The Oxford Brookes Formula Student team recently used a Correvit S-Motion two-axis optical sensor from Kistler Instruments to obtain key data on tire slip angle, needed for accurate, real world tire modeling.
The university decided that better tire modeling was essential for their 2018 campaign than the data provided by a sandpaper belt test rig, courtesy of the Formula SAE Tire Test Consortium.
Head of tire modeling, Brad Mallinson, explained, “While vertical load, inclination angle, ride heights, and vehicle roll angle are relatively easily measured, tire slip angle is very difficult but critical to the development of an accurate tire model. Kistler’s S-Motion sensor accurately measures vehicle longitudinal and transverse speed and slip angle with a high logging rate, which is essential for the relatively low-speed Formula Student driving events.”
The S-Motion unit was mounted on the 2017 Oxford Brookes Formula Student car, along with load cells, infrared tire temperature and laser ride height sensors, to collect as much tire data as possible. A major benefit of the S-Motion system is the time-saving plug-and-play capability, which drastically reduces vehicle preparation time – essential to take full advantage of the short timeframe for tire testing after the Formula Student season. A further benefit provided by the Correvit system is the ability to automatically transform speed and slip angle measurements to any point of interest on the vehicle. These were transformed to the center of gravity where yaw rate was measured, simplifying tire slip angle calculation during steady-state tests.
Testing consisted of increasing velocity runs on a constant radius skid pad for a minimum of three cold inflation pressures and three static camber settings to capture the quadratic relationships in the lateral force model. Quantities derived from measurements were calculated in Matlab before being passed to the tire model tool. Roll angle measurements from the S-Motion and damper displacement data were used for lateral weight transfer models to determine inclination angle and total vertical load. Steered angle of each front wheel was used to calculate front tire slip angles using vehicle slip angle from the S-Motion.
Pics: Brad Mallinson
March 1, 2018
