Wheel Speed and Suspension Travel Sensors

New to our 2024-2025 vehicle is a subsystem featuring wheel speed sensors and linear travel sensors on all four corners. Using Hall-effect sensors, we measure revolutions directly off our steel brake rotors, eliminating the need for additional timing wheels or sensing targets—saving both weight and complexity. Each shock is equipped with a linear travel sensor, providing precise wheel displacement readings within fractions of an inch. By combining these data points, we can record more accurate logs of vehicle performance during cornering. 

This subsystem is essential for analyzing the dynamics of individual wheels, particularly with the integration of sprag clutches, which allows wheels to lock under power and freewheel while coasting. Whereas last year our locked system allowed us to extrapolate wheel speed from gearbox RPM, this year, each wheel is able to spin at a different rate. These measurements, paired with vehicle speed data from our GPS system, allow us to identify wheel spin and skid, which is reported in real-time on the dashboard.

Dashboard

Our 2024-2025 Season Dashboard iterates upon our last year's design. We maintained the same form factor with two seven-segment displays, two LCDs, and various status LEDs. However, we've also introduced two rear-mounted buttons. One button gives the driver control over what data is displayed on the LCDs, and the other adjusts between predefined brightness levels. We also made several upgrades to the housing design. A new polycarbonate front cover is more durable to impacts and stresses than our acrylic cover from last year, and a sunshade reduces glare and reflections on the displays in sunny environments.

Wireless Data Transmission

Another new subsystem on our 2024-2025 vehicle is a wireless data transmission system. This subsystem receives all vehicle datapoints over the CAN bus and sends them to a base station via LoRa. This base station is located nearly 30 feet above ground level to keep our connection as reliable as possible. As it receives LoRa packets, it transmits them via Bluetooth to a nearby PC which then visualizes all of the datapoints using Serial Studio. In Serial Studio, we are able to see a live view of the vehicle's speed, engine RPM, GPS location, orientation, and more. This subsystem proves useful in two situations. First, during our testing phase, we are able to see live data at higher transmission rates and a shorter range. Then, during our competition season, we are able to toggle a switch on the transmitter and receiver to go into long range mode, which transmits less frequently but at a much longer range. Here, we are less concerned with fast updates and more focused on GPS location and the state of the vehicle.

A CVT, or Continuously Variable Transmission, is used in Baja SAE vehicles to eliminate the need for a standard geared transmission. As the vehicle speeds up, the gear ratio between the primary (left) and secondary (right) changes. The primary is directly connected to the engine, and therefore spins at the same RPM as the output shaft. The secondary is connected to the rest of our drivetrain system to transfer power to the wheels. We designed an Infrared Transmitter and Receiver pair to count each revolution of these sheaves. This data is then used to calculate engine RPM and CVT speed ratio.

Our goal for the 2024-2025 season was to improve the mechanical robustness as well as the software for higher polling rates and accuracy. We designed custom PCBs for the sensing modules with connectors so that modules can be easily replaced. This year, we also introduced dual temperature sensors. This provides another layer of redundancy in our sensing as well as more data about the temperature gradient in the CVT case. We also increased the size of the hood around the infrared emitter to narrow the cone of light that hits the sheave.

Inside the main processing enclosure, we added a set of potentiometers that can be used to fine tune the sensitivity of the infrared receivers so that our readings are as reliable as possible. Our software also takes advantage of both the dual cores and dual ADCs on the ESP32 microcontroller for even faster data processing.

The Data Acquisition System is essential to batching all of the vehicle's data and saving it to an SD card. Onboard the logger is a GPS module, providing latitude, longitude, altitude, velocity, heading, and GPS time. Additionally, an accelerometer and gyroscope module is able to capture all of the vehicle's movement. Together with the rest of the data from the CVT Tachometer, pedal sensors, wheel speed sensors, and other subsystems, the logger saves all of the timestamped data to an SD card for later viewing. Because of the CAN-Bus implementation, upgrading and adding subsystems with additional data requirements is very straightforward.

This season, we upgraded to the Ultimate GPS Breakout from Adafruit which offers a 10Hz polling rate. Compared to our 1Hz rate last year, we are able to capture a much more detailed picture in quickly changing scenarios such as jumps and cornering. We also increased the user interface to include two push buttons and a toggle switch. A second aviation plug connection in the enclosure allows us to quickly hook up our PCAN-USB CAN Bus analyzer for troubleshooting data transmission.

Enclosures and Waterproofing

With all of the splashes, mud, and hard impacts that Baja vehicles take, we wanted to ensure our electronics would be well-protected in the harshest enviroments. This means making sure that any openings are watertight, and all materials can withstand the heat of the Arizona sun.

Capturing driver input data is essential to our data logging. With all of our data being transmitted over CAN-Bus to the data acquisition logger, we can sync pedal data with the data about how the vehicle reacts. For example, the position of the accelerator pedal can be mapped to the vehicle's acceleration and speed. We use two rotary hall effect position sensors to record this driver input. Since they do not have any internal physical contacts, they are ideal for withstanding repeated use and maintaining high accuracy despite the vibrating environment.

CAN Bus System

When deciding how to transmit data from point to point in the vehicle, there were many factors to consider. Most notably, the system had to be durable and compact. One option could have been a spoke-hub distribution, where each subsystem would have its own wiring to transmit data back to a central data acquisition system. However, this wiring would be very complex, and it would limit the access of information between subsystems. Therefore, we implemented a CAN-Bus communication system. CAN-Bus is a two-wire differential voltage protocol, making it extremely compact and resistant to electrical noise. It also allows every node in the system to have access to all information transmitted over the system. 

We standardized all of our subsystems to use ESP32 microcontrollers, which have a CAN-Bus controller built in. Adafruit's TJA1051T CAN transceiver modules were also used via the built-in CAN controller. Because of the speed requirements for these subsystems, we were also able to take advantage of the ESP32's dual cores. One core of each subsystem is dedicated to solely transmitting and receiving CAN data, while the other is used to update displays, read sensors, and other related tasks.