sae nis effi cycle 2014

SAE NIS EFFI-CYCLE 2014

DESIGN REPORT

Team ID : 14036

Team Name : ThunderBolt 2.0

College Name : National Institute of Technology

City : Warangal, Andhra Pradesh

Team Captain : Rohit Chowdhury

Report Author : Srivatsa Yeluripati

Report Co-Author : Hardik Jain

1. ABSTRACT:

The main objective of Effi-cycle 2014 is to promote

innovation and generate consciousness amongst the

young engineers towards environment friendly mobility

solution. Keeping this in mind, team Thunderbolt2.0 has

made sincere efforts to design and fabricate an energy

efficient human cum-battery powered two-seater trike

which is safe, economical in design and delivers high

performance promoting ‘greenovation’. This report

contains an overview of the design work for each of the

involved subsystems.

Team targets are listed as follows:

Providing flexible and independent power

transmission to integrate various powers.

Comfortable manoeuvring: low centre of

gravity, smooth steering, electronics

systems.

Swift trike with considerable acceleration,

braking and targeted velocity of 35 mph.

Ensuring ergonomics and safety with

features like Smart Charger and IEA.

Economical design that can be modified for

mass production for commercial purpose.

Special features of the trike include ignition locking

system, impact energy absorber, foot straps for pedals,

lock levers of brakes, brake accumulator, smart charging

systems, load sensing systems etc. The ten member team

Thunderbolt 2.0 of National Institute of Technology,

Warangal consisted of engineering students from various

backgrounds. Drawing upon multidisciplinary

engineering knowledge, the team members were divided

into various departments: Designing, Finite Element

Analysis, Steering, Transmission, Braking, Suspension

and Electrical Systems.

Fabrication is under process and the entire team is

excited to complete a successful Effi-cycle.

2. TECHNICAL SPECIFICATIONS:

DIMENSIONS

Length 96.5’’

Width 51’’

Height 59’’

Weight of Chassis ~70kg

Wheel Track 46’’

Wheel Base 59.5’’

H-Point of Driver 23’’

MATERIALS

Material Purpose

IS 4923 Chassis Fabrication

Aluminium A3105 Flooring and doors

Clear Acrylic Sheet Roof of Vehicle

ELECTRICAL AND ELECTRONICS

Motor 24V 400W

Speed control 24V 30A

Battery Charger 29.4V 6A

Sealed lead Acid Batteries 12V 35Ah

FRAME SET

Front Suspension Hydraulic Telescopic fork

Suspension

Rear Suspension Twin Shock Regular

Swing Arm Suspension

Vertical Travel 4’’

Chassis Type Backbone Tube

PERFORMANCE

Maximum Speed 28.6kmph

Maximum Torque 3.05Nm (by motor)

Turning radius 2.98m

Brake Set Cantilever brakes

POWER TRAIN

Derailleurs 12t-28t 6 Speed

Sprockets 18t and 14t

Chain Wheel 48t

Power Integration At the Idler Shaft

3. PROJECT PLAN:

4. DESIGN, CALCULATION AND SELECTION

4A. Frame configuration, Design and Material:

The vehicle is of Tadpole configuration which is

designed with aerodynamic and ergonomic advantages.

Backbone frame design, with a strong rectangular spine

gives strong and rigid structure so as to ensure

reliability. The frame design is made to enhance the

protection of the drivers from various impacts. The

chassis is designed so as to accommodate two drivers

comfortably and keeping in mind to incorporate steering

and suspension systems.

Chassis design considerations:

Protection to the drivers from possible impacts.

Low centre of mass for better steering and

manoeuvrability.

Symmetric design: Equal weight distribution on

front and rear wheels.

Weather protection and protection from direct

sunlight.

Reducing the Stress concentrations using

appropriate cross section and fabrication

process.

Ample Clearance for drivers.

Sturdy design using fewer members hence

reducing the weight.

Better steering and wheel base to track width

ratio of 1.3 to 1.5.

Cross-section of the beams is selected by comparing

flexural and torsional rigidity of the members.

TYPE OF

beams

CIRCULAR

beams

RECTANGULAR

beams

Cross-Section

used

Outer Diameter=

26.9mm

Inner Diameter =

22.3mm

Outer= 32*32

mm^2

Inner = 28*28

mm^2

Thickness 2.3mm 2mm

Flexural

Rigidity

13563.53 mm^4 36160 mm^4

Torsional

Rigidity

27127.07 mm^4 72320 mm^4

Comparing the values of Flexural and Torsional Rigidity

and simultaneously performing simulation on ANSYS

for both the cases, selected Rectangular cross-section so

as to satisfy the design considerations.

Material Selection:

Material selection for the chassis is done by minimising

the cost at the same time meeting the required

performance targets of the design.

Comparing various properties of materials allowed such

as tensile and compressive yield strength, ultimate

strength, density etc. we were finally left with two

materials AISI 1018 and IS 4923. By detailed

optimization using ANSYS and considering weight and

cost of the material IS4923 YST 310 grade was selected.

Analysis of Chassis:

The final design of the chassis is tested against various

impact loads to ensure the safety of the driver. For the

analysis of impacts FEM analysis software ANSYS 14.5

was used. Front, rear and side impact analysis was

performed and results are listed as follows:

Type of

test

Load

Applied

Max.

Deformation

Factor

of

Safety

Remarks

Frontal

impact

4G* 0.4386mm 2.5067 safe

Rear

Impact

4G 0.87484mm 1.88 safe

Side

Impact

2G 0.20356mm 3.391 safe

*4G = 350Kg*4*9.81

Modifications were made in the chassis based on the

analysis results and ended up with a safer design against

any kind of impact loading.(Refer Page: 10)

Sections of Beams used:

Rectangular Cross section 60mmX40mm

Square Cross section 32mmX32mm

Circular Cross section for the curved part

23.9 mm diameter

Weight Distribution in the Vehicle:

• Weight of the chassis = 70 kg

• Weight of Motor along with batteries = 30kg

• Weight of Passengers = 115 kg each

• Utility Box = 20kg

• Total weight = 350kg

Location of Centre of Gravity: (Refer Page: 10)

Distance from Front axle = 787.6mm

Height from the ground = 635mm

4B. Drive Train:

Transmission drive trains designed are independent for

Human and Motor powered transmissions. It is achieved

by using both the sides of the wheel through dual

mounting wheel hub. (Refer Page: 10,11)

Human Powered Drive Train:

Human Powered drive train consists of a parallel

transmission of both drivers combined at the

idler shaft before transmitting it to the main

driven wheel.

The power of the both the drivers add up when

at the idler shaft if they drive at same speed.

Motor powered Drive Train:

The Motor drive train consists of a 400W BLDC

electric motor mounted with gearbox of

reduction ratio of 10.

The motor is controlled using a 24V, 30A speed

controller and is driven by two 12V batteries

connected in series with a total discharge of

35Amp.hr.

Motor drive train is installed with two

derailleurs so as to provide large range of

torques and speeds.

TABLE 1: Motor and Battery Specifications

BLDC Motor

1. Power 400W

2. Voltage 24V

3. Rated Rpm 1500Rpm

4. Rated Torque 2.5 N.m

5. Weight 11Kg

Battery

1. Type Sealed Lead-acid

2. Make Amaron

3. Output voltage 12V

4. Maximum

Discharge

35Amp.hr

5. Weight 10Kg

Why BLDC Motor?

Less maintenance due to absence of brushes.

High efficiency, no voltage drop across the

brushes.

Reduced size due to superior thermal

characteristics.

Higher speed range- no mechanical limitation

imposed by brushes or commutator.

Brushless motor offers higher reliability, less

noise and longer lifetime.

Disadvantages of BLDC Motor:

High cost of construction.

Requires control strategies which are both

complex and expensive.

Controller Specifications:

Input : 24VDC

Direction reversible on external contact

Dynamic brake on request

Factory set current limit of 25A

Over Temperature cut-off

Factory set soft starter

Over voltage and under voltage cut-off.

Independent Transmission and Torque Availability:

Trike is designed so that it can be driven by both

the drivers and also electric motor. The Motor and

Human powered transmission are made independent to

prevent the problems in case of failure of one of the

drive trains. (Refer Page: 10,11)

The Motor drive train is equipped with two

derailleurs providing us about 36 different speed and

torque ranges. We used the concept of varying reduction

ratios using derailleurs so as to obtain high torque of

about 125 N.m and also higher speed of nearly 29Kmph.

TABLE 2: Power Train Specifications

Power Train Specification Value

Maximum Torque Requirement(On Slope

of 5deg)

141.28N.m

Minimum Torque Requirement 14.54N.m

Maximum torque given by Motor 3.05N.m

Battery Run Time at Rated RPM 1.67 hrs.

Battery Run Time at Critical Torque

Requirement

0.9 hrs.

Reduction Ratio Obtained 7.34 to 40

Average Speed in low Torque conditions 28.6kmph

Average speed in Maximum torque

conditions

4.75kmph

Maximum Obtained Human Power* 282 W

Sustainable Power from one Driver* 137W

Average Torque Obtained by Human

Power

14.46N.m

*Source: Bicycling Science (3rd Edition) by David

Gordon Wilson

Because of the derailleurs used in the motor drive train

we obtain wide range of reduction ratios of the RPM

from the motor. The motor is initially stepped down by a

ratio of 10 with the help of a Gearbox. Different

reduction ratios obtained are shown in the table given

below:

TABLE 3: Some of the Reduction ratios of RPM

obtained in the motor drive train

Red

uct

ion A

t th

e

Gea

r box

spro

cket

mounte

d

spro

cket

s on

der

aill

eur

Red

uct

ion p

rovid

ed sprock

et

mount

ed

paralle

l to

deraill

eur

Spro

cket

s on

der

aill

eur

Red

uct

ion p

rovid

ed

Tota

l R

educt

ion

on

th

e

mo

tor

on

rea

r

wh

eel

10 14 12 /1.16 14 12 /1.16 7.34

14 x1

14 x1 10

16 x1.14

16 x1.14 13.0

18 x1.28

18 x1.28 16.5

20 x1.42

20 x1.42 20.3

22 x1.57

22 x1.57 24.6

24 x1.71

24 x1.71 29.3

28 x2

28 x2 40

Finally a maximum reduction of 40 and minimum

reduction of 7.34 is obtained in the speed was obtained.

Torque Calculations:

To choose a motor(s) capable of producing enough

torque to propel the vehicle, it is necessary to determine

the total effort (TE) requirement for the vehicle.

While calculating the minimum torque requirement of

the vehicle various considerations are required based on

the context. Two cases were considered: one is cruising

condition on flat road and other is moving on a gradient.

For torque calculations we consider the theoretical

weight of the vehicle to be 350Kg along with drivers.

Hence Gross Weight of the Vehicle = 350*9.81 =

3433.5N

1. Effort required to overcome rolling Friction:

Rolling Resistance (RR) is the force necessary

to propel a vehicle over a particular surface.

Force required to overcome rolling

friction = GVW*Friction coefficient

Friction Coefficient = 0.01

Hence total effort required = 34.335N

2. Effort against the gradient:

This calculation is made using the maximum

angle or grade the vehicle will be expected to

climb in normal operation.

In Gradient test there is a Force of

Mgsin (α) Acting on the vehicle:

Inclination

Effort against

Gradient

3 degrees 179.69N

4 degrees 239.5088N

5 degrees 299.249N

Combining both the above cases total torque required is

calculated

Torque = (Total Effort * Radius of Wheel *

Resistance Factor)

85% efficiency of the drive trains (resistance factor =

1.15) was considered

Minimum torque requirement on flat road:

Total

Effort(N)

Torque

Required(min)26''

wheel

Torque

Required(min)29''

wheel

34.335 12.83Nm 14.45Nm

Minimum torque requirement on gradient:

Incl

inat

ion

Effort

against

Gradient(

N)

Total

Effort

(N)

Torque

Required(mi

n)26'' wheel

Torque

Required(mi

n)29'' wheel

3

deg

rees 179.69N

214.0

25

79.9918437

5

90.6492186

3

4

deg

239.5088

N

273.8

438

102.349120

3

115.985172

3

rees

5

deg

rees 299.249N

333.5

75

124.673656

3

141.284023

4

Finally it is necessary to check whether the wheel can

transmit the required torque or not. So we calculated the

maximum tractive torque of the drive wheel for the

reality check.

* 50-50 weight distribution was considered in the

vehicle in front and rear.

Max Torque That can be transmitted = (%wt. on driving

wheel)*g*(friction factor of floor)*radius of wheel

*We took floor to be concrete with friction factor 0.4

Hence Maximum torque that can be transmitted came up

to be 252.7Nm which is more than our maximum torque

requirement.

4C.1) Suspension: (Refer Page: 11)

Suspension system in the trike is designed in order to

have a smooth and comfort drive. For front suspension,

telescopic fork suspensions (Figure 1) are used and for

the rear suspension Twin shock regular swing arm

(Figure 1) was installed. The Twin shock swing arm

suspension has a vertical travel of 4inches so as to keep

the motor and chassis shock free and intact.

TABLE 4: Specifications

Natural eye to eye length of spring 16.7cm

Natural length of actual spring 9.5cm

Stiffness constant of Springs used 210.66kN/m

Maximum Compression Available 5.8cm

In twin shock swing arm, two springs are used in

parallel. Hence effective spring constant is 421.33kN/m

To obtain the vertical travel without any intersection

with the body of the vehicle, the length of the swing arm

(Lswingarm) is taken as 20 inches (0.508m).

Calculations:

At static conditions sag is assumed to be 20% and hence

the force on the springs is given by F

F=K*x, where

F is the force exerted by the eq. spring

X is the initial compression due to load of

drivers and chassis

F=421.33*1000*(20% of 0.058)

F=421.33*1000*0.0116

F=4.888 KN

Since the system is at rest (equilibrium), net moment

about pivot is zero

F*L - Fr*Lswingarm + W*Lw= 0

Where,

Fr is the reaction force on rear wheel =2060 N

W is weight of the swing arm = approx. 50 N

Lw is the distance of C.O.G of swing arm from

pivot= approx. 20cm

L = (Fr* Lswingarm – w*Lw)/F

L= 21.4 cm

Hence, the spring force must act at a distance of 21.2 cm

from the pivot.

Under Max Torque 140 Nm from motor, at constant

velocity:

L*F = Fr*Lswingarm + Fc*Cos (T)*Rspr – Fc*Sin

(T)*Lswingarm – Ftr*Rw – W*Lw

Where, Fc is the tension in chain, such that

Fc*Rspr= 140, i.e. Fc = 2413.7 N

Rw is the radius of wheel = 14.5 inches = 36.83

cm

T is the angle between Fc and horizontal=2.64

degree

Rspr is the radius of largest sprocket= 5.8 cm

Ftr is traction force. Since trike is in constant

velocity, net moment about cogwheel is 0.

Hence Ftr*Rw=Fc*Rspr i.e. Ftr= 380.125 N F = 4.568 KN

Now, F = K*x

X = 1.08 cm this is the net compression under

max torque conditions.

Similarly, under Minimum torque 15 Nm, at constant

velocity:

T=0.17degrees Rspr =2.48 cm

L*F = Fr*Lswingarm + Fc*Cos (T)*Rspr + Fc*Sin

(T)*Lswingarm – Ftr*Rw – W*Lw

F = 4985.34 KN

Therefore compression is spring

X = F/K = 1.2 cm

Hence, for l = 21.4 cm, a compression of less than 1.2

cm is maintained, both at rest and uniform velocities.

Hence max compression available after sag = 5.8 –

1.2 = 4.6 cm

Now to obtain a vertical travel of 4 inches, the swing

arm rotates an angle of about 11o

Assuming the travel of the spring to be almost linear, the

spring is positioned at an angle of about 61.55o

4C.2) Braking System:

The trike used cantilever shoe brakes on all wheels

which can be locked simultaneously as desired. The

front two cantilevers are controlled by a double barrel

lever which can lock both the front wheels

simultaneously to prevent any skidding or slip. This also

prevents the toppling of the trike.(Refer Page: 11)

Reason for Cantilever Brakes:

Over disc brakes-

Disc brakes are heavy compared to rim brakes.

It involves a complex mechanism involving

hydraulics

Lighter disc brakes are expensive

Over calliper brakes-

It has high stiffness factor. Thus high braking

power needed for the weight of the trike

Weight Transfer during braking:

Where,

f1, f2 are friction coefficients on front and rear wheels.

N1 and N2 are normal reactions on the wheels.

X+Y = B = Wheel Base

2N2+N1 = 350g = 3433.5

Calculating moments about contact point of the rear

wheel,

2N2 (B) = W(X) + m (f1g)*h, where f1 = f2 = 0.6

2N2 (1498.6) = 3433.5*711 + 350*0.6*9.81*635

Hence N2 = 1250.961N and N1 = 931.576N

%weight on front wheels = 72%

%weight on rear wheel = 28%

4C.3) Steering :( Refer Page: 12)

The steering geometry of our trike is basically an

Ackerman mechanism, which is driven by a Single Tie

Rod and Drag Link arrangement.

Calculation of the links of Ackerman:

According to our design,

Wheel track, w = 46 inches = 116.84cm

Wheel base, l = 59.5 inches = 151.13 cm

Link length d is set to a comfortable value.

Representation of Ackerman Links

Using the formula,

Eq 1.

A graph is plot between i vs (Blue Curveis plotted

for different values of β.

Using Ackerman perfect Steering condition,

i.e., cot δ - cotδi = 0.773……... Eq.2

Perfect steering curve (RED Curve) is plotted using Eq2.

The curves plotted using the Eq1 are compared to that of

Eq2 so as to obtain the values of β for which the curves

almost coincide for large range of angles.

The process is repeated for different values of d and

corresponding value of β is obtained.

d (in inches) Negligible error up to i =

7 21 degrees along the curve 30

8 19 degrees along the curve = 30









17 14 degrees along the curve = 26 The highlighted data represents the values of link length

d and for which there is negligible error between the

two curves up to large values of i.

The value of d is comfortably chosen as 12 inches.

Now, the lengths of the Ackerman are given by

LAB = 116.84 cm = 46 inches

LBC = 30.48 cm = 12 inches

LCD = 88.22 cm = 34.7 inches

LAD = 30.48 cm = 12 inches

To obtain Perfect steering Conditions we solve Eq1 and

Eq2 simultaneously.

i = 17.01 degrees

= 13.90 degrees

At these perfect Steering Conditions are satisfied

Radius of curvature at these angles is 5.57m

Calculation of Turning Radius: (Refer Page: 12)

To calculate the turning radius, the outer radius of the

vehicle during turning was assumed to be 3.8m (As we

require 4m of outer radius to pass the manoeuvrability

test).

Therefore, outer steering angle,

= Sin-1

(l/Ro)

= Sin-1

(151.13/380)

= 23.44 degrees

Inner steering angle is obtained by solving Eq1.

i = 39.95 degrees

Turning radius can be calculated as

R= Sqrt[ (Ro*Cos() – (w/2))^2 + a^2 ]

R = Sqrt[ (380cos(23.44) – (116.84/2))^2 + (71.1)^2 ]

Hence, Turning Radius, R = 2.98 m

Calculation of lengths of Driving links and turning

angles:

Other required link lengths are calculated with the help

of sketcher in SOLIDWORKS.

Hence LEF = 13.5cm and LGF = 63.2cm

When the vehicle takes sharp right turn, the steer of

handle bar is calculated to be,

R =52.33 degrees When the vehicle takes sharp left turn, the steer of

the handle bar is calculated to be,

L =59.5 degrees Calculation of Critical Speed:

Critical speed gives the maximum speed at which the

vehicle can take a turn for a given turning radius. It is

calculated as follow,

Critical speed, S = sqrt(u*R*g),

Where,

μ = 0.6 is the coefficient of friction between the tyre

and the ground

R is the radius at which the vehicle turns

g is acceleration due to gravity = 9.81 m/s2

TABLE 5: critical speed at different radii

Radius CRITICAL

SPEED (m/s) CRITIACAL SPEED

(km/hr)

3 4.20 15.12

4 4.85 17.46

5 5.42 19.52

6 5.94 21.39

7 6.41 23.10

8 6.86 24.70

9 7.27 26.20

10 7.67 27.62

11 8.04 28.96

12 8.4 30.25

4D. Wheels and Tyres:

The Wheels used in the trike are reinforced 29’’

diameter wheels and width of the tyre is 1.5’’. Following

are the selection criteria that we have followed for

wheels:

Larger wheels have less rolling resistance.

They have greater leverage and less

deformation.

Smaller wheels involve higher chain and hub

friction losses.

4E. Seating Arrangement, Seat design and features:

Comfortable Bucket seats at the backrest angle

of 105 degrees. The Seat includes head rest and supports

entire torso and thighs. The specifications of our the

design is based on an average human’s posture with the

sole aim of providing a cosy ride so as to extract the

maximum out of him/her while not bargaining on

luxury.

H-point: 23’’ from the ground for both the drivers

4F. Safety Features:

In order to ensure the complete safety of the drivers and

the by standers many safety features were installed in the

design of the trike.

Some of the key Safety features in the trike include,

Roll over and weather protection structure of the

trike.

Grills for the protection from the side impact.

Impact Energy Absorber, which reduces the

stress rate acting on the vehicle.

It also contains Rule-Book safety features such

as

o Helmets and knee pads

o 3 point seat belts

o Manual control kill switches

4G. Other features:

Head lights, tail lamps and indicator lights are

provided to ensure convenience and safety of the

driver.

Trike contains Storage spaces at two convenient

positions providing ample storage capacity.

5. Ergonomic Features:

The Trike contains considerable Ergonomic features to

compete with the market keeping in mind the comfort of

the driver. Some of the features include,

On board Charger and Battery level Indicator

Maximum Efficiency Indicator

On board cover for the vehicle

Mobile phone Charging Facility and Mobile

holder

Smart Charging System to prevent over

charging

Large Storage Space in the form of utility boxes

in front and rear.

Foot Straps in pedals for comfortable pedalling

without slipping.

The brakes are installed with lock levers, which

can be used as hand brakes.

The Trike is installed with Ignition key locking

for security.

6. Innovations Proposed:

Transmission designed in the trike is

Independent for motor and pedal transmission

and also resolves the problem of compromising

speed for torque. This transmission provides

high torque and also high speed of about

30Kmph.(For details refer Transmission section)

Brake lever is redesigned as double barr brake

accumulator so as to control both the front

wheels simultaneously. The Trike is intalled with Smart charging

syatem which would cut-off the circuit in case

of Over charging. Overloading of the vehicle is a problem in India

which is the reason for several accidents due to

failure of steering and braking. To solve this

problem the trike is installed with Load Sensing

Device which indicates the overloading of the

Vehicle.

ANSYS Reports

Frontal Impact [4G]

Side Impact [2G]

Rear Impact [4G]

Different Views of Chaasis

Schematic Representation of COG

TRANSMISSION

Layout of Motor Driven Power Train

Layout of Human Powered Driven Train

OverView of Transmission

Load Analysis Chart of 24V, 400W BLDC Motor

SUSPENSION

Figure 1 Figure 2

BRAKING SYSTEM

Double Barrel Brake Accumulator

Cantilever Brakes

STEERING

Single Tie Rod Drag Link Mechanism

Calculation of Turning Angles

Graph Showing the curves obtained from equations 1

and 2

ELECTRIC CIRCUIT DIAGRAMS

Block Diagram of Load Sensing Device

Smart Charging System

Circuit Diagram in the Vehicle

Impact Energy Absorber

OUR SPONSERS:

sae nis effi cycle 2014

Documents