Baja is made up of distinctive subsystems where members can apply their knowledge and expand upon their skills.
The brakes subsystem designs a reliable hydraulic system that slows and stops the car based on driver input. The system works by converting kinetic energy to thermal energy. Pressure, wheel speed, and acceleration are investigated to validate and tune vehicle dynamics.
The Chassis design is very important to protect the driver in case of a crash or roll-over as well as connect all the different subsystems to create a cohesive car. To make the structurally-sound tube frame using 4130 chromoly steel, we machine and weld the chassis to take the shape of the model we design in our CAD software. We know that the chassis is able to withstand the trials of competition because of the extensive testing we do to ensure the safety of our driver and car. For example, we test the Halo Tube (the tubes that protect the driver’s head in case of a roll/crash) to failure; this testing validates just how much stress our chassis can endure before failure and explains how the driver stays safe. The chassis is one of the most crucial subsystems and having an excellent chassis allows us to continue pushing Cal Poly Racing’s Baja car to its limits.
Composites designs, manufactures, and tests composite components used throughout the car. These components include the skid plates, which protect the car and driver from the impacts of off-road racing, as well as the light weight carbon fiber body panels. In addition, composites researches and tests the use of advanced composite materials to save weight in parts throughout the vehicle, ranging from the steering wheel to the transmission case.
Our vehicle features an eCVT (electronic Continuously Variable Transmission). This type of transmission is a fully-automatic transmission by which sensor inputs are fed into a controls loop which outputs the current desired ratio, after which motors actuate a set of V-belt clutches to achieve an infinite number of ratios. Our take on this design challenge is one of a kind—we are the only team in the Baja SAE competition in which both the primary and secondary clutches are actuated via electronics. This gives us a distinct advantage in our ability to tune our transmission rapidly and effectively, as this allows us to specifically tune our transmission for different events. Additionally, we develop powerful simulations to predict our desired tuning parameters to turn valuable testing time into validation time. This design project touches on all facets of mechanical engineering, including controls, structures, heat transfer, thermodynamics, fluids, composites, mechanical vibrations, and mechanical layout design.
The Electro-Mechanical Integration subsystem is responsible for the packaging, mounting, and wiring of all of the electronics used on the Baja car. The primary system consists of a main enclosure in the rear of the car and a dashboard enclosure in the front of the car. Both enclosures are 3D printed out of PETG and designed to hold up under significant stress and maintain an IP67 sealing rating to protect our electronics from dirt, water, and mud. The two enclosures are connected by a wiring harness that transmits power and data across the car, protected by thick glue-lined heatshrink. The EMI subsystem is also responsible for setting up the majority of the sensors on the car, which includes thermistors, hall effect sensors, and encoders. These sensors must also be protected from impacts, mud, as well as getting caught in moving parts in order to transmit accurate data and protect the control loop for the eCVT.
The electronics subsystem is responsible for the design, implementation, and testing of the various electrical systems on the Baja car. These systems include the eCVT (electronic continuously variable transmission), the daq (data acquisition), and sas (semi-active suspension). There are two sides to these designs: hardware and software. The hardware is the design of the circuits and pcbs (printed circuit boards) that control over 30 sensors and actuators that control various systems and transmit valuable data for analysis. The software is the design of the code to run these systems. We are continuously pushing the limits of what electronics look like in Baja SAE.
The goal of ergonomics is to design components that integrate well with other subsystems to improve driver’s performance and comfort. Driver performance is crucial for our team’s performance, especially in the 4 hour endurance race. Integration with the other subsystems is also important because the driver doesn't interact with the components directly, instead ergonomics must bridge that gap.
Our student-run manufacturing team uses state-of-the-art CNC machine tools to manufacture high-precision components out of aerospace grade alloys. We consistently hold tolerances of less than one thousandth of an inch (.001”) in order to maximize vehicle performance. We also work closely with our heat treatment and gear cutting sponsors to ensure that our parts arrive in spec and on time.
The powertrain is responsible for delivering power from the engine to our custom AWD system by controlling how the vehicle transmits torque. In the rear of the car we use an electronic Continuously Variable Transmission (eCVT) with a fixed-ratio transfer case to transmit power from our new Kohler CH440 engine to the rear half-shafts to turn the wheels. To transmit power to the front of the vehicle we use two sets of bevel gears to drive a prop shaft and Spool type differential. In order to maintain good steering characteristics and improve efficiency, we use a set of custom freewheels in each front hub that only transmit torque in one direction. All of our wheels use Rzeppa style constant velocity joints to allow for high suspension travel. Finally we use special light weight off road wheels and tires mounted on custom hubs to put the power to the ground and send our car barreling down the track.
Special Projects is dedicated to researching and enhancing the car through projects that have a high price-performance ratio. Last year, we successfully introduced carbon fiber shafts to our team through rigorous destructive strength testing. This implementation proved to be highly successful, resulting in a weight reduction of 1.8lbs. Building on this achievement, our plan for this year is to further extend the applications of carbon fiber shafts. Additionally, we aim to seek support from sponsors to fund exciting projects that are being currently worked on.
The Baja car's steering system consists of a custom molded wheel attached to a hollow steel tube, which drives an aluminum pinion and rack system in order to steer the car left and right. The rack and pinion interface is designed to provide tactile feedback and predictable handling for the vehicle. Steering assists suspension in creating favorable vehicle dynamics, with the main goal of preparing the car for the maneuverability event at competition.
Suspension kinematics is responsible for selecting ideal handling characteristics for the vehicle such as wheel travel and steering angle. These characteristics are achieved by utilizing various simulation tools such as Simscape Multibody to place inboard and outboard points for the control arms and analyze the system’s response to different scenarios. Suspension structures is responsible for designing the physical parts of the suspension system including uprights, A-arms, links, and mounting tabs for the shocks and control arms. Structures performs various calculations and FEA simulations and motion studies to ensure parts are strong enough to stand up to the most rugged obstacles. Structures also collects data for impact loading to determine real loads on the system.
Cal Poly Racing’s Baja car is equipped with a semi-active suspension set-up where the shocks damping is controlled electronically by the driver and via a premade controls program for optimal performance for high-speed cornering and rock crawling. Shocks and semi-active are responsible for tuning the shocks on our shock dyno, selecting springs and spring rate characteristics for the coil-overs, and developing cornering simulations and shock internal fluid dynamics simulations tools to help write controls for the semi-active system.
Testing is responsible for validating the maximum potential of each subsystem and integrating them to design the optimal car. Using previous years' vehicles and components, we collect valuable data through different methods and jigs. A notable example is acceleration testing, where multiple components on the car like the eCVT, tires, and shock stiffness are adjusted to achieve the fastest time for competition. Subsystems use this data to redesign parts for our current car. We also provide drivers with valuable experience and training on various courses with the car. Setting up different challenges or obstacles over various testing days helps our drivers better prepare for competition.