Atv Design Report

ABSTRACT

The objectives of the mini-Baja competition are to design and manufacture a “fun to drive”, versatile, safe, durable, and high performance off road vehicle. Team members must ensure that the vehicle satisfies the limits of set rules, while also to generating financial support for the project, and managing their educational responsibilities. This vehicle must be capable of negotiating the most extreme terrain with confidence and ease.

The 2012 SRM UNIVERSITY Mini-Baja Team, THE CONRODS met these objectives by dividing the vehicle into its major component subsystems. By examining the 2011 entry, the team was able improve on many design features to better meet the stated requirements. Function Diagram (QFD) to determine which parameters were the most critical. These key parameters ranging from most critical to least critical are safety, reliability, low cost, ease of operation and maintenance, and overall performance.

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TECHNICAL SPECIFICATIONS:

ENGINE Type Displacement Compression Ratio Max Power Max Torque DRIVE TRAIN Transmission Gear Shift Mechanism SUSPENSION Front Suspension Rear Suspension Ground Clearance Shocks and Springs Front Susp. Travel Rear Susp. Travel WHEELS Front Tyres Rear Tyres BRAKES Working Fluid Type Pedal Ratio M C Bore Dia W C Bore Dia Brake Disc Dia STEERING Type Mechanism Steering Ratio Lock to lock angle 4 Stroke, OHV,B&S 304 cc 8:1 7. 5 KW @ 3600 rpm 18. 5 Nm @ 2600 rpm Mahindra Champion Alfa (forward Orientation) Sequential Double Wishbone Double Wishbone 11. inches Customized 5 inches 6. 5 inches 22*8-10 22*8-10 Dot-3 Oil All Wheel Disc 4:1 0. 8 inch 1. 6 inch 6 inch Ackermann Rack and Pinion 10.

INTRODUCTION&CONSUMER INFLUENCES THE CONRODS

BAJA SAEINDIA vehicle is designed as a prototype for manufacture by an outdoor recreation firm. The ideal vehicle is safe, simple and inexpensive. Additionally, the vehicle is attractive to potential buyers in both its visual appearance and performance. These characteristics are considered in design of the following major vehicle subsystems: frame, suspension, steering, and braking.

Before any design could begin, we had to understand exactly who our customers are and their needs. To gain this understanding, we did extensive research that included market survey and interviewing both professional and nonprofessional local off-road enthusiasts. With this research, we determined that our customers are the BAJA SAEINDIA event and non-professional weekend off-road enthusiasts. We felt it necessary to distinguish between the two to ensure that we followed all rules set by SAEINDIA INDIA and to accommodate the weekend off-road enthusiasts in a safe manner within the SAEINDIA rules.

With all necessary design parameters determined for each customer base, we were able to combine them for an overall list of design specifications that met all SAEINDIA requirements. We used these parameters to create a Qualitative 1|P ag e Turning radius 2. 7 meters CHASSIS/OVERALL DIMENSIONS Chassis Material IS 3074 CDS1 Tubular Frame Overall Length 2100 mm Wheel Base 1490 mm Wheel Track 1143. 2 mm Height of Vehicle 1520. 0 mm WEIGHTS Front Wheel Assembly 10 Kg Rear Wheel Assembly 11. 8 Kg Engine(with engine oil) 23 Kg Transmission(with 17 Kg lubricant) Chassis 55 Kg Dampers 8 Kg Expected Kerb Weight 260 Kg

TARGET SPECIFICATIONS: Parameters Speed Stopping Distance Acceleration Gradability Turning circle dia. Ground Clearance Emissions Values 40 km/h 7m 11. 6 seconds 82. 2% 5. 4 m 11. 6 inches BS III the planes created by the roll cage and the driver’s helmet. SAEINDIA also require a 3 inch envelope when a straight-edge is applied to any two tubing. Emphasis was placed on creating an easily manufactured roll cage with few parts, minimal welding and yet is still both light and strong, hence the numbers of bends were kept to a minimum.

Roll hoop Overhead members and Forward Bracing Members are one continuous bent tube. Lower Frame Side tubes are straight and are bent inwards to connect to the front suspension mounts. The Side Impact Member is a single tube with a single bend that encompass the car from the Rear Roll Hoop forward. The foot box of the vehicle is shaped by the LFS, SIM and straight tubes welded to the upper side impact tube forming a hexagonal front bulkhead taking into consideration the suspension design and reduction in dead space based on experience from the 2011 entry. A 3-D view of the car is shown below: FRAME DESIGN

OBJECTIVE & FRAME CONFIGURATION

The objective of the chassis is to encapsulate all Components of the car including a driver efficiently and safely. With a limited amount of power, the focus is primarily on the power to weight ratio of the vehicle. The only means to improve this critical parameter is to reduce the overall vehicle weight. Great care is taken in laying out the chassis. SAEINDIA requires each vehicle conform to a 95percentile male for all ergonomic evaluations of the design. The pertinent information is taken from “Body-space Anthropometry, Ergonomics and Design” by Stephen Pheasant.

Several key safety factors in the design process dictate chassis roll cage layout and foot box design. For the roll cage, SAEINDIA requires 6 inches of clearance measured from the inside of Principal aspects of the chassis focused on during the design and implementation included driver safety, suspension and drive-train integration, structural rigidity, weight, and operator ergonomics. The number one priority in the chassis design was driver Page | 2 safety. With the help of the 2012 Baja SAEINDIA Competition Rules and Finite Element Analysis (FEA), design assurance was able to take place.

Rear Impact Next rear, impact analysis was done while assuming 15,000N as the impact force. STRESS: SMX-172. 22 N/mm2 FOS:2. 43 MATERIAL SELECTION: Two materials were considered for the construction of the chassis: AISI 4130 and IS 3074 CDS 1. IS 3074 CDS 1 steel with an OD of 25. 4 mm and a wall thickness of 3 mm was chosen because it exceeds the bending stiffness and strength requirements of SAEINDIAINDIA which gives increased protection to driver. PROPERTY Tensile strength(N/sq. mm) Yield strength(N/sq. mm) Elongation on 50 mm G. L Density (g/cc) IS 3074 438 376 32% 7. 872 AISI 4130 760 460 27% 7. 5 Side Impact The next step in the analysis was to analyse a side impact with a 5000N load. As a side impact is most likely to occur with the vehicle being hit by another MiniBaja vehicle it was assumed that neither vehicle would be a fixed object. STRESS: 237. 49 N/mm2 FOS: 1. 77 It was found out that the bending stiffness and bending strength of IS 3074 CDS are greater than those of 1018 steel having a circular cross section of 25. 4 mm and 3 mm thickness LOADING ANALYSIS: To properly approximate the loading that the vehicle will encounter, an analysis of the impact loading seen in the various types of impact scenarios was required.

To properly model the impact force, the deceleration of the vehicle after impact is generally assumed to be zero. To approximate the worst case scenario that the vehicle will see, research into the forces the human body can endure was completed. It was assumed that this worst case collision would be seen when the vehicle runs into stationary, rigid object. Front Impact The first analysis to be completed was that of a front collision with a stationary object. In this case a deceleration of 20,000N was the assumed loading. STRESS: SMX-177. 81 N/mm2 FOS: 2. 36

Rollover Impact The Final step in the analysis was to analyse the stress on the roll cage caused by rollover with a 5000N load on the cage. The Loading was applied to the two upper forward corner of the perimeter hoop with a combination vector sideways and downward. The load was chosen to be on two corners as this would be a worst case scenario rollover. STRESS: 267 N/mm2 FOS:1. 57 FABRICATION To maximize the geometrical consistency of the fabricated chassis, all fixturing and measurements were based on a single fixed coordinate system 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 Page | 3 in critical sections such as the suspension pickup points, correlated closely with the design specifications. In addition, measuring from aFixed location minimized tolerance stack-up due to measurement error and component movement results. We have decided to fabricate the second hub since it has minimum weight and optimized FOS. *Material Used to manufacture the hubs-High Carbon Steel *Hardening Process Done-Cyaniding

SPACE IN DRIVER COMPARTMENT:

DRIVER EROGONOMICS Driver ergonomics has been our major concern during design of the frame and also during positioning of various systems in drivers cabin. Cabin is made spacious for safe and comfortable. All the cables and wires are routed properly so that they would not interfere with driver legs or hands. all the routings are done in design stage itself and ROH is raised to a suitable height so that it would give proper vision to the driver

DRIVERS VISION WINDOW: SUSPENSION

Objective: A Mini-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 over steer/under steer handling characteristics. The non-professional weekend off road enthusiast requires a vehicle which exhibits both safe, stable, responsive handling; and a soft, comfortable ride .

DRIVERS VIEW OF THE CABIN: Alternatives considered:

Several different types of suspension system were considered before selecting the independent unequal arm double wishbone suspension system for both front and rear. Unequal double A-arm: In the design, suspension is supported by triangulated Aarm at the top and bottom of the knuckle. Advantages: *Improved ride quality *Good road holding *Rigid links *More control over geometry *Wheel control is precise *Negative camber gain during vertical suspension travel. Page | 4 FRONT SUSPENSION Setting static roll Centre: A two dimensional sketch was made after estimating the Centre of mass of the vehicle on paper.

Various references were taken to make a 2D sketch these include: ? ? ? ? Track width of vehicle Front hub king pin axis inclination, king pin length, ball joint dimension Rim off set(for king pin positioning) Wishbone mounting point lengths rebound. Since we could not find springs that were less stiff than this we decided to go for the Auto springs as it satisfied our ride comfort requirements. A stiffer spring was required in the rear to achieve the coupling effect of suspension so as to convert the pitching motion into a bouncing motion.

REAR SUSPENSION:

The primary concern in designing the rear suspension was to get the maximum possible travel (jounce and rebound) such that the rear driving wheels were always kept in contact with the ground. The camber change in the rear wheels should be such that there is not much appreciable change in camber throughout the travel of the wheel. The other factor taken into account was that we were having issues with the rear suspension in last year’s design as it was observed that the drive shaft coupling was coming in contact with the lower wishbone in the rebound condition and this issue has been addressed and rectified in this year’s design.

The rear suspension wheel rate was fixed such that the natural frequency of the rear suspension is 20% greater than the front suspension thus providing a flat ride over bumps by converting the pitching motion of the vehicle to be converted into bouncing motion.

DAMPER SELECTION:

Method for selecting springs The process began by selecting an appropriate wheel rate for the front axle. A typical road frequency of 3. 7 Hz may be encountered at the competition. This is based on a vehicle speed of 40Km/h and a road surface with bumps spaced 3m apart. The natural frequency of the suspension should be kept well below 3. Hz in order to avoid any unwanted excitation. A front suspension natural frequency of 1. 20 Hz was deemed to be suitable. The wheel rate required to obtain this natural frequency was established using the following equation (assuming sprung mass of 72kg/wheel) . 2 ? ? We need to calculate the damping ratios for the front and rear suspensions. The design process will commence by iteration only. First we find the ratio for sprung and unsprung with respect to the model. Sprung mass was found to be 71. 456kg the sprung weight was determined while the sprung mass was 288. 54kg. The ratio is 0. 247. The natural frequency of the front suspension is set at 1. 2Hz. Weight on each front wheel is 57. 71 kg. The max force of damping is given by Fcd =2*Msp*wn. Critical damping force for the front suspension system is 1085. 73 Ns/m. For the un-sprung mass natural frequency would be Wn=((Ks+Kt)/Ms)^0. 5 The combined stiffness of tire and wheel is 53. 24N/mm. Amplitude ratios were calculated for a range of damping ratios. These amplitude ratios represent the ratio of applied displacement and the displacement that actually reaches the sprung mass.

Amplitude ratios were plotted against the ratio of applied frequency and natural frequency of the sprung mass. This graph shows the ideal damping ratio that should be used. This value as obtained from graph is 0. 7 which gives a damping co-efficient value of 760 Ns/m. In the similar manner the rear suspension has a ride rate of 1. 56Hz. The critical damping force is 1960 Ns/m. The graph of amplitude ratio vs frequency ratio shows an ideal damping ratio of 0. 7 the damping co-efficient is = 0. 7*1960=1372 Ns/m. ? fn ? k wheel ms

The ideal wheel rate for the front suspension was calculated to be approximately 40N/mm. 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. k wheel ? (MR) 2 ? k spring We need to set the motion ratio according to the wheel travel we require for our suspension. A travel of 50 mm was required and a list of springs were collected and measured for their stiffness characteristics. According to this calculation the motion ratio for auto spring A’s (Ks=58. 57N/mm) wheel rate (Kw=41N/mm) the motion ratio was 0. 8366. Travel of spring per unit wheel travel)The travel obtained by this spring was lesser than was required we could only obtain 26mm of travel in Page | 5 STEERING DESIGN: Objective of steering system in Baja vehicle ? ? ? To provide easy maneuverability of the vehicle over the undulating terrain. It must be durable to sustain the harsh off–road racing course. Less bump steer and return ability in steering Customer requirement:

DESIGN OF WHEEL HUBS

Our wheel hubs have been designed and fabricated after an extensive research. Effort has been made for minimum scrub radius and obtains the best possible wheel geometry.

Adams and Ansys have been used to Simulate and analyse the behavior of these hubs respectively. We have two major design concepts: 1. 2. 3. 4. Optimum sensitivity Low turning radius Minimum feedback Low cost and easy maintenance Basis of our design: We have decided to opt for a 400 degree lock to lock rack and pinion steering with Ackerman geometry. Helical cut teeth will be used for the rack and pinion due to the following advantages over spur gears: ? ? ? ? They take higher loads. They are quieter and smoother.

HUB 1 SCRUB RADIUS FACTOR OF SAFETY HUB

2 8 mm 4. 6 1460gm. 15 mm 5. 2 2506gm

Rulebook Constraints: All vehicles must be equipped with positive wheel lock? to? lock stops and adjustable tie rod ends must be constrained with a jam nut to prevent loosening Tie rod of vehicle should be secured by bumper in front or any other safety device in rear in order to avoid damage of tie rod during collision. WEIGHT Hence taking various factors in to consideration HUB 2 is considerd for fabrication and stress analysis is done on it.

ALTERNATIVES CONSIDERED: STRESS DEFORMATION

Rack and Pinion Good High Low Light 1. Extermely Simple 2. Gives good driving feel Recirculating ball screw Very High Low

The picture of the complete rack assembly Page | 7 Values No. 1. 2. 3. 4. 5. 6. 7. Item Symbol Formula Spur Gear 2 20° 11 zm/2 + H zm D cos? 35 22 Db 20. 67 23 24 Rack Module Pressure angle Number of teeth Height of Pitch Line Centre Distance Pitch Diameter Base Diameter M ? Z H Ax D

Adams results : CALCULATION OF FORCES ON RACK AND PINION

R=steering wheel radius = 165mm r=pinion pitch-circle radius t=number of pinion teeth = 6 p=linear or circular pitch =22mm E=input steering-wheel effort = 2 * 20N W=output rack load If the pinion makes one revolution; input steering wheel movement Xi = 2? Output rack movement Xo = 2? R = txp = 82. 86mm Therefore; Movement ratio (MR) = Xi/Xo=2? R/2? r=2? R/tp=R/r= 165/11=15 15= W/E, w=600N force is to be applied on to the pinion to move the rack. ? ? ? ? ? ? ? ? Ft = Transmitted force Fn = Normal force. Fr = Resultant force ? = pressure angle Fn = Ft tan ? Fr = Ft/Cos ? Here ? =20 degrees therefore Fn=194. 95NFr=630N Opposite wheel travel Fig 3: Graph 1: camber angle vs wheel travel Graph 2: roll centre height vs wheel travel Graph 3: wheel rate vs wheel travel Fig1:Shows the single wheel travel vs toe change and scrub radius

To reduce vibrations transferred to the chassis from the engine, it is mounted on rubber bushes. The drive shafts are welded properly so that they are inline and no vibrations occur during rotation. The gearbox is mounted firmly in such a way that there is a minimum contact between gearbox and chassis which means minimum transfer of vibration to chassis. The fuel tank capacity is 4 litres.  Fig2: Shows roll steer vs wheel travel Driveline Power is transmitted from the engine to the wheels in the following way Engine Stub Axle Chain Drive Wheels Gearbox Driveshaft

Opposite wheel travel fig 4: Graph 1:roll centre vs roll angle Graph 2: camber vs roll angle Graph 3: roll stiffness vs roll angle The Driveshaft consists of dowel pin on the gearbox side and rzeppa joint on wheel side . This design ensures transmission of power with minimal losses and allows transmission at longer wheel travel. Reverse engine orientation resulted in problem with weight distribution and increased vehicle length. Using the transmission in forward helped to shift the center of gravity towards vehicle’s center. Due to decreased reduction it also results in increased vehicle speed. It also provides faster acceleration and higher top speed due to this reason we decided to use the transmission in forward orientation.

To calculate vehicle speed at different engine speeds in different gears, we used the formula V= (2*3. 14*engine speed*radius of wheel/Gear ratio)*(60/1000) km/hr. The gear ratios obtained are: Chain Drive gear ratio = 28/28 =1 1083 818. 36 1708. 91 The following graph is obtained: Tractive effort is calculated by formula F=Engine torque*Gear efficiency/wheel radius The curves obtained are: ratio*transmission First Gear Second Gear Third Gear Fourth Gear Reverse Gear High speed for acceleration and speed trials. High torque for towing and hill climbing events.

It should be reliable and light weight. It should transmit power in any driving conditions. ? The gearbox operation should be smooth and easy for driving comfort. The engine used has low power to weight ratio, so its necessary to transmit power with minimal loss through drive train. It should be such that it can be easily couple with the engine. Alternatives considered: We had three options while deciding the transmission system cvt mated with Mahindra gearbox. A custom made manual gearbox. Use of Mahindra champion gearbox coupled with chain drive. 3000 2000 1000 0 0 2000 4000 ractive effort in 1st gear tractive effort in 2nd gear The maximum Tractive effort obtained is 2240N at 2600rpm in 1st gear. Providing an acceleration of 5. 6 m/s^2. The variation of full throttle power with road speed is shown below with different gear ratio Our previous experience with cvt had problem of belt slipping at high torque conditions. Also it resulted in increased weight. So we decided against using this. As we already had 2 champion Alfa gearboxes, we decided on using this gearbox alongwith a chain drive due to the following reasons: Reduced chassis width.

Can be easily coupled with the engine. Equal drive shaft lengths; increased ground clearance. Minimum rear overhang; better vehicle dynamics. 60 2nd gear 40 1st gear 20 0 0 2000 4000 3rd gear We had 2 options for the orientation of gearbox: A) Forward engine with engine in the front rear axle. B) Reverse engine orientation with engine behind of the rear axle. Total resistance of the vehicle at 3600rpm is found out by the formula R=k AW^2+KW+WsinO. Where k= coefficient of air resistance N-m^2. Page | 10 A=frontal area of the car, m^2. V= vehicle speed, km/hr. K=constant of rolling resistance.

W= weight of car,N O=gradient angle, degrees. The value of resistance comes out to be R=442. 64+2452 sinO. We put this value in formula RV/3600nt=power of engine By solving the above equation for o, we get o=33 degree at 2600 rpm in 1st gear. Stopping Distance Braking Efficiency Parameters Master Cylinder Diameter Caliper Diameter Brake pad height Diameter of the disc Co-efficient of friction of the brake pad Force generated by both the brake pads per wheel Braking Torque per wheel Weight of vehicle(with the driver) Wheelbase Height of COG Dynamic front axle load Dynamic rear axle load 0. 11 m 56% Magnitude/value 19. 05 mm 32 mm 27 mm 162 mm 0. 38 3431 N 1040 N 360 Kg 1397 mm 601. 3 mm 1780 N 1650 N 70 60 50 40 30 20 10 0 0 2000 4000 gradabilit y in 1st gear Gradabilit y in 2nd gear Gradabilit y in 3rd gear BRAKING DISTANCE VS SPEED: This shows that the vehicle is capable of climbing a 30 degree slope in 1st gear. This is more than enough for heavy off-road conditions. BRAKES: The criterion of designing the brake system, as stated by the rule book is that, all the wheels must lock simultaneously as the driver presses the brake pedal.

Our ATV consists of disc in all the four wheels, as disc brakes are safer, reliable and more effective than drum brakes. Brake circuit used is Independent in order to ensure safety We are using rotors of the same diameter for all the four wheels. Special ATV rotors and wheel calipers have been imported from Taiwan and Tandem Master Cylinder of Maruti 800 is being used. Brass linings and Rubber (flexible) brake hoses are being used in the circuit. A Pro-E model of the brake circuit in the vehicle Brake specifications Force of the driver on the pedal Average circuit pressure Pedal ratio Deceleration 400 N 5. 16 N/sqmm 4:1 5. 5m/sqsec

BODY PANELS: The criteria for selecting the material for body panels firewall and belly pan was as follows:

Safety of the driver Rulebook constraints Weight of the panels Recyclability of the material used Cost of the material Serviceability of the vehicle INNOVATION: Solenoid Operated Fire Extinguisher The body panels are divided into three parts: Side panels, front bumper and rear panels. For increasing the serviceability of the vehicle, the panels and front bumper have been mounted using easily detachable clips.

The materials used for the firewall and belly pan are 1. 5mm thick aluminium alloy sheets, which are both lightweight and 100% recyclable. For body panels, 0. 2mm thick sheet metal is used. It is also 100% recyclable. We have decided to incorporate following safety features in our vehicle: All disc brakes with cross circuit. Corrosion resistant stainless steel bolts with nylon lock nuts for all fastenings. fire extinguishers. First aid kit Spill guard and splash shield for fuel tank. Four point harness seat belts. Wide open throttle stop at the pedal. . Reverse alarm and brake lights. Two 01-171 Ski-Doo kill switches. Steering stop at the wheels. Rear view mirrors. Ignition switch for engine, apart from pull start. Electronic operated fire extinguisher. Seat belt engine kill system. Driver emergency communication system This novel kind of fire extinguisher arrangement is operated electronically through a solenoid valve. In case of fire the valve is opened by a manually operated button and a jet of CO2 is released in the engine compartment through various angles.

This effectively extinguishes fire in the engine compartment and stops it’s further propagation. Seat Belt Engine Kill System: This system is designed such that the driver will not be able to start the car until he engages his seat belt. The seat belt acts as a switch to operate the relay connected to the engine kill wire. When the seat belt is disconnected, the engine kill wire is grounded. Thus, the car cannot be started. As the seat belt is engaged, relay operates, and the engine kill wire circuit is now open enabling the driver to start the.

COMMUNICATION SYSTEM

PURPOSE: This is a two way communication system wherein messages and signals can be transmitted from the pit to the driver and vice versa. FEATURES:

The system uses two microcontroller based Arduino boards fitted with an ZIGbee communication module.

It is a transceiver. The signals are sent and received with the help of color coded Push Buttons and LEDs. The actual tested system arrangement is shown in figure.

BILL OF MATERIALS: All the parts of the ATV are classified into eleven blocks and are given a unique ten digit part number.

The cost of procurement of the part or the material is mentioned and all the machining operations are stated clearly. The spread sheet calculates the cost of machining also. Finally, the sub total of the procurement cost and the machining cost is obtained which helps in grand total of the costs.

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