The Hong Kong Polytechnic University                            http://www.ic.polyu.edu.hk/imgs/logos1.gif

 

 

Department of Mechanical Engineering

IC349 - Manufacturing Projects

Portable Electric Monocycle





Supervisor: Patrick Ng

Co-Supervisors:

Ivan Lam, Arda Fu

Group members:

Chan Chi Fat       

11562630D

Cheung Chun Hin

11538561D

Cheung Kin Po 

10189256D

Ho Siu Sing

10563492D

Huen Shuk Yee

09277278D

Hui Chun Hung

10117095D

Wong Siu Man

10023115D

Siu Chung Man

09153549D

Li Ka Hin

10240567D

 

Content

Acknowledgement                                                                                                           P.3

Introduction                                                                                                                       P.4

Objective                                                                                                                             P.4

Design                                                                                                                                  P.5-10

-          Customer requirements (QFD)                                                                      P.5

-          Division of labor                                                                                                 P.6

-          Engineering Specifications                                                                              P.7

-          Proposed Design                                                                                                P.7-8

-          Final Design                                                                                                         P.9-11

Manufacturing                                                                                                                  P.12-18

-          Work Flow (Division of labor)                                                                        P.12

-          Techniques                                                                                                          

o   Sheet Metal                                                                                           P.14

o   CNC                                                                                                          P.14

o   Machining                                                                                              P.15

o   Welding                                                                                                  P.16

o   Surface finishing                                                                                  P.16

o   Electrical system                                                                                  P.17

o   Assembly                                                                                                P.17-18

Problems encountered                                                                                                  P.19

-          Problem statements                                                                                         

-          Possible solutions                                                                                              

Financial aspect                                                                                                                P.20

-          BOM                                                                                                                       P.20-21

Conclusion                                                                                                                          P.22     

Self-Reflection                                                                                                                                 P.23-26

 

Acknowledgement

We would like to offer our special thanks to our supervisor, Patrick Ng, with his guidance throughout the whole project. Advice given by Ivan Lam has also been a great help during our progress for guiding us to design and manufacture our product.

Special thanks must also be given to all the staff and assistants in the Industrial Centre. With their teaching and help, we can finish our project on time while learning new techniques at the same time.

 


 

Introduction

Green and sustainable transportation is the future trend of global development. Our project titled ‘Portable Electric Monocycle’ aims to design and fabricate a portable electric monocycle. The Portable Electric Monocycle is expected to be a green-powered, light-weight personal transportation device with lower energy consumption while maintaining high flexibility. It is designed to be a flexible and good alternative to mono-rail or bicycle in car-free park or places having green development such as the Park Island, Discovery Bay, or the West Kowloon Cultural District in Hong Kong.

 

The target user of our monocycle ranged from teenagers to elderly with weight not exceeding 100kg. Our monocycle has a wheel-like shape with an outer diameter 20 inches, inner diameter 16 inches and a thickness 5.12 inches. It weighs about 12.5kg. It will be powered by long NiMH battery and controlled by an S-shaped handle using an open-source electronics prototyping platform ‘Arduino. It can go for a distance of 5 km continuously with the user standing still on the footstep and recharged for later use.

 

 

 

Objectives

The objective of our project is to introduce an environmental and user-friendly design into the monocycle market. In that case, we aim to design a rechargeable battery powered portable monocycle which is light enough in weight that can be carried by a person easily. Moreover, the monocycle has to be compact in size after folding up the footsteps and handle so that users can carry it comfortably in a convenient way.

 


 

Design Stage

Relevant research has been conducted on similar products on the market. Design is carried out based on the research result and brainstorm ideas of the team with the fabrication process are also included with schedule.

QFD

Before we started to design our product, we have done some online research to understand more the consumers’ concerns; A QFD was produced to find out what requirements the customers look more important, so that we can design a user-friendly product:

 

 

 

 

 


Customer Requirements

Customer Rating (1: least important, 10: most important)

Engineering characteristics

size

speed

Material use

Moving mechanism

Electrical system

Cost

8

6

6

9

3

1

User friendly

9

6

6

1

6

3

Light weight

4

9

1

6

1

3

Safety

9

3

6

6

9

6

Appearance

5

3

 

3

1

 

Reliability

7

1

3

9

9

6

Durability

6

1

6

9

6

9

Absolute importance

193

217

291

267

197

Relative importance %

16.6

18.6

25.0

22.9

16.9

Rating

5

3

1

2

4

 

From the QFD, we found that the choose of materials for the monocycle is the most important thing we need to consider, as it may affect the safety aspect and the cost much, which are some of the most important customer requirements. The moving mechanism and speed is also important for our product to work smoothly and safely.


Division of labor (Design Stage)

Exterior Design

Huen Suek Yee

Siu Chung Man

Wong Siu Man

Electrical Design

Hui Chun Hung

Ho Siu Sing

Li Ka Hin

Mechanism Design

Cheung Chun Hin

Chan Chi Fat

Cheung Kin Po

 

Engineering Requirement and Specifications

1.     Size and weight

Since the largest size of bearing provided in the market is only 16 inches which limited the choice of diameter for the wheel, we decided to use wheel with diameter of 20 inches. In order to have a good use of space, the handle can be folded with different joints and help its storage in a limited space.

In order to be light weight, we use light material with reasonable strength in designing the product. Aluminum is used for the handle and bearings. The motor and battery used are mini-size, which just weigh 3.01 kg and 2.8 kg respectively. The wheel used is in medium size and weighs 0.5kg.

2.     Safety

A handle is provided to accelerate or decelerate the monocycle and give a sense of confidence and safety to the user. Moreover, the centre of gravity must be located in the lower part of monocycle in order to prevent toggling which would hurt the user and so the motor, battery and footsteps which contribute most of the weight would be put in the lower part of the monocycle.   

3.     Cost

A monocycle is used for short distance travel and thus its function is similar to that of a bike. As it is an electrical product and so its cost must be higher than that of a bike just by considering its electrical components and motor installed. The cost of the monocycle is expected to in the medium range between a common bike and the motor bike.

 

 

 

4.     Moving  Speed

 

(1) OD of wheel = 500 mm

                                    (2) Rotational speed of motor = 350 rpm

                                    (3) Radius of Rotor = 30 mm

 

Circumference of wheel = 2 * pi * OD of wheel/2 = 0.5 * pi = 1.57 m

Step down = Radius of Rotor / OD of wheel /2 = 30/250 = 0.12

Moving speed = 350 *0.12 *60 *1.57 = 4 km/h

 

5.     Ideal travel distance

 

(1)  Battery’s voltage = 36V

(2)  Battery’s capacity = 12Ah

(3)  Motor output power = 350 W

(4)  Moving speed ~ 4 km/h

By P = IV

            I = 350/36 = 9.7222 A

Total time = 12 / 9.72222 ~ 1.23 hour

Total distance = 1.23 * 4 = 4.96 ~ 5 km

 

Engineering Specifications

Outer Diameter of wheel

20”

Thickness

5.12 in

Speed

~4 km / hour

Torque of motor

1.11N.m

Battery power

5 km / full charge

Overall Weight

12.5 kg

 

 

 

Proposed Design

Design of the monocycle was divided into two parts: Outlook design and design of the mechanism. We first designed these two parts separately in order to brainstorm more drafts, then amendments are made based on each other’s restrictions to come out the final design.

Outlook design:

There were some basic criteria since the beginning of the design stage. For example, the handle part and the footsteps should be foldable so that users and carry the monocycle on hand in a more comfortable way; the wheel part should be large enough for the storage of motor and battery, etc. Below are some of our first few drafts of our monocycle:

Stage 1:

           

    

 

 

 

 

 

Stage 2:

Macintosh HD:Users:joansiu:Desktop:420433_10150590240591373_541807975_n.jpg mono.bmp Macintosh HD:Users:joansiu:Desktop:530494_325012234224520_1874835573_n.jpg

Stage 3:

photo2.JPGhttp://a7.sphotos.ak.fbcdn.net/hphotos-ak-snc7/403829_10150619913708918_492129491_n.jpg http://a2.sphotos.ak.fbcdn.net/hphotos-ak-snc6/251862_380349438690799_403786945_n.jpg

 

Final Design

In the final design stage, we confirmed the material used and the monocycle assembly in the design drawings. Most of the components are made of aluminum with some made of steel or brass.

In order to maintain balance, the motor and the battery is placed at the bottom of the monocycle to help lowering the center of gravity. The S-shaped handle is made up of two 3mm thick sheet metal and both the handle and the footstep are foldable for easy carriage of the monocycle.

Moving Mechanism: The wheel is moved by friction as the powered motor rotates and carries two “O” rings which are attached on the roller to rub against the racing track of the wheel.

 

Roller assembly:

The roller assembly is supported to the monocycle by a shaft which is installed at the pivot and the whole assembly can turn on a pivot. A motor is placed on the aft side of the assembly and the roller is placed between the pivot and the motor and the “o” rings are contacted to the racing track of the wheel. An action is act on the racing track from the roller. Due to the leverage, this action is magnified around 1.5 times of the motor weight. That imply more friction can be acted between the racing track of the wheel and the roller. So the efficiently of the transmission is increased.