Duke University Pratt School of Engineering
Mechanical Engineering and Materials Science
Duke University Motorsports
Duke University Motorsports is a student-run organization that designs, builds, and races a single-seat formula racecar every year. We begin designing the racecar during the summer before each academic year in order to have a complete racecar modeled in Solidworks and some components built by the end of the first semester. The construction of the racecar is completed during the middle of the second semester, and the latter half of the semester is dedicated to testing and tuning the racecar in order to get ready for the competition.
The team roughly consists of the following design groups
Suspension
The suspension team is responsible for designing the geometry, weight balance, stiffness and damping characteristics of the racecar to optimize vehicle dynamics
performance. The design begins at analyzing tire data, specifically looking at the longitudinal and lateral acceleration data (friction ellipse), tire slip data,
and stiffness and damping of the tire alone. Then the rest of the suspension must be designed together due to the inter-dependence of all suspension parameters and
their effects on vehicle dynamics.
In terms of geometry, the design group considers parameters such as wheel camber angle, toe angle, and caster angle, roll center location as determined by wheel track and angles of suspension linkages, Ackermann (steering), etc. These parameters are adjusted such that a good compromise in terms of performance is reached.
In terms of dynamics, the design group considers parameters such as roll stiffness, compression/rebound stiffness, and in general the resistance of the aircraft to changes in suspension geometry. It is also important to consider natural frequencies of the vehicle, trasmissibility, and the response of the system to disturbances.
In terms of testing and tuning, the suspension team fine tunes the damper settings, camber and toe angles, brake bias, and weight distribution in order to obtain the best possible handling characteristics on the track.
Engine
The engine team is responsible for selecting the engine, designing and manufacturing the air intake, exhaust, and cooling systems. There are several options alone
to consider when selecting the engine, such as the displacement, number of cylinders, and whether to design a supercharged or turbocharged system.
The intake design is also important because all intake air must flow through a single 20mm restrictor, limiting the mass flow and forcing teams to actually design the system to maximize power and torque. The intake starts with a throttle followed by a converging-diverging nozzle, and a plenum that splits into separate runners that go into the engine cylinders. Design decisions revolve around nozzle dimensions, plenum shape, and structural integrity of plenum during backfire.
The engine team is more heavily focused on manufacturing and tuning. The team is moving toward an intake completely made of carbon fiber, and has led the rest of the team in exploring various methods of creating carbon fiber-epoxy structures, having used both wet lay-up and vacuum bag methods. Another important responsibility of the engien team is tuning the fuel map in order to maximize power and torque over a wide range of RPMs. This is done through programming the engine control unit (ECU).
Brakes and Wheel Assembly
The brakes and wheel assembly design team is responsible for the brake system as well as all components inside and including the wheel. Due to the complex geometry of components
resulting from a greater need for weight reduction, this group focuses heavily on Solidworks, finite element analysis, and CNC machining in order to produce the lightest
components possible.
There is a higher priority to reducing the weights of wheel assembly components because they are so-called "unsprung weights". Heavier unsprung weights lead to worse vehicle dynamics. However, it is also necessary to have a stiff unsprung structure such that the overall system is resistant to changes in suspension geometry under driving loads. Therefore, the main design challenge is to find a compromise between stiffness and weight. Also for this reason, the brakes and wheel assembly team works closely with the suspension team.
The major components of the wheel assembly are the wheel, connected to the hub, then connected to the spindle, then connected to the upright, which is connected to the suspension linkages. The placement of the wheel bearings depends on the type of spindle. Typically front wheels have fixed spindles, so the wheel bearings are placed in the hub. Rear wheels must have rotating spindles, so the wheel bearings are placed in the upright. Another typical trend is wide structures or shell-like structures for hubs and uprights. This is aimed at increasing the stiffness-to-weight ratio of the components.
The main goal of the brake design is to satisfy the competition safety requirement that all wheels must be able to lock at the same time when fully applying the brakes, which demonstrates that the car has sufficient braking power. This means that the front and rear brakes should be sized appropriately, taking into account the weight transfer that occurs under maximum braking loads. This involves selecting the master cylinder bore size, brake caliper piston size, and brake pad location for both front and rear wheels. Fine tuning of the brake bias is then done during testing to improve vehicle handling.
Drivetrain
The drivetrain team is responsible for selecting the differential and designing the power transmission components between the engine output shaft and the rear
wheels. This is another design team that is focused more on Solidworks, CNC machining, and weight reduction. The main components are the sprocket, differential,
differential housing, drive shafts, and tripod housings.
Electrical
The electrical team is responsible for designing the wiring scheme for the racecar, integrating the ECU with the engine, and installing the data acquisition
system. There are several requirements based on rules and safety, such as a brake light and a brake over-travel switch, voltage regulator and car battery. The ECU
must be wired appropriately to interact with the engine, various sensors, and fuel injectors. The data acquisition system stores performance data during testing.
Frame, Bodywork, and Aerodynamics
The frame design involves building a rigid structure that houses all the racecar components. There are many safety regulations involving the frame, mainly regarding
tube placement for crash protection. Another objective is to design a rigid structure, again to resist changes to suspension geometry.
The bodywork team is responsible for creating a streamlined outer body for the racecar. This group focuses heavily on Solidworks surface modeling and carbon fiber manufacturing.
The aerodynamics team is responsible for designing and manufacturing an aerodynamic package that can be installed onto the racecar to provide downforce and increase the maximum acceleration of the car, especially during cornering.