k a e Spneek THE NEW
“why do we bother?”
“It’s time to start living the life you’ve imagined.”
4 DEEP INSIGHTS
INTO THE NEW CAR
• drag & downforce • new tires • critical battery selection • Drivers control
DESIGN PHASE IS RUNNING TOWARDS THE END THE FINAL ADJUSTMENTS ARE HAPPENING DURING THE CHRISTMAS HOLIDAYS AND BJÖRN PÅLSON WILL END THIS FIRST HALF OF CFS15. From an examiners point of view it has been an exciting and at the same time demanding autumn since this is the first time I’m in this position for Chalmers Formula Student. It was long ago that I participated in the project myself as a student and it has been rewarding to catch up with the progress that CFS has made over the years regarding both engineering and project management skills. During the fall we’ve seen the project evolve from a phase of more or less adventurous concepts such as unsprung front wing and wheel motors into something simpler but still advanced. This is the first time that CFS has designed an electric powered vehicle from the ground up, and on top of that the car features a full carbon fibre monocoque. It can be argued that the CFS15 is the most advanced CFS design so far. Overall the project has progressed well and as I write these lines all parts on the car but the aero package is set for design finalisation before Christmas. During the course of the project it is not only the design that has evolved. It is also the team’s
way of working and their understanding of the project that has changed with time. In the beginning the team members tinkered with concepts on an individual and subgroup level. Later on in the design phase interactions with other subgroups’ solutions became more apparent and compromises had to be made. The students have also realised that the challenges in a larger engineering projects lies not only in the technical solutions, but in organisational and financial aspects as well. And compromises between these dimensions are not always easy to measure and judge with the same stick. Finally, I’d like to quote writer Joseph Conrad saying that words are the great foes of reality. Therefore I hope and suggest that you will come and visit any of our presentation events or the launch to see the results of the team’s effort with your own eyes. God Jul & Gott Nytt År!
BJÖRN PÅLSSON Examiner
TIME FOR MANUFACTURING working hours in front of the computer is over
BUILDING AN ECO FRIENDLY CAR WITH GREAT DRIVING PLEASURE NEW TIRES AND A WIDER TRACK ARE JUST A FEW OF THE CHANGES THIS YEAR
The suspension subgroup welcomes many new benefits of the electric drivetrain. One of them is the lowered centre of gravity of the drivetrain. This open possibility leads to many packaging solutions. The suspension group also challenges the old paradigm that electric cars are not only eco friendly, but also fun to drive. The predecessor is powered by a robust four-cylinder engine. The replacement electric drivetrain will be lighter and the total target vehicle weight is reduced to 185 kg. The other major change is the tire choice. Based on benchmarking and extensive analysis using Calspan data, the new tire will have a different compound composition and will be slightly narrower. The gain is highly desirable. The new tire and rim setup will be a staggering 5kg lighter compared to the predecessor. The new narrower rim opens a wider gap for the aerodynamic subgroup to induce cooling air into the hub. Insufficient brake cooling has been a design flaw inherited over the last two generations of CFS vehicles. Upright design has also included
the new tire and rim setup will be a staggering 5kg lighter cooling to aid heat dissipation surrounding the hub. Heat dispersion into fast passing air is studied. Drawing heat away from the brakes through hub and upright by conduction is also examined. Lastly, to fully resolve brake-overheating issue, light has been shone on brake piston material. Steel, although heavier than aluminium, has a lower heat diffusivity value. ISR 4 Pot callipers with 25 mm diameter piston are chosen in the end. Longitudinally, wheelbase is kept short to produce an agile car. Laterally, wider track is desirable as it minimizes load transfer and higher lateral acceleration can be
attained. Yet, car with wider track cannot tackle tight corner as fast as a narrower car. Finding a good balance between these criteria is crucial for the performance of the car and is evaluated using software from IPG. This software is also used to evaluate the, to the suspension group, most interesting feature of the new electric drivetrain; torque vectoring using two independent rear driving wheels. This allows for even faster cornering and a new level of propulsion customization. On the technical side, virtual swing arm length is reduced from 1150 mm down to 1000 mm. A shorter arm increases camber gain, compensating for effect of vehicle roll. Steel wishbones will be replacing carbon fibre ones due to durability and in-house manufacturing capacity reasons. The suspension system will continue using ZF dampers and Lesjรถfors springs. Both companies have been solid CFS partners for many seasons.
THE NEW CHALLENGE OF A FULL ELECTRIC POWERTRAIN AND HOW DOES THE BATTERY SELECTION AFFECT THE COOLING? The electric powertrain group is exploring a new area for Chalmers Formula Student. The results produced by the subgroup so far have indicated that electric drivetrain is delivering higher performance than internal combustion engine drivetrain. The first thing about electric vehicle that comes to peopleâ&#x20AC;&#x2122;s minds is the accumulator and its range. The subgroup is seeking battery chemistries that are both lightweight and low volume. The team shortlisted a number of battery candidates based on energy density, price, lifecycle and chemical stability considerations. In the end, the accumulator is designed and to be constructed out of 190 LiCoO2 battery cells manufactured by Melasta.
The designed accumulator will house 7 kWh of energy and deliver 80 kW of power (per rule regulation). The cells are air-cooled using fans. The accumulator is housed in a box within the carbon fibre monocoque and the isolation gives rise to cooling issues. Maximum operating temperature of the battery cells should not exceed 60 celsius. This temperature specification does not seem to be a concern in the wintery Scandinavian country at first. However, the battery cells build up heat during discharge. If cooling airflow is not properly designed, dangerous situations such as thermal runaway may occur. Thus, the subgroup is working closely with the aerodynamic subgroup on cooling duct design. The battery cells weigh around 40 kg. Including the accumulator casing, the overall package will weigh about 50 kg. Solid state welding, resistance welding and mechanical fastening methods to connect the cells are investigated. At the moment, ultrasonic welding process is the most favourable. The centre of gravity location on the electric vehicle is lowered in comparison to combustion engine vehicle. This will improve handling characteristic from suspension teamâ&#x20AC;&#x2122;s dynamic point of view. The team is constructing two
accumulators. This is a very costly decision. Having two battery packs will give the team more testing time on the track. More importantly, giving the battery sufficient amount of time to cool down and recharge will prolong its lifecycle and maintain its capacity. Charging time is still a downside to electric vehicles. The motors are generously provided by AROS. The stator are wound up in-house. The motors will be water cooled, and the engineers are carefully calculating the required cooling water flow rate and associated efficiencies. On the mechanical side, the gearbox connecting the motors and the driveshaft has been redesigned. The new gearbox utilizes an 8 to 1 ratio, a taller ratio compared to previous 7.5 to 1 reduction. This decision is based on speed data from previous endurance runs and motor performance characteristic. The engineers have examined the mean speed and motor efficiency map. The ratio allows the motor to perform at the highest efficiency range and the gearbox casing has been carefully investigated to further reduce weight. The low voltage electronic engineers have been working actively on control units. The front CPU control sensors and dashboard gadgets, while the rear CPU
If cooling airflow is not properly designed, dangerous situations such as thermal runaway may occur control sensors and the safety circuits. STM32 CPU is selected for its compatibility with Matlab, which is shared with the suspension team. Suspension team is working with the low voltage engineers to design torque-vectoring algorithms. The CAN bus communicates between the two CPUs. The safety circuit constantly monitors the system. If any system alarms, e.g. insulation fail, the required action will be taken to ensure safety of the vehicle and the driver.
GLIMPSES DESIGN WORK, FALL 2015 a sneak peek on the new website
THE TEAM ALSO GOT A NEW SUIT! THE GRAPHICAL PROFILE HAS ENTERED OUR LIFE AND IS OVERTAKING US STEP BY STEP. The Art of Engineering has always (and will always be) the heart of Chalmers Formula Student, but we found ourselves out grown our suit this year. Therefor a major work has been put in to update of our graphical profile and we hope that you like our new outfit. The brand identity is important to the Formula teams and we are proud to represent the community and have high ambitions to spread the knowledge about the initiative at Chalmers, Gothenburg and Sweden and abroad. But to build awareness we can’t wait for the audience to come to us, hence we have attended 7 events in the period of three months, we have posted 56 times on Facebook, updated our website, Instagram and Twitter accounts. Although this won’t make us win the coming competitions, let us look above
that for a minute. The reason why we put all the effort in this work is mainly for two reasons. The first, and most crucial one, is to inspire students and teenagers to engage in technology and product development. - Without talented students we won’t have a next years’ car. Here we have to take into account what students we want to attract. During the mid-design presentation we got a question why we only have one girl in the team. The answer at the time was bad marketing, and that does not only go to the gender aspect, the question could just as well have been with respect to educational and cultural background, but yes a diverse team is something we strive for. The second one is to show people what the university and our great partners can achieve together. By sharing wisdom for ideas we develop
the vehicles for the future, and how well the school environment can work together with the industry. This relation must be seen and that goes both ways. CFS is proud to partner with our future employers and the companies get personal contact with interesting students. So in the end it is not just a word mark or a logotype that you see, you see a stamp of quality in our work, in our relations and you see the engineers for tomorrow.
VISIT OUR WEBSITE AND HAVE A LOOK
THE TRADE-OFF BETWEEN DRAG AND DOWNFORCE THE WINGS THAT KEEP US ON THE GROUND AND SYNERGY BETWEEN COMPONENTS. With the help of aerodynamic devices such as wings, the aerodynamics group can reduce lap times by increasing the contact pressure between the tire and the ground. This increases friction forces so that we can increase cornering speed and reduce braking distances. The primary objective of the aerodynamics subgroup is to design an efficient high downforce aerodynamic package with the focus on vehicle stability. The aerodynamics group started solving their task by looking at lift-to-drag ratio from a high level perspective. They used point mass simulation to analyse the effect of increasing the lift to drag ratio on a vehicleâ&#x20AC;&#x2122;s performance, measured by lap time. Baseline analysis is performed to evaluate the new parts. The objective is to reduce lap times as much as possible. This means a trade-off between drag and downforce can be viable as long as the gain in downforce is high enough. With the help of point mass simulations the minimum
ratio for break even between downforce and drag is calculated. Ideally, the centre of gravity position on a vehicle should coincide with the centre of pressure point to maintain predictable handling over all speeds. However, due to packaging constraints and because generated lift as a function of air speed is not equal between the different aerodynamic devices, the realistic ambition is to minimize the distance between the two points. Currently, one main objective is to push the centre of pressure location towards the front of the car as much as possible. This is due to a powerful rear wing and a much more restricted front wing. CFD analysis is used to design a complete aerodynamic package with enough adjustability so that further adjustments during testing can ensure that the aero package delivers maximum downforce with predictable and balanced vehicle handling. Examining the front wings in detail, it is noticed that the main wing segment uses an in-
further adjustments during testing can ensure that the aero package delivers maximum downforce house design. The airfoil was designed for performance in the given height location, which is limited by the rulebook. The nose of the chassis design is well underway. The motivation is to direct as much air to the underside of the car as possible to feed the floor and side-wings. The cooling system is looking very different this year compared to last year.
The electrical motors generate significantly lower waste heat compared to previous combustion powered power plants. The job of cooling is still of highest importance to ensure that the powertrain and brakes work within their specified operation temperature ranges. Without having a large radiator and exhaust manifold on the sides of the cockpit, the side pods are replaced by side wings. The purpose of the side wings is to minimize rear wheel drag and lift by directing air over the exposed wheels while producing downforce. With the addition of the side wings and under body venturi ducts that feed air to the sides, the diffusers overall size could be drastically reduced this year. Further evaluations are still needed to understand the impact of this new underbody design and how the diffuser can be refined further.
Rear wings also see some changes dues to rulebook regulation updates. The rear aerodynamic device utilizes high lift and low Reynolds number airfoils optimized for low speed. Paired up with the front wings, the rear wing’s main purpose is to maximize downforce while balancing the centre of pressure location to provide a well handling vehicle. The keyword for the aerodynamics subgroup this year is “synergy”. The engineers are looking at several independent components and trying to optimize their contribution. The iterative design process starts from the front wing and then progresses rearwards to the rear wing. CFS engineer Magnus Urquhart describes the work as very meticulous, as a small change in the front wing can have large effect on the rest of the car, therefore the entire aero-package has to be designed in unison. The simulation
work is carried out using processing power provided by C3SE, which is a scientific and technical computing centre at Chalmers. Chalmers’ C3SE is one of six Swedish National Infrastructure for Computing (SNIC) cluster. The team and aerodynamic subgroup in particular would like to express gratitude towards our partner DIAB and EVONIK for providing high sheer and flexural strength foam core. The products stand for lightweight design and offer the CFS15 the high performance needed. Last but not least, the team would like to thank Per Österdahl from CD-Adapco. The STAR-CCM+ software provided by the multinational computer software company has been the backbone for the design stage.
INTRODUCTION TO THE WORKSHOP THE CRITERIA TO ENTER THE WORKSHOP IS HIGH, AND THE TEAM IS THOROUGHLY EDUCATED SO THEY CAN WORK INDEPENDENTLY DURING THE MANUFACTURING PHASE
VISIT OUR FINAL DESIGN PRESENTATION ON THE 21ST OF JANUARY. JOIN OUR PRESENTATION WHERE WE SPEAK OF OUR ACCOMPLISHMENTS AND FUTURE TASKS. During the presentation you have a chance to ask questions, meet the team during the break or just sit an listen if you prefer. Usually we serve lighter snack (fika). We hope to meet you and show some renderings of the CFS15 car!
COME AND MEET US THE 21ST OF JANUARY VASA A - CHALMERS 18.00
CREATING A POSITION WHERE THE DRIVER HAS MAXIMUM CONTROL WITH EASILY ACCESSIBLE DASHBOARD FOR COMMUNICATION AND A SEAT DESIGNED TO SUIT.
Ergonomics and Driver Control subgroup is looking to take driver comfort into a higher level. Here are some items that the team is investigating. The headrest is being redesigned to offer better head and neck support. It is better adapted for the petite population. Shoulder support and backrest on the previous seat sees room for improvement in both areas. Specifically, the material of the backrest surface is too hard for occupants. This causes potential discomfort, or even worse - pain. Dashboard, which hosts various Human-Machine-Interfaces, will feature an easy configuration of buttons positioning regarding the frequency of use during driving. The impact attenuator will be constructed out of aluminium
honeycomb for weight saving. The steering wheel insert is redesigned to improve fatigue reliability. The steering wheel is connected to the steering shaft via a quick release. The interface between the steering wheel and the quick release has developed some undesirable play after intense driving. After inspection, the aluminium insert embedded in the steering wheel, which is subjected to high sheer stress due to steering torque, has shown sign of wear. Geometry configurations have been modified to address this issue. Since the nose of the CFS15 car will be slightly raised in comparison to previous cars, the pedal box will be lifted in order to accommodate the diffusor beneath the car. The ergonomists have to look for a
comfort position for the driver with his legs uprights. A major issue in the past were small pebbles jamming the pedals, preventing free travel and creating safety problems. The engineers are working hard to resolve this issue, as safety is always paramount. Pedal side plates, which restrict the foot from sliding off the pedal laterally, saw some minor adjustments and will be increased to prevent any eventual loose of heel grip. Detail work has also been done on the initial inclination of the pedal faces. The angles of the pedal faces are made to be as flush as possible to improve ergonomics.
WELCOME OUR TRAINEES! LATER ON DURING THE FALL A FEW SELECTED TRAINEE STUDENTS GET THE CHANCE TO JOIN THE TEAM AND THIS YEAR WE ARE GLAD TO PRESENT!
TRAINEE CREW 2015
SIVAN SAMIR POULES
AREZ MOHIDEEN AGE: 22 years EDUCATION: mechanical engineering at Chalmers university of technology. OTHER ENGAGEMENTS: except from CFS me and my dad is about to start a cheesecake store here in Gothenburg and I also work at NK from time to time. LIFE PHILOSOPHY: It’s time to start living the life you’ve imagined.
WHY DID YOU APPLY FOR A TRAINEE POSITION AT CHALMERS FORMULA STUDENT? Cars are one of the biggest interests in my life. I think that being a part of Chalmers Formula Student gives me the opportunity to contribute to one of the main things that my life has orbited. I do
also believe that, being a part of Chalmers Formula Student, makes me realize whether studying Automative Engineering during the Masters is right or not. Last but not least, who doesn’t want to say that they build a great formula style race car?
maintain good atmosphere and experience from the team. WHAT DO YOU THINK WILL BE YOUR BIGGEST CHALLENGE DURING THE YEAR? As soon as I see a car with an open bonnet, it feels like someone is communicating with me in an unknown language. That is how lost you got me. However, Chalmers Formula Student is looking for willingness and ability to learn, dedication and genuine interest in the project. Therefore, I believe that my lack in practical skills do not have to be a disadvantage. Instead, this will give me the opportunity to develop a lot of knowledge.
WHAT DID YOU KNOW OF CFS SINCE BEFORE? Well, I thought that I knew a lot about it. Then I realized that Chalmers Formula Student is more than building a good car and competing with it. To be able to manufacture a high performance car, there are many points on the road that should be considered. You need an efficient team with common goals. Constant communication between partners and the team, where feedback is obtained should also exist. WHAT QUALITIES DO YOU THINK YOU Moreover, Chalmers Formula Student is WILL BENEFIT MOST FROM? I work also a brand that needs a lot of marketing. as a vendor on weekends and holidays which means that I get the opportunity to WHAT ARE YOUR EXPECTATIONS meet and discuss with a lot of people. My FOR THE COMING YEAR? My biggest attributes as a retailer could therefore be expectations are to gain as much experience beneficial when negotiating with partners. as possible to be prepared for upcoming year Also, my general interest in cars makes me as Project Engineer. I believe that learning eager to always learn something new and as from previous years mistakes, develops the a mentioned before, there is a lot to learn. project, which gives the team ability to aim for better results. An important way to do IF YOU WOULD DESCRIBE CHALMERS this as a trainee is to study the procedure FORMULA STUDENT FOR YOUR during the Formula year. Pre-study, design GRANDMOTHER WHAT WOULD YOU and manufacturing are vital phases where SAY? It is like knitting! You start with a lot of knowledge could be gained. In nothing, but slowly develop something addition, communication and discussing useful and amusing that warms your body with the other engineers in the squad is of and soul. course something else that is important to
wishes Chalmers formula student