Department of Mechanical Engineering

2011/2012 Semester 3

43078 BEng (Hons) Mechanical Engineering

 

IC 349 Integrated Manufacturing Project

Reducing the rolling resistance of a human powered vehicle (ME11)

Group Member:

LAI Alexander Sun Wah

11543731D

FUNG Wai Choi

11531492D

LO Wai Cheong

11540570D

NG Chun Cheong

11541123D

LAI Yun Sang

11533320D

LAM Chun Kit

11511340D

LAM Ka Hei

11553853D

POON Pui Ho

11583102D

YIU Ka Chiu

11500847D

Supervisor:  Martin Wong, Louis Sze

Date: 27-07-2012

 

Supported by:

polyu_ic

Sponsored by:

 

 
IMG_20120704_145713


Abstract

The 24hours pedal kart grand prix have always been a playing ground for teams to show their design of pedal kart and test their kart to the very limits. From the previous year’s experience, there is still a lot of room for our karts to advance for a better result. For the coming event, a pedal kart will be built to reduce the rolling resistance as well as increase its performance; ultimately to receive the glory of campaign on the podium.  A group of mechanical engineering students have focused on numerous designs from the previous entry kart of polyu to the trikes, quadracycle and go kart all around the world in search for the best design for simple and competitiveness.

 

The newly designed pedal kart with a look of go kart combine with a quad steering wheel and formula style suspension may be the hope for the success for the coming pedal kart event. These students make use of all of their manufacturing skills that they have acquire in their lifetime to construct the latest pedal kart. They have stayed in the work shop for 3 grueling months for the hot welding and casting, highly precise job of milling and lathe machine and exhausting testing in order to build the pedal kart on time. During the manufacturing, a design change of the chair suddenly occurs. However, after discussion between these students, some special T joint and L shaped plate was used to resolve the problem and the end result was adequate for the kart to work properly. The team work hard and put effort in making the parts to the desire dimension and accuracy, they manage to tighten all bolt and component to bring the kart successfully. The pedal kart has been built and will be further upgrade and fine tune for the very best performance.

 

 


Acknowledgement

Apart from the efforts of our teammates, the success of the project depends largely on the encouragement and guidelines of many others. We take this opportunity to express our gratitude to the people whom helps have been instrumental in the successful completion of this manufacturing project. We would like to show our greatest appreciation to Martin Wong and Louis Sze. We cannot say thank you enough for their tremendous support and supervision. We feel motivated and encouraged every time during the project in progress. Without his encouragement and guidance this project would not have materialized and finished within our expectation.

 

On the other hand, we would like to express our gratitude towards to the technical assistant in the industrial centre for their kind cooperation and encouragement which help us in completion of this project. We do not say that we can properly use the instruments and perform correct procedures of the manufacturing process without the supporting from technical assistant. Our thanks and appreciations also go to facility supporting from PolyU in developing the project and people who have willingly helped us with their abilities.

 


Contents

Abstract 1

Acknowledgement 2

Chapter 1 - Introduction. 5

1.1        Introduction. 5

1.2        Objectives. 5

1.3        Scope. 5

Chapter 2 - Design Concepts and Evaluation. 6

2.1        Product Requirement & Design Specifications. 6

2.2        Research Study. 6

2.3        Initial Investigation. 8

2.4        Main Design Features. 12

2.5        Material selection. 23

2.6        Simulation. 29

2.7        Design Optimization. 30

Chapter 3 - Manufacturing Process. 38

3.1        Process Planning. 38

3.2        Welding. 40

3.3        Casting. 42

3.4        CNC machining. 43

3.5        Machining-Milling & Turning. 44

3.6        Assembly and Alignment 44

Chapter 4 - Testing and Result 46

4.1        Testing Background. 46

4.2        First Run. 46

4.3        Time Attack. 48

4.4        Testing result 49

Chapter 5 - Problem Solving. 50

5.1        Design problems. 50

5.2        Manufacturing problem.. 51

Chapter 6 - Conclusion. 52

Chapter 7 - Further Development 53

Chapter 8 - Team-working & project management 54

8.1        Project activity schedule. 54

8.2        Work distribution. 56

8.3        Bill of materials. 59

Reference. 60

APPENDIX A: Conceptual Drawing. 62

APPENDIX B: CAD Drawing Layout 75

Chapter 1 - Introduction

1.1  Introduction

The main purpose of manufacturing project is to improve the performance of a human powered vehicle (HPV) for a coming Hong Kong 24-hour pedal kart competition. The general approaches to achieve the purpose include maximizing propulsive forces generated by the human, and minimizing resistive forces generated from the vehicle and external environment. And, utilization of the data collected from the previous HPV and modification of the HPV design will be main concerns of our team for the design of new pedal kart. In this project, our team focused on reduction of rolling resistance of the HPV, such as the material and geometry of the frame body and wheel.

 

1.2  Objectives

The project is to reduce the rolling resistance of the pedal kart and those resistances could be affected by the frame structure, material weight, steering system, performance on speed, racing time through the researches. The new design has to consider the requirement of 24 hours racing duration and fabricated in the manufacturing phase.

 

To achieve the objective, it has to classify which part is the most effective affect the friction. And then redesign it to achieve the goal. In design phase, it has also considered about the manufacturing process which ensure alignment error would not be occurred. Before design the pedal kart, material selection and calculation (stress and strain) should be thought correctly.

 

1.3  Scope

To reduce the rolling resistance, it should consider about the weight and properties of material. The component and frame using the right materials which ensure there are not over design. Also, the alignment of shaft, brakes and pedal should be high accuracy which can reduce friction and heat loss. In addition, the design of the frame should be considered the loading distribution. The evenly loading distribution can reduce the extra energy losing through moving.

 

Also, the losses may because of the bad suspension alignment which affected by toe, castor and camber. The track, width and bending of the frame will also affect the stability and cornering. The design should also consider the ergonomic which provide the best sitting position for the driver.

 


Chapter 2 - Design Concepts and Evaluation

2.1  Product Requirement & Design Specifications

As the objective of our project is to reduce the rolling resistance of the pedal kart, the design of the new pedal kart was focus on performance, structure, and aerodynamics areas to reduce the resistance.  Numerous research has done and information is collected from other design, such as trike, go kart and others racing kart in others grand prix in the world. The design of the new pedal kart is based on statistics facts, the ideas from group mates and inspiration from others. The design and function of the kart was tried to make use of the regulation from the organizer listed below.

 

Ø   Number of Road Wheels

Ø   Configurations of Road Wheels

Ø   Dimensions

Ø   Motive Force

Ø   Maneuvering

Ø   Braking

Ø   Mirrors

Ø   Seating

Ø   Fairing

Ø   Safety

Ø   Identification

Ø   Lighting

 

2.2  Research Study

In order to distribute the work, the kart has to be divided into parts. The main parts are: frame, suspension, steering, transmission, and seating. Therefore, work is allocated for these 5 main parts and will be further evaluated on the following page.

 

Functional requirement

Ø   Rear wheel drive

Ø   Differential or single drive

Ø   Front wheel steering by steering wheel

Ø   Adjustable toe and camber

 


Previous design information

描述: F:\py.bmpFrom the previous race experiment, POLYU have entered 2 pedal karts in the 24 hours race. First kart with front wheel drive (FWD) and steering (FWS) and the second kart with rear wheel drive (RWD) and front wheel steering (FWS).

 

The race result shows that the second kart was faster.

Due to:

Light weight ~25kg

Rear wheel drive

Front wheel steering

Go balance of wheel base length

Differential drive

 

As the function of steering and driving is separated into front and rear, better acceleration and braking for FWS and RWD kart. Also as the function are separated, it is easier to repair and maintenance. In addition, in order to be more competitive, the new pedal kart will include adjustable camber, castor and toe to adjust the kart to suit the race track.

 

Weight distribution on both shafts

The other major design concern is the weight distribution. It affects on the pedal kart performance.

 

Three major weight distribution types:

Weight type

On or Above front wheel

 

Between both wheels

On or behind rear wheel

Pros

Ø Conventional

Ø More weight on the front wheel

Ø easy to manufacture

Ø large leg room

Ø steering between seat and front wheel

 

Ø  More practical use of length

Ø  Good on acceleration and cornering

Ø  very little momentum lost

Ø  balance distribution of weight on both wheel

Ø  Weight distributed on rear wheel

Ø  Good on acceleration

Ø  steering between seat and front wheel

 

Cons

Ø Weight distributed

Ø On front wheel or above

Ø Momentum lost while cornering

Ø  Unconventional

Ø  Larger frame

Ø  limited leg room

Ø  steering above front wheel

Ø  Higher height

Ø  Larger frontal area is consume

Ø  unconventional

 

 

描述: F:\1.bmp      描述: F:\2.jpg      描述: s3.jpeg

 

1. On or above front wheel         2. Between both wheels             3.On or behind rear wheel

 

 

The between both wheels type weight distribution is selected due to its good performance, acceleration and cornering characteristics. Also, it will be possible to install an adjustable suspension arm on this type of kart due to less weight is situated on the front wheel.

2.3    Initial Investigation

20120307_094033As primary purpose of improving of performance of HPV, the geometry of the existing FUN pedal kart was first investigated. As the modification for the existing one, the vehicle is disassembly, and features and dimensions of the different parts were measured, to investigate the possible improvements for the performance.

 

Features of the pedal kart:

General geometry (mm)

Technical details

Weight(lbs)

Length

1504

Custer angle

Body shell

20.5

Width

778

Camber angle

Chair

10

Wheel Base

720

Kingpin angle

30°

Chassis

24

Ground clearance

170

Maximum turning angle

21.55°

Steering

7

Seat height

340-310

Turning radius

1.55m

Driveshaft and front frame

16

Net weight kart

92.5

 

FWD/RWD drive

The steering behaves under power is dependent on the weight distribution and the friction coefficient of the tire and road surface.

 

The design of existing pedal kart is front wheel drive adjustable bottom bracket (BB) with double drive chain. For front wheel drive (FWD), the steering behavior will be oversteering, and weight is thus distributed to the front wheel more than rear wheel with a ratio 60:40 or higher. However, during accelerating the pedal kart, weight will transfer to the rear tires, giving less traction to the drive wheels and the front tires are being overworked when cornering by being required to both apply power and steer the vehicle. If the functions of braking and steering of the pedal kart are separated, that can reduce the problem. Therefore, a RWD will handle better and be faster than a RWD car.

http://jetrike.com/fwd-or-rwd/figure7.gif

For rear wheel drive (RWD), the steering behavior will be under steering, and the weight distribution of front to rear wheel is about 30:70. The steering and braking systems are separately located at the front and rear wheels.

http://jetrike.com/fwd-or-rwd/figure3.gif      http://jetrike.com/fwd-or-rwd/figure5.gif

 

Furthermore, the chain line system of FWD is relatively simple in comparison t o RWD. For the existing FWD pedal kart, its transmission system basically composed double crank, gears and free wheel with double chain line to drive the front wheels; whereas in RWD, the system is more complicated, a chain line is driven to carry rear wheels with a differential gear.

 

Steering system

For the steering system, above seat steering (ASS) has commonly been applicable to the recumbent style trike overseas, and the trial of the availability of ASS in the competition is our main concern rather than using traditional under-seat steering (USS). The ASS system is relatively uncomplicated mechanically, and easier for the beginners to master the vehicle, and simpler to attach fairings to the handlebars.

 

Centre of gravity

Moreover, from the investigation, the ground clearance of the existing pedal kart was about 170 mm. During driving, if the centre of gravity of the pedal kart closed to the ground, it benefits the stability, and thus prevents overturning. As the ground clearance can be reduced, the centre of gravity has a tendency to be lower and close to the rear wheels.

 


Frame structure

The frame has major change compare to previous pedal kart. Hexagonal arrangement of frame of space frame structure. For RWD, the shape of frame has to also be modified for more light weighted with a rigid structure.

 

http://t1.gstatic.com/images?q=tbn:ANd9GcQTi3TXtjtJh1uZQhz1zRFHi6VSANHmNV3zSXCXKWepSs6SFDfPaAThe other major change is the suspension geometry. From the research, this mainly depends on the caster, toe, and kingpin angles at the front wheel. First, during pedal kart cornering, the wheel and body will roll over, so the tire contact patch become larger, and thus the rolling resistance will increase. The negative camber can improve performance of the pedal kart during a corner. If the camber angle has been adjusted properly, the wheel will roll over to zero camber. Therefore, as turning a corner, the rolling resistance between tire and road surface will be minimized.

 

Second, toe can be altered on the front wheel by adjusting the toe control rod ends. As the competition site has mainly curved shapes pathway more than straight roads, toe-out encourages the initiation of a turn for pedal kart. The toe-out favors the quick steering response, and also reduces the tire wear and power loss in order to reduce the rolling resistance. In addition, the kingpin angle, along with the castor angle, affects the self-centering action of the steering. A little degree of positive castor angle will provide stability and make the steering wheel straighten out after cornering. And, in general, kingpin angle is set to get the pivot point as close to the tires contact point on the road as possible. That prevents the wheel to scrub the ground when turning.

geometry_11302383064

 


Drivers comment

During our investigation, some previous drivers have been inviting to enquire their experience and suggestion for pedal kart. Here are the remarks:

·          short wheelbase, seating is as straight as possible

·          polyu racer have a better speed and braking but will roll over for fast and sharp corner, the fun kart is heavier and may lock the wheel during braking but have a good stability when cornering in dry condition, drifting may occur during on wet roads.

·          Driving for USS is a bit shaky if light and will pull the handle towards the driver

 

By analyzing, it’s good characteristic of braking and speed is due to its light weight and wheelbase. However the rollover of the kart is due to the height of the seating. For the fun kart, it has an opposite characteristic of the racer. It has a good track which helps it corner neatly but due to FWD and steering and light rear, it may drift  during slippery condition. In addition, the shaky of USS is the nature of itself  and the drivers tend to pull both steering handle together during driving unintentionally.

 

Design Parameters

After the research, these parameters are set to be followed:

Total weight: 15-25kg

Wheelbase: 1100

Track: 870

Overall length: 1500

Drive: rear

Steering: front steering wheel (ASS)

Ground clearance: 165mm

Adjustable toe and chamber


2.4    Main Design Features

 

Frame

描述: f1.JPGThe frame design focus on the structure, dimension require and the manufacturability. Hence in order to reduce weight, smaller square tubes are used as the building block of the frame. A flat frame was an idea developed. In the researched information, a medium (800-1200) length of wheel base and around 800mm track which gives better stability during the acceleration and deceleration. Also the seating was designed to put the driver at the center back of the kart. Combining with rear wheel drive, it is expected that the frame will give the kart a good acceleration and handling characteristics.

 

描述: f2.JPGSquare tubes are used because it is easier to weld and machine. The tubes are about 25mm to 32 mm for SI unit and 1” and 1 1/4” for American unit.

 

The frame is generally a flat type frame. The target is to use the similar length or reduce the length of tube compare to last year kart and achieve a frame about 5-7kg. Multiple small tubes are used and arranged into triangular and hexagonal shape to mimic the space frame structure.

 

As the frame becomes a semi space frame structure, it will provide better stability, flexibility and distribution of force. The frame is expected to add the rear upright, upcenter and front spindle and suspension arm using bolt and nuts. This feature helps the alignment to be adjusted if any problem occurred. The addition of these components can also provide more dimensional support. They can also suspend the frame to a lower position for a lower ride height.

 

描述: altube.jpgThe frame will use aluminum instead of mild steel tube. Due to aluminum light weight and good strength enables us to produce a high performance kart. Further information of material selection will be listed later.

 

描述: c1.JPG

Seating

The seating uses an ordinary trike chair. The chair consists of “L” shape plate and extendable rods on the rear. The use of this chair is because the seating height can be greatly reduced. The chair can be tilted in various angles for different driving style. Also the chair position can be changed using fitting nut in holes on the frame.


Suspension

Since the nature of racetrack is a football playground with minimum bumps, installation of vibration damper is not necessary and excluded from the suspension design.

 

1. Front suspension

camber_and_scrub_radiusA pair of suspension arm is adopted for the front wheel suspension, in order to remain simplicity of the design and support the front wheels. The special design front suspension arm is made by bended circular tube connected to a circular “t” joint and threaded round cylinder for adjustable camber and castor.  Rod ends are used in to the arm for better maneuver of the arm. The spindle and suspension arm are inclined with a caster angle in attachment of the front axle steering to assist steering of the pedal car. By loosen or tighten the rod ends and screw, the castor, camber and ride height can be adjusted.

 

2. Rear Up-right/upcenter bracket

Unlike the design of the front bracket, the rear one utilized a perpendicular holder block. This would help lower the ride height and hence the center of mass of the pedal car for better cornering characteristics. The blocks consist of upright and upcenter. They are the main supporting of the rear to support the weight of the kart and the force of the driver (power and weight). The two holes on each block are used to allow the drive shaft to pass through and install a supporting bar for better structure of the rear alignment. A small hub is drilled to install bearing for the supporting of the shaft and to eliminate friction.

The previous pedal kart design was more complicated and more supporting was needed due to more strength is added on the front wheel. The advantage of the these design is the simplicity of the rear suspension due to lighter weight and less function is subject to the rear.

 

            

 

Steering

The steering system of a vehicle is the combination of steering-related components, also linkages among these components and the vehicle main body. The function of steering system is to make the vehicle able to follow the desired direction when travelling. The overall steering performance may be affected by several parameters setting like kingpin angle, caster angle, camber angle, toe value… and their effects are always interactive to one other. An ideal steering system means highly effective, compatible, operable and taking good balance between stability and flexibility.

 

In Human Powered Vehicle (HPV) project, an entirely hand–operated simple mechanical steering system is adopted. The working principle of this steering system is to turn the front wheels into desired inclinations by applying steering torque which transmitted mechanically. It mainly consists of handling (e.g. steering wheel, U-bar), transmission (e.g. steering column, universal joint), linkage (e.g. tie rod, drag link) and connective parts (e.g. bellcrank, knuckle lever).

 

1. Design Considerations

While designing the steering system, the main considerations include:

  1. Geometry of the kart, especially the structure of chassis, location of front wheels, track width and seat position.
  2. Selection of linkage system, to beware of any potential collision and reduce complexity.
  3. Handling performance, like ease of operation, synchrony and sensitivity (related to steering ratio).
  4. Cornering performance, like steering tendency and effectiveness, which depended on different steering geometry, e.g. Ackerman compensation, camber, caster, toe...
  5. Ergonomics and comfortness.

 

The consensus is to build a simple and effective steering system, which is also highly compatible with the geometry and other parts/components of the kart. And the final solution is adopting Over Seat Steering (OSS) with Forward Dual Drag Link System. Below shows some general comparison between the over seat steering (OSS) and under seat steering (USS) and further explanations about the decision.

2large2
2. Comparisons between 2 major kinds of steering solution for pedal kart

Steering Wheel (OSS)

U-Bar (USS)

  • Shorter steering  torque length
  • Longer steering torque length
  • Smaller body motion
  • Larger body motion
  • Shorter drag links required
  • Longer drag links required
  • Without interfering foot motion
  • Easy to interfere rider’s heel (also the chain)
  • Natural and sensitive control
  • Sportier and lighter control
  • Extra lateral support maybe required
  • Better lateral support

 

Basically, the OSS has the advantage of lower weight and simpler structure, also a more natural control. Besides, it is safer than USS since rider’s range of motion is smaller and their hands can be kept away from rotating wheels, ground and external. More importantly, the OSS facilitates the setting of linkage system, as the length of drag links is much shorter, it helps to increase the transmission efficiency of steering torque, and also it will not cause any interfering to pedaling motion and the suspension part of the kart. Other reasons for choosing OSS include a narrower track width configuration, smaller frontal area and hence improved aerodynamics. However, the OSS may have the problem of causing arm fatigue under long term riding and have greater challenger on designing ergonomics.

 

Possible drag link setting if adopt:

Red line: Steering wheel (OSS, Forward Dual Drag Link)

Blue line: U-bar (USS, Aft Crossed Dual Drag Link)

 
                 

 

From the graphic shown on above, it is easy to discover the U-bar system set in the aft section of the kart is less compatible with other parts and has a higher possibility of blocking foot motion while pedaling.

 


3. Main Components and Parameters

Components:

  • Steering Wheel/handle
  • Steering column
  • Bell crank
  • Kingpins
  • Drag links with ball  joint ends
  • Universal Joint
  • Adjustable supporting column

Parameters:

  • Steering Wheel/handle Size
  • Steering column length
  • Steering column inclination
  • Drag link length
  • Knuckle lever length/inclination (may affect the Ackerman geometry)
  • Kingpins angles and length

 

Since an over seat steering is adopted, there is a steering wheel in handle form, which is set in front of the driver. Its shape and size may affect the ease/comfortness of handling. Also, there is a steering column for transmitting the steering torque to the bell crank, and then to the Knuckle lever of the kingpin via the drag links .An universal joint is used to connect the steering column and bell crank, instead of fixing them together for enabling an adjustable steering column inclination. Also, there is a length adjustable supporting column, which provides a collapsible function and increase the convenience of getting on or off the kart when replacing drivers.

 

Steering handle and Shaft:

Handle size         

- 250 mm

Steering column Inclination

-35O ~ 90O

Steering force required

-30 ~ 50N

Kingpin:

Kingpin angle

-12o

Knuckle lever length

-115mm

Caster angle

-0 ~ 5o

Camber angle

-5 ~ 5o

Bell crank and drag links:

Bellcrank arm length

-57mm

Turning ratio of handle to wheel

-2:1

Drag link length:

-365 ~ 375mm

 

Some important design parameters are given above. The arm length of the steering handle is 250 mm and the expected steering force required under static loaded situation (total weight of kart and driver) is around 30 - 50N. The kingpin angle is set to 12o while the camber angle and caster angle can be tuned within a certain range, from -5o to 5o and 0o to 5o respectively. In addition, the length of knuckle lever is 115mm while 57mm for the bellcrank arm.The steering ratio of handle to wheel is about 2:1. The drag link length is also adjustable from around 365-375mm for setting toe in or out value. Functions and details about these parameters has been discussed in perious sections.

 

4. Linkage System

 

   

 

As mentioned, a very direct Dual Drag Link System is selected in this project, mainly for better fitting with the forward kart structure and easier installation or tuning, since there is no knuckle-to-knuckle drag link which may line across the whole pedaling space. The bellcrank is installed nearly on the same level of the knuckle lever from view of front to improve the torque transmission. However, they are not parallel from view of top and the lengths of bellcrank and knuckle lever are not equal. Also, during manufacturing process, there is no inclination between knuckle lever and kingpin from view of top for the reason of lowering difficulty of welding them together. These factors may diminish the Ackerman compensation, or even cause anti-Ackerman effect. Beside, another effect of unequal bellcrank and knuckle lever length is causing a less sensitive steering (steering ratio about 2:1) and hence smaller steering torque input is required.

 

5. Analysis on Steering Effectiveness

To analyze the steering effect basically, some simple simulations are done by Solidworks to find out the steering geometry under different toe setting, hence to figure out the optimized parameter. For each case, only situations of totally pointing forward and maximum steering (steering wheel turned angle = 35o) are considered. Besides, calculation of the smallest turning radius of the kart is as below:

Smallest possible turning radius: track / 2 + wheelbase / sin (steering angle in degrees)

Where track = 880mm and wheelbase = 1100mm

 

Length of drag link: 367 mm

Static toe out: 0o

Wheel inclination (Outward): 21.34o

Wheel inclination (Inward): 17.01o

Average wheel inclination: 19.18o

Smallest possible turning radius: 3748 mm

Length of drag link: 370 mm

Static toe out: 2.5o

Wheel inclination (Outward): 18.53o

Wheel inclination (Inward): 18.53o

Average wheel inclination: 18.53o

Smallest possible turning radius: 3861 mm

Length of drag link: 372.565 mm

Static toe out: 3.7o

Wheel inclination (Outward): 16.33o

Wheel inclination (Inward): 19.80o

Average wheel inclination: 18.07o

Smallest possible turning radius: 3986 mm

 

One of the problems found is the Anti-Ackerman effect. Normally, the outward wheel is travelling in a path with larger radius than the inward one during a turning and this result can be achieved from Ackerman compensation. Without Ackerman effect, the wheels are parallel (parallel steering) or turning center is diverged out by the inward and outward wheels (Anti-Ackerman steering). This may cause wheels scrubbing instead of leading the kart to turn while cornering (under steering), hence cause the tires to wear out and increase the steering difficulty. Anti-Ackerman effect has a more significant influence during slow cornering and large steering angle, but affect slightly if the steering angle is small and is counteracted if a certain static toe out is adopted (see from the simulations).

 

6. Improvements

In fact, the Anti-Ackerman effect does not mean bad all the way. There is no firm answer to say whether Ackerman or Anti-Ackerman is better under all situations although most of vehicle adopt Ackerman geometry since it sounds more reasonable and practicable. On the other hand, the Anti-Ackerman design can still be found on some race car. Some researchers claimed that Ackerman geometry should be a function of tire curve and Anti-Ackerman should have a better performance for fast cornering situation since it can help to maintain steering stability without losing high speed while turning.

 

Nonetheless, some measures have been done to relieve the negative effects brought by Anti-Ackerman effect. Firstly, the steering angle is limited within a small angle (maximum not exceed 20o) by a steering limiter. Secondly, static toe is applied, which can partially compensate the Anti-Ackerman effect (mainly consider the maximum steering angle as the Anti-Ackerman affect slow cornering more). However, toe out is also one of the sources of rolling resistance and may lead to further wearing of the inner side of the front wheels, so it should be considered very carefully (usually not more than 3o toe in/out is still acceptable). Besides, apply back a parallel steering (connecting the two steering knuckle lever directly by a tie rod) is another way to relieve the Anti-Ackerman effect. The advantage of this method is only a little static toe out is needed to compensate the Anti-Ackerman. This can be done by adding a specially designed tie rod which can dodge all components and pedals in the forward section of the kart. But it may increase the overall weight and complexity of the steering system.

 

The blue part in the graph on top shows the tie rod connecting the two steering knuckle lever directly without causing any collision.

 

The dotted lines shown on the bottom graph indicate that the tie rod can help to achieve a parallel steering geometry under zero toe setting, which should theoretically provide a better steering effect than the original design.

 

 Moreover, as this effect only influences slow cornering with small turning radius, but the smallest corner radius of the vane is about 10m (smallest possible turning radius is about 3.6m only ), which means serious scrubbing will not happen so easily if a larger turning radius is adopted while racing.

 

Other improvements include redesigning the steering wheel to provide a better shape/size for long term operation and adding an extra universal joint on the steering column to increase the degree of inclination for better ergonomics. Loosen parts may also cause the delay feeling and increase the handling difficulty, so it is better to ensure all parts are connected firmly by adding pins, installing fixer and filling up the cavities between contact surfaces.

 

Transmission and rotation support

In the system of transmission, front and rear are divided for illustration

 

1. Front wheel

描述: s2.JPGFront Wheel is the free wheel. Although there is no power transmitted over it plays role to steer and brake. For the design of Front wheel spindle, some spaces should be saved for installing the brake disc and brake caliper. As it is specially design for the pedal kart, wheel change is very common during race. It is installed by nuts and spacers for the prevention of wheel separation during operation. The frictional forces between the wheels can be reduced by adding the bearings on the stud shaft.  

 

描述: s1.JPGThe spindle of front wheel is the common part for steering and braking system. The brake system is separated to two parts, brake caliper and brake disc, the brake is mounted on the wheel. When the wheel has to replace, the brake disc will be replaced while the brake caliper will be remain on the spindle. A rod is tilted out on the spindle for the installment of the steering rack.

 

For the consideration of Kingpin angle, the inclination of 12 degree is made at the joint point between shaft and suspension. The 12 degree is common used and suitable due to the space needed to remain for brake and steering. A smaller angle is not likely due to space limitation and higher scrub radius and larger angle will cause excessive height change due to cornering.

 

描述: s3.JPG2. Rear wheel

Rear Wheel is the driving wheel and is connected to the cookie, connector and shaft for power. There is no braking system as compare to front wheel. The brakes on the rear is not necessary due to the speed of the kart will not be too fast to cause wheel spin. For rear wheel, the major concern is the connection of the shaft and wheel.

 

3. Rear connector and cookie

描述: s4.JPG描述: s5.JPGThe shaft of rear wheel is the one of major parts of the pedal kart. The design of shaft is the most concerned due to power output. The torque subjected to the shaft is very high that the diameter of shaft should be considered properly. A standard shaft of 17mm diameter is used provide by samagaga. To install the wheel, nuts are used to mount on the cookie’s hole. The torque transferred is mainly on the cookie, which means the dimension of stud for locking the wheel is not crucial, it is supposed 10 mm diameter will be fine. The connector is the loading region for the kart weight which will also install into the upright, due to the high concentration of weight the diameter should be larger, about 20 mm diameter. The last part of shaft is the connection between shaft and connector and cookie. Grub screw and key are used to join them together to the differential gear and the cookie respectively.

 

4. Gear

描述: F:\IC349\photo\IC349 photo\IMG_20120626_153443.jpgThe previous years freewheel and differential are used in separated karts, the kart with differential was rank higher after the race, and the universal joint of one shaft was borken on the other kart.This shows us the reliability and go performance by differential.

 

Since there is the velocity difference between left and right side when the kart is turning, the wheel will slip if a solid shaft is connected to both wheels. A differntial is a device to provide the right amount of torque and turns to two wheels while cornering. A differential is suggested to use from samagaga.

 


 

 

 

 

 

 

5. Gear Ratio

The gear ratio uses a common 53 to 16 ratio. The main reason is that it is a ratio that is moderate for the pedal kart. As the pedal kart have to start and run during high speed, the ratio of 16 as the second gear to first gear of 53 is suitable for all rounded situation.

 

 

 

 

 

 

 

 

Bottom Bracket and support

描述: p1.JPGBottom bracket is a common part of bicycle. It provides a freely driving medium and holds the crank and pedal. It also under a lot of torque and stress due to the power is produce on this place. In order to reduce weight, the joint method can be modified. In the design, two square tubes and a bottom bracket to arrange a triangular support with a long tube on the frame hold on it.

 


 

2.5    Material selection

The common possible materials for frame of bicycle:

Aluminum Alloy, Magnesium Alloy, Fibre Glass, Carbon Fibres, Steel

 

 

Availability

Cost

Density

Yield strength

Machinability/ Processability

Total scope

Aluminum alloy

4

4

3

2

5

52

Magnesium alloy

3

3

2

1

3

36

Fibre Glass

2

2

4

4

2

44

Carbon Fibre

1

1

5

5

1

43

Mild Steel

5

5

1

3

4

50

Weighting rate

3

4

5

2

1

52

1= the lowest scope, 5 = the highest scope

 

From the above material selection process, aluminum has highest rating for the main raw materials of the frame. Thus aluminum is selected to replace mild steel used in existing vehicle for the major frame structure and parts as aluminum is relatively easily to be brought, machined, and recycled. With its mechanical properties, aluminum has moderate density with high elastic modulus and tensile strength. In addition, there are different series of the aluminum alloys in the market. A few of the commonest aluminum alloys in the market are selected to further compare their suitability of raw material of the frame.

 

Table comparing properties of various common aluminum alloys:

Wrought alloys

 

Characteristic

Pros

Cons

5000 series

Alloyed with magnesium, non-heat-treatable, commonly used in decoration

Relatively cheaper, good welding characteristics, good corrosion resistance

Heavier weight with lower strength, less elastic, less machinability

6000 series

Alloyed with magnesium and silicon, heat-treatable, commonly used in construction, buildings

good formability, good corrosion resistance, relatively cheap price, moderate weight with medium strength,

ease of welding, high availability

Need heat treatment for hardening

7000 series

alloyed with zinc, commonly used in aerospace and automotive

The most light-weight, with strong strength, highest machinability

Very expensive,

relatively lower availability

 

After that, the 6000 series aluminum alloy is found to be the most suitable for the material of the frame. By the way, among 6000 series Al alloy, 6063-T6 which have been processed by solution heat treated and artificial aged, and is also the commonest metal used. And, its tensile strength (45,000 PSI) and yield strength (40,000 PSI) are high enough to achieve the requirements of the material of the frame theoretically. However, 6063-T1 may loss half its total strength when welded. Therefore, a post heat treatment process is required to harden it again.

 

In addition, the shape of the aluminum tube is also vital factor affecting the whole frame structure. With the loading, the frame will suffer mainly both compression and bending force, even a large impact moment if crashing. For the similar diameter to wall thickness ratio, in comparison with the round-shaped aluminum tube, square-shaped one can resist higher downward loading stress before buckling according to mechanic properties of solid. More importantly, the square-shaped tube has an advantage of ease of design and manufacturing process as the edge of round-shaped tube need to cut the curve fixed between joints for welding. That will consume more time and increase uncertainties of the frame. Therefore, the square-shaped Al tube is selected for the frame structure.


Reference information

 

Al5000

 

Al6000

 

Al7000

 

Testing in laboratory

For testing the actual mechanical properties of the tube, a sample of 25mmx 25mm with 2.5mm thickness of square-shaped 6063-T6 aluminum tube were cut into a specific shape and carried physical tests in laboratory. And the testing results are shown below.

 

1.      For the stress-strain test,


 


Specimen

Grip Separation

mm

Thickness

mm

Width

mm

Peak Load

N

Peak Stress

MPa

Strain At Break

mm/mm

Modulus

MPa

Mean

121.090

2.570

25.580

11870.063

180.6

0.158

66506.326

Specimen #

Break Load

N

Elongation At Break

mm

Elongation at Peak

mm

Stress At Offset Yield

MPa

 

 

 

Mean

9522.983

3.948

2.786

145.366

 

 

 

 

2.      For bending test,

 

Ultimate Tensile Strength

266.2

MPa

Modulus

72652.831

MPa

Peak Load

201.459

N

 

Experimental funding:

From experiment, the tested sample had resisted 201N bending force and 11kN tension force respectively at maximum. And, its tensile strength is about 260MPa with 66GPa of elastic modulus. That showed the sample had a relatively higher bending and compression resistance. For the exact square shape of aluminum tube, the mechanical strength will be much stronger, so it is suitable for the material of frame preliminarily. And, further testing and prototype are needed to ensure the material achievement the performance of supporting perfectly.

 

Tolerance:

The standard tolerance used in the project follows International Tolerance grade as the common standards in engineering.

 


2.6  Simulation

-Factor in static / rough motion (deflection, safety factor, stress)

 

The frame is the most influential consideration of the pedal kart design and thereby the simulation is needed to give the supporting and the result analysis of the frame’s design and thus to ensure its stability and also set some scenario during the simulation by using SolidWorks. The following will list out the result analysis:

 

Different cases

Analysis ( Loading: 1000N)

Front back deformation

As the result shown out, there is 1.32 mm of the maximum deformation in y-axis displacement. It is an acceptable value by simulate the real case of the frame’s design. Moreover, the force concentrate on the position of the seat and the result is similar with our ideal weight ratio which is 3:7. It means 3 in the front and 7 in the rear.

Left right deformation

As the result shown out, there is 1.319 mm of the maximum deformation in x-axis displacement. It is an acceptable value by simulate the real case of the frame’s design. The result analysis is similar with the y-axis displacement.

Safety factor

Refer to the standard searched on the internet, there is necessary to consider the safety factor on each product design. Therefore, we simulate the SOF and have the expectation to fulfill the needs (around 3).

As the result shown out, the frame’s safety factor is nearly 3.5. It‘s definitely achieve our requirements. So that is an acceptable value of the design.


2.7  Design Optimization

In fact, the final design of the pedal kart has been modified many times for different reasons. From the existing pedal kart to the exact the new one, a huge of design concepts were generated, and continuously changed for improvement of the performance of the functions, the control of cost, reduction of the over-designs and simplification of the manufacturing process. Here, the various designs generated for different systems of pedal kart were shown with reference to the existing one.

 

Frame

Previous Design

1.       Mild steel frame was the main source of the heavy weight of pedal kart.

Initial Design

1.       It is difficult to produce the frame rod with angles  with 3 axis and also make the fixture for welding

2.       Any inaccurate angle at the front will lead the frame accumulation errors

Final Design

描述: f2.JPG

1.       For the horizontal frame, it is easier to manufacture and weld each part into a frame.

2.       The frame structure has been further simplified.

Seating

Previous Design

1.       The supporting rod of the seat was not compatible with the frame design.

 

Initial Design

1.       The prototype of the design was very uncomfortable for the driver.

Final Design

1.       For simply the process, the original seat was used, with a seat jointing to the frame.

 

 


 

Pedal

Previous Design

 

 

 

 

 

 

1.       For FWD, two 53 gear discs with double chain line were used at BB.

Initial Design

1.       For RWD, two sheet metals were designed to hold the pedal, but the bending resistance was weak, and distortion might occur.

Final Design

1.       Triangle structure made of Al tubes was used to support the pedal to raise the bending resistance.

 


 

Supporting

Previous Design

1.       The supporting for the rear shaft was composed of mild steel tube, and thus increased the weight.

Initial Design

1.       The rear shaft system was only supported by two aluminum brick, so that lead high stress concentration factor at contact surface.

2.       With applying strong twisting force, the frame would have a large degree of deformation. 

Final Design

     Upcentre                                 Upright

 

1.       Al tube was added to the back to enhance the twisting resistance.

2.       4 Al brick were used to distribute the loading more evenly for the rear shaft.


 

Steering

Previous Design

1.       For under seat steering.

Initial Design

1.       For above seat steering, the steering rod had a large vibration, and that reduced the steering sensitivity.

Final Design

1.       For ASS, an extra steering rod and L-shaped guider were added to fix the steering rod in position.

2.       Thrust bearings were added at some contact surface to reduce constraint.


 

Suspension

Previous Design

1.       The design could not adjust the kingpin, castor, and camber.

Initial Design

1.       C-shape oriented at a specific degree with the frame. That increased difficulty of manufacturing.

2.       The design of C-shape was not able to adjust the kingpin, castor, and camber.

Final Design

1.       The design can adjust the castor, kingpin and camber easily.


 

Power Transmission

Previous Design

1.       The transmission shaft was composed of two freewheels to drive the front wheels.

Initial Design

1.       The design was composed of a differential gear and freewheels to drive the rear wheel.

Final Design

1.       The design was similar with the progress one.

 


 

Overall Design Optimization

Previous Design

Initial Design

Final Design


Chapter 3 - Manufacturing Process

3.1     Process Planning

Manufacturing process is the most important process that to make the prototype of a design. It is a systematic sequence of actions that combines resources to produce output a new product. And the project will undergo different types of manufacturing process, such as Milling machine, lathe, CNC (Computer Numerical Control), welding…etc. The process planning is described as the following:

 

 

After the optimized design have finalized the manufacturing process then planned based on the shape of raw materials, characteristics of materials, tolerances, etc. The frame was planned to be fabricate firstly and joining all rods welding, then paid attention to the casting and machining by CNC or manual operation. If the parts are qualified including surface finishing and dimensions, then it will pass to the assembly section to join all parts together by use of screws and nuts to form a final product for the next step. The following is the description of manufacturing process for each part:


 

Parts name

Manufacturing process

No. of process

Frame

Frame_Block

Manual milling, drilling, welding

3

Frame_Rod_1

Manual milling, drilling, welding

3

Frame_Rod_2

Manual milling, drilling, welding

3

Frame_Rod_3

Manual milling, drilling, welding

3

Frame_Rod_4

Manual milling, drilling, welding

3

Frame_Rod_5

Manual milling, drilling, welding

3

Frame_Rod_6

Manual milling, drilling, welding

3

Frame_Rod_7

Manual milling, drilling, welding

3

Frame_Rod_8

Manual milling, drilling, welding

3

Frame_Rod_9

Manual milling, drilling, welding

3

Frame_Rod_10

Manual milling, drilling, welding

3

Frame_Rod_11

Manual milling, drilling, welding

3

Pedal _Tube

Manual milling, welding

2

Front axle

Steering_T joint

Punching, drilling

2

Suspension_rack_Tube

Manual milling, bending

2

Rear axle

Rear_axle_part_1 (screw rod)

cutting

1

Rear_axle_part_2 (connector)

CNC turning, drilling

2

Rear_axle_part_3 (cookie)

CNC turning, drilling

2

Rear_axle_part_4 (key)

Manual milling

1

Rear_axle_key

Manual milling

1

Rear_support_ball bearing

Standard component

0

Rear_support_upright

Sand casting, manual milling, CNC milling, drilling

4

Rear_support_upcentre

Sand casting, manual milling, CNC milling, drilling

4

Seat

T_Joint

Standard component

0

Seat_Joint Plane

Manual milling, drilling, welding

3

Steering plate with steering guidance

Steering_Plate_Sheet

Punching, drilling

2

Steering_Plate_Tube_1

Manual turning

1

Steering_Plate_Tube_2

Manual turning

1

Steering support

Steering_supporting_shaft_part1

Manual milling, drlling

2

Steering_supporting_joint_part1

Manual milling, drlling

2

Steering_supporting_joint_part2

Manual milling, drlling

2

Steering_supporting_shaft_part2

Manual milling, drlling

2

Steering wheel

Steering_steering wheel

Cutting, bending, drilling

3

Steering_steering shaft

Cutting, drilling

2

Steering_U joint_connect

Manual turning, drilling

2

Steering_U joint_Part 1

Manual turning, drilling

2

Steering_U joint_Part 2

Manual turning, drilling

2

 


3.2    Welding

 

Welding fixture> Welding

IMG_20120528_164824First of all, the frame have been separated into 3 parts and thus to make us easier considering the fixture. Then, a fixture is used to fix the welding point of the frame and thereby increase the accuracy of the welding position and alignment.

 

By consideration of the cost, wood & nails are used to create the fixture. As product design, to optimize a product, process design is also considerable. The product obtained after process must be at target in terms of value of size, tolerance to be acceptable. For this reason, a product which is not affected by uncontrolled parameters must be planned on, in process design.

 

IMG_20120528_164853When these expectations mentioned to achieve standard production and continuous challenge are considered, the fixture is necessary to be created and fulfill the needs of welding standard. Moreover, welding fixture is designed and welding parameters, affecting distortions and residual stresses, such as welding speed and reverse distortion are taken into consideration.

 

 

 

Requirement of the fixture:

IMG_20120530_161026

 

 

ü   Support is mostly stable on fixture, it holds the work piece

 

ü   In the initial stage to locate part with required rigidity and in proper position, locating surfaces are determined


Welding methods:

There are three common welding methods used in general engineering field, let’s have a briefly introduction of them first.

Metal Inert Gas (MIG)

Arc Welding

Tungsten Inert Gas (TIG)

A continuous and consumable wire electrode are fed through a welding gun automatically

Strength higher than arc welding

More user-friendly than arc welding

Using a welding power supply to create an electric arc between an electrode and the base material to melt the metals

More nimble than MIG welding since it would not limited by the size of the gas nozzle at the welding gun

Using a non-consumable tungsten electrode to produce the weld

Most commonly used to weld stainless steel and nonferrous material like Aluminum

Applied for building up the whole aluminum frame

 

In our product manufacturing process, welding is the most important process to build up the whole frame of the pedal kart. In final, two types of welding method are chosen; they are TIG-Tungsten Inert Gas welding and electric arc welding.

 

TIG welding is finally chosen because of the specification of our material selection. Aluminum is selected and the thickness is decided around 2.8-3.0 mm. Therefore, welding process can carry out easier.

 

TIG Welding Benefits:

ü   Superior quality welds

ü   Welds can be made with or without filer metal

ü   Precise control of welding variables (heat)

ü   Free of spatter

ü   Low distortion

 

File:GTAW.svg

The process of welding:

Lists of the parts undergo welding process:

Parts

Frame_Block

Frame_Rod_1

Frame_Rod_2

Frame_Rod_3

Frame_Rod_4

Frame_Rod_5

Frame_Rod_6

Frame_Rod_7

Frame_Rod_8

Frame_Rod_9

Frame_Rod_10

Frame_Rod_11

Pedal _Tube

 


3.3    Casting

IMG_20120607_142907There are some parts of our design, need to use casting technology to manufacture. In final, sand casting is chosen rather than investment casting. The comparison between two methods will be listed out in the following:

 

Sand casting is used to make large parts (typically Iron, but also Bronze, Brass, Aluminum). Molten metal is poured into a mold cavity formed out of sand (natural or synthetic). The processes of sand casting are discussed in this section; include patterns, spruces and runners, design considerations, and casting allowance.

 

On the other hand, investment casting, a shape is formed (usually out of wax) and placed inside a metal cylinder called a flask. Wet plaster is poured into the cylinder around the wax shape. After the plaster has hardened, the cylinder containing the wax pattern and plaster is placed in a kiln and is heated until the wax has fully vaporized. After the wax has fully burnt-out, the flask is removed from the oven, and molten metal is poured into the cavity left by the wax. When the metal has cooled, plaster is chipped away, and the metal casting is revealed.

 

Comparison between sand casting and investment casting:

Sand Casting

Investment Casting

it can't allow for undercuts in the pattern, the pattern needs to be pulled out of the sand after it is packed

Lower- cost than investment casting

Easier operation and shorter time

Less steps and higher success rate

 

It can allow for undercuts in the pattern, the pattern is vaporized with heat

Hollow castings and thinner sections can also be made more readily

A better surface finish is generally achieved

It is a much more timely and expensive

It has a lower success rate than sand casting

 

By consideration of the time we have and the budget limitations, we decide to use sand casting to make some parts, such as up-right, up-center. After the sand casting manufacturing process, the parts will be machined in CNC machining process- Milling and turning.

IMG_20120607_151936IMG_20120622_170326
3.4    CNC machining

CNC machines used G and M-codes programming to control tools numerically for fabrication of parts automatically with high precision. The codes of parts geometry and the tools parameters encode into the program, and the tooling pathways can be preview and simulated on the screen of the machine. That facilitates the large production of specific parts with high precision.  

 


For the parts with low tolerance (.02mm), they were machined by CNC machine; for the parts with higher tolerance, they were processed by lathe and milling machine. In fact, the alignment of the two axles of the pedal kart is first priority of considerations for reducing the pedals rolling resistance. Therefore, the parts involved in the transmission system at the back has high accuracy to prevent any accumulative errors, in which the error will make the serious misalignment between the two axles and thus the driver waste force to overcome the resistance.

 

For simplification the manufacturing and achievement of the expected performance of the transmission system, a specific model of differential gear with two transmission shafts were ordered from Samagaga Company in Taiwan. For higher quality, the cookies and conductors used in transmitting the torque from the shaft to the rear wheels were also manufactured in CNC lathe; the uprights and upcentre used to support the rear transmission system also are milled by CNC milling machine, so that ensure they have concentric holes for supporting rear axle without frictions in the shaft.

 

IMG_20120618_165252                       IMG_20120618_165331

 

IMG_20120712_100513                     IMG_20120626_153417


3.5  Machining-Milling & Turning

IMG_20120705_164808Furthermore, for other parts such as spacers with tolerance (usually .1mm), they were produced by conventional lathe and milling machine because of the availability of the facilities and reduction of the production time. Therefore, the most of manpower were put on this manufacturing process. And, more spare parts can be produced for ready replenishment of the damaged parts during competition.

 

3.6  Assembly and Alignment

The assembly of the pedal kart consists for 4 parts.

1. Bottom Bracket, crank and pedal

2. Front suspension and spindle, steering system

3. Rear support and shaft

4. Transmission, wheels and seating

 

1. Install of Bottom bracket, crank and pedal (BB)

IMG_20120627_112739As the frame is finished welding, most of the parts are not install to it. As the bottom bracket thread container is welded on the frame, there is not necessary to move any parts or realign it. Therefore the bottom bracket and its related part- the crank and pedal can be install first.

 

2. Install the front suspension, spindle and steering system

IMG_20120621_171545IMG_20120625_090204After install the bb, the front suspension can be installed on the frame. There are two blocks each contain one hole for making a M10 thread to install rod ends. Meanwhile, the front suspension arm containing 3 rod ends can joint with the front spindle together. After that the combine arm and spindle can attach to the rod end on the frame to finish the suspension assembly.  Together, the front steering system-steering wheel, steering rod, steering support can also be installed on the frame and the suspension to further adjust the alignment. This moment, the steering can be adjusted to toe in/out, castor +/- or camber +/-. The adjustment must to be as symmetric as possible for a better ride.

 


IMG_20120627_1529333. Mounting the rear support and shaft

IMG_20120627_153723Once the front suspension and steering is done, the rear assembly comes next. The rear assembly consists of the upright, upcenter, rear support and the shaft, connector and cookie. The upright, upcenter and rear support bar is first assembly to the frame to find the correct position for the wheel base to be symmetric. The wheel base and height is measured on the flat platform in order to find a right wheel base and geometry of the kart. The rear assembly is adjusted during the measurement and clamped well.  Then holes are drilled on the frame and the block for assembly.  After that, the shaft, differential, connector and bearing can be installed on the frame with the block of upright and upcenter. The cookies are installed on the outside of the upright for the wheels later.

 

IMG_20120703_1058324. Attach the wheels and transmission and seating

IMG_20120705_105222Finally, the wheels can be attached on the shaft and spindle on the frame.  Then some suitable holes can be drilled on the frame to attach two pulleys. These pulleys can guide the chain when it is moving. Next a long chain with suitable length is connected between the front bottom bracket gear and the differential gear. After that, 4 holes are drilled on the frame for the assembly of the seat. 2 holes are for ordinary people and 2 for taller people. The seat is attached to these holes with two extendable rods will support the rear of the chair. These rods will be connected to the rear support bar for more strength.  Finally, all of the parts of the kart is adjusted and tighten before the kart can be driven.

 

5. Fine tune the pedal kart

IMG_20120628_091753The assembly is arranged in an order that the alignment can be correct on all 4 wheels. It is advice to drill require holes on the frame before welding. However, as the frame is expected to be deforming a bit after it is welded, the holes are drilled afterwards. Therefore the parts are assembly on the frame without any deformation.   Similarly, the threads for the attachment of the rod ends are threaded after the welding for the same reason. The adjustable toe, camber and castor benefit us for the correct alignment of the kart. Although most pars are welded correctly, it is until assembly part that a minor distortion was occurs during welding. Fortunately, the adjustable front geometry and drill holes can realign the frame back to good shape.


Chapter 4 - Testing and Result

4.1  Testing Background

Operational testing is a crucial and obligatory procedure in accurately evaluating the performance of a product; plus finding out unwanted / unpredicted defects contributed by errors in manufacturing or incomprehensive designing.  For the sake of the aforementioned reasons, the prototype pedal kart was subjected to be functionally analyzed twice on the campus podium between W & Y core.

 

PANO_20120716_160904

 

The choice of testing ground location was indeed controversial, as the place is not long enough for any high-speed assessment purposes, nor wide enough to observe dynamic response of the prototype to consecutive and complex aggregation of various turns. Nonetheless, this was the only venue available for the test-runs due to limitations of insurance policies and legal liabilities. Therefore, unfortunately, the results of the tests were predestinated to be failed in presenting a complete picture of general performance of the prototype vehicle. Technical details and observations made during the dry-runs will be revealed in the up-coming sections.

4.2  First Run

IMG_20120716_144252Initial trial-run of the custom vehicle was conducted on afternoon of 9 July 2012. The vehicle was successfully being circulated around the testing site as driven by various members of the task team. This served as a validation of fundamental design concepts of the pedal kart. However, a number of flaws in operational details of the kart were observed; which, with problem identifications plus associated solutions, will be explained in details below.

 


1. Sluggish Acceleration

Level of difficulty and delay of accelerating the prototype during the trial-run were greater than initial expectations. Further investigations revealed that this issue was contributed by two independent defects.

 

IMG_20120712_095016Mismatching of teeth numbers between the pedal gear and ring-gear of differential device was the first glitch. The numbers were supposed to be in odd values which help ensure smooth power transmission via a roller chain attached to the gears. Yet, such ideal matching was no longer guaranteed since the ring-gear has 16 teeth, even though teeth value of pedal gear is 53. Thus, there was a considerable probability that the chain would not smoothly fit-in the teeth of ring-gear when sudden pedaling is applied during acceleration. This led to hindrance in speeding up or even producing a “bang!” which was heard during the original test.

 

IMG_20120712_100441Owing to the fact that option of replacing ring-gear was abolished because of budget issue, the roller chain was tightened by lowering the position of rear pulley as an interim solution, inducing a reduction of effective chain length which helps avoid the mentioned encumbrance from happening. Conversely, installation of a rear derailleur is being proposed as an ultimate solution; as this device would constantly secure an optimum chain length for accommodating the disparity in teeth numbers of the gears.

 

Another factor accounted for the sluggish accelerating is dynamic friction as the pulleys were firmly pressed by mounting brackets, together with continuous rubbing of roller chain at the openings of the chain tube. This issue was solved by introducing spacers at the pulley brackets and slight shaping of the tube openings.

 

2. Surge of Front Wheels

IMG_20120704_143249Observed lateral oscillation of the front wheels was found to be relating with their erroneous mounting method. Since the brake disc is directly attached with the front wheels, the lateral movement of latter also led to misplacement of disc from its optimum position and even abrasion of the disc with brake pads. This caused the over-heating of brake assembly on the front left of the vehicle during the first test. All details concerning the resolution of this particular problem will be discussed in the next chapter.

3. Fine Tuning of Steering System

Attempt in refining the cornering performance of the prototype was conducted as well in the first trial. Two different sets of static toe angle were utilized in different specific runs, and the results were summarized in the table below.

 

 

Slow Corner

Fast Corner

Static Toe-out

+

Static Toe-in

++

– –

 

The testing outcomes suggested a combination of slight static toe-out with the implanted reverse Ackermann steering of the kart. This could be illustrated by adding the dynamic toe-in effect of reverse Ackermann into consideration:

 

IMG_20120712_095346I.            Small steering angle in fast turns would generate tiny dynamic toe-in effect, thus the toe-out setting is virtually unaffected and the relatively superior turning ability at high-speed turns is reserved.

 

II.           Slow and sharper corners, on the contrary, require large steering angle and resulting to significant dynamic toe-in effect. Such outcome would surmount the static toe-out settings and bring to a toe-in configuration which has a better performance in such turns.

 

IMG_20120712_095915        IMG_20120712_100007

 

4.3    Time Attack

Second test-run of the prototype vehicle was conducted on 16 July 2012. Prototype kart was brought to a competitive comparison with a racing model kart of the previous year. The latter would serve as an entrance baseline of performance of ultimate racing karts in Hong Kong on account of its impressive achievement in last year competition.

 

 

The vehicles, pedaled by all of the four participating test-drivers, would perform a 25-meter dash in the first part of the test. Time taken for the dashing of each kart was averaged before being compared with another vehicle. The same mechanism was applied on the second half of the trial-run, which consisted of circling 10 consecutive elliptical laps in clockwise direction. Each lap represented a length around 63.8 meters, and the vehicles were under rolling-start condition. Measured results and related findings were summarized into the following table:

 

 

Prototype

Racing Model

Min. Turing Radius [m]

3.15

1.80

0 – 25m dash [sec]

9.08

8.12

Avg. acceleration [ms-2]

0.606

0.759

Avg. Torque [Nm]

13.2

15.4

Time req. in 10 laps [min]

2.17

2.04

Avg. Speed [km/h]

17.3

18.2

 

The data indicated an inferior racing performance of the prototype vehicle, while specific details of each evaluating items were regarded as distantly comparable.

4.4  Testing result

IMG_20120716_141603It is reminded again that the conclusion drawn from above data might not be applicable in general, as the prototype kart was designed for racing in circuit at a speed twice of the testing speed. Moreover, the prototype was not thoroughly lubricated in testing due to miscommunication among team members. Hence the new kart might have a potential of reaching the level of performance of the old racing kart, given additional amendments and fine tunings were introduced.


Chapter 5 - Problem Solving

5.1  Design problems

Steering:

1.) Replace steering rod’s material because of the material property

The material change from AI 6063 rod to stainless steel because the former can’t provide the required torque to support the system

 

2.) Stability of the connection points

Limited point are set to control the turning angle and width, so that can reduce the probability forming the impact between the steering shaft and the suspension parts and thus to avoid the failure occur during the operation

 

3.) Selection of the bolt & nut dimension

This decision can has a better force distribution and support and thus to make a higher safety factor. The more suitable dimensional bolts & nuts are used to support the system, which can achieve a higher safety factor and make the system steadier

 

4.) Difficult to control

It needs more strength to control it, because different horizontal level will create some friction. Therefore, some spacer and plane are used to reduce the differences of the level.

 

Frame: 

1.) Parts connection

It is the most important process of the frame. Three teammates are arranged to learn and practice more because it’s quite difficult to control the TIG welding and does it better.

 

2.) Fixture materials and limitations

Based on the budget limitation, we select the solid wood become the material of the welding fixture. The wooden fixture burn up while the high heating power emit out by welding process. Therefore, the design is more far away distance of the fixture and the welding parts and thus to reduce the probability that the wooden fixture burn up.

3.) Stress and force deformation

Based on the consideration of the safety factor and the pedal kart’s stability, the frame structure are re-designed and simulated in SolidWork again.

 

Suspension:

1.) Accuracy angle adjustment (Camber’s angle, king-pin angle…etc)

 

2.) Rear wheel supporting (e.g up-right, up-center)

 


5.2  Manufacturing problem

During manufacturing process, three were definitely different problems we encountered, so problem solving skill was important task for the success of the projects. In fact, even the situations were improved; there were some room for further modifications of various parts.

IMG_20120712_100319

Firstly, one of the problems is the spindle part was broken after welding as there might be crack in the spindle part at the joint. After that, the parts were welded again, and then cool down by heat treatment in oven. In theoretical, through annealing, the material properties of the parts such as hardness and ductility were strengthened. Alternatively, addition of solder layer on welded joints can be further increases its strength.

 

IMG_20120712_101123Secondly, the lateral movements of the front wheels were about 1-2 degree. That would increase the friction between parts. With welding deformation, 10 mm stud used had leaded the some degree of its clearance between bearing and spindle respectively. That could not lead the front wheel fix the shaft tightly. Therefore, spacers were made to solve it. And, the lateral movements of the wheels were reduced less than 1 degree. For further reduction of the lateral movement of the front wheel, the stud can be machined with the spindle, and keyed jointed for the shaft could be designed for higher reparability of the parts.

 

IMG_20120712_100148Moreover, during cornering, if the steering wheel were turned with sharp motions, the front wheels would scrub the ground seriously. That would increase the rolling resistance as cornering. Therefore, a limiter should be added into the steering plate to limit the maximum steering angle around 20 degrees. Simply, the front of the steering plate was machined into L-shaped. The situation had been improved. Actually, a new limiter can be further designed to avoid sharp turning.

IMG_20120703_111840

In addition, for steering system, the steering wheel was found to be not aligning the best position for driver after manufacturing. For the alternative, the steering wheel can be designed into down “u” shape or addition of universal joint. And, for bearing adjustment, as the bearing support was insufficient, there were some extent of movement in bearings. Therefore, the upright can be redesigned to install larger bearing.

 


Chapter 6 - Conclusion

To conclude the new pedal kart has achieved the project aim of reducing rolling resistance by reducing the weight dramatically (from 42 to25kg). The weight decrease is mainly due to the design of the kart and use of material. The wheel alignment of the kart was also well position in order to minimize the effect of welding deflection. Each teammate has participated in the design stage and manufacturing stage and gain a considerable amount of knowledge in these areas.  Knowledge such as automotive technology for suspension and car dynamic geometry (wheelbase, track, camber, castor and toe in/out) and also the mechanism of how parts are work (differential, pedal, chain, steering, braking). In terms of manufacturing, things such as TIG welding, CNC machining code and purchase material type are also valuable experience gained during the project.  The other things were learnt are the communication and mediate skills between each others. Team work is also an important aspect acquired for this project, as not everyone is capable of doing everything.  There are still rooms for improvement for the kart to be more competitive. Things such as the rotation of the wheels & parts, steering and further weight reduction can achieve a higher performance kart. These measures can be implemented to the kart for the coming months. In addition, further testing of the kart and fine tune will be needed in order to find the best setting.   Hopefully, the new kart can bring pedal kart technology into a new lever of playing ground and produce flying colors in the future.

 

IMG_20120716_141515


Chapter 7 - Further Development

For design, as the purpose of lowering the centre of gravity, and taking the reference from a common trike, the kingpin angle is set to be about 12 degree. However, the kingpin was a little bit large and leads to negative scrub radius. The tire will not turn on its centerline, hence increase friction. For reducing this resistance, the kingpin should be adjusted to about 20 degree, to better align the kingpin axis to the wheel axis to achieve a zero scrub radius. However, this creates another problem, such as the tire inclination during cornering will be larger. If a smaller kingpin angle e.g. 7 degree is achieved, the tire inclination will be less but it will be harder to align the kingpin with the tire axis well due to space is needed to leave for the brake system. Hence to determine the best kingpin angle, scrub radius and tire inclination have to be consider, to choose in between performance or steering resistance.

 

The length of steering rod on the spindle can be further longer, so that make the steering plate more collinear. Therefore, that will lead the steering more accurate to Ackerman steering style. The rotation support for the spindle and rear connector should be made as one piece to have a concentric between the wheel and the connector or spindle. Also a flat surface can be machine for the bearing installation. The bearing hub for the upright and upcenter can thicken to install a larger bearing or one more bearing for better alignment of the shaft and connector. The steering system can be modified. As commented by many people, the steering wheel can be larger or lower by adding an extra universal joint. For the next time, under seat steering can be used to replace the over steering.

 

In addition to reduce resistance from air drag, a light weight fairing is expected to be added. The fairing will be made of thin PVC film in the future. The fairing can be covered all the kart or only the frontal area of the kart (depends on the design). The fairing is estimate to be support by some thin metal wire for a better structure. There will be a transparent part of the fairing for the drivers view and most part will be painted for a better apparent. If things are possible, a small bumper will be constructed using the same material for the protection of the kart and others.

 

For Miscellaneous part, it is expected to reduce the pedal kart weight further by machine the rear support blocks (upright, upcenter). Also the rotation of the wheel and pulley will be considered for improvement. A specially made bearing will be made to hold these rotation part firmly and they will be tested to verify the design. The seating can also be a factor for investigation. Different seating angle can be tested for the driver’s comfort and maximum propulsion force.


Chapter 8 - Team-working & project management

8.1  Project activity schedule

The project can be divided into three phase as the followings:

 

1. Design Phase

Week 1: Project identification

Identify the project objectives and understand the basic components of HPV

Week 2: Design Research.

Study the principle of each sub-system, such as frame structure, steering, braking, power transmission, ergonomics, aerodynamics, and manufacturing

Week 3: Initial investigation.

Investigate the design of example of the previous generation that measuring the dimensions, studying the advantages and disadvantages of the design and make it as reference and consideration.

Week 4: Parts and cost estimation

Research for the cost of materials and what raw materials and standard components 

Week 5: CAD drawing and simulation

Transfer the conceptual design to CAD drawing and make a simulation to the kart structure

Week 6: Presentation

Present the design idea

2. Preparation Phase

Week 7: Design estimation

Evaluate the previous design and estimate which parts should be modified to improve the performance

Week 8: Design modification

Actually make decision on the design modification

Week 9-10: Pre-manufacturing and Purchase of materials

Estimate what the manufacturing methods used for the fabrication of the product such as CNC, metal cutting, milling, turning, welding

3. Manufacturing Phase

Week 11-12: Parts fabrication

Participate in manufacturing process that translate the raw materials into the parts for the vehicle

Week 13-14: Assembly

Assemble all parts together to form a final product

Week 15: Testing and commissioning

Measuring and testing, making correction on the defeat, tuning the variable parameter

 


Gantt chart of the project schedule

8.2  Work distribution

Design stage

The design stage is the further evaluation from concept design. The group have conclude a concept of how the kart length, dimension and specification. Then the design stage will validate these concepts into virtual model before manufacturing stage. The group for design stage was mainly divided into 5 groups:

 

  1. Drawing
  2. Ergonomics
  3. Parts features / main structure
  4. Mechanism of sub system
  5. Simulation

 

IMG_20120605_171852The design team was divided in the above groups, some sub groups can be divided according to the kart features such as steering, transmission and others. However, parts like steering and seating can be  conclude as ergonomics part and the drive, transmission  can be conclude into mechanism parts. As the team is less divided, things can be sorted out quickly during design stage. For example the leg room for the frame is related to group 3 & 4: structure and ergonomics group. The frame should be compact without losing too much leg room. The 2 group sorted out by measuring the suitable length and dimension for the frame and later give these figures to the drawing group for the adjustment of the length

 

As a result, the 3D CAD (computer aided design) model has come out just before manufacturing stage.


Manufacturing stage

The manufacturing stage is the stage where the kart is built and adjusts before testing. The dividing of the manpower is crucial in building the kart on time for testing.  The project group for manufacturing was divided into 4 groups:

 

1.           Welding

2.           Machining

3.           Casting

4.           Assembly

 

IMG_20120703_105821The manufacturing team was divided into 4 groups. As manufacturing stage requires the correct timing of manpower and workshop booking, the order of manufacturing process is not ideal As a result, due to time limitation the welding was the first thing to do. After a welding lesson of the whole team, 3 group mates was chosen as welding group for their good performance of welding. The remaining group mates are divided into machining, casting and assembly   individually. Casting of the rear block supporting is followed by welding the frame and spindle.  After all welding and casting are done, the team will focus on machining in both CNC and manual type. CNC type machining is generally used in rotation parts and alignment part such as upright for great precision. The other parts are done by manual machining. Machining team started together with the manufacturing stage, as parts e.g. frame, sand cast mold needed to be machined for welding, casting. But the team work is further intensified after the welding and casting parts are done as the others part such as transmission and supporting.

 

IMG_20120625_090158The assembly team assembly the parts directly to the frame after the part is done to see if the parts is needed to be remake or adjust by further machining. Also the team will see if any necessary parts such as spacer, bearing are needed for alignment. Specific holes may be drilled for the alignment or the frame may be done if needed.

 


Work distribution in manufacturing stage:

Parts

Quantity

Person in charge

Frame

Frame_Block

2

LAI Sun Wah

Frame_Rod_1

2

FUNG Wai Choi

Frame_Rod_2

2

FUNG Wai Choi

Frame_Rod_3

2

NG Chun Cheong

Frame_Rod_4

1

LAI Yun Sang

Frame_Rod_5

2

LAM Chun Kin

Frame_Rod_6

2

LAI Sun Wah

Frame_Rod_7

2

LAM Ka Hei

Frame_Rod_8

2

LAM Ka Hei

Frame_Rod_9

1

LAI Yun Sang

Frame_Rod_10

1

LAI Yun Sang

Frame_Rod_11

2

LAI Sun Wah

Pedal _Tube

1

NG Chun Cheong

Front axle

Steering_T joint

1

POON Pui Ho

Suspension_rack_Tube

1

LO Wai Cheong

Rear axle

Rear_axle_part_1

2

LAM Ka Hei

Rear_axle_part_2

2

LAM Ka Hei

Rear_axle_part_3

2

YIU Ka Chiu

Rear_axle_part_4

2

YIU Ka Chiu

Rear_axle_key

2

FUNG Wai Choi

Rear_support_ball bearing

4

n/a

Rear_support_upright

2

POON Pui Ho

Rear_support_upcentre

2

NG Chun Cheong

Seat

T_Joint

2

n/a

Seat_Joint Plane

1

LAM Chun Kin

Steering plate with steering guidance

Steering_Plate_Sheet

1

POON Pui Ho

Steering_Plate_Tube_1

1

NG Chun Cheong

Steering_Plate_Tube_2

1

NG Chun Cheong

Steering support

Steering_supporting_shaft_part1

1

LAI Sun Wah

Steering_supporting_joint_part1

1

YIU Ka Chiu

Steering_supporting_joint_part2

1

YIU Ka Chiu

Steering_supporting_shaft_part2

1

LAI Yun Sang

Steering wheel

Steering_steering wheel

1

LO Wai Cheong

Steering_steering shaft

1

POON Pui Ho

Steering_U joint_connect

1

POON Pui Ho

Steering_U joint_Part 1

2

LO Wai Cheong

Steering_U joint_Part 2

1

LO Wai Cheong

 


8.3  Bill of materials

The table shows the amount of money paid for the pedal kart project. Some purchases are used in welding training, extra material and special tools (keychain). The total value doesn‘t imply the actual value used on the kart.


Reference

 

Hong Kong Human Power Vehicle Association: International Pedal Kart Specification

http://www.roundtablehongkong.org/storage/pedal-forms/HKHPVA%20Kart%20Specifications.pdf

 

Design reference

http://www.rswart.org/fourwhel.htm

http://conceptcycles.net/TRIP_PICS.html

http://www.contesengineering.com/athos.html

http://jetrike.com/fwd-or-rwd.html

http://blog.modernmechanix.com/2007/07/30/u-s-makes-new-bike-shift/

http://jetrike.com/ergonomics.html

http://www.bhpc.org.uk/home.aspx

http://www.los-gatos.ca.us/davidbu/pedgen/pppm_science.html

http://www.roversd1.nl/sd1web/suspension.html

http://www.lancerevoclub.org/faq/handling.php

http://www.autozine.org/technical_school/handling/tech_handling_6.htm

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=4

http://www.ihpva.org/projects/practicalinnovations/index.html

http://www.sherline.com/alignart.htm

http://www.mech.uq.edu.au/courses/mech3100-old/steering/s1.htm

http://tractors.wikia.com/wiki/Wheelbase

http://nathanielhill.com/Archive/august-10---suspension.html

http://www.quadbikexcycles.com/

http://www.angletechcycles.com/dnu/trikes/index.htm

http://www.ihpva.org/projects/tstrike/steering.htm

http://www.biketo.com/bbs/thread-263484-1-1.html

http://www.utahtrikes.com/SPECIALPROJECT-Catrike_Quad.html

http://www.diygokarts.com/vb/showthread.php?t=3813

http://www.bcot1.com/karting/

http://www.advancedracing.com/products2.php?prod=kartchassissetup

http://gokarthandling.com/files/77/File/PDF_203-210_lock.pdf

http://www.red4est.com/pdapi/body.html

http://dremel.ovh.org/pliki/UN-AXLE-A.pdf

http://dremel.ovh.org/pliki/DG72catatlogF1.pdf

http://users.frii.com/katana/biketext.html

http://www.staton-inc.com/store/products/Differential_3_4_x_38_inch_794652-184-0.html

http://www.pedalcars.info/

http://www.recumbents.com/forums/topic.asp?TOPIC_ID=3856

http://photogrange.com/album/index.php?main_page=index&cPath=16

http://www.etotheipiplusone.net/?p=249

http://www.velovision.com/showStory.php?storynum=715

http://en.wikipedia.org/wiki/Steering

http://www.ihpva.org/Projects/PracticalInnovations/index.html

http://www.smithees-racetech.com.au/ackerman.html

 

 


Manufacturing reference

http://www.mig-welding.co.uk/aluminium-welding.htm

http://www.learn-how-to-weld.com/mig-welding/mig-welding-aluminum.html

http://www.lincolnelectric.com/en-us/support/welding-how-to/Pages/guide-aluminum-welding-detail.aspx

http://en.wikipedia.org/wiki/6061_aluminium_alloy

http://bikepapago.blogspot.com/2008/06/60617005.html

http://tw.myblog.yahoo.com/awei5160/article?mid=13&prev=36&l=f&fid=7&sc=1

http://5i01.com/topicdetail.php?f=318&t=1325973&p=2

http://www.aircraftspruce.com/catalog/mepages/4130tubing_un1.php

http://www.millerwelds.com/resources/articles/Best-Practices-for-GTA-Welding-of-4130-Chrome-Moly-Tubing

http://www.netwelding.com/Welding%204130.htm

http://www.aedenterprises.com/4130/TubeAdapters.htm

http://www.aedenterprises.com/4130/roundtube.htm

http://www.onthegroundperformance.com/metalsales.html

 


 

 

 

 

 

 

 

APPENDIX A: Conceptual Drawing


1


2
3
4
5
6


7
8
9
10
11

 

 

 

 

 

 

APPENDIX B: CAD Drawing Layout