Analyse the performance of a Formula Student race car using a lightweight and compact data acquisition system.
Using an NI sbRIO-9636 device with two signal-conditioning NI C Series modules programmed with NI LabVIEW system design software to record data from a range of sensors for later analysis with NI DIAdem software.
Gerry Woods - Dublin Institute of Technology
Kevin Irvine - Dublin Institute of Technology
Formula Student, an international competition organised by the IMechE, challenges third-level students to design, build, and test a single-seat race car. It is the proving ground for young engineers, and the leading motorsport teams and the automotive industry seek out many of the participants. Approximately 120 teams from around the world compete each year at Silverstone Circuit in the United Kingdom, with cars that can accelerate from 0 to 60 mph in under four seconds and reach top speeds of 80 mph. The Dublin Institute of Technology (DIT), under the FormulaDITguise, have participated in the UK Class 1 event for the past three years. The teams have made progressive improvements moving from 42nd place to 21st place over the three-year period. In 2013 the DIT team was among the top four in the UK and Ireland. The team gradually developed the telemetry system starting with NI CompactRIO hardware. The team recently moved to the NI Single-Board RIO platform, which is more lightweight with greater functionality.
In 2013, the FormulaDIT team started to further develop the existing system based on CompactRIO with the primary goals of reducing weight and improving functionality. Acceleration, cornering, and vehicle handling are important criteria for success in the competition because of the nature of the Formula Student events. Therefore, we needed to perform testing prior to competition and to have a comprehensive data acquisition system on board the vehicle to measure aspects related to vehicle handling, such as suspension displacement, acceleration, and steering angle.
By employing an sbRIO-9636, an immediate weight saving in excess 1kg was achieved, while the addition of two signal-conditioning C-Series modules via the Rio Mezzanine Card allowed all the functionality of the larger CompactRIO to be maintained.
Both accelerometers and strain gauges require specialised signal conditioning, including excitation, amplification, and filtering, to read their measurements accurately. The NI 9234 module and NI 9235 module, with built-in signal conditioning, provided a simple, accurate, and easily implemented solution for data collection from these types of sensors. Two PCB Piezotronic single-axis IEPE accelerometers measured both the lateral and longitudinal acceleration forces that the car experienced on track. Strain gauges mounted to the suspension components helped the team evaluate deformation under stress.
In order to gain an accurate picture of how the car is performing, it is important to examine all measurements in context of one another. By simultaneously taking measurements of suspension displacement via analogue linear potentiometers and acceleration, a reference could be made between body-roll, lateral acceleration, and how the suspension wishbones and pushrods react to varying loads.
Understeer and oversteer could also be evaluated by comparing measurements recorded from an analog voltage steering angle sensor against lateral acceleration forces, while longitudinal acceleration was compared to brake pressure to help assess brake performance. Correlating brake pressure to front/rear suspension displacement gives an indication of the weight transfer under braking, and how the brake bias should be adjusted to compensate for this.
Using the digital input ports on the sbRIO, signals from Hall Effect sensors mounted to each wheel were continuously monitored, providing data on locked or spinning wheels, and also the distance which the car had covered. Excessive wheel spin may indicate poor suspension setup, while wheels which are prone to locking may point toward a poorly adjusted braking system.
Interface with the car’s ECU and Power Distribution Module was achieved over a robust CAN bus network with communication being handled directly by the sbRIO-9636, rather than with a separate C-Series module as in the previous CompactRIO setup; a further reduction in weight. A Wi-Fi router connected to the sbRIO via its Ethernet port allowed wireless telemetry of sensor readings, for real-time analysis during the car setup procedure.
Collecting performance data is the first step, but putting this data to good use requires detailed analysis and the expertise to flag problem areas quickly. Microsoft Excel is the de facto choice for data analysis within many engineering applications and was used previously within FormulaDIT. However, NI DIAdem software offered a more functional solution that incorporated mathematical functions, analysis tools, and the ability to synchronise video footage from onboard GoPro cameras with the recorded data. The team could put meaningful data behind the driver’s assessment of the car’s performance by analysing physical sensor readings from Diadem.
NI hardware and software provided great flexibility in the development of the telemetry system for the Formula Student car. We obtained data regarding suspension and other parameters that was critical to optimising the car setup during the test phase prior to Silverstone.
The student involved with this project received excellent employment opportunities as a result of his experience with NI hardware and software. The student now works in LabVIEW software development for Valeo Imaging Systems, an innovator in automotive vision applications that is based in Galway.
In the future, we hope to continue to take advantage of the sensor connection options and CAN bus functionality of the NI Single-Board RIO device, and examine further possibilities for vehicle control and monitoring through LabVIEW.
Dublin Institute of Technology
Dublin Institute of Technology