e29 iGNITE Full Interview
University of Florida's Department of Mechanical & Aerospace Engineering - Solar Gators
University of Florida's Department of Mechanical & Aerospace Engineering provided the "e29 iGNITE" program with a "behind the scenes" with their innovative solar racing team as they share their journey, challenges, and vision for the future of sustainable transportation.
e29 iGNITE In Depth Interview with Solar Gators
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Introduction
1
e29: Could you give a brief overview of the Solar Gators team and its mission?
"UF Solar Gators: Solar Gators is a fully student-run engineering design team at the University of Florida. We are passionate about driving innovative and sustainable technology in the automotive industry. We design, build, and race solar-powered cars to inspire the next generation of engineers and innovators through providing hands-on technical experiences as nearly all our research, design, manufacturing, and component testing is accomplished in-house. Along with this we are dedicated to creating a cutting-edge solar vehicle to race in and win the American Solar Challenge, and Formula Sun Grand Prix."
2
e29: What key challenges has the team faced and overcome throughout the Solar Gators project?
"UF Solar Gators: Some key challenges in recent history have been the retention of members and knowledge throughout the years. Due to us being a team that is ran 100% by students, we sadly have to say goodbye to many of our senior members after graduation. This means that in the 3-4 years that our members are here we must quickly train them, have them design and build a car, and then be the next generation that trains others and repeat the process. The key to overcoming this obstacle has been setting a culture of hard work and pride in this work allowing for many of our members to harness their creativity and grit and project this to their projects to create new innovations on the way.
Along with this, Solar Gators has prioritized documentation and has implemented a system of integration which allows us to educate and prepare a very large number of new members each year. On the side of funding, our team is not for profit, meaning that most of our funding comes from donors and through the support of our parent organization (UF's College of Mechanical and Aerospace Engineering). With this limitation to funding and necessity to reach out to companies, we have developed a very strong business acumen within our team dedicated to marketing and showcasing our passions and efforts in hope of receiving support from folks like those at ELEMENT 29."
Project Management and Deliverables
1
e29: How does the Solar Gators team manage risk throughout the project lifecycle? What strategies are in place to identify, evaluate, and mitigate potential challenges?
"UF Solar Gators: The key practice which we use to manage risk throughout the project life cycle is design reviews. This allows us to get as many eyes on a particular design as possible and prevents us from going too far with designs that will not work or have the potential to be further optimized. In addition, we find it extremely useful to engage our solar gators alumni in our design review, due to both their experience with solar gators and their experience as practicing engineers."
2
e29: How does your team track progress and ensure effective communication across all members, especially when deadlines are tight? Are there specific tools or systems you rely on?
"UF Solar Gators: Our team has used several communication and project management platforms, including Microsoft Teams, Slack, Clickup, etc. However, regardless of which platform we use, the biggest challenge and most important factor is making sure that all of our project leads are consistent in using these platforms."
3
e29: What are this year's key milestones and deliverables for the Solar Gators project? How do you prioritize tasks to make sure they are done quickly?
"UF Solar Gators: This year, our team has one clear goal: Finish Car four (Flare) before the end of the school year. To accomplish this, each of our sub-teams (Aero, Suspension, Structures, Battery Pack, Breaks, and Electrical) must finish their deliverables in the correct order.
We are currently in a spot where all of the teams are working on their sections in parallel; Aero and Structures are working on Carbon Fiber Layups for the Body and Chassis of the car, Suspensions and Brakes are busy CNC machining parts, and battery pack is 3D printing the module structures for the battery cells, and electrical is assembling and testing PCBs. As we move into the second semester, it will take great coordination to ensure everything is finished on time and in the right order, for example, the chassis needs to be installed inside the aero shell, then suspension on the chassis, and then brakes on the suspension, and of course electrical goes in after all that."
Engineering Design and Materials
1
e29: How do you measure success beyond just the car's performance? For example, do you track team growth, knowledge transfer, or community impact?
"UF Solar Gators: While we love racing and are always pushing to build better and better cars, our real mission is to train the next generation of engineers by turning engineering students into engineers. To this end, we are always looking to grow our team, so seeing an upward trend in attendance and membership is a great sign that people are passionate about coming back and that the team is doing well. In terms of knowledge transfer, the ratio of new members to old members is a great indicator of success.
To elaborate, as we get further into each semester and our integration process wraps up, if there are a large number of new members to old members this means that we were able to transfer knowledge in a way that these new members keep showing up and are taking up the mantle while the older members act more in a mentorship role, and aren’t actively doing all the work."
2
e29: With three iterations of the Solar Car completed, what materials were chosen for the latest edition, and what advantages do they offer compared to previous designs?
"UF Solar Gators: All our three previous vehicles up to this point have utilized metal spaceframe chassis (both aluminum and chromoly). For our new vehicle, we have upgraded our design to a carbon fiber monocoque. This offers huge weight savings, at approximately 50% reduction to our previous chassis. However, it comes with a unique set of challenges.
Successful design of a carbon fiber monocoque is much more difficult than that of a metal structure. Improper design can lead to a vehicle chassis that is too flexible or unable to react to high suspension loads from bumps and turns. Costs are also much higher, which have required us to seek sponsorships from many composite companies willing to donate material. Regardless, we believe this new chassis will give us a large advantage."
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e29: Are there specific trade-offs you’ve encountered when choosing materials, and how do you balance performance, cost, and sustainability?
"UF Solar Gators: The main trade-offs which we are constantly evaluating are cost vs performance and cost vs time required. We are lucky to have a large number of material sponsorships (companies which sponsor us through their products as opposed to cash); this allows us to get quite expensive materials, usually composites for cheaper prices, this makes the cost vs performance decisions much easier, however when we can't get materials sponsored, we have to have very in-depth discussions about where on the team our limited budget should be spent.
In some cases, we must weigh the cost of buying or outsourcing something vs doing it ourselves. As one of our main goals is training new engineers, if doing something ourselves does not involve a bunch of new expensive tools, we will almost always choose to do it in house. For example, our previous aero body molds were made by a boat manufacturer who makes molds for small boat hulls. However, because we were able to acquire sponsored time on a large format CNC machine, we were able to create the molds ourselves this year."
Energy System and Efficiency
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e29: Could you explain the type of solar cells used and how the energy is stored? Specifically, what type of battery does the system utilize, and what is its capacity?
"UF Solar Gators: Our Car uses Monocrystalline Silicon solar cells, which are commonly found in residential solar panels; the cells that we use are only slightly more efficient than those found in utility and residential panels, at about 25% efficiency. We are allowed up to 4 m^2 of solar cells on our car, meaning that at 1000 W/m^2 of solar irradiance, our solar array will produce about 1000W. Our battery uses Samsung 21700 LI-ION cells.
Each of our battery modules consists of 10 parallel cells, and the entire battery consists of 29 modules in series, representing 290 total cells. This results in a Nominal Voltage of 104.4V and minimum and maximum voltages of 72.5V and 121.8V, respectively. Each cell has a rated capacity of 5000mA hours, giving the battery a rated capacity of 5.22 kWh."
2
e29: What is the efficiency of the Solar Car, and how does the team ensure it achieves optimal performance?
"UF Solar Gators: For Electrical Efficiency we generally look at three different metrics:
- Drive Efficiency: This represents the efficiency of the drive train components, from the output of the battery to the motor. Our motor was purchased from MITSUBA corporation in Japan and was custom-wound to the weight of our car. When used with the MITSUBA motor controller, we can achieve >95% efficiency depending on drive conditions. The only additional components that sit between the battery and motor controller input are the contactors, which are basically large relays and the main fuse; the power loss across these devices is negligible.
- Collection Efficiently: Our car can collect energy from two sources, the solar array and regenerative braking. The solar array's efficiency is limited by the efficiency of the cells themselves, as well as the solar array encapsulation, which is the plastic layers above and below the solar cells. In addition, there are a number of special coatings used to reduce the reflection of the encapsulation. In addition, the solar array output is run through three Maximum Power Point Trackers (MPPTs), which are used to maximize the efficiency of the solar cells and match the voltage on the solar array to that of the battery. Our MPPTs have a peak efficiency of 99.2%. In addition, we use regenerative braking. It is difficult to characterize the efficiency of regenerative braking. However, we are limited by the maximum charge current of battery cells which is 49 Amps.
- Reliability: The reliability of the vehicle is critical to our performance. Ensuring that we are on the track for all 24 hours of racing is critical, as it allows us to drive as efficiently as possible while still using our entire battery pack."
3
e29: Have the dimensions of the car body changed since the project's inception? If so, what benefits have these changes provided?
"UF Solar Gators: The general size of the car is dictated by the maximum area of solar cells, which is 4m^2; this leaves us with the main decision of the ratio of length to width, and on this front, we attempt to make the car as slim as possible without comprising the stability of the vehicle, this is something which we definitely push to the limit as demonstrated by our third cars three rollover incidents.
The newest version of the competition rules, which will come into effect in coming years, allows for 6m^2 of the solar array, meaning we will see many new designs."
Design Enhancements
1
e29: The Sunrider has already demonstrated record-breaking performance. What design changes or innovations would you consider implementing to further improve its capabilities?
"UF Solar Gators: We are currently working on a number of improvements for our fourth car:
- Active balancing: We are currently working on a new Battery management prototype that uses active balancing. This allows us to actively transfer charge from the stronger battery modules to the weaker ones.
- Automotive Ethernet: We are also working on prototypes for Automotive ethernet, which we will likely implement next year, this will increase the maximum data rate between boards on the car, as well as reduce the size of the wiring harness by using power over ethernet.
- Cellular Telemetry: this year we are adding a cellular module to our telemetry system this eliminates the base station in our pit needed by the old radio telemetry system.
- Carbon Fiber Chassis: This year, we are creating a new carbon fiber chassis, explained further in materials section
- New suspension designs: Trailing Arm for Rear suspension and double wishbone for front suspension."
Performance in Various Conditions
1
e29: Is regenerative braking incorporated into the Solar Car? If so, how does it impact energy management and overall performance?
"UF Solar Gators: We do use regenerative braking. It is difficult to characterize the efficiency of regenerative braking. However, we are limited by the maximum charge current of battery cells which is 49 Amps.
In addition, it can be difficult to create an intuitive control method for regenerative braking as stated the maximum charge current of the battery is 49 Amps, and the current off the solar array is constantly changing between 0 and about 10 amps, meaning the maximum allowed regen current is constantly changing."
2
e29: Has the team tested the car's performance under adverse weather conditions, such as cloudy days? How significant is the impact on the car's functionality, and what measures have been taken to mitigate performance loss?
"UF Solar Gators: Our competition does not stop the race for rainy conditions and thus we use a number of methods to ensure our car can perform in any conditions. First, we conformal coat, and 3D print enclosures for all of our PCBs to ensure they are isolated from any water and highly conductive carbon fiber dust, which has caused problems in the past.
In addition, we take measures to ensure water does not get into the car itself. Cloudy and rainy days certainly do harm solar array production; on race days, we generally have strategy discussions before and after each race day so that we can plan for weather, for example, if the second day of racing calls for a few hours of rain we may race slower on the first day to ensure that we can drive at the most efficient speed thought the entire race."
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