depth that
overcome current measuring hurdles. However, the analysis was conducted in post-processing from
pre-recorded footage due to the large computational expense of the image processing. This opens the
opportunity to adapt and optimise these techniques to achieve real-time processing speeds required for
these camera-based sensors.
This study builds on Botha (2015) with a real-time implementation which allows for online measurements
to be made using inexpensive, off-the-shelf cameras with dedicated software. This will
eventually provide systems such as ABS, stability control schemes and semi-active suspension with
real time vehicle side-slip angle and rut depth with a cost-effective camera-based sensor. The aim of
the present study is to develop and test two systems that can measure the side-slip angle and rut depth
The side-slip angle is measured using a single camera pointing down on the terrain and digital image
correlation. It is shown to measure accurately and in real-time. The sensor is tested on a flat surface
using a rig that allows for validation.
The rut depth is measured using multiple cameras pointing at the terrain and digital image correlation
to create a 3D map of the terrain. Three methods for determining the rut depth from the 3D map is
investigated, with varying degree of accuracy and processing speed.
Dissertation (MEng)--University of Pretoria, 2017.