WWU Racing's Formula SAE Race Car

Who we are

We are WWU Racing, a team from Western Washington University making full size race cars from scratch. We compete in the Formula SAE Michigan competition with a new car every summer. The competition involves both business and engineering events that put our work to the test, furthering our experience for the next car as well as life after graduation. The car's performance is tested through Acceleration, Skid Pad, Autocross, Endurance, and Efficiency events. The static events (Design, Cost, and Business Presentation) judge the process behind the physical design of the car, theoretical production cost, and a marketing and distribution plan for a consumer version of the car.

What we're doing

We're building our first electric car, Viking 63. We've been working on this car since the start of the pandemic, and will be taking it to competition in June 2022. The car has an Emrax 228 motor and a Cascadia Motion PM100DXR motor controller.

There's a lot that goes into the electronics system, and a lot of custom PCBs designed and assembled in-house. Here’s an overview of a few of the PCBs on our car:

Battery Management System

Our car has a lithium ion battery pack, made of 768 18650 cells (96 in series, 8 in parallel, split into six segments of 16S8P). With lithium ion battery packs, it's necessary to measure the temperature and voltage of the cells in the pack, and to balance the pack voltages to increase battery life. We use the MAX14920 IC to interface with the batteries, which talk over SPI to STM32 microcontrollers. The microcontrollers control two contactors, which turn off the high voltage exiting the battery pack if the BMS sees a problem. The BMS also controls the precharge circuit - because our motor controller has a significant amount of capacitance, it is necessary to precharge the HV system through a current limiting resistor so that the transient current when switched on is not too high.

We've got a PCB on each segment that interfaces with the batteries. The nickel strips that connect the batteries together also extend upwards and get soldered to this PCB, into the slots you can see on the edges:

We also have a main controller that interfaces with the other circuits in the car:

Low Voltage Accumulator Breakout

This one is fairly straightforward - our HV battery pack has a low voltage connector on the outside, and this needs to be wired to the many LV devices inside the battery pack. To simplify wiring, this is all done on a PCB. The DC-DC converter that powers the low voltage system from the high voltage battery is also mounted on this PCB.

Brake System Plausibility Device

Per the FSAE rulebook, we are required to turn off the car if the throttle and brake are pressed at the same time. The idea behind this is that if the throttle pedal is stuck in the on position, mashing the brake pedal should cut off power to the motor so that the car can stop. To do this, thresholds are set with comparators, and their outputs are connected with an AND gate. This signals a 555 latch to keep the car off. We put a capacitor inline with the signal before the 555 to delay the signal, and prevent false positives.

Because this PCB is located in the front of the car, we’re also using it as a controller to put sensors onto the CANbus. CANbus is a digital network going throughout most modern cars that allows many sensors and microcontrollers to communicate over just 2 wires. All of the analog sensors on the front of the car go to this PCB to get transferred onto the CANbus, where they go to either the motor controller or the datalogger.

The odd shape of the board is due to the enclosure we're using, which is a ModICE mini-ME enclosure.