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This Just In.. Why Formula Student Electric? The CAE connection Glimpses of Prithvi 3.0 Innovation follows passion Research at IITB Racing
PITSTOP Follow us at www.facebook.com/iitbracing
Presented at the launch of
EVo 1
India’s First Electric Race
2 | Pit-Stop June 2012 “When you spend all of your time doing any one activity, that activity will become more important than anything in the world to you. If you give up so much of yourself for a quest, there will be a part of you which will live in the excitement of, and die in the failure of that endeavor. It is blissful and unfortunate, it is terrifyingly exciting, and it is endlessly adventurous. Our quest was one ...of racecars, and it is the same story foranyone who has ever been part of a Formula SAE team. We get addicted. We can’t help it. It is part of our love for engineering and our drive to be the best. People wonder why we are obsessed and we wonder why they’re not. Someone asks us why we spend70 hours a week building a racecar and we just look at them like a dog looks at a mime. Why? What do you mean,Why? Because racecar. That’s why.” ~Racecar by Matt Brown
Why Formula Student Electric?
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By Prateek Sharma
he IIT Bombay Racing team participated in Formula Student back in 2008 and 2009 with an IC engine powertrain. After a hiatus of 3 years, wherein the team built further competence by winning laurels at national competitions such as SAE India Baja, we decided to remark our entry into Formula Student 2012 with a newer and bigger challenge; the electric powertrain. This shift in technology was primarily envisioned keeping in mind the global impetus received for electric vehicles owing to reasons of energy security and environmental concern. India is many miles away from mass scale commercialisation of EVs, one of the major reasons being the prohibitive cost of technology. In our capacity as a student organisation, The IIT Bombay Racing team aims to develop indigenous technologies for the EV thus aiding their much anticipated growth in India. Formula Student provides the perfect platform and motivation for students to work on teams in a time bounded fashion and with a competitive spirit towards achieving a fixed set of deliverables. This new challenge has made the project a lot
more inter-disciplinary than before with major involvement of students from the Electrical and Electronics engineering background. It has also thrown open new vistas for development of technologies such as motor controllers, battery management systems, electronic differential, telemetry systems etc which the team intends to pursue in further versions of the car in close association with both academia and industry Lastly, the idea of a skull and cross bones sticker on the car was just too fascinating to avoid! Thats why, Electric! Specs of EVo1 Motors: Flat axial gap PMDC motors by Agni Motors. 16kW @ 72 V continuous, 30 kW peak (5 secs) Motor Controller: Programmable Kelly Controller KDH14451A Battery: Superior Lithium Polymer Battery (SLPB) from Dow Kokam BMS: Passive balancing Elithion BMS Aceleration: 0 to 100 kmph in 5 seconds Top Speed: 115 kmph Weight: 280 kg Power: 32 kW maximum Range: 35 km in one charge Charging Time: 3 hrs Energy Capacity: 9 kWh
Pit-Stop June 2012 | 3
THE CAE CONNECTION By Sonu Manjhi and Mudit Dandwate
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his year, the BAJA SAE India witnessed the lightest car to ever race on its tracks– our very own Prithvi 3. The long hours spent before computer screens earned us the ‘Lightest Sustainable Vehicle Award’ for being the lightest vehicle to complete 4 hours of the punishing Endurance Race. Prithvi 3 was 50kgs lighter than her predecessor and yet, more reliable. This high degree of optimization in design was possible only with the extensive use of Computer Aided Engineering (CAE) tools by all our design teams. Every single design was put through rigorous Finite Element Analyses (FEA) thus ensuring that nothing was over or under-designed. Driver safety is of paramount importance in motorsport. Various dynamic analysis carried out on our chassis ensured the safety of our driver in all impact scenarios. Long hours and heavy computations with tools like ANSYS Explicit Dynamics and LS DYNA ensured that our vehicle was impact–safe,without us having
to ram one prototype into a wall! Driver comfort is a prime concern, especially drivers have to endure 4 hours of merciless terrain and competition. A badly
designed chassis can make a driver nauseus every time he revs the engine. Comprehensive modal analyses performed by the design team
Torsional Rigidity Validation Setup
ensured that the natural frequency of the chassis never matched that of the engine, ensuring a comfortable ride. We are particularly proud of the fact that we not only analysed the design with CAE tools but also ran a battery of real world tests that validated those computer simulations. Our comprehensive, end to end approach–right from conceptualization to computer models, to real world testing, was highly appreciated by judges at this year’s BAJA SAE India. The efforts of the team in leveraging the power of CAE were recognized by ANSYS India who awarded us the”Best Use of CAE Tools” and a generous sponsorship. This award and association inspires us to push the limit in this journey of building highly optimized race cars. We would like to thank ANSYS India for signing on as our CAE partner. We look forward to a long association. We end with a speciaks thanks to our professors without whom we would’nt even know what stresses and strains meant!•
Accolades of P Baja SAE India
Highest number of aw 1. AQ Peer’s Choice Aw the best team by pe 2. 1st in ANSYS CAE for tools for engineerin 3. 1st in light-weight an lightest car at the ev 4. 2nd in Speed award
Prithvi 3.0 at a 2012
wards won by any team ward for being adjudged eer teams r the best use of CAE ng design nd sustainable ATV for being the vent to complete the endurance race.
6 | Pit-Stop June 2012
Innovation follows Passion: 2 way telemetry system a funny one. Two laps into the race, suddenly the GPS dot stopped moving. Everyone gaths engineering students, one of the cool ered around sombrely, “kya hua? Breakdown things we have always felt about the toh nahi na?”, when someone shouted, “koi F1 races is their pits and control room. nahi, engine chal raha hai, bas pileup hoga.” Tens of computer screens throwing up numAnd sure enough, the car started moving and bers and graphs and senior engineers staring the pits erupted with joy. To our neighbours, at data with rapt attention and giving instrucwe must have seemed like idiots looking at tions to the driver! Seems an interesting job, computer screens and grinning happily at the and so when IITB Racing decided to have tefalse alarm. lemetry on Prithvi 3.0, Then eight laps into the race, we realised we were super excited. that something was Wheel rpm Telemetry is a techwrong with the RPM Controller Board GPS Tracking Display sensor nology that allows numbers, the car wasn’t remote measurement running at its optiand transmission of mum. Hurriedly we information. Telemcalled Sharma in for etry is an important a pit-stop. Shanu and factor in F1, because Vallari ran to the car, it allows engineers to detected the fault in collect a huge amount the throttle cable and of data during a race. corrected it in two minThe data can then be utes. That intervention, interpreted and used based on the real-time to ensure that the car data we had procured is performing at its helped us gain at least optimum. We were Data Acquisition GUI Dashboard five race positions. We breaking new ground finally knew, what it implementing Telemetry on a Baja Vehicle. going to a war, you go in meant, to be race engineers! Building anything from scratch is never easy boys, you return back as men. Every moment Our “IITB-Racing” custom made data acand after many night-outs, wirings and short- is an adrenaline rush. Harshad Kunte, our af- quisition system has features that cover most circuits; our own Data Acquisition system was fable captain always used to say, “I am going to of the requirements in a race vehicle. We realin place. We were tracking four parameters: car pour a bucket full of water on you dashboard, ized the “economical” advantage of our 10,000 position (via GPS), speed, engine RPM and and its still gotta smile at me and say ‘Wel- rupee system when we saw BAJA organizers the g-forces on the car, all real-time. Also, we come’, coz that’s what the endurance race is all struggle with the reliability of their systems had two-way wireless communication with about.” He was not joking; two laps and our which had cost them lakhs. Further, with its our driver via his dashboard. We had just two sleek silver car looked dirty mud brown. But modularity and scope for expansion, it is an laptops in our “control room”, but looking at we were prepared and we did it. For four full excellent development tool. A well set goal all those graphs while the car was running in hours, sitting 1.2 km away, we could see at all is half done, and we wish to take this costfront of us was just amazing! moments, exactly where the car was, what it effective innovation forward and develop it Our system went through two and a was doing, how it was performing. into a full-fledged product. • half months of rigorous testing, numerous Two incidents come to mind. The first was
A
By Devdatta Patankar
iterations in which its performance and reliability were worked upon. Along the way it helped tune the CVT of the car and measure suspension forces as a part of the Design Validation Plan. But the real challenge was the fabled endurance race of four hours in the heat, dust and mud of those wretched Natrip tracks of Pithampur. The Baja Endurance Race is an experience of a lifetime. You pit a full year of engineering effort against the forces of nature. It is like
Pit-Stop June 2012 | 7
Research at IIT Bombay Racing: The Active Electronic Differential
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By Vallari Gore
or the 2013 edition of Formula Student Electric (EVo 2), the IIT Bombay Racing Team is looking forward to implementing its own active electronic differential. With this new feature, the car will be able to negotiate sharp turns while accelerating, let alone high speeds, without any wheel slipping. The driver is guaranteed to have a thrilling experience with better handling and quicker response of the entire vehicle. An electronic differential (aka E-diff) ; essentially consists of an ECU (Electronic Control Unit) which calculates the differential ratio (ratio of rpm of the outer and inner driven wheels) to negotiate the required turn. The controller then regulates power from the electric source so as to give the desired angular velocities to the respective wheel. In an electric vehicle with two motors driving the wheels independently, its job is the same as a conventional mechanical differential, except that it is much more compact, light, and accurate and has no rotational inertia. What is special about this E-diff is its “Active” adjustment of torque. Technically known as “Torque vectoring” under this scheme greater torque is applied to the wheel with greater grip, creating a torque bias in that direction (left or right). The active torque vectoring (variable according to requirement, updated in every time step) provides an additional yaw acceleration ie. better ability to corner while accelerating by giving an understeer or oversteer wherever applicable. This improves vehicle response.
Execution plan for implementing the E-diff on EVo 2 Electronics: The execution of the Active E-diff will comprise of developing a highly programmable controller and independent drive trains for the two motors. The electrical team is looking forward to fabricating its own electronic controller which will have features such as rpm and power control. The controller will take inputs of throttle and brake level, steering angle to find the differential ratio. Controls, Modelling & Simulation: Feedback of actual yaw rate from wheel accelerometers will be taken and used to calculate desired yaw rate iteratively. The control function will be a combination of these parameters,
weighed in a manner that would give minimum lap time and number of overshoots from the ideal track. This will be done by simulating sample runs of the car on the FS Silverstone track in MATLAB. A major challenge will be modelling the car in full detail, from head to toe. For this, we have started developing small
segments of the sub systems in Simulink. It requires modelling the geometry as well as the responses of various systems in the form of equations. This will then be combined with the crucial on-road data collected by the comprehensive Data Acquisition System installed on EVo 1 to formulate the driver inputs and track characteristics which will make the model functional. Mechanical (Transmission/ Chassis) Another challenge is designing a suitable transmission which is compact, light and allows the two trains to run independently. This also opens new and exciting avenues of integrating it with the chassis In order to build a reliable controller inhouse, it is essential to do ample physical testing of the control algorithms. For this, the team will conduct extensive dry testing on the powertrain of EVo-1, with this new configuration. Besides technical skill, the implementation of such an ambitious project would require careful planning and prompt implementation. The team structure includes students from the second and third year for execution and fourth and final year students to plan and supervise. We look forward to guidance and support from the institute and our sponsors so as to successfully complete this undertaking for a fruitful racing season in 2013!•
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