High-Performance Electronics for a Formula Student Race Car

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""NI hardware and software allows us to be open to experimentation and fast adaption, which is very important in automotive development.""

- Abhi Mittal , University of Manchester

The Challenge:
Implementing a portable and scalable data acquisition system for the University of Manchester Formula Student single-seat racing car that can test multiple vehicles.

The Solution:
Using Multisim and LabVIEW software with NI CompactRIO programmable automation controller (PAC) to simulate the vehicle, collect data, and use the data to create custom alarms.

Author(s):
Abhi Mittal - University of Manchester

We are creating a system to acquire data and show whether or not a car is running in accordance with the IMechE safety regulations. The system will give designers an insight into the vehicle dynamics for future design decisions in real-time for trackside fault detection, and in the form of logged data for future reference. The data acquisition system should be portable and scalable to accommodate multiple cars or stand-alone parts of the vehicle in the workshop or dynamometer (dyno) room.

With Multisim, we can to simulate the entire wiring loom and power distribution circuits of a vehicle prior to buying any components or PCBs, saving us time and unnecessary costs. CompactRIO provides us with a rugged and re-programmable data logger capable of accepting inputs from a multiple sensors. Using LabVIEW and a standard Wi-Fi router, we implemented a wireless telemetry system that handles around 20 channels of analogue data together with another 18 channels of CAN bus data. With LabVIEW, we can view the data in a useful format and create custom alarms.

The Institution of Mechanical Engineers’ Formula Student competition challenges engineering students to conceive, design, fabricate, and compete with small Formula-style racing cars. The cars are built over a period of one year, and are then taken to Silverstone for judging and comparison with other competitors from across the world. Ninety-five teams competed in 2008 in the main and low-emission cars categories.

Virtual Wiring Loom

The loom simulation in Multisim ensures that the system functions in accordance with safety rules by allowing us to check the operation of various safety cut-outs. We can simulate current flows to estimate battery performance and optimise PCBs to handle those loads in UltiBoard, particularly the very wide tracks for starter motor currents. Using the mechanical CAD facilities, we can be sure that our circuits will fit inside the enclosures.

Data Acquisition and Telemetry

The chassis frame, suspension, cooling and drive-train are some of the key areas where validation of designs based on analysis of real-world data is crucial. Weaknesses or areas for optimisation cannot easily be seen by simple simulation in CAD packages. Data is not only used in the design stages of the vehicle but also in trackside tweaking of suspension and cooling systems.

CompactRIO provides us with an all-in-one data acquisition and real-time monitoring system with unparalleled flexibility on input types and data viewing. With 512 MB of onboard storage, high-resolution data capture is possible. It provides a much higher channel density (number of inputs to size ratio) than most other solutions, even those designed for motorsports. Thanks to a simple Wi-Fi link, we don’t even need to hold a radio license for telemetry. The removable and wide-selection of C-series modules make CompactRIO a sustainable choice. We can change the configuration as our needs grow or we identify new areas for measurement. It also allows for a wide operating voltage, important in automotive supplies with frequent engine restarts when the voltage can fall by up to 25%.

We worked closely with NI field engineers to tailor hardware to suit our purpose. Our unit has an eight-module chassis with the NI 9237 simultaneous bridge module, the NI 9205 analogue input  module, the NI 9411 digital input module, the NI 9211 thermocouple module, the NI 9233 dynamic signal acquisition module for IEPE measurements and the NI 9853 high-speed CAN input module. The CAN input allows us to monitor data from the ECU connected sensors such as RPM, oil temperature and oil pressure. This avoids installing duplicate sensors or fabricating sensor buffer circuits. The combination of quick re-programming and single-unit portability means we can easily use CompactRIO both on the car and in the dyno room for more detailed, engine-specific measurements. It’s just a matter of uploading the appropriate VI over the network and connecting the sensors.

Live Monitoring

The ability to monitor the data in real time is important for finding problems before their consequences are severe. During testing, the team can check that the engine remains at constant temperature without having to stop the car. Testing sessions are more productive as the team can prepare to make suspension changes while the car is still running, meaning the drivers get more practice behind the wheel.

Immediate feedback to the driver is also an effective way to improve his driving style. A good racing driver must always keep the car in control, just within the limits of traction. By viewing throttle position, brake pressure and steering angle data while driving, a driver is informed of areas of improvement in his technique.

Vehicle Dynamics

Using linear and rotary potentiometers, the car’s weight transfer characteristics can be quantifiably observed. By measuring the suspension and steering angle, we can see how car tilts around corners. The shock absorbers can then be tuned to minimize travel and maximise grip.

On a racing car, it is important to look at the behaviour of all four wheels. We use a Hall effect sensor mounted on the uprights to measure the speed of each wheel. A specially-designed toothed disc placed behind the brake disc triggers the sensors as the wheel rotates. These provide a transistor–transistor logic (TTL) compatible switched output. Using the NI 9411 digital input module and a high-priority timed loop in LabVIEW, we can ensure the sensors are sampled at a sufficient rate. The wheel speed data, coupled with intended direction data from the steering angle sensor, is used to understand and verify the operation of the limited slip differential, traction control and launch control. The engine control unit (ECU) provides controls for adjusting the aggressiveness of the latter two. By measuring the wheel speeds around corners, or off the start line, we can find the optimal settings.

We use the NI 9237 Bridge modules to interface with strain gauges on the suspension wishbones and chassis tubes. Although there is little we can do with this data on a car already built, this data will be very useful when designing future cars. For example, parts can be re-engineered to save weight if they are not being stressed as much as initially predicted.

The NI 9233 module has four simultaneously-sampled 24-bit inputs, enabling simple 2-wire connection to accelerometers. Lateral-acceleration can be quantified and compared against different combinations of camber and tyre pressures. Getting these right means our car can speed around tighter corners at higher speeds.

Conclusion

NI hardware and software allows us to be open to experimentation and fast adaption, which is very important in automotive development. The Formula Student team produces a new car every year (much like any professional racing team), so the ability to ‘chop-and-change’ is crucial. Most off-the-shelf automotive data loggers do not offer the wide connectivity of the CompactRIO, particularly to passive sensors like strain gauges. The MAN09 car, due to compete in July 2009, is our first vehicle to carry the CompactRIO onboard. This first set of data will deepen our insight into automotive design.

The CompactRIO has been highlighted for future use as a controller as well as a logger. Its FPGA-based operation would be suited to applications such as active suspension, anti-lock brakes and hybrid drive train management.    

Author Information:
Abhi Mittal
University of Manchester
Tel: 07878732643
formulastudent@manchester.ac.uk

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