FSAE Electrical System Design
The design of the University of Toronto’s electrical & data acquisition systems were made to facilitate tuning of the engine, suspension, aerodynamics and braking systems while also being easy to troubleshoot and most importantly, reliable. The notion of providing on-track data for the team to use as a method of judging the performance of the vehicle’s subsystems was viewed as an important goal for the team in 2017. The objective was to work with fellow section leads to determine the key subsystem metrics to monitor throughout the testing season.
The goal was to develop a more efficient process of reading and analyzing performance data from the vehicle during on-track testing sessions. In the past, we were restricted to reading the data on an external computer only after we had completed our test runs.
Designing a dashboard that incorporated peripheral devices such as a tachometer and LCD screen, would provide data in real-time, which would improve the team’s ability to track vehicle setup-related performance metrics. The added LCD screen would read out live data from sensors installed throughout the vehicle, and would also facilitate the ability for the driver or on-track engineers to input the vehicle’s given suspension setup that was currently being tested at a given moment.
The driver would interface with the LCD through the use of a pushbutton and digital encoder. The tachometer, which would include rev lights and a seven-segment display, would serve to give the driver both a quantitative and qualitative reference in regards to the engine’s current rpm. Underneath the dashboard panel, a microcontroller would control these new functions, and the final circuit would be a combination of terminal wiring and a soldered protoboard. The microcontroller would attain the given vehicle performance metrics through CAN (Control Area Network) communication with the team’s onboard data logging unit.
On a given testing day, after setting up the vehicle’s tire pressures, camber & toe settings, etc., the typical struggle for the team was keeping track of which physical setup was being used for each batch of testing data. The new dashboard system aimed to solve this issue. To do so, the driver or on-track engineer would be able to press the momentary pushbutton, which would take them to the testing setup menu. From there, the LCD display would show a list of settings to be modified such as the number of utilized camber shims, individual tire pressures, etc. Each setting could be toggled through and modified via the use of the rotary encoder. The encoder would also facilitate entering other subsequent tiers of the menu system via the built-in pushbutton on the encoder. To illustrate this concept, refer to the top image on the left. The green box represents the initial entry to the menu, the blue boxes represent menu options, and the orange boxes represent modifiable values whose increments and ranges were set in the program’s code.
The lower images to the left illustrate the program flow while in either live sensor readout mode or vehicle setup mode.
In order to achieve the goal of a reliable power system, general best practices were carried out including minimizing unfused wire lengths and as much as possible, keeping wires away from radiant heat sources in order to eliminate the possible deterioration of wiring insulation.
The batteries, fuses and relays were relocated behind the vehicle’s firewall to reduce wire lengths and improve overall routing. The wiring featured a clean but fully serviceable layout complete with labeled and color-coded wires.
In order to provide proper fusing to critical components such as the auxiliary and starter batteries, current sensors were used to get a sense of their standard operating current in all conditions. For example, the starter battery received significant initial current draw due to the start-up torque of the engine’s starter motor, but settled in at around 65A with successive cranking. For this reason, and taking into account potential de-rating of the fuse due to ambient heat in the electrical box, it was deemed appropriate to size the starter fuse to 80A. A graph depicting the current being consumed by the motor can be found in the images on the right.
The primary purposes of utilizing data acquisition were to:
- Increase the performance of the current and future vehicles by using data to make informed decisions regarding vehicle setup changes
- Allow for driver performance feedback during testing and competitions
- Inform on-site engineers of the status regarding critical vehicle parameters (e.g. coolant temperature, battery voltage, etc.)
Regarding the first point, the first step in achieving this for the current set of design leads, was to work with them to select key performance metrics that each of them would be able to use to both validate their current year’s design, and to provide feedback for the next year’s design team. Once these metrics were selected, I looked into what individual or combination of sensors could be used to monitor these metrics. I then purchased those sensors, calibrated them and wired them throughout the vehicle. Their data was then fed into the team’s data logging unit, and would subsequently be made available to the design leads for analysis both on and off the track. The chart to the left indicates every performance-tracking sensor that was installed and their individual purposes for each section lead.
The graphs to the right represent some examples of the metrics that the design section leads were trying to monitor:
- Front-Right Tire Temperature – The suspension lead wanted to see that the inside regions of the tires were wearing more than outsides to validate tire pressures and camber settings.
- Steady-State Rotor Temp – Used to determine the steady-state operating temperature of the rotors & brake pads. Optimal brake pad compounds could be selected based on comparing the steady-state operating temperatures to the various pad coefficient of friction curves.
- Cornering Performance – Allowed on-track engineers to see how the driver was entering the corners. If the driver was turning prior braking, they could be coached based on whether or not it would be advantageous to be trail-braking into the given corner.
- Brake Pressure Profiles – Profiles can be analyzed to determine if drivers were decelerating effectively on-track. The profile on the bottom represents an effective braking effort by our team driver, where the pressure level spike was instantaneous and ramped down uniformly. This is especially useful to ensure that the drivers are making the most of their speed when entering corners.