Purdue Electric Racing Systems Engineering Work
Some of the most critical work in creating our car happens in the first stages of design. One of my roles on the team, and one of the things I have been doing longest, is working to determine how we can create a system from battery to motor that is designed to work together. This was inspired by a piece of feedback we received from a judge during our design competition my freshman year. It was pointed out that our inverter's maximum operating voltage was way above our motor and battery specified operating voltage, and that our battery voltage was not optimized for our motor either. The main reason that we found for this mismatch was that the structure of our team as a whole caused the sub teams within to act as if they were isolated from each other. Since that competition I have tried to participate in multiple sub teams both to learn more about the car as a whole, but also to help integrate systems that span between multiple groups. In terms of electrified powertrain our new strategy has been to pick a motor based on math and simulations from the drivetrain subteam, then pick an inverter whose electrical characteristics most closely match the motor, and finally a battery which operates at the edge of the maximum motor rating at full charge and can support the typical power needs of the motor over a wide operating range.
Since the second semester of the 2019/2020 school year I have been part of the group managing our hub motor introduction / integration project, and starting in the summer I started to take a more active role in managing the project as a whole. It was a great learning experience stepping outside of pure engineering work and figuring out how to manage and motivate people on a team where everything is done on a volunteer basis. I got a lot of good advice from former and current team leaders and have learned how to work with them to organize this project around the resources and capabilities of a team like ours. The hub motor project is unique for our team because instead of falling within the typical 1 year design and manufacturing cycle we work in a typical school year, this project is scheduled to run across school years and into 2022. This is a challenge not only to stay on task when timelines extend much further, but also to contend with the rapidly changing makeup of the team and knowledge transfer between members. As it stands now most of the core members of the project itself are seniors on the team and next year won't be part of the project at all. It is important to establish robust and accessible documentation for rising members so that they can easily pick up where others left off. It is also important to start bringing those members in now so the transition is smoother. By leading the direction of the project I have been able to apply a lot of my systems knowledge and experience to creating methods we can use to design systems we have never designed before. A great example is drivetrain component selection. Like in previous years it has always started with the motors but there are other factors to consider such as the challenges of distributing the physical power delivery system, considerations for power splitting and torque vectoring, as well as the impact larger motors have on unsprung mass. It has been a good challenge to brainstorm new considerations and figure out how we need to change our design and organization methods to work on such a project.
Update 9/18/2022:
Two years on from these initial statements, I am happy to say that we as a team were able to make a lot of headway in figuring out what makes the best car for our competition. Studying the specifications of different motor / controller packages available we decided that it may actually be beneficial to select a package with less overall peak power in the name of weight and overall system efficiency / complexity. We also came to this conclusion through study of competition data itself seeing that average speed is low and therefore despite a maximum allowed power of 80kW it is rare that over 40kW discharge is reached during the highest value points events. Even with less peak power available, we may still be able to beat other teams. The same tactics were applied to the battery where my simulations were used to shrink our overall capacity by 30%. A similar weight savings was achieved until our team decided to switch to a liquid cooling solution. I'm excited to see where the team takes the philosophy from here and I am hopeful they will continue to push the boundaries of creating a lighter and more efficient car.