Design Launch 2015 Edition
Contents
What’s New R&D
Electrical
Design and Improvements
Mechanical
Design Weekends
01 02 E-Differential Rocker Assembly 03 Steering Assembly Braking System 04 Gearbox 05 Wheel Assembly 06 Mechanical Powertrain Accumulator 07 Battery and BMS Data Acquisition 08 System Integration 09 Low Voltage Safety Chassis, System Integration 10 Composite Manufacturing 11 Diffuser Design Energy Meter 12 Improvements Planned Wing Prototype Design 13 Tire modelling and importance 14 Our Sponsors
Design Weekends
Design Weekends Pratyush Nalla Weekends couldn’t have been more fun. With all energy soaked out after tiresome academic weeks, Design Weekends are the only source of rescue from this strenuous situation. You might be thinking – How can “Design Weekends”, of all the thousand other fun things which one can do in a weekend, be so cool? Well, my answer is that one couldn’t have asked for a better weekend than a Design Weekend. It’s a perfect way to spend a weekend with friends, enjoy and yet come up with something really productive. Every weekend, the team members assemble and sit together to make the major design decisions. This involves a scope for immense co-operative learning which makes gaining knowledge lot more interesting and easier. But these Design Weekends do not comply with the famous proverb “All work and no play, makes Jack a dull boy”. Rather the weekends are more like “Some work and some play, makes Jack a smart boy!” These weekends also aid bonding among the team-mates as they start understanding other team members’ thoughts and ideas in a better way. It also helps to bloom the extraordinary creativity lying dormant within the young nurturing minds of team members. To ensure that these weekends transpire in an efficient manner, the topics of discussion related to various subsystems are pre-decided. This is followed by a rigorous definition of the problem-statement. The major focus of the weekend lies in devising a solution to the problem-statement which will best satisfy the needs of the rulebook and the designer requirements. But, hey! A good solution can’t be formulated by a single person alone. It requires team-effort, idea suggestion by team-mates which assists in exploring different methods of attacking the problem and quality group discussion which helps in coming up with an optimised solution. Hence the Design Weekends! The major advantage of these weekends is that one can know about the design progress of the
complete car and widen his knowledge base by knowing about other subsystems from the people who work in those subsystems. It’s a wonderful mechanism through which knowledge is shared. It also ensures that the design of the car is being conducted in fast and proficient ways. It promotes interactive learning, cultivates professionalism in work and generates a positive working spirit among the team members. It makes a boring difficult process easier, interesting and entertaining. Apart from team benefits, it helps in personal development as one is exposed to copious resource of information ready to be delivered by his fellow team-mates. The time-management skill of each individual is also enhanced as they start developing a correct mix of work and play. As I mentioned before, these weekends are not all about work, it involves a lot of fun too. Cracking jokes, playing games and quizzing each other are one of the many ways in which we have fun. Not to miss, the lunch treats add extra spice into the weekends. Unknowingly, these weekends turn into being the most memorable moments of one’s life.
All these foster a healthy relationship among the team members which paves the way for harmonious learning. The true essence of the goals aimed by the team is effectively conveyed to everyone reinforcing their thought process towards meeting those goals. There could be no better way in which the experienced team members could share their experience to underpin the design process Design Weekends have turned out to be a huge success this year. An exponential enhancement in the design of the car, as compared to last year’s, is already visible as a direct result of these weekends. It has turned out in being a perfect way to synergise the efforts and hard work put in by the team members. It has rather redefined the techniques of know-how and learning making it more enjoyable. Not to forget, these weekends also provide an awesome opportunity to hang out with friends. Now, isn’t that cool? So, what are your plans this weekend? Come. Let’s Design!
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Pitstop, January 2015
Design and Improvements: Mechanical Subsystem E differential Bhoumik Shah
Race car design engineers usually design a vehicle for some expected performance of the vehicle considering situations such as high speed cornering and straight line acceleration. However, the aberrance between the actual car and the virtual design usually comes in because of the unaccounted transient behaviour, inertial effects and manufacturing errors. Since a mechanical differential is not tuneable with respect to its parameters, it is not possible for it to give any kind of feedback and account for the above mentioned deviations. Electronic differential system has two independently driven motors driving the rear wheels whose RPM can be independently controlled. The proposed system thus takes various vehicle parameters as input and computes the desired vehicle performance and compares it against the current state of the vehicle. By providing appropriate feedback in the motor-controller input signal, it is possible to converge the
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vehicle’s state to the desired performance. As we use more high torque BLDC (brushless DC) motors this time, which can provide more torque than frictional force on tyres. This may lead to slipping of tyres which leads to poor control while turning. In E-diff our main aim is to use feedback provided by various sensors of car to control current of each motor to stop tyres from slipping. For that we have developed a dynamic model of car to predict the behaviour of car before actually implementing on actual car.
We have also developed a driver model in which you can enter parameters of track and predict various performance factor of car on that particular track. This helps us in tuning our Electronic differential for different track. This driver model could also be used to train driver to drive in a way that optimizes vehicle performance.
Design and Improvements: Mechanical
Rocker Assembly Prahlad Kumar
Suspensions is the part which maintains the balance of the car in all situations, be it racing on a straight track, taking sharp turns or travelling over bumpy roads. More technically, it is responsible for ensuring that enough grip is always available to the tires of the car. It also takes care of the comfort of the driver. The parameters concerning the springs and dampers are decided based on ride-roll calculations. Taking the formula student competition in consideration, it has been done such that the suspensions allow faster transient
response at corner entry, less ride height variation and allows for better rear wheel traction (being a rear wheel drive car) on corner exit. A full car model has been developed to show the response of the car for acceleration, braking, bump and cornering, in form of displacements and velocities of the center of gravity of the wheels and sprung body of the car and also the angle and the angular velocities of pitching and rolling of the car. The Bell Crank or Rocker assembly is responsible for translating the bumps on the road to the springs and dampers. This year, a roll stiffness adjustable
Anti-Roll Bar assembly has been designed. A set of two bars can be adjusted in the assembly to give 31 different front-rear roll stiffness combinations. The purpose of the Anti-roll bars is to resist the roll of the car during cornering which cannot be provided by springs alone. The adjustability is important as it helps controlling understeer or oversteer of the car. Being a part of this team for more than a year and working on the design of our next car has been a wonderful experience for me. It has been a great learning medium for me not only concerning vehicle dynamics but other subsystems of the car as well. We have worked days and nights together with each other discussing and working on challenging designs. Working in this team, guided by our superb seniors and awesome alumni, is the best thing which has happened to me in IIT Bombay. We have also developed a driver model in which you can enter parameters of track and predict various performance factor of car on that particular track. This helps us in tuning our Electronic differential for different track. This driver model could also be used to train driver to drive in a way that optimizes vehicle performance.
Steering Assembly Vaibhav Ojha
The steering system of a Formula Student vehicle must be designed in order to provide the necessary steer angle at the two front wheels so that the driver can negotiate the turn at the fastest speed possible. To achieve this, the first step is to get the steer angles as a function of the radius of turn. The steer angles are obtained using the ‘Two Track Roll Axis Model’. This was developed by the previous season’s Vehicle Dynamics Team. Few changes were made to the model this year which dramatically brought down the execution time (using MATLAB’s Global Search algorithm), had a slightly better algorithm for minimizing the objective function, and incorporated Sprung and Unsprung mass separately, giving better results. After obtaining the angles, the steering geometry to achieve these angles was prepared using Microsoft Excel as it allows for dynamic updation of data to give better control over how the quanitities should vary. The geometry was also checked for providing necesary feedback to the driver.
The next phase involved design of different components using Solidworks and analysing the components in ANSYS for predetermined forces and constraints, ensuring a minimum safety factor, and at the same time having the minimum weight. This way an optimum Steering assembly was designed for our vehicle. Working in the team has given me the opportunity to learn a lot of softwares useful for designing of mechanical
components, and also provided me the opportunity to get a first hand experience of a lot of theory courses that I have learned. I was also exposed to a lot of challenging problems, which were solved by the efforts of all members, seniors and juniors alike, providing a once in a lifetime experience of interacting and working with bright, innovative and passionate young minds of the country!
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Pitstop, January 2015
Braking System Parth Pandya
The aim of the braking system in a Formula Student vehicle is to provide maximum deceleration possible and ability to lock all wheels at appropriate driver pedal force to produce a complete stop. The first step is to analyze the tire data obtained from Tire Testing Consortium to obtain various plots like ‘Coefficient of Friction VS Normal Load’ and ‘Coefficient of Friction vs Slip Ratio’. From these curves, maximum traction force available during braking is found and hence maximum deceleration. Now, the driver must be able to produce a torque on wheel greater than that obtained from road to lock the wheels. Thus, driver force is appropriately multiplied (x57) mechanically and hydraulically to achieve this. I designed the various components to achieve this multiplication so as to minimize weight. Truss-like structures were used to design the pedal and carbon-fiber
composite footrest were used which lead to a weight reduction of about 50 % compared to previous year. The placement of Master Cylinder behind the pedal lead to a decrease in pedal assembly housing weight by 80 %. This was only possible due to Finite Elemental Analysis in ANSYS software. The next phase involved selection of calipers and design of brake discs. Semi-floating rotors were upgraded to fully floating to reduce mechanical wear, distortion and brake fade. I selected smaller calipers for front and rear which lead to 42 % weight reduction. Brake discs were analyzed structurally and thermally for the first time. Structural analysis was done to minimize torsion of disc brakes while locking. Using CFD and transient thermal analysis, a regenerative brakes heat transfer model was made to reduce maximum temperature of disc brake and maintain uniform temperature field.
All these design problems have lead me to an understanding of real engineering work and helped me apply ideas and concepts learnt in class to real life. Working in the team has given me invaluable shop-floor experience. The superb guidance from my seniors and alumni will always be cherished.
Gearbox Gagan Makhija
The main use of a gearbox in any car is to bring down the high speed of motor to appropriate road speeds while increasing the torque. The two main events at the competition are the acceleration run in which a given distance needs to be travelled in least time and endurance run where 22 laps of 1km each are to be completed in least time. Both the events demand high acceleration of the car. An optimal gear reduction ratio has to be decided for the best acceleration performance. The optimal gear ratio was calculated to have best performance in the acceleration run. This gear ratio came out to be 8. After further considerations of constraints from the side of gearbox manufacturing, 7.85 ratio was finally fixed. This means that the speed of motor is always 7.85 times the speed of wheel. The main consideration for designing the gearbox for this ratio was the weight and space of the gearbox. A regular planetary gearbox similar to previous year with such a high gear ratio came out to be very bulky and big. So we decided to go for compound planetary gearbox with stepped planet gears. This gearbox was very good in all aspects of weight and space.
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But due to high precision requirement, it could not be manufactured. We had to think of a better design which could sort all these issues. We finally came up with a hybrid design. Here the reduction is achieved in 2 stages. First there is a single step reduction and the reduced output from this is supplied as an input to the sun gear of planetary gear train (also called epicyclic gear train). This resulted in an axis shift and the input and output axis were no longer along the same line. This had the problem of elongating the gearbox. To reduce this shift, we used an internal gear as the output gear for single step reduction.
This design served all our requirements of weight, space and manufacturing. Also this gave a freedom in integration to have non concentric motor and wheel. Coming up with this design and building the entire gearbox around it was a once in a lifetime experience. It took a lot of brainstorming and creative thinking to finally build a gearbox which is compatible with the car and that is what made it so interesting. I thoroughly enjoyed the design phase. IITB racing is the best thing that happened to me.
Design and Improvements: Mechanical
Wheel Assembly Ajinkya Bhagat
In the world of motorsports, mass is our biggest enemy- the more the mass the less is the acceleration and poor is the performance. So the design engineers try to shave off every possible gram they can from each and every component going on the car. With this philosophy of light weight components the team decided to optimize components for minimum mass without compromising on strength. This was achieved by using the optimization solver called ‘Optistruct’ provided by Altair Hyperworks software. After reviewing a number of success stories of optimization by many Formula Student teams using Optistruct the team decided to make full use of it this year. The wheel assembly components are a part of the unsprung mass of the car.
For a race car it is always desirable to have a light-weight unsprung mass because less mass means less inertia, more responsiveness, better handling and better performance. This was the driving force towards optimizing the wheel assembly components for minimum weight without compromising on strength. Using Optistruct we achieved weight reduction for each and every component of the wheel assembly. The most challenging parts during the optimization process were the correct assignment of the FEA variables such as loads and boundary conditions, the optimization problem variables such as the design variable and various manufacturing constraints and the interpretation of the final optimized design. A number of optimization runs were sometimes required to get a valid manufacturable optimized design.
COMPONENT
THIS YEAR’S WEIGHT
LAST YEAR’S WEIGHT
The front upright The rear upright
681.41 grams 705.76 grams
789.10 grams 760.17 grams
% WEIGHT REDUCTION 13.65 7.16
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Pitstop, January 2015
Mechanical Powertrain Nilesh Bansod
With the mission of getting a position in the top 20 at FSUK 15 we set out to revamp our powertrain to match the best in the world. This year we decided to make the much discussed move from brushed DC motors to brushless DC motors. We also adopted new, more compact cells to help us size and shape the accumulator such that it simplifies rear chassis packaging. The aluminium honeycomb chassis and the cooling requirement of the new motor and controller pair meant that we had a severe space crunch in the rear chassis. As such mounting the motor and gearbox on the upright was considered but was deemed not worthy of the risk associated with all ready so many new elements in this year’s car. Finally after much thought we adopted a unique design where the gearbox was mounted from outside the chassis while motor was mounted inside the honeycomb frame. After choosing the best available motor, the next task was to design the optimum gearbox for this motor. The optimum gear ratio was calculated at 8 applying well tested algorithms. The models also confirmed that this year’s design could actually be traction limited. A diffuser was put in place to take care of the same. The gearbox design was an intense process during which more than six different designs were considered and analysed before we finally zeroed in on a
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hybrid gearbox which minimized the weight while keeping in mind the space constraints which arise in case of a gearbox which is situated between the A-arms. Plans for a compound planetary gearbox had to be cancelled due to inadequate manufacturing facilities in the country. The hybrid gearbox has a step gear with an internal gear as the driven gear to reduce the overall size of the gearbox. This followed by a planetary gearset and all the components including the casings were optimized to save weight. The powertrain team also had to design a cooling system for the motor and motor controller.
A pump and fan were decided according to the cooling requirements of the motor and a radiator was designed in conjunction with a manufacturer of custom automotive radiators. The design phase was a thought-provoking and enjoyable experience like no other. The design looks splendid and I am looking forward to see it materialize into a beautiful machine. We are already looking in to possibilities like 4WD, custom motors and in-hub powertrain for next year’s car.
Design and Improvements: Electrical
Electrical Subsystem Accumulator Meet Patel
One of the most important part of the powertrain is the accumulator. The accumulator is the part where all the energy is stored. Because the amount of energy is quite large, it can also be a very dangerous part if not handled properly. The accumulator will therefore be divided into several modules in order to keep the voltage at a safe level during most of the assembly phase. The most challenging task while designing the accumulator was devising the cell interconnection mechanism as the cell tabs are very small and very little separation is present between the two tabs of the cells thereby making the assembly quite risky. Therefore, we will use 3D printed Nylon PA 12 material components, which will act as insulating barrier between the two tabs and also provide firm strength to hold the cells in their place in the modules. Moreover, highly conductive copper busbars are used to compensate for high current passage through the small size of the cell tabs.
Because of high current, the accumulator will get hot, therefore a cooling mechanism is introduced for increasing the efficiency and reducing the heat generation in the pack. Weighing the pros and cons of different types of cooling mechanism, we have decided to go for Air cooling for our accumulator by incorporating eight cooling fans in the accumulator container – two for each section.
The accumulator container is made up of woven carbon fibre material, in association with ST Advanced composites, to reduce the weight and thickness of the container. It has been designed to withstand high accelerations of 20 g vertically and 40 g in lateral as well as longitudinal directions, for a safe attachment of the accumulator and its components to the car.
Battery and BMS Meet Patel
Battery: Being the Power supply for the whole tractive load of the vehicle, Battery (or Accumulator as some might call) needs to be very carefully designed. The task begins with analyzing the previous data and computing the total amount of energy and the power requirement of the events of the competition, the reason being we would not like to carry any extra weight than is necessary. • Energy required is the capacity of the battery i.e. from the time of complete charge to the state of complete discharge, the battery must be able to complete the entire event at a stretch. • Power is the power that we provide to the motors which appears at the wheels. Unlike energy, Power has an upper cap so as to normalize every car at the event. Once you figure out how much of what you require, then comes the strenuous task of searching for individual cells to make the Battery.
The one with the highest energy to mass ratio and least total weight wins the spot. (We are using 288 cells in 96S3P configuration, each being 3.7V 6.25Ah capacity and weighing 126 gram, giving a total of 352V and 23.98MJ Energy.) Battery Management System (BMS): Every High Voltage storage device needs a safety gear to cut off the power if at all and when anything goes wrong. Cells being of Lithium Polymer chemistry,
proper handling is utterly important. A BMS essentially monitors the cell voltages their ambient temperature and keeps track of all the activities and ongoings of the Battery. Expansion in this direction requires taking a step into the unknown as it is not an easy task, transferring from off-the-rack system (as used in the previous year – Elithion Lithiumate Pro) to a customized system (underway this year – LTC6803-4).
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Pitstop, January 2015
Data Aquisition and System Integration Jainesh doshi, Shashank Gangrade As the name suggests, this system acquires the data from all the sensors installed on the car. An obvious question is why we need this system. And its answer is hidden in the reply to the next question, on how do we “design”. Designing a car requires huge amount of data (very crucial for mechanical design engineers) in order to ensure its reliability. Thus it’s the fundamental requirement for any design engineer which is fulfilled by the Data Acquisition subsystem. Apart from this, DAQ helps in real time monitoring of vehicle parameters and helps a lot in debugging of onboard electrical systems. This year, the Data Acquisition system acquires the following data: RPM, Throttle, Brake, Steering, Yaw rate data, Suspension press, Motor temperature, Brake pressure, Battery Temp, LV (low voltage) battery voltage and current and diagnostics data from LV Safety system. All this data will be floored and processed in the BeagleBone Black, (a single board computer we are using for processing our data) which in turn is sent wirelessly to the remote substation to analyze it in real time. This year we have focused on software end of our system, and we are implementing parallel programming for the first time. Various data streams from ports of BeagleBone Black are acquired in parallel. We are running the different
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processes independently for streaming data from the various sensors mounted on the car. This allows us the optimal usage of the processing power of the Beaglebone black thereby greatly improving the accuracy of monitoring the crucial parameters of the vehicle. We would be using hybrid parallelism in order to have data acquisition, processing and transmission working independently. When you receive an electric signal from point A to point B, you would certainly think of a copper wire in between. Our work starts here. We have to think of what type wires gauge are needed and then how to route them in the car. And wait this definitely doesn’t mark the end. Once we have got the wiring right, their ends are still left, then the connectors and then their integration in enclosures. The idea goes on, and this builds up a subsystem called ‘System Integration’. System Integration does not involve mere wiring of two ends, rather it calls for a neat integration of systems that should not only be technically sound but also artistic. The story doesn’t end here, the system should be mechanically robust and should satisfy industry standards of waterproofing. Compared to previous year’s design, we have done a lot of work in harness simplification, thus instead of lots of untangled wires their will a specific buch
going from point A to point B, which helps a lot in debugging as well improving the overall aesthetics. Also we have replaced last year’s bulky sensor connectors, with much smaller better sensors connectors. and Combined connectors have been used at at DASH and Side Panel instaed of individual connector for each Switch/Led. Learning from last year’s mistakes connectors boards will have a much better mechanical robustness, and each of the connector board will be supported by several studs so that the force doesn’t come on connector solder. Two high voltage connectors have been combined, thus resulting in ease of handling and better integration.A pump and fan were decided according to the cooling requirements of the motor and a radiator was designed in conjunction with a manufacturer of custom automotive radiators. The design phase was a thought-provoking and enjoyable experience like no other. The design looks splendid and I am looking forward to see it materialize into a beautiful machine. We are already looking in to possibilities like 4WD, custom motors and in-hub powertrain for next year’s car.
Design and Improvements: Electrical
Low Voltage Safety Utkarsh Sharma
When it comes to high speed race cars, powered by High Voltage batteries, safety becomes the most important factor. The Formula Student UK rulebook requires all the teams to fulfill some safety norms and the Low Voltage Safety Electrical Subdivision comes into picture, right then. Low Voltage Safety system makes use of various sensors placed on the car to detect errors and cut off the 400V connection between the Accumulator and the Motor Controllers, which are used to drive the motors. The main aim is to stop the car from running with a
fault (which protects the driver and anyone in the vicinity of the car) and to protect anybody who touches the car from the High Voltage, by not letting the high voltage out of the accumulator, when there’s a fault. So suppose, if one of our battery cells starts drawing too much current, or gets too hot, or suppose our car crashes or if the brakes fail, our safety circuit quickly detects the fault and cuts off any high voltage signals coming out of the battery. 555 timers have been used in bistable mode to detect errors and 5-pin relays have been used as electrically driven
switches to react to those errors and cut off the Accumulator-Motor Controller connections. Inherited from EVo 3.0 is a noise-tolerant design with filters and appropriate pull-up/pull-down resistors in place. Another thing that has been incorporated in our System is it’s collaboration with the Data Acquisition (DAq) System. There’s an on-board Mini-AT microcontroller that relays all important data to DAq, as well as to the DASH, where there are LEDs on place to indicate any fault that occurs.
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Pitstop, January 2015
What’s New Chassis, System Integration and Composite Manufacturing Shreyas Tejawat
CHASSIS For a formula race car to go fast, it should be three things powerful, light and aerodynamic. To make the car light and aerodynamic the chassis should be as small as possible while still having sufficient roll stiffness and space to mount all the component. The team is building spaceframe chassis for past 3 years, and had optimized it so that no significant weight reduction was possible if we had made a spaceframe this year too. So the team decided to explore lighter designs. Considering various parameter like cost, final weight of the car, manufacturability in the institute, panel sizes available in the market etc. the team decided to make an Aluminum Honeycomb Monocoque Chassis. SYSTEM INTEGRATION System integration is the process of bringing together the component subsystem of the car into one system and ensuring that the subsystems function together as a Formula race car. In order to keep the rear chassis light and small an effective packaging of all the components is essential. Every component of each sub-system has its own constraints and which together with various inter dependent relations between these components forms a complex dynamics. Meeting the constraints of all the component requires many compromises and good communication between all the sub-systems. Considering various constraints we have come up with a unique system integration design. By mounting the gearbox outside and the motor inside the chassis we have created a lot of space for other parts. Placing all the electrical components on the top gives them very accessibility. COMPOSITE MANUFACTURING PROCESS: R&D In order to make the car lighter and faster the team is exploring various composite manufacturing processes, so that in the future the composite part can be made in the institute by the students with a cheaper price tag
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What’s New
Diffuser Design Divyanshu Sharma
As a car becomes better in terms of design and performance, aerodynamics begins to play a pivotal role in improving handling, especially on a FS track. The aim this year in terms of aerodynamic devices was the implementation of a diffuser for EVO4. A general FS car generates lift on its own and thus at higher speeds this can lead to loss in traction and slower cornering and braking. A diffuser is a device used to modify the underbody so that the car generates negative lift, or downforce. This helps increase traction with minimal gain in mass of car thereby increasing cornering speeds and allowing better braking. The diffuser design required setting up of Computational Fluid Dynamics (CFD) simulations to simulate the flow around the car and measure downforce and drag force generated. This involved three things: • Making a solid CAD model of the whole Car and diffuser • Running a simulation with this to get Force values • Post processing to study the flow and modify the design Each simulation took around 5 hours to complete. The initial iteration of the diffuser gave a coefficient of lift (measure of downforce) of -0.4. After 16 iterations the final design was arrived at giving a coefficient of lift of -0.9. In winter we plan to verify the CFD simulations with wind tunnel tests The design process faced a lot of difficulties due to a diffuser being added for the first time to the car. It required me to find workarounds to software problems which seemed trivial but proved to be difficult to get rid of. Having put in more than 200 hours of designing into the project and spending countless nights setting up simulations and solving errors, the final result has more than made up for all of it. The feeling of joy when a design change brought the lift down by just 0.1 is indescribable. Overall it has been a ride to remember and cherish for my whole life.
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Pitstop, January 2015
Energy Meter Abhishek Vishwa
Energy Meter, as the name suggests is an instrument to monitor the energy or power that is being supplied by the battery to drive the vehicle. Monitoring the amount of energy being utilized by the car is essential since a rigorous analysis of energy is required in order to design the powertrain system of the car. For example, the energy requirements of the car for which the battery is to be designed is calculated from previous year’s data of the endurance run. Until now, we were using the energy meter at the event only and the meter was provided by the FS people. So all the data of the performance of the car was retrieved by what they give us. Since we do not had the data of the car’s energy requirements, we did not knew until after the event that a great amount of battery voltage has been dropped across the internal resistance of the battery. Keeping the problem that we had last year in mind, we decided to design an energy meter of our own which would provide two benefits: firstly, we would know the data beforehand so that we can optimize the car’s performance, secondly at the time of event we can compare the two data’s one of ours and other one of the meter that they give us. We have used M-bed Microprocessor to monitor the current and voltage from the battery and then logging the corresponding data to SD-Card. For voltage measurements, we have used octo-coupler based circuit which will give the scaled voltage to be fed to the uP and current measurements are done via Hall Effect current sensor, both the voltage and current are then sampled by the microprocessor and then scaled up and then multiplied to get the instantaneous power and then these values are logged into the micro SD card for the future use and the analysis of the data so as to optimize the overall performance of the car.
Research and Development Improvements planned Manthan Mahajan
The plan of Research and Development subsystem of this year’s was aimed at working on different improvements possible for next year. Since major Improvements require investment of more time and in-depth research we started working on these improvements well before so that we have a prototype model of the car ready for next year. The biggest improvement in the next years prototype is design of an Individual wheel drive; commonly known as 4 wheel drive system. The motors available in the market do not suffice the requirements of a 4WD system for our car, hence custom motor design and manufacturing is one of the major advancements undertaken under R&D department, along with designing a motor controller, so that the driver input from the throttle can be converted to the parameters familiar to the motor; i.e. current and voltage. A research on the same topic suggested that transforming a rear wheel drive car into a four wheel drive car adds up to 25kg of weight in the car, keeping everything else the same. While on the other hand, even with this extra weight the cars acceleration times are on an average 0.6 seconds better that it’s rear wheel drive version, and has better controls. Another challenge that is considered in the R&D department is the integration of the wheel assembly and the powertrain assembly. This is a challenge for most of the subsystems as the wheel assembly needs to be compact, and so does the gearbox and motors. This year gearbox have been designed compact by taking help of advanced softwares such as Kisssoft, hence this experience would benefit in designing even more compact gearboxes for the prototype. The plan ahead is to work in synchronisation with few motor manufacturers so that the prototype can be as close as possible to the manufacturable standards. Also once the prototype is ready, then the team will be deciding whether or not it is possible to make this prototype into a product for next year based on other external factors
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Research and Development
Wing Prototype Design Vikas Garg
In the design of a race-car within a given class, a multitude of parameters such as vehicle weight distribution, engine power, and aerodynamics must be optimized in order to achieve maximum performance. Aerodynamics is among the most significant of these parameters, as the aerodynamic characteristics of a vehicle can dictate its strength in categories that greatly matter to automotive racing, such as top speed, lateral acceleration and stability under heavy braking. Aerodynamics of race car includes CFD, wind tunnel and vehicle testing. For a race car to become faster while cornering, more traction is required. The wing is a device that is designed to generate “Downforce” i.e. negative lift with a minimal gain in mass of car. This happens by the difference between pressure at lower and upper (higher) surface. Positioning of the wing is decided on the basis of hand calculation then designing required setting up of Computational Fluid Dynamics (CFD) simulations to simulate the flow around the car and measure downforce and drag force generated. This is done in the following way • Making a cad model of whole car and wing using solidworks • Running a simulation in ansys fluent to get the drag and lift values • Post processing to study the flow and modify the design Each simulation take more than five hours for a single element wing which increases significantly for multi element wing. As wing prototype is being made the first time it took a lot of time and in depth study of each parameters for designing. Working with the team helped me in learning a lot of softwares and use my theoretical knowledge in practical way. While designing I get to face a lot of real life challenges which I am able to do with the help of all team members.
Tire Modelling and it’s importance Chinmayee Panigrahi
Tires are what keeps the car on the road. By Newton’s third law of motion, the frictional forces provided by the tires provides motion to the car. Hence the characteristics of a tire are of great importance when designing the car, especially the vehicle dynamics. The tire are made of viscoelastic material and hence do not follow the Newtonian laws of friction. Each type of tire has its own characteristics and can be studied by semi-empirical methods only. One such method is the Similarity Approach adopted by the Pacejka model of the tire. The R&D department of the team took up the Pacejka modelling of the certain tires. Once this model is obtained, it will accelerate our performance in the competition. It helps us design a suspension and steering system that closely resembles the forces acting in real situations. It will also help us in choosing the tires to enhance or performance. It helps improves the designing of E-diff and the drivetrain. Currently, this model is being built in MATLAB. The experiments on the tires was done by FSAE TTC and the data was provided to the participating teams in Formula Student. The first step is to filter this data using best- fit nonlinear curves. Then, we use this curve to obtain the Pacejka Coefficients (rightly called the ‘magic numbers’). These coefficients help us model the lateral force, longitudinal force and aligning moment as a function of vertical load, inclination angle, slip angle and slip ratio. Having a custom built tire model gives a greater edge in the competition. Using it along with MotionSolve in Hyperworks, we can simulate exactly how the tire will behave in a track. This is the ultimate goal of the project.
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Pitstop, January 2015
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Pratyush Nalla Team Leader and Chief Organizational Head +91 9167 921 637 pratyush.nalla@iitbracing.org Atishay Jain Chief Marketing Manager +91 9821 405 905 atishay.jain@iitbracing.org