Measurement of the Forces from the Ground on the Tires for a Baja SAE Vehicle

Knowledge of the forces on the vehicle is necessary for designing most of the Baja vehicle subsystems, however little knowledge of the dynamic forces on small off-road vehicles is available. To measure the vertical and longitudinal forces on the tires of a Baja vehicle, a custom strain gauge system was designed and combined with Quarq tire pressure sensors while running in off-road conditions. The strain gauge system consisted of a half-bridge Wheatstone bridge of 350 Ohm resistors in bending, feeding the change in voltages into the 20-bit ADC of a Cypress Semiconductor PSoC 5LP microcontroller for data interpretation and then recorded onto an SD card for later analysis. Quarq Tyrewiz tire pressure sensors were placed on both the front and rear tires and the recorded pressures were converted to forces on the tire through calibration. Experimental data was found to agree with suspension models. Data from the strain gauges and tire pressure sensors are in agreement and when used to measure the forces on a 470 lbf Baja SAE vehicle with a driver inside, the dynamic bump forces were found to be as high as four to five times the static corner weight of the vehicle.