Synthesized Literature Review

The working subsystems— ChassisSCADASuspensionCoolingSteeringBattery PacksDrivetrain, and CarMan, CellMan have each preformed a literature review and identified a problem space that requires senior level engineering and design throughout the fall semester.

Structurally, at the base of any good racecar’s design is a good chassis, the chassis is the core of the car and is a crucial part in the design of a good car. Because the chassis is where all the subsystems come together, it is imperative that the chassis design is solid. Naturally, when designing the chassis, you are going to want to make sure that it is the best that it can be. Now we have to get into what defines a good chassis, and the two main factors that go into defining a chassis design as good are light weight and sufficient torsional stiffness. When testing the current chassis to determine the torsional stiffness of the chassis it is important that we take notes on the strengths and weaknesses of the design. This way, when we start to design the new chassis, we will have a basis of what to go off of and know where we need to improve. Another big thing to consider is the construction of a test rig that is easily adjustable and can accommodate a wide range of mounting points. This will allow us to experimentally determine the torsional stiffness of the chassis and will set future teams up for success when they go to validate their own chassis designs. Chassis design work, experimentation, and proper documentation will create the opportunity for the club to complete integration of multiple subsystems.

The suspension on a racecar needs to be integrated with the chassis and steering system to get the intended results. The suspension attachment points integrated into the chassis largely affect the dynamics of the system. Additionally, our front suspension must be designed to create safe steering conditions as shock deflection can change wheel steer angle, camber, caster, etc. These same angle effects of the rear suspension deflections can cause instability in corning as well. While each subsystem has an individual function, we see that they are very interconnected, making cross subsystem study and integration is of vital importance. The Lafayette formula hybrid car currently contains a double A-arm configuration with a pushrod operated bell crank front suspension and a double A-arm with a linear coil over shock design. It is key that that the senior design team identify key parameters for intended performance, test the current suspension to see if these parameters can be met, and modify the suspension system to reflect these parameters within reason. It is also the team’s intention to begin design of a new suspension that can more closely represent ideal performance expectations.

This means defining the most important characteristics of our cars’ performance and understanding where compromises must be made. Both [1] and [3] give a good overview on first steps to take and how iterative design is necessary. The tire is of utmost importance as it is a massive factor in vehicle handling. This must be one of the first design choices to be made as tire size needs to be decided on before suspension geometry can be developed [1]. Angles and points like that are determined by ride height and ball joint placement rely on wheel size. [3] Additionally, traction is determined by how much of the tire is on the ground. What tires to use is a compromise between maximum contact area and acceleration that can be achieved with larger moments of inertia. [1] The geometry of the suspension can then be worked on with elements such as roll center, camber, toe-in, and caster. These parameters affect each other in complex ways that are in part laid out in [1], [2], and [3]. [1] Specifically not only outlines steps that must be taken and a basic design criteria that need to be set, but goes in depth on the different outcomes of specific geometric changes. This source gives information on how we can reduce rollover threshold, prevent jacking, and numerous other critical factors in suspension design. The structural components of the formula hybrid car allow for the integration of powered and control elements such as the drivetrain system.

The drivetrain system of the formula car is important because it ensures the ability to deliver the maximum power and efficiency from the motor to the car and remain as light and stiff as possible. The system consists of a drivetrain housing, Emrax 208 liquid cooled axial flux synchronous motor, emDriver 500 motor controller, a limited slip differential and a chain-driven system with a single gear ratio. Due to past drivetrain housing flexural issues in previous years, the new housing design which contains all these components has been manufactured but has not been tested for rigidity, while ensuring the maximum performance. A rigid housing was fundamental to ensure stiffness and reduce vibration isolation which would further limit the power output of the car. This year’s main design consideration is to test the system’s rigidity in simulation and controlled environment and develop a better transmission to maximize the EV performance of the vehicle and range as such it can reach a maximum acceleration of 0-60 mph under 4 sec and ensure there is sufficient range to complete the race while maintaining efficiency at high speed. The most important aspect of the drivetrain sub-team will be surrounding testing the reliability of the system. This will involve using [4] to create a model that represents the system well, using [5] to test and confirm previous engineering results, and then if time allows using [6] to develop a more sophisticated multi-speed transmission system to improve the efficiency of the car while achieving a higher top speed and deliver more torque. It is also important for the team to develop an eddy-current chassis dynamometer testing facility on campus so that the drivetrain team can test the performance of the drivetrain in a controlled environment. There is a lot of information available related to the drivetrain for EV and not becoming overwhelmed with the information is difficult. Having the newer version of the drivetrain housing already manufactured from previous seasons will allow the drivetrain team a jump start, and a great opportunity to start the testing phase for efficiency earlier than starting from scratch. The drivetrain system requires a properly validated cooling system to ensure the system does not overheat.

The cooling system consists of several components listed in the following: the pump, reservoir, tubing, temperature sensor, flow rate sensor, and radiator. The coolant used for the motor and motor controller will be water. Essentially, the heat generated by the motor and the motor controller will be transferred directly into the water, heating the liquid to a higher temperature relative to the surroundings. That water will then be transferred via a pump directly through a cross-flow radiator. In the radiator, heat from the water will be transferred by conduction into the radiator’s fins, and then air will be directed into the radiator fins by a 12-volt fan to transfer heat into the surroundings through convection. The cooled water will then be circulated through the reservoir and then through the flow rate sensor and temperature sensor for data acquisition. Additionally, the motor and motor controller’s internal temperature sensor will also be used to collect data on whether or not the motor is operating under ideal temperatures. The flow rate and temperature readings from the sensors will be used to determine whether or not the motor and motor controller is sufficient temperature to operate efficiently. Information collected by the cooling sensors will be monitored by the data acquisition system, SCADA.

The SCADA software has two separate purposes: a debugging tool and a high speed data acquisition tool. The speed at which the software runs is the most important part of high speed data acquisition. [6] outlines the importance of choosing a computing language and the impact this decision has on the speed of the software. Balancing the time allowance for the project with the desired speed of the software helps identify which language should be chosen. For example, software runs fastest when written in machine code. However, the time it would take to construct the software is typically greater than the time allowance of the designated engineering team. Currently, the SCADA software is written in python. However, in terms of software speed, it would be beneficial to transition the new FASDAQ subsystem to the C programming language. Moving past computing language, the current central processing unit (CPU) is a Raspberry Pi. [7] discusses what should be evaluated when choosing a CPU. The base data sampling frequency of the CPU should be evaluated before even creating software. If the base rate of the Raspberry Pi does not meet the needs of the FASDAQ software, then a new CPU needs to be chosen. The SCADA system, in its current form is crucial for examining the battery packs and measuring the voltage being provided to the accumulator and drive train.

Annotated Bibliography

[1] de Paula Eduardo, Gabriel. Formula sae suspension design. No. 2005-01-3994. SAE Technical Paper, 2005. http://users.telenet.be/AudiR8/suspension%202005-01-3994Formula%20SAE%20Suspension%20Design.pdf
This article discusses various tests that were conducted during the design of the Formula SAE suspension from the year 2005. This includes diagrams and detailed explanations as to why certain decisions were made. This can be useful when assessing the design of our current suspension system because we can conduct similar tests that will help us understand how effective our system currently is as well as what changes should be made if necessary.

[2] Milliken, Douglas L., and Terry Satchell. “Chapter 17 and 19.” Race Car Vehicle Dynamics: Problems, Answers, and Experiments, SAE International, Warrendale, PA, 2003.
These chapters specifically focus on suspension and steering systems for race cars. The suspension portion informs us about different suspension choices including benefits and drawbacks. Additionally it familiarizes the reader with important ideas, jargon, characteristics and values in suspension design. The steering section highlighted here gives information of common steering geometries and the effect different design choices have. This ties into how suspension and steering are correlated components that affect each other. When contemplating design changes and the functionality of our current design, this source can inform us on what to keep in mind. Values like steer angle, caster, camber, kingpin angle, and roll axis are all important when looking at suspension and integrating steering into that system.

[3] Wirawan, J. W., Ubaidillah, Aditra, R., Alnursyah, R., Rahman, R. A., & Cahyono, S. I. (2018, February). Design analysis of formula student race car suspension system. In AIP Conference Proceedings (Vol. 1931, No. 1, p. 030051). AIP Publishing LLC. https://aip.scitation.org/doi/pdf/10.1063/1.5024110

This article focuses on a suspension type known as unequal double wishbone, however, the author describes that “suspension design may vary depending on the road terrain and the vehicle purpose itself, such as high speed or off-road vehicle.” The author talks about why such a design was made and includes equations as well as detailed explanations to support it. This will be helpful in designing our suspension because the article provides important equations that can be used to make relevant and necessary calculations related to our current model. In addition, we can learn from this team’s experience based on what was successful and unsuccessful.

[4] Rodriguez, Carlos. “Design of a High-Speed Transmission for an Electric Vehicle.” Core.ac.uk, July 2018, https://core.ac.uk/download/pdf/160238923.pdf.

This article goes over modeling and equations for the transmission of an electric vehicle. This is especially useful because it includes equations specifically for the drivetrain of an EV, unlike the modeling in the wind turbine article [6].

[5] Joshi, Prathamesh, and A.S. Ugale. “Overview of Transmission System for the Electric Vehicle.” Www.irjet.net, June 2020, https://www.irjet.net/archives/V7/i6/IRJET-V7I6164.pdf.

This article is a brief overview detailing the construction, testing, and data metrics of a single speed transmission system as well as a two speed transmission system for FSAE hybrid vehicles. The article offers an introduction to these systems and introduces the relevant constraints and metrics that the architecture must follow. This is relevant to us because we could use this information to help design a two speed transmission system in the future. The article talks about efficiency using both these systems. We currently have a single speed design, which is fine, but if we could improve efficiency by designing and implementing a two speed design performance could increase for future teams.

[6] Girsang, Irving P., et al. “Gearbox and Drivetrain Models to Study Dynamic Effects of Modern Wind Turbines.” Ieeexplore.ieee.edu, 28 Oct. 2013, https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6646795&tag=1.

This article goes over the modeling of drivetrains for wind turbines. While a wind turbine is not the system we are designing, this article still provides some very useful information regarding the development of a physical system and the matlab modeling of a drivetrain.

​​[7] “Data Acquisition.” Data Acquisition Products for ANY Application and Budget, Dataq Instruments Inc., 2021, https://www.dataq.com/data-acquisition/high-speed/secrets-successful-high-speed-data-acquisition.html.