The Hong Kong Polytechnic University

IC349 Manufacturing Project

Report

Project No.: IPD02

Project Topic: Combining two Tricycles for 24 hours Pedal Kart Grand Prix

 

 

 

Groupmate:

Cheung Tuen Ho 11601671D

Law Wai Lam 11555350D

Lee Ling Ling 10584684D

Pang So Sum 10611654D

Un Cho Kei 10704103D

Vu Thi Ha 10368735D

Wong Kwan Yu 10351718D

Wong Wing Shan 10033330D

 


 

Content

Project Brief (Vu Thi Ha) 4

1.1        Project background. 4

1.2        Project aim.. 4

1.3        Abstract. 5

1.4 Acknowledgements: 5

Specification . 6

2.1 Tournament requirement (Lee Ling Ling) 6

2.2 Required specification for project (Lee Ling Ling ) 7

2.3 Prioritize the requirement specification (Vu Thi Ha) 7

Project management (Wong Kwan Yu) 8

Research. 10

3.1 Braking System (Lee Ling Ling) 10

1.      Rim brakes. 10

2.      Disc brakes. 10

3.2 Transmission System (Un Cho Kei) 13

3.3 Center of Gravity Location( Law Wai Lam) 15

3.4 Camber Angl (Wong Wing Shan) 16

3.5 Caster angle (Pang So Sum) 18

Details Design and Analysis. 19

4.1 Conceptual design (Vu Thi Ha) 19

4.2 3-D Modeling Structure: Bottom- up Design (Wong Kwan Yu) 20

4.3 Material use (Law Wai Lam) 21

4.4 Weight Distribution (Vu Thi Ha) 21

4.5 Centre of Gravity (Wong Kwan Yu) 22

4.6 Rear-Wheel Drive (Law Wai Lam) 22

4.7 KPI and scrub angle (Law Wai Lam) 22

4.8 Positive castor angle (Law Wai Lam) 23

4.9 Steering Ratio (Law Wai Lam) 23

4.10 Camber Effects( Wong Kwan Yu) 24

4.11 Wheel base(Un Cho Kei) 24

4.13 Main frame development( Wong Kwan Yu) 25

4.12 Frame adaptor(Vu Thi Ha) 25

4.13 Ergonomics Design Factor(Lee Ling Ling) 28

Manufacturing Process. 32

5.1 Fork(Pang So Sum) 32

5.2 Frame adaptor(Pang So Sum) 34

5.3 Brake connector (Cheung Tuen Ho) 35

5.4 Drum(Pang So Sum) 35

5.5 Handle connector(Pang So Sum) 36

5.6 Steering arm(Pang So Sum) 37

5.7 Steering adaptor(Un Cho Kei) 37

Analysis and Simulation. 38

6.1 Fork (Wong Wing Shan) 39

6.2 Frame Adaptor (Wong Wing Shan) 40

6.3 Whole Kart (Wong Wing Shan) 41

6.4 Posture (Wong Wing Shan) 45

Motion Study (Wong Wing Shan) 46

Problem and solution. 47

8.1 Problem 1(Un Cho Kei) 47

8.2 Redesign Brake Connector(Un Cho Kei) 51

8.3) Problem 2(Pang So Sum) 52

Improvements. 57

9.1 The Steering handles (Cheung Tuen Ho) 57

9.2 The brake connector (Cheung Tuen Ho) 58

9.3 The seat (cooperating with the function of adaptor) (Cheung Tuen Ho) 59

9.4 The surface finishing of parts (Cheung Tuen Ho) 59

9.5 The drum disc (Cheung Tuen Ho) 59

Mini-Conclusion (Cheung Tuen Ho) 59

Further investigation (Cheung Tuen Ho) 60

Work distribution( Vu Thi Ha) 61

Bill of material (Wong Kwan Yu) 63

Budget (Wong Kwan Yu) 64

Individual Report. 65

Wong Kwan Yu. 65

Wong Wing Shan. 67

Lee Ling Ling. 69

Un Cho Kei 72

Law Wai Lam.. 75

Vu Thi Ha. 78

Cheung Tuen Ho. 80

Pang So Sum.. 82

 


 

Project Brief

1.1  Round Table Pedal 2007 21st 24-Hour Pedal Kart Race (二零零八年香港格蘭披治大賽 圓桌會第二十二屆二十四小時腳踏車賽)Round Table Pedal 2007 21st 24-Hour Pedal Kart Race (二零零八年香港格蘭披治大賽 圓桌會第二十二屆二十四小時腳踏車賽)Project background

Round Table Pedal 2007 21st 24-Hour Pedal Kart Race (二零零八年香港格蘭披治大賽 圓桌會第二十二屆二十四小時腳踏車賽)

 

 

 

 

 

 

Hong Kong Grand Prix, previously known as Pedal is a long-established charity race in Hong Kong, has risen over millions of dollars for charity since its inception. During the activity, each team is required to drive their corresponding pedal kart continuously for 24 hours; the team which can finish the racetrack within the shortest time will become the champion.

Each year, this activity attracts more than 30 organizations and parties to join, including Cathay Pacific Airways Ltd, Hong Kong Aircraft Engineering Co Ltd, Hong Kong Electric Co. Ltd, etc. To support the local charity activities, PolyU has also become one the participant since 2010.

 

1.2  Project aim

This year, we become one of the representatives in PolyU to take part into this event. We are going to design and fabricate some critical components of the pedal kart, including steering system, braking system, forks, and adaptors. The designs are base on theoretically study of caster and camber angle, centre of mass, length of track and wheelbase and ergonomics, follow by computational test and experimental test. We not only regard the 24 hours pedal kart racing event as a competition, but also respect it a chance to learn how to become an engineer.

 

Objective of the project:

 

¯  To design and construct a functional and reconfigurable prototype for iterative design refinement.

¯  To explore new design configuration for better racing performance

¯  To evaluate and modify the design through series of test driven.


 

1.3  Abstract

To achieve the objective of our project, we have proposed the adjustment of the camber angel and caster angle to a certain value, so to improve the kart’s velocity, acceleration, stability, and ease of control. Besides, we have proposed the position of the seat so as to adjust the position of centre of mass. This enhances the stability of the kart.

For testing whether our design could fulfill the objectives, we have created 3D models for the kart and the steering forks on Solidworks, which is one of the modeling systems. After that, we could do simulation and analysis for the kart. If the results of analysis fulfill what we required, we would make a prototype by Rapid Prototyping to test if it is practical in reality. And also, we will implement the fork to the kart and drive the kart to experience the driving feeling and determine which design is better.

1.4 Acknowledgements:

Special thanks to the KMX Karts Limited which sponsor the seat and frame

 

LogoVR Retail Shop

It was our honor that we can cooperate with the expert, who is called Mr.Corbett Rowell.

 

Industrial Partner: Mr. Corbett Rowell, Velocity Racers


Specification

2.1 Tournament requirement

 

²  Maximum overall length 2030mm

²  Maximum overall width 1125mm

²  Maximum overall wheel diameter (measured over the inflated tire) 560mm (Pre Rule Date Karts: 765mm)

²  Maximum height of uncompressed seat cushion (above ground level) 610mm

²  Minimum distance between center of wheels 650mm

²  Minimum distance between front and rear axles 650m

²  Mirrors, if fitted, shall not extend outside the widest part of the kart as measured at any point perpendicular to the center line

²  Steering shall be provided such that the kart has a turning circle of not more than 10,000mm diameter (which includes the width of the kart) when underway.


 

2.2 Required specification for project

1. Speed

The target speed of the pedal kart is 45km/hr (12.5m/s). Speed is highly correlated with centripetal force, the higher the speed, the larger the centripetal force.

By using value of target speed, the centripetal force while turning can be calculated. It is highly related to the design of the centre of mass (C.G.) of the kart. After designing the kart, the C.G of kart can be found out, and thus, the centripetal force can be used for dynamics simulation of the kart.

 

2. Stability

Stability is one of the crucial factors upon the design of pedal kart, it also has an inverse relationship with speed, that means stability of pedal kart increase only if speed decrease. This effect is obvious especially in turning situation of the kart. However, by experience, it is found that stability is highly related to centre of mass (C.G) of the kart, and considerate stability can be maintained if the (C.G) is concentrated at the bottom of the pedal kart

 

3. User Comfort

Customers’ comfort or needs are the design criteria for engineering. To fulfilled customers’ need, the design parameter for seating and pedaling will follow the theory of ergonomics. Theoretically, the most comfortable posture for user is to lying down on the kart; however, it seems not appropriate for a racing kart. 

 

4. Aesthetics

It is the main consideration for the design of most products in market. Whether it can draw users or customers attention is mainly because of its outlook.

2.3 Prioritize the requirement specification

Stability > Speed > User comfort > Aesthetics

The most important requirement for the pedal kart is speed and stability because it is used for racing. As in discussion, it is known that most pedal karts in the competition perform similar speed, whereas stability of each pedal kart performs quite differently. Therefore, our pedal kart will have superiority if its stability can improve significantly. 

User comfort is much more important that aesthetics issue since it is only a racing kart instead of leisure kart. Each participant need to ride for more than one hour in this pedal karts, in order to maintain constant performance, it is important to include user comfort as one of the criteria in the design.

Project management

Number

Activities

Duration/days

Start

Finish

Predecessors

 

Design phase

 

 

 

 

1

Research

21

Tue 6/3/12

Tue 3/4/12

 

2

Prepare 3D model (SolidWorks)

16

Tue 20/3/12

Tue 10/4/12

1

3

Design of fork

8

Wed 2/5/12

Sat 12/5/12

2

4

Design of steering connector

7

Wed 3/5/12

Sat 12/5/12

2

5

Design of Brake connector

7

Wed 3/5/12

Sat 12/5/12

2

6

Design of drum

8

Fri 1/6/12

Tue 12/6/12

2

7

Design of frame adaptor

8

Fri 1/6/12

Tue 12/6/12

2

8

Design of handle connector

8

Fri 1/6/12

Tue 12/6/12

2

9

Design of L-shaped adaptor

8

Fri 1/6/12

Tue 12/6/12

2

10

Testing by simulation

2

Thu 14/6/12

Fri 15/6/12

3,4,5,6,7,8

11

BOM

33

Wed 2/5/12

Fri 15/6/12

 

 

 

 

 

 

 

 

Fabrication phase

 

 

 

 

 

Manufacturing of  fork

 

 

 

 

12

RP Modeling

9

Mon 2/7/12

Tue 10/7/12

3,10

13

Sand Casting

6

Thu 26/7/12

Tue 31/7/12

12

14

Milling

8

Wed 1/8/12

Wed 8/8/12

13

15

CNC

8

Tue 8/8/12

Wed 15/8/12

14

16

Drilling

1

Wed 15/8/12

Mon 15/8/12

15

 

Manufacturing of Steering connector

 

 

 

 

17

Punching

2

Tue 7/8/12

Wed 8/8/12

4,10

18

Bending

1

Wed 8/8/12

Wed 8/8/12

17

 

Manufacturing of L-shaped

adaptor

 

 

 

 

19

Cutting

1

Mon 30/7/12

Mon 30/7/12

9,10

 

Manufacturing of the drum

 

 

 

 

20

Turning

2

Tue 31/7/12

Wed 1/8/12

6,10

21

Drilling

1

Wed 1/8/12

Wed 1/8/12

20

 

Manufacturing of the frame

adaptor

 

 

 

 

22

Milling

 

 

 

 

 

Manufacturing of the handle connector

 

 

 

 

23

Milling

2

Wed 8/8/12

Thu 9/8/12

8,10

 

Manufacturing of the Brake connector

 

 

 

 

24

Punching

1

Mon 13/8/12

Mon 13/8/12

5,10

25

Assembly

1

Thu 16/8/12

Thu 16/8/12

16,18,19,

21,22,23,24

 

 

 

 

 

 

 

Monitor and Control Phase

 

 

 

 

26

QC of manufacturing parts

15

Wed 1/8/12

Mon15/8/12

14 - 24

27

Pre-Test

1

Mon 20/8/12

Mon 20/8/12

25

28

Redesign

9

Mon 20/8/12

Tue 28/8/12

27

29

Final Test

1

Wed 29/8/12

Wed 29/8/12

28

 

 

 

 

 

 

 

Close Phase

 

 

 

 

30

Preparation of presentation

4

Mon 27/8/12

Thu 30/8/12

 

31

Report

7

Fri 31/8/12

Thu 6/9/12

 

 

Four main phases:

 

Design phase: 6/3/12-13/8/12

 

Fabrication phase: 2/7/2012-20/8/2012

 

Monitor and Control phase:

1/8/2012-24/8/2012

 

Closing phase: 24/8/2012-6/9/2012


Research

3.1 Braking System

A bicycle brake is used to slow down or stop a bicycle. There have been various types of brake use today. The three main types are: rim brakes, disc brakes, and drum brakes. Most bicycle brake systems consist of three main components: a mechanism for the rider to apply the brakes, such as brake levers or pedals; a mechanism for transmitting that signal, such as Bowden cables, hydraulic hoses, rods, or the bicycle chain; and the brake mechanism itself, a calliper or drum, to press two or more surfaces together in order to convert, via friction, kinetic energy of the bike and rider into thermal energy to be dissipated.

http://upload.wikimedia.org/wikipedia/commons/thumb/f/f4/Dual-pivot_calliper_brakes_.JPG/170px-Dual-pivot_calliper_brakes_.JPG

1.          Rim brakes

Rim brakes are so called because braking force is applied by friction pads to the rim of the rotating wheel, thus slowing it and the bicycle. Rim brakes are typically actuated by the rider squeezing a lever mounted on the handlebar.

Advantages

Rim brakes are cheap, light, mechanically simple, easy to maintain, and powerful.

Disadvantages

Rim brakes perform poorly when the rims are wet. They require regular maintenance. Brake pads wear down and have to be replaced. Over longer time and use, rims become worn. Rims should be checked for wear periodically as they can fail catastrophically if the braking surface becomes too worn.

 

2.          http://upload.wikimedia.org/wikipedia/commons/thumb/2/21/BrakeDiskVR.JPG/220px-BrakeDiskVR.JPGDisc brakes

disc brake consists of a metal disc attached to the wheel hub that rotates with the wheel. Calipers are attached to the frame or fork along with pads that squeeze together on the disc. A bicycle disc brake may be mechanically actuated, as with a Bowden cable, or hydraulically actuated, or a combination of the two.

 

Advantages

Disc brakes tend to perform equally well in all conditions including water, mud, and snow. Since the braking surface is farther from the ground and possible contaminants like mud which can coat or freeze on the rim and pads. Disc brakes are less prone to fading under heavy or prolonged braking compared with rim brakes, and the heat is not dissipated into the tire. Disc brake pads when fully retracted ride much closer to the braking surface than rim brake pads. This better prevents a buildup of water or debris under the pad. There are holes in the rotor, providing a path for water and debris to get out from under the pads. Wheel rims tend to be made of lightweight metal. Brake discs and pads are harder and can accept higher maximum loads. Disc brakes do not create wear on the rim unlike rim brakes, especially if grit becomes embedded in the brake pads. Disc brakes permit a bicycle with a buckled wheel to be ridden, which would not be possible with a rim brake since the buckled wheel would bind on the brake pads. When riding a mountain bike with rim brakes in thick mud, the first point that the mud builds up is usually on the rim brakes. A mountain bicycle with disc brakes is usually less susceptible to mud buildup provided the rear frame and front fork yoke have sufficient clearance from the wheels. Moreover, the brake disc is easier and cheaper to replace than a wheel rim or drum

 

Disadvantages

Disc brake assemblies are heavier than rim brakes, and are generally more expensive. Disc brake applies a potentially large torque moment at the hub. In this case, the torque moment must be transmitted to the tire through the wheel components: flanges, spokes, nipples, and rim spoke bed. Engineering for this moment inevitably leads to a heavier wheel. And the front disc brake places a bending moment on the fork between the caliper anchor points and the tip of the dropout. In order to counter this moment and to support the anchor points and weight of the caliper, the fork must be thicker and heavier.

 

3.          Drum brakes

http://t2.gstatic.com/images?q=tbn:ANd9GcSGViasKZCF-LmRMwuyb_8JnwP0FOrdkM-GcL2yrrf3VROIh6NFBicycle drum brakes operate like those of a car, although the bicycle variety uses mechanical rather than hydraulic actuation. Two pads are pressed outward against the braking surface on the inside of the hub shell. Drum brakes have been used on front hubs and hubs with both internal and external freewheels.

 

 

 

Advantages

Drum brakes provide consistent braking in wet or dirty conditions since the mechanism is fully enclosed. And brake drums are less susceptible to wear than lightweight wheel rim sidewalls. Drum brakes required less maintenance. Due to the fact that a drum brakes friction contact area is at the circumference of the brake, a drum brake can provide more braking force than an equal diameter disc brake. The increased friction contact area of drum brake shoes on the drum allows drum brake shoes to last longer than disc brake pads used in a brake system of similar dimensions and braking force.

 

Disadvantages

Drum brakes are heavier, more complicated, and often weaker than rim brakes. Drum brakes do not adapt well to quick release axle fastening, and removing a drum brake wheel requires the operator to disconnect the brake cable as well as the axle.


 

3.2 Transmission System

The gear ratio of a gear train is the ratio of the angular velocity of the input gear to the angular velocity of the output gear, also known as the speed ratio of the gear train. Actually, gear ratio can be computed directly from the numbers of teeth of the various gears that engage from the gear train. Take it simply, gear Ratio means the ratio of the number of gear teeth of the chankset and that of the cassette of cogset.

 

http://www.ebike.com.tw/intro_parts/images/Triple_Chainwheel_Cranks.gifA chankset is the front part of the gear. People step on the pedal crank arm and turn the gear to give power to the bicycle. A chain is connected the chain rings with the cassette.

 

A cassette has a series of straight splines that form the mechanical connection between the sprockets and the cassette compatible hub, called a freehub

http://upload.wikimedia.org/wikipedia/commons/thumb/6/6e/Free_Wheel.jpg/220px-Free_Wheel.jpghttp://upload.wikimedia.org/wikipedia/commons/thumb/2/2c/Freewheelandhub.jpg/220px-Freewheelandhub.jpg

 

Theoretically, the maximum gear ratio determines the maximum speed of a bicycle, and the smallest gear ratio to determine how steep the bicycle can go.

 

Looking at the most common folding bikes SP8 system configuration, the crankset “53T,i” and freewheel “11-32T,i”, we can calculate the maximum gear ratio is , and the smallest gear ratio of  With such a configuration, riding SP8 can reach a top speed of 50km/h. Therefore, this 20 inches folding bicycle has a good sports performance and wider adaptability.

 

 

 

Form the equation, when the Wheel diameter is larger, the speed will be higher. Therefore, the speed is also determined by the diameter of the wheel.

 

There is an advantage on using with two chains in pedal kart. When the car is turning, the speed of the both sides of the tire can be sustained and will not slow down. We can having a higher speed in turning when comparing with only one chain of the PEDAL KART. But there is not much difference on straight line.

 


 

3.3 Center of Gravity Location

The location of the center-of-gravity (CG) of a race car is one of the most fundamental determinants of performance because tire cornering force capability is very dependent on the vertical load applied to the tire.

Total Vehicle Horizontal (x and y) Location of the CG

Data Required: First, record the individual wheel weights. At the same time record the loading condition: with or without driver. Measure the front and rear track width; measure the wheelbase.

WI + W2 + W3 + W4 = W = Total Vehicle Weight

 

If tF = tR = t,

 

 

 

 

3.4 Camber Angle

Camber angle is a measurement used in the wheel alignment of motor vehicles. It is an angle between a tire and the vertical axis when viewed from the front or back view of an automobile. Camber angle directly affects the way a vehicle handles, which need to take into account when there is a suspension system. A wheel that is perfectly vertical would have zero camber. Moreover, those wheels should be always perpendicular to the road in all circumstances.

Below is a table that has concluded some influences caused by different camber.

Image Detail

Zero camber:

Ÿ  Has the most contact with the ground

Ÿ  To enhance straight-line acceleration

Positive camber (tilted outward):

Ÿ  Top of the tire is farther away from the vehicle than the bottom

Ÿ  Usually used for the inside wheels in cornering to achieve greater contact patch

Negative camber (tilted inward):

Ÿ  Bottom of the tire is farther away from the vehicle than the top

Ÿ  Improves grip when cornering

Small negative camber:

Ÿ  To develop a maximum cornering force

Incorrect camber:

Ÿ  Improper tread wear or poor handling

Ÿ  Tire wear and impaired handling

Excessive camber:

Ÿ  Creation of uneven wear on the inside or outside of the wheels

Unequal camber:

Ÿ  Causes the vehicle to pull to one side.

 


If a four-wheel car is only required to move in a straight line motion, it should be designed with zero camber due to the enhancement of straight-line acceleration. However, our pedal kart is designed for participating in the 24 hours race, which has several corners to turn. To achieve a better result in cornering, we could not design the kart with zero camber angle.

If the wheel has zero camber, the inner edge of the contact patch would start to lift off the ground. This would reduce the area of the contact patch. To compensate with it, negative camber angle could be applied to the wheels so to maximize the contact with the ground, but it is only suitable for the outside wheels during the turn. The perfect design is to apply positive camber to the inside wheels. Because of the racing track, which has both right and left turns, we could not adopt this design.

For our design, we have finally designed to apply the same camber angle to the left and right wheels. In our project, finding an optimum camber angle to fit our kart is one of our targets, hence testing would be done to choose the best camber.


 

3.5 Caster Angle

Caster angle is the angular displacement between the vertical axis to the ground and the angle of inclination of king pin. Caster angle helps the front wheel to self-centering and enhance the directional stability when moving. The greater the castor angle, the greater the “jacking effect” on the chassis, and the greater the over-steering the kart will develop. The greater the caster angle, the heavier the steering, and the kart will tend to self-center. If the castor is too little, the kart will tend to under-steering. For racing kart, the negative caster angle is used to improve the weight and feel of steering and improve the camber gain when cornering, and the caster angle used is commonly 20 to 25 degrees.

Castor Angle

 

 

Meaning

Advantage

clip_image001

The wheels on the turning side will come off from the ground

improve the directional stability

clip_image001

The wheels opposite the turning side will come off from the ground

improve the camber gain when cornering

 

Details Design and Analysis

4.1 Conceptual design

 

After brainstorming, we have come up nine issues that we need to pay attention. All of our design, sketching will based on these preliminary considerations. Most of the design will be created in 3-D model and following by simulation testing not only in static but also in dynamic condition. We will choose design which has the best simulation result, and then have the prototyping.


 

4.2 3-D Modeling Structure: Bottom- up Design

A bottom-up approach is the piecing together of system to give rise to grander system. In our project, bottom-up design is used during the development of CAD model in solid. First, we assemble standard components like wheels, handle, and crank, to name a few. These parts do not change their shape and size unless we choose a different component. These will then become sub-assemble part which available for the final assembly.

 

 

 

Text Box: Level 2Text Box: Level 3


 

4.3 Material use

Aluminum alloy

Aluminum has high strength, low weight and ease of manufacturing, so we consider using aluminum as the major material for manufacturing. Also, in order to minimize the weight of the kart, thin aluminum sheets are suggested for some parts which does not need to withstand high shear force or longitudinal force.

For the frame adaptor, because the whole body weight is added on the linking pin inside the adaptor, we choose stainless steel.

 

4.4 Weight Distribution

Before having preliminary design of the pedal kart, it is important to pay attention onto various factors, including weight distribution, center of gravity and so on, because they are highly related to the dimension of our design.

The weight distribution is the ratio of the horizontal weight displaced between the front and rear wheels. It directly affects a variety of vehicle characteristic, including handling, acceleration, traction, and component life. In our design, we applied more weight on the rear wheel so as to reduce the possibility of turning over of the kart. According to our previous research of the competition, we found that performance on straight path of different pedal kart were similar, on the contrary, their performance on turning were different. Therefore, finding solution to improve the cornering and stability of the kart is the key element to win the competition and we tried to let our pedal kart with 40/60 weight distribution.


 

4.5 Centre of Gravity

Centre of gravity is the ratio of top to bottom vertical weight. It is as crucial as weight distribution for the obtaining of optimum pedal handing characteristics. However, different from weight distribution, the ratio of centre of gravity will not affect stability of handling. Instead, if all the weight is placed well below the axle, the pedal kart is going to have excellent handling regardless of weight distribution. That means considerate stability can be maintained if C.G is concentrated below axles.

 

4.6 Rear-Wheel Drive

The combination of front-wheel steering and rear-wheel drive gives the driver control over both ends of the vehicle. When compared with the front-wheel drive, the rear drive is more focus on control rather than stability. During acceleration, weight is shift to the rear (the driving wheel), which improves traction. Also, the project supervisor provides RWD standard part for us, which mean we can simplify our manufacturing process.

 

4.7 KPI and scrub angle

The kingpin in a solid front axle is the steering pivWith a positive spindle length the car will be raised up as the wheels are steered away from center.

 

 

 

 

 

 

 

 

 

 

 

 


 

The more the kingpin inclination is tilted from vertical, the more the car will be raised when the front wheels are steered. The effect is to aid centering of the steering at low speed.

The scrub radius is negative. If failure in one of the brake circuits, it also provides center point steering in the event of a tire deflation, which provides greater stability and steering control in emergency situation. Our kart’s break design is independently installed on both front wheels. It may have the chance of failure in one break.

 

 

4.8 Positive castor angle

More trail means that the tire side force has a larger moment arm to act on the kingpin axis. This produces more self centering effect. More trail will give higher steering force, and less trail will lower the steering force.

Caster angle, like kingpin inclination, causes the wheel to rise and fall with steer which is opposite from side to side. The effect of left steer is to roll the car to the right, causing a diagonal weight shift.

Our kart has positive caster angle which affects steer-camber. With positive caster angle the outside wheel will camber in a negative direction while the inside wheel cambers in a positive direction, again leaning into the turn. It is favorable during steering.

 

4.9 Steering Ratio

The overall steering ratio is defined as degrees of steering handle angle divided by corresponding front wheel angle. For race cars it varies from over 20: 1 for Superspeedway cars to less than 10: 1 for Formula One cars on tight street circuits and very fast steering for go-kart with nearly 1: 1. We use direct steering which has two positive effects.

 


 

1: As the steering bars are directly fixed on the fork, we can have direct feedback from the group. It helps the driver to determine the steering condition of the kart also the road situation.

2: We want the vehicle to respond a lot quicker in the track because the track is narrow with a lot of kart. We need to have fast reaction to prevent accidence.

 

4.10 Camber Effects

IMG_0621.jpgCamber angle is defined as the angle between a tilted wheel plane and the vertical. We are asked to optimize the effect on different camber angle from positive to negative camber angle. In order to test difference camber angle, we decide to make 3 pair of fork with different camber angle to analysis the effect. Since other components are fixed on the fork, we use screws and nuts to combine them together instead of welding.

 

 

 

4.11 Wheel base

700mm short wheelbase is used in our pedal Kart because of the requirement of the tournament. It created a tighter turning radius with faster and sportier handling. The smaller wheelbase have more compact frame because it is stiffer and lighter. Short wheelbase can distribute more loads on the rear wheel to prevent the kart roll.

 

Wheels

20 inch wheel are used to meet the upper limit of the tournament. Larger wheel can achieve faster top speed.

 

 

4.13 Main frame development

 

 

The dimension of final design is shown in the above diagram. The frame is separate into frame and rear frame in which they are connect by frame adaptor

4.12 Frame adaptor

http://images.gamme.com.tw/news/2012/05/5/ppyRpqGbkaaVp6Q.jpgMost of the pedal karts have possibility to turning over according by experience. It is found that the accidents were related to the degree of caster angle and the occurrence of centrifugal force upon cornering. From research, we found that:

¯  Too little caster can cause wheel instability, wandering, and poor wheel recovery.

¯  Too much caster can result in hard steering, darting, over-steer, and low speed shimmy

Since our pedal kart is design for 24 hours competition, we therefore design to have small positive caster. From search, positive caster helps pedal kart to gain stability in straight path because it creates a force in the front wheels, which tends to keep them tracking straight ahead. However, positive caster also tends to make the steering axle wheels return to straight ahead position, that means, when the front wheels of the kart are turning, one side of the pedal kart raise slightly and the other side is lowered. This condition gives risk to the accident of turning over.

Second, centrifugal force is produces during cornering. It is the apparent outward force that draws a rotating body away from the center of rotation, and it is caused by the inertia of the body as the body’s path is continually redirected. Theoretically, centrifugal force increase in the condition of small radius. In most case, cornering force due to elasticity of the tire can withstand the centrifugal force; however, net outward force will still produce if the radius of playing-field is too small.

 

The radius of playing-field for the 24 hour competition is 10 meters, which is not a small radius. However, the pedal kart still has chance to turning over if the cornering speed is too high. To prevent the accident, we have imposed two solutions:

 

¯  Insert a frame adaptor between front and rear bar of frame

¯  Using wheel with small negative camber angle

 

 

 

 

 

 

 

 

 


 

Condition 1: Ride along straight path

-Both front and rear bar are static

Condition 2: Cornering

-Front and rear frame are independent

-Connect using a shaft in the adaptor

-Horizontal movement of front frame does not affect rear frame

 

Insertion of frame adaptor helps movement of frame in two conditions.

When the pedal kart is riding on a straight path, both front and rear bar are static, they will not affect the movement of frame. When it is cornering, the adaptor helps to separate front and rear bar and make them become independent. During cornering, only the shaft inside the adaptor will move, this shaft helps to connect two bars. Since both the front and rear frame has become independent, therefore, the horizontal movement of front frame will not affect.

 

The second solution to prevent turning over of pedal kart is using negative chamber angle. As we have discussed before, there are two conditions when negative camber is used.

 

¯  Straight path: Bottom of the wheels tilt outward

¯  Turing: Wheels on the turning side tilt toward center then tends to become zero camber

      Wheels opposite the turning side tends to become more negative

 

However, Due to the lift of the wheels caused by the caster angle when cornering, Camber angle of wheels opposite the turning side becomes less negative

 

¯  Increase contact area between the wheels and the ground -> Increase friction

 

Therefore, use of negative camber and frame adaptor can helps to increase cornering force, and that will lower the possibility of turning over of pedal kart.

 

 


 

4.13 Ergonomics Design Factor

In initial stage, we did some research about ergonomic consideration. We knew that a good design should involve ergonomic design factor.

 

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