See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/281345427
Baja SAE UTEP 2014 Design Report- Team Jaabaz, VIT University Research · August 2015 DOI: 10.13140/RG.2.1.43 10.13140/RG.2.1.4307.8889 07.8889
CITATIONS
READS
0
9,011
1 author: autho r:
Raghuram Nagubandi Pennsylvania State University 1 PUBLICATION 0 CITATIONS
SEE PROFILE
Available Available from: Raghuram Nagubandi Retrieved on: 24 September 2016
VEHICLE NUMBER-21
TEAM JAABAZ BAJA SAE (UTEP 2014) DESIGN REPORT Debidutta Mishra Team Captain, VIT University N.Raghuram VIT University
Copyright @ 2014 SAE International
ABSTRACT This report tries to summarize the steps taken in finalizing the design in a nutshell. The requirements of roll cage, front and rear suspension systems, steering and drive train are considered here. The objective of the design team was to satisfy these functions while meeting the SAE’s rules and regulations with special considerations given to safety of the occupant, ease of manufacturing, cost, weight (dynamic behavior) and overall aesthetics and performance.
INTRODUCTION This report describes the methodology followed by Team Jaabaz to design, fabricate and test an all terrain vehicle that will compete in Mini Baja event in UTEP. The purpose of this competition is to simulate a “real world” engineering design project in which collegiate teams design and manufacture a prototype of a “rugged, single seated off-road recreational vehicle intended for sale to the non-professional week-end off- road enthusiast”. The design should be durable, safe and easy to maintain and must be able to negotiate rough terrain in all weather conditions.
VEHICLE DESIGN Main design focus – The main design focuses with the completely new 2014 vehicle are a lighter and more rigid and ascetics oriented frame, a more robust suspension design, and a more versatile drive train. With gained easy access to a tube bender the team was able to increase the number of bends in the vehicle and in turn use more continuous members. The weight of the car was also reduced by switching to 1 mm thick tube in SIM. Similar robust and durable designs were adopted in suspension, transmission and brakes system. In addition to these design focuses the team also wanted to address the failures that occurred during the 2012 competition.
FRAME DESIGN
Material selection: Material selection is one of the key factors in designing the frame of the ATV as it is the measure of safety, reliability, performance and strength of the roll cage. We conducted a thorough research on the tube materials and compared them in multiple categories.
Material
AISI 1018
AISI 4130
Duplex 2205 steel
Duplex 2205 steel
Outside diameter
2.540 cm
2.540 cm
2.540 cm
2.540 cm
Wall thickness
0.2 cm
0.2 cm
0.2 cm
0.1cm
Bending stiffness
2791 2 Nm
2791 2 Nm
2171 2 Nm
Bending strength
390 Nm
382 Nm
454 Nm
260.4 Nm
1.6615 kg/m
1.2444 kg/m
1.1475 kg/m
0.8790 kg/m
Weight/meter
Since the Duplex steel(2mm tube) has a higher strength than 3mm tube of AISI 1018 steel, we opted for this steel which ensured better weight savings. The overall weight was further reduced by using 1mm tube as secondary members. Welding: The final rollcage was fabricated after making the pipe model and thereafter making the necessary modifications Duplex 2205 is a austenitic-ferritic stainless steel and has good weldability due to presence of Nitrogen. Duplex 2205 is low carbon content stainless steel. Considering the compatibility along with cost and availability, 308L electrode was found to be suitable.
Finite Element Analysis of the Models: The following tests were used to check the design Front Impact Test, Rear Impact Test, Front Wheel Bump, Rear Wheel Bump, Heave and Twisting. The results are shown in Fig.3,4,5,8,9 and 10.
SUSPENSION:
STEERING SYSTEM
Objective: A BAJA suspension must be engineered which will provide the ability to compete in the every event with practical features like ground clearance and suspension travel which results in good comfort and control to the drive allowing proper navigation in a rough terrain.
Objective-The objective of steering system is to provide directional control of the vehicle, to withstand high stress in off terrain conditions, to reduce steering effort and to provide good response from road to driver.
Design: The designing process is done where the parameters like camber gain, motion ratio were analysed which are required for designing ATV suspension. The mounting points of the front and rear suspension were designed in SolidWorks. Then using these mounting points the analysis was done in Optimum-K to verify the assumed parameters. Analysis of output is done in terms of graph between the parameters like wheel travel Vs camber change etc. 1.
2.
3.
Front Suspension:. The front suspension is a short & long A-arm wishbone arrangement (fig.2). The roll centre is kept at the optimised height (7.85 inch) to reduce the body roll. The upright is manufactured by CNC and is symmetric,has good strength to absorb loads. The upright also provides a location to mount the brake calliper (Fig.7). In order to compensate for dive-effects during aggressive cornering, the camber angle for the front suspension has been set at 0° at ride height. In addition to that, the camber angle has been set to decrease when the shock absorber compresses during turns. As the suspension is double wishbone, front and rear arms are made from 1 inch OD MS material. The length of the front control arms allows for a positive travel in the front of the car to be 11.81 in& the camber gain angle varies from -3deg to +0.5deg (fig.15). Rear Suspension:4 link H-arm(fig.13) suspension was chosen instead of 5 in order to replace the toelink and better capability to adjust to various parameters. Also the loads are shared on the 4 mountings which will reduce the stress concentration. As like the front suspension, the rear upright (Fig.8) is also a single manufactured piece which provides for the connection of the A-arms and callipers. Shock Absorbers: The front shock absorbers were mounted on lower arm. These Powersports shock absorbers have stiffness of 600N/inch. Because of the uneven distribution of weights, the stiffness of the rear absorbers is kept high. The rear shock absorbers were mounted on upper arm. The rear shock absorbers are stiffer than the front absorbers. The stiffness is 650N/inch.
Design : We chose fast ratio rack and pinion which travels from one end to other end (5 inches) in 1-1/2 turns of pinion. steering ratio of 4:1 is achieved which means for every 4 degree rotation of steering wheel tires will be turned by 1 degree. 1.
Adjustable steering column: (fig.14.a)This year we have come up with adjustable steering which means the driver can adjust the steering wheel angle according to his height and comfort. A plunger type mechanism is used to change the angle of steering column which is present inside a mounting rod to which a plate is welded.
2.
Tie rods : The material we chose is high hardened steel to which one side ball joint is attached and to other clevis joint. The lengths of the tie rods for steering assembly were found to be 15.81 inches using three instantaneous centre methods.This time by using 15.81 inches tie rods we eliminated bump steer till 160mm bump. Simulations were done for correct tie rod length and to study bump steer effects (toe, camber change).
3.
Correct steering angle: While taking turns, the condition of perfect rolling is achieved if the axes of the front wheels when produced meet the rear axis at one point. This is the instantaneous centre of the vehicle. the inner wheel deflects by a greater angle than the outer wheel. larger the steering angle, smaller is the turning circle. The steering angle of the inner wheel can have a maximum value of about 44 degrees. The geometry has been demonstrated in fig.14.b Steering specifications steering ratio rack travel front track width wheel base inner lock angle outer lock angle castor SAI camber scrub radius toe rack length rack mounting height Turning radius
4:1 5 inches per 540 deg pinion rotation 59.09 inches 54 inches 42 deg 28 deg 5 deg 6 deg 0 deg in front and 10 deg in rear 30 mm 0 mm 15 inches 3.30 inches 3.30 m
Therefore Smallest Gear Ratio = (3.6X(3.14/30)X3800X0.31)/(60) = 7.39
TRANSMISSION Objective: The main objective of the drive train is to vary the torque in the most efficient way possible. This is being done through proper gear reduction for the needs of the vehicle in the competition. We picked a manual transaxle over CVT because of the following reasons Wider gear ratios range Gives better acceleration Lighter and economical Slippage losses are less in manual gear box Heat generated in manual transmission is less due to the time gap between the shifts .
1.3 Piaggio ape mini gear box overall gear ratios Since the desired range of gear ratios was close enough to that of Piaggio Ape Mini Truck’s gear box, hence we selected Piaggio Ape Mini Truck’s gear box.
Clutch gear and countershaft reduction Sprocket Reduction st 1 gear ratio
ENGINE: The engine provided by SAE is a 10 hp Briggs and Stratton make generating a torque of 19 Nm. The SAE Baja rules state that the maximum rpm of the motor for the competition has to be set at 3800 rpm and the idle speed has to be 1750 rpm. Design Methodology: In our previous year’s design we used direct coupling between the engine and transaxle. Due to this configuration the length of the rear A-arms had significantly reduced which adversely affected our ATV’s suspension system. So in order to increase the length of the rear A- arms without increasing the track width of the car, the engine was placed over the transaxle. We used a chain and sprocket system (fig.17) to couple the engine and transaxle .A chain guard was fabricated enclosing the entire chain drive.(fig.20)
nd
2 gear ratio rd 3 gear ratio th
2.20
0.9
5.80 2.73
1.66
4 gear ratio
1.12
Differential ratio
4.17
Net gear reduction: Gear ratio x clutch gear reduction x sprocket reduction x differential gear ratio e.g Net 1st gear reduction: 5.80x2.20x0.9x4.17=47.89 2. Speed and Acceleration Calculations: Max Speed of Engine=3800RPM Max Torque of Engine=19 N.m Diameter of the wheel=0.635 m Mass of the vehicle= 380 kg(approx.) st Considering forward 1 gear Speed = 3800/47.889 = 79.35 rpm=9.44 km/h Acceleration calculationTorque=19*47.889=909.891N.m 2 A=F/M =T/Mr = 909.891/ 380*0.3175= 7.542 m/s Chain Configuration Considering the standard chain drive calculation formulae and service factors, the following chain configuration was adopted.
1.
Transaxle Design Details: We did a market survey with the available transaxles of three vehicles in Indian market: Mahindra Alfa Passenger, Piaggio Ape Mini Truck and Mahindra Geo Mini Truck. 1.1 Maximum Gear Ratio =
Radius of tyre, r = 12 inch = 0.31m Mass of vehicle, m = 380 Kg(approx) fr = rolling resistance coefficient = 0.035 α = Maximum Angle of Inclination = 45°
η = Efficiency of Manual Gear Box = 0.92
Hence, Maximum Gear Ratio = (400X9.81X0.31X(0.035Xcos45+sin45))/(19X0.92) = 48.38
The Smallest gear ratio of the gear box is given by the equation: 1.2 Minimum Gear Ratio =
GEAR
Net reduction
Max speed (km/h)
Max acceleration (m/s2)
1 2 3 4
47.889 22.54 13.71 9.247
9.44 20.06 32.98 48.90
7.542 3.55 2.167 1.449
3. CHAIN CONFIGURATIONS:
n = Speed of engine(rpm) = 3800 v = Speed of vehicle (kmph) = 60
Type = DR 50 Rolon Chain Centre distance = 14” (360mm) Number of teeth in Engine pinion = 19
Number of teeth in Gearbox pinion=17 Length of chain =38.5 Inch(978mm) Pitch diameter of engine sprocket=75mm Pitch diameter of gearbox sprocket=67mm
BRAKES: Objective: The purpose of the braking system is to increase the safety and maneuverability of the vehicle by statically and dynamically locking all four tires on both paved and unpaved surfaces. Design: The exploded view of rear wheel assembly has been shown in fig.18 which displays the calipers and discs fitted to the hub.
Name of the component
Description
Front Disc diameter (in.) Rear Disc diameter (in.) Front caliper piston diameter Rear caliper piston diameter Front master cylinder bore diameter(in.) (ABP Racing master cylinder) Rear master cylinder bore diameter (in.) (Wilwood Master
7.87 8.6614 1.063 1.496 0.625
Pedal ratio Co-efficient of friction of brake Weight of the car with driver(lbs.) Brake biasing
6.25 : 1 0.4 815
0.75
64:36
Our hydraulic brake system is controlled by a single pedal in line with two separate master cylinders. The use of two separate master cylinders is a safety interlock, in case one fails, the other will still be operable. Another advantage of using dual master cylinders is the ability to adjust brake bias. The brake circuit we have used is of the horizontal split type. This was used due to the fact that the tires have positive scrub radius. Hence, one cylinder will control the front braking system and the other the rear system.
Brake configuration: By mounting the master cylinders on the top of the nose, we ensured easy maintenance. The pedal & balance bar are from Wilwood with a pedal ratio of 6.25:1 for maximum leverage and power multiplication. Different master cylinders were chosen for the front & rear because the front required considerably more pressure than the rear due to smaller rotors in the front. Armored steel braided brake lines run through the length of the car and flexible rubber lines at the A-arms in the rear for suspension travel. These were chosen due to their flexibility and their strength and ability to maintain high line pressure values. The reliability of our braking system is improved by having separate disk and calipers on each wheel. The front brakes consists of discs from 2010 Safari 200 ATV from Powersports motorsports, right caliper from TVS Apache RTR 180 bike & the left from Suzuki
GS 150R bike. Different calipers were chosen for the right & left front wheel to ensure that the bleeding valve faces upwards for easy bleeding. Dual piston design was chosen because of increased piston area and more uniform gradual pad wear. The rear discs are from Honda CBR 250 & the calipers are from 2013 Safari 200 ATV from Powersports. These calipers were chosen due to their small size giving acceptable values of clearance, whilst maintaining good braking capabil ity. All four calipers are floating type because of the fact that they are very compact and easy to package on vehicles. In addition to that, they have fewer leak points as compared to fixed piston types. Analysis of the brake system was performed on the vehicle with a velocity of 30 MPH. For an input force of 100 lbs on the pedal the resulting deceleration was around 0.9 g. At this deceleration, it would take the car around 1.5 s to stop. The analysis on the rear hubs manufactured from EN08 material has been shown in Fig.(12)
ELECTRICAL SYSTEM: Certain electrical components have been installed in the ATV to ensure its safety. Two kill switches have been mounted with easy accessibility, which instantly kill the engine. Brake lights, reverse light and reverse alarm pertaining to SAE standards have been used. A GPS module has been mounted in the driver’s cockpit area which displays the co-ordinates and speed of the vehicle directly to the driver. A transponder is being used which relays the number of laps completed to a timing device on the track. All electrical components are powered from safely secured 9V batteries .
CONCLUSION: The final product manufactured by Team Jaabaz for BAJA UTEP 2014 is a result of collaborative multidisciplinary team design . Material selection for each and every component remained a priority for the team considering an optimum strength to weight ratio, durability, cost effectiveness and feasibility. Before initiating the actual fabrication, real time conditions were simulated using various FEA packages like Solidworks, ANSYS, Optimum-K and critical parts of ATV were analyzed for safety and optimization issues. The parts were manufactured in techniques which can be considered suitable for mass production of this model, if introduced in market. Apart from manufacturing issues, the team also has to focus on other aspects like managing funds and working with a budget plan, achieving targets within deadlines, project management, marketing and sales, making its members competent automobile engineers and tech savvy, in short attempting to make the team members ready for real time industry experience.
REFERENCES: 1. SAE International BAJA SAE Rules 2014 http://www.sae.org/students/2014_baja_rule s_8-2103.pdf 2. Race car Vehicle Dynamics: Milliken and Milliken 3. Car suspension and Handling: Geoffrey Donald Bastow 4. Automobile Engineering, Kirpal Sings 5. Engineering Data Book
Fig .1Vehicle Front View
Fig .2- Front Lower A arm- FOS= 1.4
Fig .3- Frame for BAJA UTEP 2014
Fig .4- 2g Side impact analysis- FOS=2.7
Fig .5- Front Impact analysis-8500N at front =
Fig.7-Front Upright analysis
Fig.6-Vehicle Top View
Fig.8- Rear Upright analysis
Fig.9- Rear Impact analysis- Load 8500 N at rear FOS=3.77
Fig.10- Front Bump Test-Load 1700N on front wheel, FOS=6.7
Fig 13- Rear Upper control arm analysisFOS=1.8
Fig.11- Vehicle Side View
Fig 12-Wheel hub analysis- FOS-2.9
Fig 14a- Adjustable steering assembly
Fig.15 Front left wheel camber Fig 14b- Ackermann Steering geometry
Fig.19 Oil seal for the gearbox along with clutch shaft
Fig.16 Isometric View of the Vehicle
Fig.20 Photo of the Chain drive with the chain cover
Fig.17 Transmission System
Fig.21 Photo of front A-arm fabrication
Fig.18 Wheel Assembly
