#2

Punjab Engineering College SAE BAJA 09

Anant Puri ,Abhishek Agarwal, Sanampreet Singh 4th year Mechanical

Ankit Ramuria, Chandra Mohan, Geet Srivastava, Saur av Rathi, Harish Puri, Harjinder Brar, Abhishek Kau shal 3rd year Mechanical

Copyright © 2006 SAE International

ABSTRACT

The objective of the competition is to pose the students with real-world engineering challenges of designing and manufacturing a safe, durable, economical, easy to maintain and comfortable to drive high performance off road vehicle within the limit of set rules, for mass production to sale to non-professional weekend off-road enthusiasts. Also, the student should generate financial support for the project, and manage their educational priorities. To achieve these objectives the vehicle was divided into major subcomponents like chassis, drive train, suspension, steering, braking and each component was carefully engineered, analyzed and tested. By examining the 2007 entry, the team was able to improve on many design features and enhance performance and drivability. The objective of engineering an inexpensive, rugged, single seat off-road racer was accomplished.

INTRODUCTION

Mini-Baja is an international collegiate design competition hosted by the Society of Automotive Engineers (SAE). The objective is to design, build and test a recreational vehicle intended for sale to the non-professional off-road enthusiast. The 2009 Punjab Engineering College Mini-Baja team consists of twenty one undergraduate students in Mechanical, Aeronautical and Production Engineering. This year, goal is to design and build a prototype racecar that in addition to winning races also is the most economical and reliable vehicle in the competition. However, the safety of a car is the facet that takes precedent through the forum of the design. . Creating an off road vehicle that is faster, more maneuverable, and easier to manufacture required improvements in every aspect of the car. Drawing upon multidisciplinary engineering knowledge, adherence to strict design parameters prescribed by SAE competition rules and varying levels of experience with recreational off-road vehicles, Team RPM design team sought to develop a prototype that balanced the primary objectives (safety,

durability, manufacturability and maintainability) with performance in an attempt to maximize competitiveness in each of the judged events of the BAJA SAE India competition.

The team employed engineering design and judgment to refine many of the successful design features of the 2007 entry, as well as develop several new subsystems that further improve the vehicle and meet the objectives.

These core systems include:

1) Rigid and lightweight chassis:

Based on SAE rules and regulations ad important design considerations ASTM 106 pipes of O.D. 1.25” and wall thickness of .063” was procured over suggested pipe of O.D. 1 “ and 3mm wall thickness. Several designs of chassis were modeled and analyzed in Catia to finally select a robust design. TIG welding has been done this time as compared to MIG welding which provides larger strength. Using ANSYS an appropriate calculation was carried to determine the impact and steady loads when the vehicle takes a jump of the terrain.

2) Four wheel independent non parallel double wishbone suspension. The designed components include: Double wishbone suspension are used because of its simplicity in manufacture and also because it provides much flexibility in Toe and camber adjustments. U – Arms are manufactured from seamless pipes because it provides more working space and also allows the shocker to be mounted near the ball joint so that minimum bending moment is applied on the arms. Subsequent analysis on Catia enabled us to identify the stress points in front and rear arms and therefore rear U – arms are made out of more bending stiff material. Shackles are made out of square pipes which provide better alignment and better bending stiffness. It also provides more surface area contact as compared to sheet metal shackles therefore welding is stronger in the former case.

The Procured components include the Fiat palio rear dampers because they are pneumatic and hence their response is better as compared to hydraulic dampers used last time. The springs after much iterative process finally decided to use Maruti 800 springs as it in rear and 1 coil les in the front. The maruti 800 springs performed best under rolling , bumps in test runs as compared to Indica , LML springs. Few other custom made springs buckled during test runs. The C.G height is 21” and ground clearance of the vehicle is 11.5”. Various force calculations and spring rates, wheel rates and natural frequency was predicted by using Catia which helped in predicting the performance of shockers. 3) Power Train: Massive amount of improvement has been done in this subsystem of Baja09. The procured component included LGA 340 engine along with M&M alfa transmission and differential which was common for all the teams. Since incorporating major changes in these systems was prohibited by SAE therefore we used custom built drive train. This year chain drive mechanism has been selected over direct coupling of last year to incorporate gear ratio for generating more torque out of the system and also to centerline the C.G. of the vehicle. The designed components included Sprockets, transmission shaft, differential coupling, drive shaft, stub axle, rotor hub, rim hub, chain tensioner and knuckle. The custom made wheel assembly is much lighter than the previously used maruti 800 assembly. All of the above components were first designed and subsequently analyzed in Catia for stresses developed under load conditions. 4) Four wheel disk brakes: We have procured Honda Aviator Discs and Caliper because they provide sufficient braking force and are reliable. Also, they are compact, light weight, easily available and fit well within the rim (12X6”). We have used distributor to distribute brake fluid in 40:60 ratio in front and rear tires respectively in accordance with the weight distribution of the vehicle. The reverse Pedal actuation system has been designed as it requires less braking effort. The prediction test to check the performance of brakes was done on lathe machine where for different speed and torque the braking was tested. 5) Rack and pinion steering with modified Ackerman geometry: Rack and pinion system was preferred over other systems because it is more reliable, gives + feedback, easy availability, longer life. The centre rack and pinion was self designed and made by modifying maruti esteem rack. The tie rods were also modified in length according to our requirement. The steer ratio of 9:1 was obtained by iterative process of changing rack positions and Ackerman arm settings in Catia which is much better than previous year’s ratio of 12:1. Rear tie rods are also used to compensate for manufacturability tolerance so that Toe settings can be changed as per needs later on.

Bump steer, roll steer v/s wheel travel graphs were plotted using vehicle dynamics software to predict performance under riding conditions. 6) Safety equipments: The procured safety equipments include Seat belts, arm and neck restraints, helmet, fire extinguisher, reverse and brake light of ratings as asked by event co-coordinators. Proper padding and crash test analysis of chassis was done in ansys.

MAIN SECTION

STRUCTURAL DESIGN

The chassis is the most integral part of any race car due to its interaction with every system on the car as well its primary and most important role, keeping the driver safe. The roll cage must provide a 3d space around the driver and should be designed and fabricated such that there is no failure of cages integrity. With this in mind the 2009 frame was designed as per SAE directions providing necessary clearances, focusing on safety and ergonomics first, along with strength and durability, while minimizing weight, retaining manufacturability and attractiveness.

Fig 1 – Frame concept scoring matrix

The chassis was designed using CAD software and a finite element analysis of the vehicle was done to locate areas that experience the highest loads under a variety of loading conditions. Using ANSYS, an appropriate calculation was carried to determine the impact and steady loads when the vehicle takes a jump of the terrain. From the strain data obtained, and after considering the fatigue properties, weld ability, and the heat treatment ability we chose to use commercially available 1.26” x 0.063” steel tube, which has 30% less linear weight than the specified 1.00” x 0.120” tube. This tube is stiffer and stronger than the SAE benchmark with minimal weight difference and reasonably priced. A finite element analysis of the chassis with the selected material was done to determine the strength and torsional rigidity of the design. These tools decrease waste, and increase productivity by determining all issues with potential designs before any material is machined.

Fig 2- Showing Improvement in strength level

The FEA analysis also helped in eliminating unnecessary trusses as compared to previous vehicle leading to fewer junctions and hence eases in welding operation. Bent sections have been used to improve tube strength and reduce structural units.

Fig 3 – The Final Chassis with shackles and trusses

Further improvement in vehicle dynamics has been made by adopting a favourable wheel base track width ratio of 1.23 compared to 1.07 last year which created difficulties in maneuverability during cornering.

As the vehicle is to entice a customer special treatment has been given to the ergonomics of the vehicle this year. Considering the long periods of time the vehicle has to be driven, comfort is a necessity. With this in mind the rear roll hoop is angled back at an 110º angle to provide the driver with the most natural sitting position possible. to provide the most possible knee room the side impact bars were angled out from the rear roll hoop before angling back in to meet the front bracing members. These changes have resulted in more leg, knee and head space providing comfort to the driver and directly influencing his performance.

Before the chassis design was finalized, a mock up of the frame was built out of steel rods. The mock up allowed the team to see the frame in 3D, as well as mock up the power train, steering, and brake systems to ensure that there is adequate space. To maximize the geometrical accuracy of the designed chassis, fixturing practices based on a single fixed coordinate system were used relative to a rigid table on which the chassis and all components were bolted. Through the use of this table and good fixturing

practices, the team was able to best assure that the chassis geometry, especially in critical sections such as the suspension pickup points, correlated closely with the design specifications.

Significant changes have been made to the rear of chassis this year in accordance with changes in power transmission. These changes have improved the aesthetics of the car giving it a grander and sporty look. The chassis has been TIG welded using a SS309 filler wire rod. A TIG weld produces a very strong, tight, and clean weld which further improves the aesthetics of the vehicle.

SUSPENSION SYSTEM

A SAE-Baja suspension system must satisfy the following design requirements:

• Control movement at the wheels during vertical suspension travel and steering, both of which influence handling and stability • Provide sufficient sprung mass vibration isolation to maintain satisfactory ride quality, while maintaining high tire-ground contact rate and low tire vertical load fluctuation rate to improve road holding and handling • Improve jumping performance by limiting sprung mass pitch displacement while the vehicle is airborne • Limit chassis roll during cornering to prevent roll-over, decrease roll camber, and therefore, decrease steering reaction time and slip angle induced drag forces • Prevent excessively high jacking forces by managing static roll center location and roll center migration • Limit lateral tire scrub to maintain straight line stability and minimize horsepower losses at the rear suspension • Control lateral load transfer distribution to influence both steady state and limit of adhesion oversteer/under steer handling characteristics.

Fig 4– Benchmarking and selection of suspension

Various suspension systems like trailing arm double Wishbone, McPherson strut were available. Independent Suspensions are preferable in the case of rough terrain Because they provide better resistance to steering vibrations and reduce un-sprung mass. Further Advantages of the double wishbone setup include easy Control of the roll centers by choice of the geometry of

The control arms, the ability to control track and camber Change with jounce and rebound, larger suspension Deflections, and greater roll stiffness for a given suspension vertical rate. Furthermore, the wishbone arm setup does not allow for the incorporation of kinematic camber compensation.

DESIGN OF FRONT AND REAR SUSPENSION

The front suspension and steering and rear suspension subsystems were initially modeled independently. Once the baseline geometry was designed, a full vehicle assembly was constructed to conduct a variety of relevant full vehicle simulations. The results of these preliminary simulations were used in designing suspension arms, drive shafts and tie rods. The approach to suspension subsystem development was done using Suspension Analyzer ver.2 which resulted in not only well tuned suspension kinematics but well-founded initial estimates for spring and damping mounting points. Subsequently a model in Catia was made to judge the various parameters like the camber at 0 deg – 10 deg roll was determined. Certain parameters were input in the analyzer and after the analysis front arm length “ rear suspension arms “ , toe gain .33”, camber gain -1.60” castor gain .02”, roll height 11.5” were obtained. An iterative process resulted in more optimized values. The front and rear suspension both give an estimate of 9”-10” travel according to motion ratio of .657 and .72 to utilize the full compression of 6” shocker.

SHOCKS:

Fig 5–The iterative process involved in spring selection Last year the Indica dampers and springs were used which were designed for 1000 kg vehicle. Therefore the springs were too stiff for a 400kg Baja and thus the springs were not under adequate initial compression leading to a bad control on vehicle over ditches and bumps. To overcome this problem this years vehicle uses Fiat palio rear pneumatic dampers in which modified maruti

800 springs are placed.We reached this result by undergoing an iterative process in which we got springs of various stiffness manufactured. Finally after many test drives we decided to use maruti 800 springs as it is for rear shocks and one coil less in case of front shocks. Out of the available lot the response of pneumatic Fiat Palio dampers was better than the hydraulic Indica Rear dampers. To assemble both system (Maruti Spring and Fiat Palio Damper) a custom made Bracket was fabricated.

Calculations involved in design:

Rear upper wishbone length = 375 mm Suspension mount = 270mm =>motion ratio = 270/375=.72 Similarly front lower wishbone length = 400 mm Suspension mount = 263mm =>motion ratio = 263/400 = .658.

A front suspension natural frequency of 2..00 and for rear 2.4Hz was deemed to be suitable. The wheel rate required to obtain this natural frequency was established using the following equation (assuming sprung mass of 113 lbm/wheel ):

s

wheeln m

kf =⋅⋅π2

The wheel rate for the front suspension was calculated to be approximately 42.43 lb/in and for rear 62.2lb/in. The relationship between wheel rate and motion ratio (MR) was used to deduce the location of the shock actuation point on the lower control arm.

springwheel kMRk ⋅= 2)(

From above formula the spring stiffness for front suspension is calculated to 98lb/in and for rear suspension is calculated to be two dampers were investigated, a Fiat palio damper 24” long with 6” of travel.

The free length of the front spring is 11” and that of the rear is 13”. The initial compression of the front spring I 55mm and 60mm for the rear. It is a spring of varying coil diameter with 90 mm near the brackets and bigger than this in centre.

From front view of car Angle of horizontal plane with arms: Front lower arm = -10 degree Front upper arm = 4.96 degree Rear suspension arms Lower arm = -17.77 degree Upper arm = -3 degree

Force calculation by force analysis by link mechanism (shown in the appendix ) with the help of vehicle dynamics book along damper axis. Front = 126 newton rear = 178 newton Displacement ratio = d1/d2 Angle correction factor = cos (alpha ) Installation ratio=d1/d2* cos (alpha)

Fig 6 – Camber v/s Wheel travel for front SUSPENSION ARMS AND SHACKLES

This year Double Wishbone non-parallel U-arms are manufactured. The U-arms as compared to previous years A-arms gives more working space and also allows the mounting of shocks on arms to be more near the ball joint so that minimum bending moment is applied on the arms. The arms are mirror image of each other i.e. the front upper left arm can also be used at upper front right place. This gives benefits like replacebility, easy and fast manufacturability because same fixtures can be used for left and right systems. The front suspension arms are made of 1” and 1.6mm thickness while the rear are made of 1.25” and 1.6mm thickness due to more load at rear similarly the ball joints used for front mountings are that of TATA SUMO and that used in the rear are that of JCB in accordance with the load distributions. This year Baja vehicle we have incorporated shackles made out of square pipe instead of sheet metal used previously. The advantage of using this indigenous design is that the plane of the shackles remain perpendicular to the pipe while welding. Secondly the bending stiffness of the square pipe is more than sheet which enables to bear more load. Lastly it provides more welding area than sheet metal shackles for better strength.

THE INNOVATIVE WHEEL UPRIGHTS

To improve upon the previous year, team chose to go with EN19 steel rotor hubs and rim hubs. Drastic weight reduction of 16kg in all was achieved in this years wheel assembly these custom built hubs are designed using cad analysis to reduce the stress and weight. FEA was performed in Catia. Extra material was removed and

subsequently analyzed in Catia to notice the stress points. Final design was selected by an iterative process to the suspension geometry. The upright provides good linkages for both suspension mountings, Ackermann arm and also a location for the brake caliper and provides a housing for CV bearings. The upright is symmetric and easy to manufacture. The one-piece design, is a proven tough unit, and brings together the suspension and braking system in a compact package that fits entirely inside the wheel. Through the upright the stock Piaggio splines to the CV joints. Drastic weight reduction of 16kg in all was achieved in this years wheel assembly because the knuckle, stub axle are custom manufactured as compared to last years maruti 800 assembly which was very heavy.

Fig 7 – The innovative wheel upright with axle, sus arm, caliper and Ackerman arm mountings STEERING DESIGN

Steering System

Cost (10)

Availability(10)

Maneuve-rability(10)

Weight (10)

Total

Rack and Pinion

7 9 8 7 31

Recirculati-ng ball

5 6 8 6 25

Worm and sector

5 4 5 5 19

Tractor mechanism (worm wheel)

7 8 6 5 26

Fig 8 – Benchmarking For steering system Innovation(Customized centre rack and pinion) A centre rack and pinion assembly is a major

requirement for an off road vehicle but it is not easily available. Instead of importing one the team decided to customize available rack and pinion system to save on the cost of the vehicle. A Maruti esteem rack and pinion system was taken and the longer side of rack was cut, bored and internally threaded before fastening it to the smaller section thus resulting in equal sections of 115mm(including threading) on both sides of teeth span of 165mm.

Fig 9 – The Custom made centre rack and pinion using maruti esteem rack and pinion. STEERING PARAMETERS

Overall steering ratio- The overall steering ratio is the ratio of the steering wheel angle to the average tire angle. In the previous year the driver had to turn the steering wheel 540º to bring the wheels from the center to lock. The driver had to remove his hand from the wheel at least once to complete the turn. The goal for 2009 was to allow the driver to use only 405º of steering wheel travel from the center to maximum wheel travel An overall steering ratio of approximately 9:1 or 0.0041 inches of rack travel per degree of steering wheel travel was accomplished by using a fast ratio rack and pinion steering system and suitable Ackerman arm geometry thus preventing hand-over-hand maneuvers.

Fig 10- Ackerman Geometry

ACKERMAN GEOMETRY

For all wheels to pivot about a common point the inner wheel must turn at a sharper angle than the outer wheel in reality, the tires must slip to generate lateral forces, so the outer tire should be steered at slightly higher angles than predicted by Ackerman geometry. The modified Ackermann geometry is 120% , resulting in the inside wheel turning 45º, and the outside wheel turning 29º. These were the targeted values from previous testing.

DRIVER COMFORT

Through simulation, it was determined that moving the rack rearward increases toe out and Ackerman effects while, moving the rack forward decreases toe out with steering motion. The final position of the rack is a compromise considering Interference with foot pedals and toe settings. Ergonomics were taken into account through the analysis of driver comfort in both steering wheel position and its rotation for maximum wheel angle. The steering column utilizes universal joints to place the steering wheel at a comfortable location and angle.

STEERING EFFORT

The steering wheel is a 13 inch outer diameter wheel to provide enough torque to easily steer the wheels in all conditions without fatiguing the driver. The column is supported by ball bearings, and split with two low friction sealed u-joint to provide smooth steering motion and minimize frictional losses. The higher ratio rack has inherently larger steering effort; however using a longer moment arm tie rod mount offset this effect.

Bump Steer

-15.0

-10.0

-5.0

0.0

5.0

10.0

15.0

-8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0

Bump ( i n)

Roll Steer

-6

-5

-4

-3

-2

-1

0

0 2 4 6 8 10

Rol l ( de gr e e s)

Fig 11 – Showing bump and roll steer graphs

BUMP AND ROLL STEER- Bump steer refers to the toe-in/out of front wheels with suspension travel. Any toe present would cause tire scrub and consume limited engine power. Roll steer is undesirable because it can make the steering response feel erratic. The location of the outer tie rod end was fixed by the spindle geometry, thus only the inner pivot location could be changed as per suspension geometry. Through analysis during the suspension design, the resulting 1.65 inches of rack travel were then used to calculate the location of a model tie rod point at the chassis . A distance of 17.12“ between inner tie rod pivots (eye to eye) was optimum for minimizing bump and roll steer..

STEERING RESPONSE-. The curvature of the camber vs. wheel angle profile can be attributed to approximately 6 degrees of static steering axis inclination (SAI), and a static caster angle of approximately 10.3 degrees. Caster and SAI result in a self-centering torque at the undriven wheels, which provide feedback to the driver.

SAFETY AND MAINTENANCE- Protecting the steering components was a priority, accomplished by using front bumper and running the tie rods between the control arms. Another priority was allowing for serviceability and adjustability. This was accomplished by creating a custom rack mount on which the rack is bolted, allowing for easy and quick removal. Jam nuts are provided to prevent rotation during operation. The whole steering column is removable using a splined coupler and a shear bolt at the steering wheel connection. This modular system allows any portion of the steering system to be easily accessible and serviceable . Dust boots were used at ball joints to prevent dust from entering rack. WHEEL STOPS -Wheel stops are required by SAE Mini-Baja rules. The maximum tire angles were limited to 45 degrees to prevent a rotating tire from contacting the suspension system.Rear Tie Rods- To prevent the large amount of tire scrub and straight line instability that had to be suffered last year due to change in toe settings rear tie rods were implemented.

RACK AND PINION

Based on the above requirements a rack and pinion steering concept was selected due to its simplicity, durability, and the availability of units with fast steering ratios. The advantages of a rack and pinion system are positive feedback and responsiveness to driver inputs. After considering many commercially available units, a rack having 2.5 turns lock-to-lock and 4.2 inches of total travel was selected. It provides an overall steering ratio of 9 when installed in the vehicle. A 13” diameter steering wheel is used to give sufficient mechanical leverage for the driver.

POWER TRAIN

The purpose of the drive train is to transmit shaft power and torque of the Briggs and Stratton engine to the rear wheels of the car. The 10.5 HP engine produces 14 ft-lb of torque at 3800 rpm. The objective for the Mini Baja

competition is to optimize the power delivered to the wheels regardless of the vehicle speed for the various competition conditions. High speed was desired for the acceleration and speed trials while high torque was preferred for towing and hill climbing events.

For the uniformity of the event, all teams are provided with a 10.5 horsepower LAMBORDINI LGA 340 engine, governed to a maximum speed of 3600 RPM, coupled with a MAHINDRA AND MAHINDRA transmission. Only slight modifications outlined within the SAE Mini-Baja rules are allowed, but through research it was determined that they would not significantly benefit engine performance. The aim of the team is to minimize the power losses to obtain maximum work output. To accomplish this goal the driveline was designed to allow for several different combinations of components of which chain drive design was preferred as compared to last years direct coupling of engine with transmission since a gear reduction can be given to the system for maximum power at same torque.

Fig 12– The Chain Drive system with chain tensioner To maintain the center line C.G. and desired weight distribution, the engine is coupled with a chain drive to Mahindra transmission. This is a flexible system to incorporate the gear ratio change at the time of testing to obtain maximum power at same torque. In chain drive design, engine has been mounted above transmission and both in the center line of the chassis. This design helps us to remove the problem of distribution of weight on either side of the car which was significant in our previous design of the car and keeping the center of gravity on the center line. Connected to the engine, a 13-tooth sprocket drives a 32-tooth sprocket on the transmission through a steel chain rated at 5400 lbs . The gear ratios of 1 and 1.1 have been designed as per the cad analysis and after few drive tests, a particular gear ratio has been integrated in the car. Although this design was initially very practical, it was susceptible to damage during any rear end impact and allowed the possibility of misalignments of the sprocket or chain may slip. To eradicate these problems the chain used is a standard duplex chain with 9.05 pitch. Also a custom made adjustable chain tensioner is incorporated to

keep the angle of contact of chain optimum and to take care of the slag ness which occur in the chain during usage. The test drives taken this time clearly indicate the improvement in performance of the vehicle as compared to previous year in terms of speed and acceleration.

INNOVATIONS IN DRIVESHAFTS AND CUPLINGS

FIG 13– THE EXPLODED AND ASSEMBLED VIEW OF THE COUPLING ASSEMBLY AND SHAFT ANLYSIS

For attaining maximum wheelbase and in order to achieve 43:57 weight ratio Mahindra differential coupling is replaced by a fully custom built differential coupling transferring power to the shaft of Maruti 800 as shown in fig. the maruti drive shaft is further welded to a bajaj drive shaft as the stub axle used has bajaj splines on it. This replacement is done to obtain more flexibility in the angle of operation as found in the cad analysis. Since the coupling of Maruti, which was used last time, was heavy, this time the light transport vehicle has been the frame of reference due to its rough and tough nature, light weight, compactness and ability to sustain shocks and load which are quite analogous with the ATVs. Through cad analysis the team modified the stub-axle design of Piaggio as it was found out that the bending stress in the axle of LTV was high at the region between the bearings resulting in the low life of the axle. This design was customized by reducing the length of that region hence increasing the durability and reliability of the axle. During the fabrication of the drive train a very common fault in the Bajaj autos was pointed that the drive shaft was not locked in the cup and only a movement of 9cm was allowed. This leads to a very common prevalent problem in Bajaj autos that the drive shafts usually come out while traversing in a little bumpy area. To overcome this problem a very simple solution was thought of making a groove and locking the drive shaft by inserting a ring lock in that groove.

Drastic weight reductions was achieved in this years Baja09 vehicle as compared to Baja07 vehicle. Last year maruti 800 axle,knuckle,calipers were used which made the system heavy and cumbersome, therefore the team this year went on to manufacture the stub axle and knuckle according to suspension geometry. Excess material was subsequently removed wherever necessary and carefully analyzed in Catia before finalizing the actual final design.

Fig 14- The maruti and Bajaj coupled drive shafts between non parallel U arms

These features combined create a vehicle that utilizes all of its power in a smooth, quick transition from rest to top speed, and insures minimal maintenance. By eliminating losses and creating a driveline that is versatile enough to handle almost any terrain, the team RPM Mini Baja vehicle is sure to be at the top of its class.

Fig 15 – Exploded view of the custom made wheel assembly

BRAKING SYSTEM

The goals for the braking system were

Reduce weight in the overall system, Increase reliability and improve performance.

Like previous year the team decided to go for installing hydraulic disc brakes on all the four tires independently but a lighter system was chosen to reduce power loss.3.8 mm thick and 210mm OD rotor discs of Honda Aviator had been used with. The brake rotor and caliper assembly is light and compact weighing but provides sufficient braking force for the event. As the knuckle and stub axle has been custom made rotor hubs and caliper mountings were also designed. To maintain geometrical accuracy of the design caliper mountings were CNC machined. To make efficient use of limited cockpit space, and increase leg room, a reverse actuated master cylinder pedal assembly with custom aluminum pedals and compact remote reservoirs was chosen for this year’s vehicle. This assembly allows the pedals to be mounted as close to the front of the frame as possible, while protecting the master cylinders, and utilizing virtually the entire length of the cockpit. The compact master cylinders with remote reservoirs keep the pedals as low as possible for improved foot space allowing the driver to easily enter and exit the car. Since the pedal assembly uses a 8.0” inch lever arm giving a 4 to 1 ratio of piston movement. Any driver of car will always feel safe and secure knowing the brake system is reliable and service free for years to come. The fluid lines used are easier to bleed and have been attached properly to the chassis to avoid interference with any moving member. The cut-brake enables the vehicle to negotiate much tighter corners resulting in better maneuverability and a vehicle that is more “fun to drive”.

Parameter Value Front Disk O.D. (mm) 210 Rear Disk O.D. (mm.) 210 Front/Rear Radial Pad Width (mm.)

28

Front/Rear Master Cylinder Diameter (mm.)

10

Pedal Ratio 4.0 Front/Rear No. Pistons per Pad

2

Weight of Vehicle (kg) 250 aprox Front Weight Bias Percentage (%)

40

Height of CG (in.) 21.0 Coefficient of Friction 0.45

Fig 16 – Braking analysis Parameters

TIRES AND RIMS

In an all-terrain vehicle, traction is one of the most important aspects of both steering and getting the power to the ground. Tire configuration, tread depth, weight, and rotational of inertia are critical factors when choosing proper tires. The ideal tire has low weight and low internal forces. In addition, it must have strong traction

on various surfaces and be capable of displacing water to provide power while in water.

Fig 17- Polaris AT-489 off road tires

Weight and size were the main criteria used when selecting the proper rims for the Mini-Baja car. The rims selected for all four of the wheels are ITP 10 x 6 with a four on 110mm bolt pattern. The dimensions of rims selected for all four of the wheels are of 12 x 6”. The 12-inch diameter of the rim will allow the brake components to fit inside the wheel. The 8-inch width created a sufficient traction patch for the low powered application while remaining at an acceptable weight. To make the rims completely functional in all cases, the four rims are made of aluminum to minimize weight. By reducing the width of the rim the inertia was directly affected, subsequently this also reduces overall weight. The rims are offset to optimize mounting on the suspension systems and allow for easier adjustment of vehicle track. For tires, several possibilities were considered to obtain the desired performance including the BKT and Polaris AT series. After many considerations the Polaris AT489 was chosen. As compared to 21” tire last year this year we purchased a 25” tire to obtain a good ground clearance and also top speed. The 25X8X12 tubeless tires are used by many Polaris off road vehicles. It was ideal in size and weight, coupled with an aggressive tread, which is designed to perform well in loose dirt and dry conditions, define the best tire for the situation. The rim inner dimensions were taken by the help of 3D co-ordinate machine which gave an exact inner profile which further helped in the wheel assembly. The weight of each Polaris tire (25 x 8 -12) including rim is 11.6kg.

CRAFTSMANSHIP

SUSPENSION Meticulous care was taken in manufacturing of suspension arms as they play a pivotal role in vehicle dynamics. To maintain geometrical accuracy of the designed system all points were marked by single co-ordinate system relative to a fixed table and proper fixture were used. Each tube was manually notched, according to the required geometry, in order to maintain tight fittings and minimize the requirement for filler weld metal. The front suspension control arm tubing was bent using a ratcheting tube bender; care was taken to ensure smooth, wrinkle free, high quality bends. Used ball joints at uprights which allow more articulation. We took necessary precautions and checked whether the coil spring does not become solid at complete bump travel. Chose shock absorber lengths so that they do not bottom out at full jounce travel. We used rubber bushings to ensure that wishbone moved freely and do not rub against attachment braketry.

Threaded end caps for the rear suspension inboard mounting heim joints, along with the threaded bosses for the front suspension ball joints, were end faced, turned down, drilled, tapped, and polished on a lathe. All mounting brackets were and bushings were turned down on a lathe. The tie-rods consist of a left hand male threaded bosses and a right hand male threaded boss welded on the inner end and outer end respectively, of the tie-rod tube. Female threaded heim joints are used as the inner tie-rod ends and female threaded ball joints are used.

CHASSIS Frame construction was a time consuming process, requiring patience and attention to detail. A 3d mock up of steel frames as built before actual building of chassis took place. All tube end radiusing was done by hand, ensuring tight notches and minimizing filler weld metal to maximize weld zone strength. A ratcheting tube bender with several die sizes and radii was required to create the complex frame geometry. The chassis was TIG welded to ensure strong, clean weld beads, and all exposed tube ends were capped.

Fig 18 – The precision of setting pipes

BRAKES Proper assembly of disc brake system is very important to prevent power loss and getting faster response time. The caliper mountings were CNCied and TIG welded and system was assembled with extreme care to prevent any misalignment of rotor discs from required position. After installation of the system, adequate bleeding was done to prevent any chance of failure. POWERTRAIN The manufacturing of the power train components required close co-ordination of material vendors, along with contracted machine shops. The differential output Assembly holder casing was machined from 4340 steel. The differential gear carrier was machined on a CNC lathe to ensure that the bearing surfaces of the differential gears were accurate. Material was selected to minimize component weight without compromising function. The stub axle and the transmission shaft was manufactured from EN19 material whereas the sprockets , transmission shaft housing and knuckle are manufactured from EN8 material. Specific to the drive train system, one must ensure that the support bearings are carefully installed to prevent damage to the race way surfaces. Also, one must ensure that the drive axle, sprocket, and rotor hubs are installed with an indicator dial to reduce misalignments, and improve function. Therefore thrust bearing is placed near housing to bear axial load of the transmission shaft locking it from both the side.

SAFETY:

Drivers will experience fast pace, exciting racing without risking major injury as Team RPM meets or exceeds all of the minimum safety requirements composed by the SAE. Coordinators. A number of safety features have been installed to reduce the possibility of personal injury.

• Roll cage padding protects driver’s head from impact.

• An SFI rated brake light warns other drivers of deceleration...

• A DOT rated safety helmet and neck support protect the driver.

• Safety belt has been used to protect driver in case of clash and jerks.

• Arm and Neck restraint of SFI Rating have been used to keep driver adequately restrained.

• Reverse light and alarm has been implemented to warn the driver following the vehicle.

• Fire Extinguisher has been installed.

Extraordinary measures have been taken to make driving the Mini-Baja car as safe as possible. Experience and responsible engineering have yielded a near perfect safety record and driver confidence. To further increase the safety of the vehicle, all operators should be educated in the operation of the vehicle and

made aware of possible risks. An alert, intelligent operator of the Mini-Baja car should enjoy ride without great risk of injury.

SERVICEABILITY

The vehicle was designed with several considerations in mind. Among them Serviceability had a very high weightage because of a non-professional weekend off racer as the ideal customer in mind. The ease of servicing and maintenance provided in various subsystems is explained below SUSPENISON – All suspension components are easily accessible, and designed to be serviceable. Emphasis has been laid on using symmetrical parts front upper arms, front lower arms , brackets and all suspension mountings are similar and easy to manufacture and access thus easily replaceable in case of damage. Adjustability has been provided in shocker mountings.

Fig 19 – Adjustable shocker mountings

BRAKES

The standard automotive flares, fittings, brake pads and discs are readily available. The hard lines allow for inexpensive repair. Brake pads can be replaced without difficulty when required, and the master cylinders are easily accessed beneath their protective covering.

POWERTRAIN

The final drive ratio can be tuned to maximize performance by changing the easily accessible output sprocket of the gearbox. The open chassis at the rear of the vehicle allows easy access to any power train component. The modular design of the system increases the ease of component swapping. The drive axles are hub retained; compression rings have been used at the axle end gears to increase ease of axle disassembly. Furthermore, assembly and disassembly tools for the axle and wheel bearings are available as custom tools to aid in maintenance. By locating the fill/drain holes of the

gearbox and differential carrier in obvious and accessible locations make routine maintenance problem free.

Fig 20 – The rear wheel assembly, drive shafts and U – arms

STEERING

Mounting for rack has been bolted allowing for easy replacing of the rack. Dust boot has been provided to maintain smooth functioning of rack.

COCKPIT

Frame has been constructed such that the vehicle has full integrity. Dirt and mud inside the driver compartment is an unavoidable consequence of off-road driving. Thus, quick releasing body panel clips were incorporated to allow for easy access to those hard to clean places in the cockpit. Furthermore, easy cleanup is facilitated by the fully water resistant driver compartment, which can be quickly hosed down and drained.

FEASIBILITY FOR MASS PRODUCTION:

The vehicle boasts of its futuristic looks, smooth curves, grand appearance, ergonomics and aesthetics. Also it has been designed to be feasible for production on large scale by doing proper research on the design and development of every component considering this aspect. Manufacturability was a central feature to the design of each subsystem.

Materials used for fabrication of chassis, knuckle, suspension arms, body and various mountings are easily available in market and reasonably priced. Standard, tried and tested parts have been used for brakes, shockers, engine, transmission, steering and only slight modifications have been done which could be easily adopted in a production line. Selection of standard parts saves on the high cost of fabricating custom made parts.

The complete structure could be built by semi-skilled labor using simple technology and conventional methods for process like tube cutting, tube bending, tube radiusing, drilling, fixturing, tapping and welding. The manufacturing of knuckle, stub axle, rotor hubs, and rim hubs was accomplished by simple process like turning on lathe, keyway and splines formation using milling and slotting machines. These processes could be automated.

The caliper mounting, differential couplers which have been CNC machined for the vehicle will be cast for mass production run. The output drive shaft coupling of the vehicle is also better over its predecessor Bajaj auto coupling.

The gearbox, motor, differential and rear axle would be sequentially assembled onto the chassis on a production line.

CONCLUSION

An engineering project of such high standards provided us with a valuable opportunity for hands-on learning and experience with engineering decision-making. This not only honed our technical skills but also taught us how to financially and logistically manage and balance a first year project of this scale with all other academic requirements. Team Members from different engineering disciplines discussed and debated for long hours to select components for each subassembly of the prototype based on engineering knowledge gained through undergraduate level course work, keeping in mind the SAE criteria of safety, durability and maintainability as well as provide features that would have mass market appeal to the general off-road enthusiast such as performance, comfort and aesthetics. The team used extensive physical testing, hours of simulation and analysis, and prototype construction to maximize the performance of the vehicle.

Based on research, testing and background knowledge, the team predicts following performance of the car in all dynamic events.

Expected top speed - 65kmph

Expected acceleration - 100m in 6 seconds Expected mileage - 8km/litre Expected braking -

Expected weight- 250kg approx without driver

Further testing and modifications are to be completed in the coming days, in preparation for the competition.

Since the design process is never ending, after the event time will be spent analyzing the real-world performance of the vehicle and comparing this to earlier engineering calculations. Experience gained from the competition and testing will highlight areas that require design improvements hence the design and modification will continue well beyond the competition.

REFERENCES

1) Fundamentals Of Vehicle Dynamics by Thomas D. Gillespie

2) Book By Carol Smith – Tune to win on vehicle dynamics

3) P. Kenedi, P. Pacheco “Dynamic Experimental Analysis of a SAE BAJA Vehicle FrontSuspension”.

4) Dynamics of Mechanical Systems by Harold Josephs and L. Huston

5) An Introduction to Modern Vehicle Design byJulian Happian Smith

6) MAN – Vehicle Calculations

7) The Automotive Chassis : EngineeringczcPrinciples by Prof. Dipl.-Ing. Jörnsen Reimpell Dipl.-Ing. Helmut StollProf. Dr.-Ing. Jürgen W. Betzler

8) Vehicle Body Layout and Analysis by John Fenton

9) The Automotive chassis: Engineering Principles By:- Prof.Dipl.-Ing Jornsen Reimpell Dipl.-Ing. Helmut Stoll Prof. Dr.-Ing. Jurgen W. Betzler

APPENDIX – A

Vehicle Specifications Overall Vehicle Information

BAJA 09 Track Width 56”

Height 58”

Wheel Base 68”

Estimated wt with driver 320Kgs

Weight Distribution (F/R) 43/57

Ground Clearance ( Ride height) 11.5” Estimated Top Speed - Land

65KMPhs

Cost Rs 1.37 Lacs (approx)

Power/Drive-train

Engine Lombardini 338cc, 10.78H.P,OHV Gasoline powered

Transmission

Provided by Mahindra & Mahindra, regularly used in Mahindra Autos

Differential In built in M&M transmission

Drive Axles Maruti 800 and bajaj C.V Shafts ,custom built axle

Brakes, Suspension and Tires

Brakes Four-Wheel Outboard Hydraulic Disc Brakes

Suspension Independent Double Wishbone U arm

Suspension Travel 12“

Steering Rack and Pinion

Tires POLARIS AT-489 ,size – 25X8X12

APPENDIX - B

BRIEF COMPARITIVE PARAMETERS

SYSTEM BAJA 09 BAJA 07

CHASSIS COMPARISON Chassis Material ASTM106 A108 Track width(inch) 56 54 Wheel Base(inch) 68 54

Ground Clearence(in) 11.5 8 Height(inch) 58 55

SUSPENSION COMPARISON Suspension Non // Double Wishbone Non // Double Wish bone

Suspension Arms U – Arms A – Arms Damper Fiat Palio Rear Pneumatic TATA Indica Hydraulic

Travel(inch) 12 11 Shackles Made from 1”X1” Sq pipe Made from 4mm Sheet

Spring Modified Maruti 800 springs Modified Indica Springs Ball Joint JCB- rear and SUMO- front Maruti 800- front&rear

STEERING COMPARISON Type Centre Rack and Pinion Centre Rack and Pinion Rack Customized Maruti Esteem Customized Maruti 800 Ratio 9:1 12:1

Tie Rod Modified Maruti Esteem rod Modified Maruti 800 rods Ackerman Arm 5 cm 7cm

DRIVE TRAIN Engine LGA340, 10.78 H.P LGA,9H.P

Transmission Mahindra Champion Alfa Mahindra Champion Alfa Power Transmission Chain Drive with 1:1.1 ratio Direct Coupling

Drive Shafts Maruti800’s coupled with Bajaj auto’s drive shaft

Maruti 800

Axle Custom Made Stub Axle Maruti 800 axle Knuckle Custom made Maruti 800 knuckle

BRAKES Disc Honda Aviator Maruti 800

Calliper Honda aviator Maruti 800 Pedal Ratio 4:1 6:1

VEHICLE DYNAMICS Kingpin Inclination 7º 6

Scrub Radius 33mm 16mm Castor Angle +10

Camber -2º Front , 0º Rear C.G Height(in) 21” 17”

TYRES AND RIMS Tyres Polaris AT489 (25X8X12) Baja Trax (21X7X10) Rims Polaris Rims (12X6) Maruti 800 rims

APPENDIX – C

CALCULATION OF C.G. CO-0RDINATES

APPENDIX - D

Fig – Force on rear shocks using Catia.

Fig – The Billa Vista Preliminary Spring Rate Calcu lator showing calculated prig rates of springs used

APPENDIX – E

Fig. Camber Vs Wheel travel for front Fig. Camber Vs Wheel Travel for rear

Fig. Front Roll Center Movement Vs roll center ht. Fig. Load Vs compression for Spring Stif fness

Bump Steer

-15.0

-10.0

-5.0

0.0

5.0

10.0

15.0

-8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0

Bump (in)

Toe

in (

deg)

Roll Steer

-6

-5

-4

-3

-2

-1

0

0 2 4 6 8 10

Roll (degrees)

Ste

er (

deg)

Fig. The bump steer curve Fig. The roll steer curve

APPENDIX - F

Fig - Fig – The indigenous wheel assembly with U arms

Fig – Custom Made Stub Axle with rotor hub Fig – Square pipe shackles TIG welded on C hassis

Fig – Transmission Shaft Fig – U – Arms manufactur ed using fixtures

APPENDIX - G

Fig - CNC machined Cross Rim Hub Fig – The Chain Drive mechanism wit h chain tensioner

Fig – Chassis inverted Fiat Palio Pneumatic Damper Fig – 3-D Co- ordinate Machine to take inner Dimension if rim

Fig - Side View comparison of Designed vehicle in Catia and the Final fabricated product

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