I need a report of 22 pages double space RoutineGgrocery Shopping.

Write a report of 22 pages double space 

The report should include things like the FFBD (functional flow diagram), trade-off analysis of the different designs, tests for the different performance and functional requirements.

do similar to the report that I send you

need you to address all the points The content page, sample report and previous work also send you please see the attached documents

The work is like engineering report Those that you require an image, you can indicate <insert image> I will put an image

want all 5 parts to be addressed in the report

Want A++ work avoid all types of mistake in work please check attached documents that I'll forward you

........................................................................................................................................................................

Attachment 1;

1. Needs Analysis

1.1 Operational Analysis

Deficiencies:

The grocery basket is a must-have companion of our routine grocery shopping. It is used for carrying items while we are picking grocery around the shop and queuing up for payment at the cashier. The basket is an invention with a long history of at least several hundred years. It has continued to serve us as a carrier. Our continued dependence on it shows that it will remain relevant at least in the foreseeable future. However, the grocery basket has not undergone much changes since its inception, despite several deficiencies that limited its effectiveness to fully fulfil its function as a carrier. Here, we have identified 4 key common deficiencies of existing grocery basket.

1. Most grocery baskets are incapable of keeping their structural balance when items are asymmetrically placed. They tend to swing downward around the handle’s hinges under the weight of moderately heavy objects.  

2. The loss of balance may drop the items from the basket, causing damage either to the items or injury to the shoppers.

3. Often, the handle is fixed across the shorter side the basket. It is not ergonomically friendly to shoppers as they need to carry the basket with their arms twisted to accommodate the longer side of the basket.

4. The handle does not ergonomically fit the user’s grip well to relieve the stress on fingers.

Hence, there is scope and market for improving the grocery baskets currently available in most supermarkets. With these issues identified, we can define the problem and operational objectives of our system development project. 

Problem definition: 

The existing designs of most grocery baskets do not fully fulfil their function as an effective, safe and ergonomically friendly carrier for shoppers.

Operational objectives: 

We aim to design a grocery basket that possess the following key features:

1. Capable of maintaining its balance under asymmetric load.

2. A capacity of supporting load of up to 10 kg.

3. Enable shoppers to carry it in their natural posture without twisting their wrists and arms.

4. Handle that fit naturally to the human’s grip.

5. Life-cycle cost similar to existing basket.

Features 3 and 4 helps to reduce the overall stress on shopper’s arms, wrists and fingers.

1.2 Functional Analysis 

Allocation of functions to sub-systems:

Sub-system Functions

Basket 1. To hold groceries safely within the confine of the basket.

2. To support the weight of groceries within the limit of its capacity it is designed for.

Handle 1. To act as an interface between the basket and the human, allowing shoppers to carry the basket with their hands.

2. To support the weight of the basket and groceries within the limit it is designed for.

3. To balance the weight of basket’s content.

Interfaces and interactions between sub-systems: 

Interface Between Functions

Handle grip Handle – Human 1. Mediate the interaction between shopper and handle.

2. Allow shopper to grip on the handle and ultimately carry the whole basket.

3. Disperse pressure over the fingers.

Hinges Handle – Basket 1. Connect the handle to the basket.

2. Mediate the interaction between the handle and the basket.

3. Enable free movement of the handle relative to the basket.

4. Allow handle to be flipped up or down when required.

5. Balance the weight of basket’s content.

6. Spread the weight of the basket content.

1.3 Feasibility Definition 

Improvement to the existing deficiencies of grocery baskets can be accomplished with production methods and materials currently used for manufacturing baskets. No new advanced technology and material will be used. In fact, most of the improvement merely involve changing the shape, size, design and handle’s relative orientation to the basket. The project is, therefore, both technically and financially feasible. No new risk is anticipated. The only new material that may be used is, perhaps, eco-friendly bioplastic, which could increase production cost a bit. Evaluation of performance and effectiveness can be done using established human factor engineering methods. This system development project is thus highly feasible.

1.4 Needs Validation 

Performance measures:

1. Maximum load that the handle, hinges and basket can sustain without deforming and breaking.

2. How freely the handle can move around the hinge.

3. Durability. Resistance to drop, corrosion and physical wear and tear.

4. The life-cycle cost of the improved basket.

Effectiveness measure: 

1. Stability of the basket under asymmetric weight.

2. Degree of twist around wrist and arms from their natural posture.

3. Amount of stress on fingers in terms of degree of pain experienced.

1.5 Operational Requirements 

After going through the stages of needs analysis, the following operational requirements are determined.

Category Operational Requirements 

Inherent capability 1. The basket shall not swing more than 15o from its balanced position, in either clockwise or anticlockwise directions, under asymmetrically placed load.

2. The handle, hinges and basket shall not deform or break under load of 10 kg.

Controllability 1. The handle shall be capable of moving freely around the hinges relative to the basket.

2. The basket shall have a dimension of 35 x 20 x 16 cm and weight 0.3 kg, to make it easy to be carried from place to place.

Mobility The basket shall have a dimension of 35 x 20 x 16 cm and weight 0.3 kg, to make it easy to be carried from place to place.

Ergonomics 1. The handle grip shall have a natural fit to the average human hands based on anthropometric data.

2. The handle shall be connected to the basket in an orientation that doesn’t involve the twisting of shopper’s wrists and arms.

Safety The basket shall be safe to use. It shall not cause any injury to users.

Durability 1. The basket shall be able to withstand the impact of a normal drop on floor without any deformation and breakage.

2. It shall be resistance to corrosion from exposure to water, acid or alkaline from food and drinks spillage.

3. It shall be resistance to any general form of physical wear and tear.

Environmental conditions 1. The basket shall only be used for its designated purpose as a grocery carrier of capacity 10 kg in a typical grocery shop environment.

2. It shall not be used for purposes other than its designated use, and subject to environmental conditions other than grocery shops.

3. It shall be made of eco-friendly materials, so that it will not pollute the environment upon disposal at the end of its service life.

Integration 1. The baskets shall allow their stack-up for storage within the space constraint of grocery shops.

2. It shall allow integration with digital system in the grocery shops.

Cost The basket shall not have a life cycle cost higher than the average of existing baskets.

..........................................................................................................................................................................

Attachment 2;

IE3105 Project Report  

 
Group 3  

Table of Contents

1. Introduction 1

2. Concept Development Stage 1

2.1 Needs Analysis - Operational Deficiencies and Technological Opportunities 1

2.2 Concept Exploration 2

2.2.1 Operations Requirement Analysis 2

2.2.2 Performance Requirements Formulation 2

2.2.2.1 System Portability 2

2.2.2.2 Inherent System Capability Performance Requirement 3

2.2.2.3 System Quality and Safety Performance Requirement 4

2.2.3 Implementation Concept Exploration and Performance Requirements Validation 6

2.2.3.1 Blowgun 6

2.2.3.2 Slingshot 7

2.2.3.3 Repeating Crossbow 7

2.3 Concept Definition 9

2.3.1 Functional Analysis and Formulation 9

2.3.2 Concept Selection 9

2.3.2.1 Trade-off Analysis 14

2.3.3 Concept Validation 15

3. Engineering Development Stage 16

3.1 Advanced Development and Engineering Design 16

3.1.1 System Functional Specifications/ Defined System Concept 16

Table 4: Functional Specifications for Subsystems 18

3.1.2 Risk Management 18

3.1.3 Design Specifications 20

3.1.3.1 Material 20

3.1.3.2 Dimensions 21

3.1.4 Validated Developmental Model 25

3.1.4.1 Validating Components 25

3.1.4.2 Validating Sub-systems/Interfaces 26

3.1.4.3 Validating System Model 27

3.1.5 Component Design and Test 27

3.1.5.1 Component Test Results and Evaluation 30

3.2 Integration and Evaluation 30

3.2.1 Subsystems/ Interfaces Design and Test 30

3.2.2 Integrated System Testing 32

3.2.2.1 System Level Test Results under Operation Environment 36

4. Cost Breakdown 38

5. Challenges and Lessons Learnt 39

1. Introduction  

 
This project aims to develop a better self-defense weapon for an adult traveler in the medieval era. It is intended to be better than a traditional bow and arrow system in terms of ease of carry and operability with minimal training. The weapon shall also be deployable within a short amount of time, be accurate and be powerful enough to protect the traveller against danger.  

 
2. Concept Development Stage  

 
2.1 Needs Analysis - Operational Deficiencies and Technological Opportunities  

 
The traditional bow and arrow system is a ranged weapon system consisting of an elastic launching device called the bow and an arrow. To load an arrow for shooting, the arrow has to be placed across the middle of the bow with the bowstring in the arrow’s notch. To shoot, the arrow has to be pulled back which in turn will cause the bow limbs to bend, thereby storing elastic energy. Finally, when the arrow is released, the stored elastic energy will be converted to kinetic energy of the arrow, allowing the arrow to propel forward.  

The traditional bow and arrow system is large in size as the typical bow length is over 48 inches. Therefore, it can causes great inconvenience to the user when carrying it. Furthermore, the traditional bow and arrow system relies on the user’s effort to draw back the bow and to shoot back accurately. Therefore, much training will be needed for one to be skilled in using it.

To address the technology gap, it is necessary to develop a better self-defense weapon in terms of ease of carry and operability with minimal training than the traditional bow and arrow system. Being a self defense weapon, it shall be able to deploy within a short amount of time, be accurate and be powerful in order to protect the user against danger.

2.2 Concept Exploration

 
2.2.1 Operations Requirement Analysis  

 
The CONOPS require a system to be lightweight (no heavier than 5 kilograms) and portable with width of no longer than 50 centimetres for ease of carry. The system shall allow the user, without any formal training, to incapacitate an opponent. The system shall be able to engage a target from a distance (at least 10 meters) in a rapid pace (at least 10 engagements per minute). The system shall be able to be deployed quickly (no longer than 20 seconds).  

To achieve the operational outcomes, the weapon must be able to operate effectively under operational environments and constraints to achieve the operational objectives. These are defined by the Operational Requirements of the weapon:

(a) The system shall be lightweight and portable by a single adult human user.

 
(b) The system shall be unsophisticated in deployment, without requiring any special training.  

 
(c) The system must be able to inflict damage on an opponent (target).  

 
(d) On the onset of danger, the system shall be quickly deployable. After end of operations, it shall be made portable for carry again.  

 
2.2.2 Performance Requirements Formulation  

 
In order to effectively develop a system that is capable of achieving the operational standards, the Operational Requirements of the weapon system are translated into a set of Performance Requirements defined and classified under 3 categories below:  

 
2.2.2.1 System Portability  

 
One of the essential Operational Performance Requirement for the system is to be lightweight with portable characteristics. In order to attain such properties, the following Performance Requirements are defined:  

A. Lightweight: The mass weight shall not be heavier than 5 kilograms

B. Portable: The system’s width shall not be longer than 50 centimetres.

 
2.2.2.2 Inherent System Capability Performance Requirement  

 
The critical Operational Performance for the system is to fire a projectile over a reasonable distance with sufficient accuracy, rate of fire and stopping power. In order to achieve this, the following Performance Requirements are defined:  

A. Accuracy: The system shall be able to achieve a shot grouping minute of angle (MOA) of no more than 30 centimeters per 10 meters

B. Stopping Power: The system shall be able to launch a projectile that can penetrate at least 2 centimeters into polystyrene.

C. Range: The system shall be able to launch the projectile at least 10 metres.

D. Ease of Deployment: The system shall be able to fire the projectile in no more than 20 seconds of deployment time.

E. Responsiveness: The system shall be able to fire the projectile at a rate of at least 10 projectiles a minute and shall be able to be corrected from a jam in no more than 10 seconds.

F. Operability: The system shall be operable by a single adult user with both hands.

2.2.2.3 System Quality and Safety Performance Requirement

The system must be reliable and ensure that it can be safely operated by an average human adult while travelling. To achieve this, the following Performance Requirements are defined:

A. Reliability: The weapon must withstand at least 50 cycles of use and remain functional under rainy/sunny/snowy/windy weather that could be encountered while travelling.

B. Safety: The system must be designed to operate safely by a user without specialised training. It shall have a safety mechanism to ‘lock’ the weapon and prevent harm to user and/or unintended targets. The pointed tips of the projectiles shall not be exposed when carried around unless fired.

C. Costs: The system shall be constructed out of materials with low material costs that are easy to obtain.

 
Category Operational Objectives (What we need) System Operational  

Requirements

(What system must deliver) System Performance

Requirements

(Measurable outcomes)

In-theatre The system must be able to inflict damage on an opponent from a distance in a rapid fashion The system must be able to fire a projectile in a rapid pace of 15/minute with a range of 10 meters with enough power to penetrate

2 centimeters in polystyrene Accuracy: The system shall be able to achieve a shot grouping minute of angle (MOA) of no more than 30 centimeters per 10 meters

   Stopping Power: The system shall be able to launch a projectile that can penetrate at least 2 centimeters into polystyrene

   Responsiveness: The system shall be able to fire the projectile at a rate of at least 10 projectiles a minute and shall be able to be corrected from a jam in no more than

   10 seconds  

   Range: The system shall be able to launch the projectile at least 10 metres.

 The system shall be lightweight and portable by a single adult human

user The mass weight shall not be heavier than 5 kilograms and the system’s width shall not be longer than 50 centimeters Lightweight: The mass weight shall not be heavier than 5 kilograms

   Portable: The system’s width shall not be longer than 50 centimetres.

Quality and Safety Reliable during operational time and safe to be operated by the user Must be reliable for the duration of the encounter (expected 5 cycles per encounter), and safely operated by the user Reliability: The weapon must withstand at least 50 cycles of use and remain functional under

rainy/sunny/snowy/windy weather

   Safety: The system must be designed to operate safely by a user without specialised training. It shall have a safety mechanism to ‘lock’ the weapon and prevent harm to user and/or unintended targets. The pointed tips of the projectiles shall not be exposed when carried around unless fired.

Production Cost Effective Must be easy to build and cost effective Costs: The system shall be constructed out of materials

      with low costs that are easy to obtain

 Table 1: Operational Requirements and Performance Requirements  

 
2.2.3 Implementation Concept Exploration and Performance Requirements Validation  

 
Based on the capabilities of medieval technology back in the 5th to 15th century AD, it is assessed that there are 3 possible system concepts - 1) Blowgun, 2) Slingshot, 3) Repeating Crossbow can be developed. Each system concept was evaluated and ascertained to be able to meet the system performance requirements. Characteristics of the 3 concepts are as follows:  

 
2.2.3.1 Blowgun  

 
Figure 1: Blowgun  

 
Working Principle: This system utilizes air pressure blown into one end of the barrel as a propelling force for a lightweight projectile.  

Requirement Validation: The design of this system is relatively simple and lightweight which will meet the lightweight requirements. The system is fairly accurate and will be able to achieve consistent shot groupings under fair weather conditions. The projectiles fired from this system will be able to travel a fair distance thus meeting the minimum distance of 10 meters. Reloading of the projectiles for subsequent operation is also achievable in a short duration. The system is also relatively safe to operate.

 
2.2.3.2 Slingshot  

 
Figure 2: Slingshot  

 
Working Principle: This system utilizes the stored elastic potential energy from an elastic material during the pullback phase as the energy storage medium. Upon release, the stored elastic potential energy will be converted into kinetic energy which is then used to propel the projectile forward.  

Requirement Validation: Projectiles launched from this system will travel a very long distance which will meet the minimum distance of 10 meters. The system is fairly accurate and will be able to achieve a fairly consistent shot grouping. Reloading of the projectiles can be done easily in a short span of time. The system is lightweight and small in size which meets the portable and lightweight requirements.

2.2.3.3 Repeating Crossbow

Figure 3: Repeating Crossbow  

Working Principle: This system utilizes the stored elastic potential energy from an elastic material during the drawback phase as the energy storage medium. Upon firing, the stored elastic potential energy will be converted into kinetic energy which is then used to propel the projectile forward.

Requirement Validation: This system is able to fire off projectiles over long distances in quick succession, meeting both the requirements of the minimum range of 10 meters as well as the rate of fire of at least 15 projectiles per minute. The system is highly accurate and will be able to achieve consistent shot groupings under any weather condition. Projectiles can also be pre-loaded to enable fast deployment time. Reloading of the projectiles can be done very easily in a quick manner. The system should also be safe to operate with minimal training.  

2.3 Concept Definition

 
2.3.1 Functional Analysis and Formulation  

 
A Functional Flow Block Diagram (FFBD) was used to develop the sub-functions. The functions and subfunctions are:  

1. Deployment:

1. Equipping

2. Setup

2. Operate:

1. Load [Magazine loading, Load Projectile]

2. Launch [Release Trigger, Blow, Release Projectile]

Figure 4: Functional Flow Block Diagram  

2.3.2 Concept Selection

 
The functions for the 3 concepts are analysed using the FFBD as shown in Figures 5 to 7 below:  

 Figure 5: FFBD of Blowgun System  

 Figure 6: FFBD of Slingshot System 

 
Figure 7: FFBD of Repeating Crossbow System  

For an objective analysis of the 3 different alternatives, the different performance requirements are weighted from a scale of 1 to 5 with 5 being the most important. See Table 2.

 
Performance Requirement Weightage Reason  

Range of Projectile 5 This is paramount for a successful self-defense encounter. Any distance less than 10 meters will result in allowing the perpetrator to make physical contact or possibly harm the user.

Accuracy of Projectile 4 This function is essential in ensuring that the user is able to effectively strike down the perpetrator while keeping collateral damages to a minimum.

Time to Reload 5 In order to keep a distance without allowing the perpetrator to move towards the user while the user reloads the system, a short reload time is required.

Portability 4 The system needs to be lightweight and portable such that the system does not hinder the user and will not cause the user to tire out during usage or journey.

Reliability 4 It is important for the system to maintain a high serviceable state as it will be the main source of deterrence for any perpetrators

Safety 5 Safety is of utmost importance to ensure that the user is able to defend effectively without inflicting any injury upon oneself.

Stopping Power of Projectile 5 This function is extremely important in ensuring a successful self-defense encounter as it determines if the perpetrator will view the user as a threat to himself.

Table 2: Performance Requirements and Weightage

 
In order to determine the most appropriate solution from the 3 different alternatives, each is ranked across all performance requirements with the best in the category awarded with a maximum of 3 points and the worse with 1 point. The alternative with the highest total weighted score (Weightage multiplied by ranking points) will be chosen. See Table 3 below.  

Performance Requirement Weightage Blowgun Slingshot Repeating Crossbow

  Point Score Point Score Point Score

Range of Projectile 5 1 5 3 15 2 10

Accuracy of Projectile 4 1 5 2 10 3 15

Time to Reload 5 2 10 1 5 3 15

Portability 4 1 5 3 15 2 10

Reliability 4 3 15 2 10 1 5

Safety 5 2 10 1 5 3 15

Stopping Power of Projectile 5 1 5 2 10 3 15

Total Weighted Score 55 70 85

 
Table 3: Selection of Concept  

2.3.2.1 Trade-off Analysis

 
Each individual concept’s total weighted score is computed with the Repeating Crossbow having the highest score of 85, Slingshot at 70 and Blowgun at 55. The Repeating Crossbow, having means of achieving a range of more than 10 meters with superior accuracy, stopping power, higher safety as well as the fastest reload time and good portability makes it the most effective system.  

The Slingshot, though possessing the best range and portability with fair stopping power and accuracy, pales in comparison to the Repeating Crossbow in 4 out of 7 categories due to its longer time to reload as well as poorer user safety.

The Blowgun, though the most reliable out of the 3 concepts loses out in almost every other category only to have decent reloading time and safety. Due to the nature of being air powered from the breath of the user, the projectile has to be lighter in weight as compared to the other systems and hence, will possess less stopping power. At the same time, depending on the user’s lung capacity, the range of the system may vary under different circumstances. Should the user be out of breath, the system may fail to reach the minimum range of 10 meters. The system’s long shaft may also prove to be less portable.

2.3.3 Concept Validation

 
The chosen concept - Repeating Crossbow is a highly accurate system that can allow projectiles to be pre- loaded in a magazine for quick reloading times. This meets the operational requirement of accuracy and a fast rate of fire. Furthermore, the usage of an elastic material to store potential energy can be tested and proven during tests. The relatively simple design with a few subsystems allows for the system to be easily built and cost effective. The firing process is easily repeatable with high consistency, thus enhancing the reliability and safety aspects of the system. Lastly, the projectiles fired from the Repeating Crossbow are in the form of bolts which holds superiority in stoppage power in comparison to stones (Slingshot) or darts (Blowgun).   

1. Engineering Development Stage

 
This section is focused on covering the development and building of the Repeating Crossbow system. Through the Advanced Development and Engineering Design phase, the concept is then transformed into hardware design and then tested through System Integration and Evaluation.  

 
1.1 Advanced Development and Engineering Design  

 1.1.1 System Functional Specifications/ Defined System Concept  

 
For this project, there is no prototype developed as the actual model itself will be built and tested for its feasibility. The proposed design of the repeating crossbow system together with its various components and subsystems, is shown in Figure 8. Figure 9 further elaborates on their parts.  

 Figure 8: Top View of Proposed Design of Repeating Crossbow System  

Figure 9: Side View of Proposed Design of Repeating Crossbow System

Figure 10: Repeating Crossbow System Components and Subsystems

Subsystems Functional Specifications

Bow Mechanism 1. The bow string attached to the bow shall be able to be pulled back into the notch

2. The projectile shall fire off to reach a range of 10m and stay within a ±10∘ deviation from the line of fire when the trigger is pressed

  3. The bow shall be able to revert to original position without any dislodging

 4. A safety system shall be present to prevent any misfiring

Reloading Mechanism 1. The magazine shall be able to store up to 5 projectiles to allow repeating firing

 2. The projectile shall fall from the magazine to the projectile guide rail when pressure is applied on the projectile feeder

Main Body Frame 1. The main body frame shall be able to withstand the weight of the bow mechanism and the reloading mechanism as well as the recoil force of repeated firing.

Table 4: Functional Specifications for Subsystems

1.1.2 Risk Management

Risk management and assessment were done to measure and possibly mitigate any potential developmental risks. This was carried out using MIL-STD-882D (Standard Practice for System Safety) [Gao’s Standard Practice for System Safety] safety assessment framework. Identified system and component hazards and their possible mitigative measures are show in Table 5 and 6 respectively. Although there are no hazards with the mishap risk classified as “serious”, testing done to the system will still be vigorous and stringent to ensure the risks are properly mitigated.

 
No. Component  

Hazard Probability Severity Mishap Risk

Category Risk Mitigation

1 Bowstring may snap when pulled to tension. Improbable

(E) Negligible

(IV) Low (20) Repeated Tension Stress Test on bowstring to be carried out by continuously firing projectiles off 50 times. Should the test fail, replace woven bowstring with stronger nylon bowstring.

2 Bow may snap when bowstring is pulled to tension. Improbable

(E) Marginal

(III) Medium (15) Repeated Tension Stress Test on bow to be carried out by

continuously firing projectiles off 50 times. Should the test fail, replace metal rulers with more flexible hard plastic.

3 Projectile Feeder spring device may snap during reloading. Improbable

(E) Negligible

(IV) Low (20) Repeated Tension Stress Test on Projectile Feeder spring device by doing 5 x 5 projectile-full magazine reloads continuously. Should the test fail, replace rubber band with thicker ones or larger rubber bands with bigger circumference.

4 Trigger may break when firing the weapon. Improbable

(E) Negligible

(IV) Low (20) Repeated Stress Test on trigger to be carried out by continuously firing projectiles off 50 times. Should the trigger break, replace current trigger with a trigger twice the thickness.

Table 5: Component Hazards and Risk Mitigation

No. System

Hazard Probability Severity Mishap Risk

Category Risk Mitigation

1 The repeating crossbow system may be damaged due to extreme weather. Improbable

(E) Negligible

(IV) Low (20) Conduct tests under rainy or wet weather conditions and under sunlight to make sure that the system is still serviceable.

2 The bowstring may be jammed during subsequent reloading for continuous firing. Remote

(D) Marginal

(III) Low (20) Ensure that the projectile feeding mechanism does not exert too much downwards pressure so as to allow the bowstring to slide easily backwards during reload.

3 Two

projectiles might be fed into the guide rail causing a double feeding situation. Remote

(D) Marginal

(III) Low (20) Ensure that the gap in which the projectiles are loaded into the magazine are narrow enough such that in every cycle of reloading, only one projectile is fed into the guide rail.

Table 6: System Hazards and Risk Mitigation

 
1.1.3 Design Specifications  

Using Figure 8 for reference while adhering to the guidelines as per the performance requirements, the initial design specifications of the system were developed using existing knowledge on the law of physics and material performance.

 
1.1.3.1 Material  

 
Due to the abundance of wood and metal resources (Used in forging swords and basic carpentry) during the medieval era, wood was selected as the main material for the body frame and metal for the bow. The chosen materials are strong and sturdy enough to withstand repeated use and are fairly rugged in terms of durability. At the same time, their sturdy but lightweight nature further enhances the portability of the entire system. 95% of all parts are made of wood while the main energy storage medium is made of metal (bow part). The bowstring is made of cotton yarns spun and braided into strings which is inexpensive and easily found in the medieval era. Thin wooden shafts (wooden chopsticks) with iron nails are made into the projectiles as these materials are easy to come by and can be mass produced.  

1.1.3.2 Dimensions

 
The dimensions of the repeating crossbow is first predicted using the laws of physics; conservation of energy and laws of motion.  

Conservation of Energy - Projectile Motion

  Where,

the velocity along the x-axis is Vx , the initial velocity along the x-axis is Vxo , the velocity along the y-axis is Vy , the initial velocity along the y-axis is Vyo .

acceleration due to gravity is g, and the time taken is t

 
Equations associated to the trajectory motion (projectile motion) are articulated as…  

 Where,  

the initial Velocity is Vo ,

 
the component along the y-axis is sin θ, the component along the x-axis is cos θ.  

 
With due considerations of the operational requirements concerning the minimum range and penetration power that is required of the projectile, the design specifications for the repeating crossbow is summarized in Table 7 below.  

Components/ Subsystem Material Design Specifications

Bow Metal Rulers 1. The bow must be able to withstand repeated full-length tension when the bowstring is drawn back. (At least 20 centimeter pull- back so as to enable the projectile to be have a range of at least 10 meters)

  2. The bow must rest firmly in the main frame of the crossbow with its middle aligned to the direction of the projectile guide rails so as to allow total transfer of stored elastic energy to the projectile with minimum energy loss

  3. The bow must be at least 30 centimeters in length so as to enable a smooth pull-back of 20 centimeters

Body/Support Frame Balsa

Wood 1. The body of the crossbow must be able to withstand the weight of the bow mechanism and the reloading mechanism as well as the recoil force of repeated firing.

  2. The body’s dimensions should be at least 30.0 cm x 2.5 cm x 4.0 cm (L x B x H) so as to enable the user to have a firm grip and ensure sufficient stability, especially during recoils.

3. The projectile guide rail dimensions should be 18.0 cm x 1.0 cm x 0.2 cm with a 0.3 cm gap in between so as to enable the projectile to be firmly rested on the gap.

Bowstring Cotton Twine 1. The bowstring must be between 27.0 cm to 29.0 cm such that there is always a slight tension in the bow so as to ensure that there is no energy loss when the bowstring is pulled back.

Projectile Chopstick with

attached nail 1. The projectile must be at least 5 g in weight with its center of gravity located at a position not exceeding 6.0 cm from the tip and must measure 15.0 centimeters in full-length and 0.4 centimeters in diameter (shaft). This is to ensure that the projectiles can fit in the magazine and have a decent flight trajectory with enough mass to possess sufficient momentum for penetration power.

Feeding system/Magaz

ine Balsa wood 1. The magazine needs to have dimensions 20.0 cm x 0.5 cm x 2.0 cm (L x B x H) such that it has a 0.4 cm gap in between its walls to allow at least 5 projectiles to be loaded and fitted well.

2. The projectile feeder needs to have dimensions 7.0 cm x 0.4 cm x 2.5 cm (L x B x H) such that it can be slotted into the magazine with some excess over the top for the user to be able to easily take out.

3. The supports for the magazine needs to be 0.5 cm high such that the magazine is elevated on both ends by 0.5 cm. This is important to allow the bowstring to glide through the projectile guide rail while preventing the projectile from falling out from the side of the rails.

Trigger/Safety switch Ice cream stick,

Rubber

bands,

Paperclip 1. The trigger needs to be at least 5.0 cm in length and 1.0 cm in width. A flat 0.1 cm thickness will allow the trigger to be easily flipped during firing and stowed easily during safe mode.

Table 7: Summary of Repeating Crossbow Design specifications

 Figure 11: Dimensions of Repeating Crossbow System (Top View)  

 
Figure 12: Dimensions of Repeating Crossbow System (Side View)  

1.1.4 Validated Developmental Model

 Through careful risk mitigations and engineering analysis, the crossbow system was evaluated at three levels: components, subsystems/interfaces and system level.  

 1.1.4.1 Validating Components  

 
Firstly, the main wooden frame/body must be cut with indents of suitable size and depth so as to accommodate the bow and trigger mechanism. The bow gap should be narrow enough so as to hold it in position while allowing for some bending during operation. Additionally, the wooden structure (including the main body, feeding system and trigger stick) must have sufficient rigidity so as not break easily when force is applied during repeated use and storage. Next, the team must ensure that the bow is able to withstand bends without snapping. This can be demonstrated through repeated attempts to bend the bow in the direction of pull. Moreover, the string must be elastic enough to be pulled till the trigger mechanism distance without snapping - at the tie ends with the bow or in the middle. The feeding apparatus (mounted on the crossbow support frame) should be narrow enough to only hold 1 projectile (which will be used for during) while being tall enough to stack/store 4 other projectiles in the ‘magazine’. Lastly, the rubber bands used to hold the trigger and safety mechanism is place must be able retain sufficient elastic energy to make them suitable for repeated use (minimum 50 times, as specified in the performance criteria).  

 Figure 13: The various components disassembled  

1.1.4.2 Validating Sub-systems/Interfaces

 
There are 3 key interfaces in the crossbow that must be validated before integration and evaluation of the system. The 3 interfaces are (a) launching system (composed of crossbow support frame, bow and bow string components), (b) feeding system and (c) safety system. To ensure that the launching system functions smoothly, the bow is tightly secured in the wooden body frame with a slot of the right size. The width of the bow slot is adjustable (by varying the width of the eraser in front) so as to fit bows of various widths. This might be necessary if Little Red Riding Hood wants to launch projectiles further than the current stipulated range of 10m; she can just add more steel rulers to the current bow system to increase tensile strength and thus increasing range of projectile. The feeding system is mounted on top of the launching system with an adhesive to avoid shifts in its position. This is important to ensure seamless feeding of projectiles from the ‘magazine’ storage without blockage. A pushing apparatus is added in the feeding system to hold the projectile in place and give it sufficient traction for the string to grab the projectile during launch.  

 
Figure 14: Pushing apparatus shown as a standalone (left) and in position with feeding system (right)  

 
Lastly, the safety system is fit into the main body with help of rubber bands. The advantages of using rubber band are two-fold in that rubber bands are elastic so they allow the trigger stick to return back to its place after each launch. Moreover, they allow the safety apparatus to function by allowing the trigger stick to be mounted out off the trigger groove altogether and thus preventing unintended fire.  

 
Figure 15: Rubber bands enable the trigger to be off the groove and in safety position  

 1.1.4.3 Validating System Model  

The crossbow system was then evaluated against the operational and performance requirements at the systemic level. Three requirements can be validated at this stage:

a. Weight - Portability requirements for the system state the system shall not be be heavier than 5kg. The crossbow performs exceedingly well in this measure by weighing just 200 grams, making it suitable for portable use and storage.

b. Width - Another portability requirement for the system is that its width shall not exceed 50cm. The crossbow meets this requirement as well with an end-to-end width of 33.5cm.

c. Safety - The crossbow has its sharp edges sanded off to prevent unintended injury and different interfaces are held in place with adhesives and/or rubber bands to avoid loose parts falling off during operation and storage.

 1.1.5 Component Design and Test  

 Having validated the components, subsystems and interfaces of the crossbow (that can be validated at this stage), component design and test was carried out to identify and correct deficiencies in the early stage. The components, materials and requirements of the crossbow were identified previously. A component test plan was then developed to ensure that the chosen materials fulfilled the requirements as outlined in Table 8.  

Components Material Used Test Parameters Test Plan  

Body/Support frame Balsa wood Able to withstand a fall of 5m which might occur during operation.

Ensure that the balsa wood does not crack/bend due to the force of fall, especially near the areas with the indents for bow and trigger switch. Perform a controlled release (with 0N initial force) of the wooden body from a height of 5m. Check for cracks or deformity.

 
Repeat this test 5 times.  

Bow 2 x steel rulers wound together with tape Able to bend to a degree so that the attached string is able to reach the trigger point.

 
Able to revert back to original position without being permanently curved (a permanent curvature would result in a significant drop in tensile strength). Bend the steel rulers (bow) to the required angle for 50 times. Measure the change in curvature and performance on the range of projectile after 50 attempts.  

 
The range of projectile will inevitably drop after repeated attempts due to a loss in tensile strength of ruler, but it should stay >10m.  

Bowstring Cotton Twine Able to sustain repeated stretching and release from resting position to trigger point. Stretch the bowstring from resting position to trigger point for 50 times.

    Ensure the string does Check for snaps or  

  not snap or display critical tears/unwinding of twine. unwinding of twine.  

 
Projectile Chopstick with attached  

nail Able to reach a range of

10m and stay within a deviation from the

line of fire

 
Ensure the projectile hits the target in a perpendicular manner  

(nail first), without incline/decline. Perform firing tests for 50 times and record the results of projectile landing. Ensure the landing points meet the test parameters.

Feeding system/Magazine

  Balsa wood

  Ensure the pushing apparatus of the feeding system does not break during operation.

 
Check for cracks or deformities after repeated use. Lodge and dislodge the pushing apparatus into the feeding system 50 times.  

 
Trigger/Safety switch  

  Ice cream stick,

Rubber bands,

Paperclip

  Able to withstand triggers and moving back of trigger (ice cream stick) to lock/safety position.

 
Check for any tears to the rubber band and/or cracks in the ice cream. Perform the trigger and moving back to safety position (‘locking’) action 50 times.  

 
    Ensure the paper clip is able to clip and unclip smoothly.    

 
Table 8: Component Test Plan  

 1.1.5.1 Component Test Results and Evaluation  

 
The test were conducted according to test plans and checked for the appropriate tests parameters. All the components and their proposed materials were able to meet the test parameters. Therefore, it was demonstrated that materials chosen (balsa wood, twine, ice-cream sticks, chopstick and rubber band) were appropriate to construct the crossbow.  

 
1.2 Integration and Evaluation  

 
After component testing, the components were then assembled and integrated so that the subsystems and system test can be carried out.  

 
1.2.1 Subsystems/ Interfaces Design and Test  

 
The subsystems and interfaces identified were first integrated and tested with the test plan as shown in Table 9.  

 
Subsystems Test Parameters Test Plan  

Body/Support frame Able to withstand 3 times the weight of the crossbow system.

(anticipated at 1.5 kg) Apply 1.5 kg of load on the support frame. Check for any dents or breaks.

Bow Ensure that the bow remain in place after the performing the draw back.

 
Ensure that the bow can be stretched at the angle required without breaking. Perform the draw back motion repeatedly for 50 cycles. Check that there is no dislodging or rupturing.  

Bowstring Ensure that the bowstring does not snap easily when performing the draw back. Perform the draw back motion repeatedly for 50 cycles. Ensure that there is no snapping.

Feeding system/Magazine Ensure that the projectile falls from the magazine into the projectile guided rail when the bow string is secured in the notch. Perform the draw back motion repeatedly for 50 cycles. Ensure that the projectile is in the right position each time the bowstring is in the notch.

Trigger/ Safety switch Ensure that the bow string remains secured in the notch when it is not triggered. Leave the bow string secured in the notch for 3 days. Ensure that the bow string remains in place after 3 days.

 
Table 9: Subsystems and Interfaces Test Plan  

 All the subsystems and interfaces were tested. There were no cracks or deformity found. No interfaces were found dislodged. Furthermore, the feeding system ensures that the projectile falls into the correct position and the safety system helps to prevent any unintended firing. Therefore, this gives the team confidence that these subsystems will be able to achieve the reliability and safety parameters required.  

1.2.2 Integrated System Testing

 
The sub-systems were integrated to form the fully operational repeating crossbow prototype. The assembled product is shown in Figure 13 below.  

 
Figure 16: Pictures of Integrated Crossbow System  

Tests were done in fully operational conditions (outdoors and within classrooms). The test and evaluation plan is listed in Table 10.

 
Key Parameters Critical  

Operational

Issue (COI) Key Measure

of

Effectiveness (MOE) Critical Test

Point (CTP) Measure of Performance Test Plan

Propel a Is the Can the Maximum Projectile Projectile will

projectile at repeating repeating Projectile must travel at be launched

least 10m in crossbow crossbow Distance least 10m in down a long

range effective in propel a range hallway 10

effectively propelling projectile at consistently times and

  the projectile least 10m in maximum

  at least 10m range distance

 
  in range?  

 travelled will be recorded.  

  Can the Projectile Projectile Projectile will

    repeating Accuracy must hit the be launched at

    crossbow target at least a 0.3m x 0.3m

    propel the 90% of the target at a

 
  projectile with reasonable accuracy to the desired impact point?    

   time 

  range of 10m.

    Can the repeating crossbow propel the projectile with little loading time in between launches? Rate of Fire Time taken per projectile to be launched will be calculated. The number

of shots able to be fired off in a minute will then be extrapolated Repeating crossbow will fire off 5 shots as fast as possible.

Time taken will be recorded.

  Can the repeating crossbow propel the projectile with a reasonable amount of power? Projectile

Stopping

Power Projectiles must penetrate at least 2cm into the target. Projectile will be launched at a polystyrene target 5 times at a distance of 10m.

Penetration of the projectile into the target will then be measured.

  Can the repeating crossbow be operated from rest in a reasonable amount of time? Deployment

Time Projectile must be launched off in under 20s Repeating crossbow will be operated to launch a projectile from an unloaded state and the time taken will be measured.

Operate reliably Will the bowstring snap after prolonged usage? Is the bowstring still intact after prolonged usage Structural strength

Reliability Bowstring must not snap after testing. Repeating crossbow will launch 50 projectiles and the conditions of the

 Will the bow store elastic energy after prolonged usage? Is the bow still able to launch the projectile after prolonged usage? Stored Tensile

Power

Reliability Bow must still be able to launch projectile after testing. repeating crossbow will be observed after.

 Will the repeating crossbow be efficient in any weather condition? Will the repeating crossbow be able to launch a projectile in any weather condition? Impact of

Environment Repeating crossbow must be able to launch projectiles without misfires. Repeating crossbow will launch 10 projectiles in a rainy and windy environment.

User

Operability Is the repeating crossbow easily operable by any user? Will any type of user be able to launch the projectile using the repeating crossbow? Ease of

Operability All users must be able to fire off a projectile with the repeating crossbow Right handed, left handed, male and female adult users will be tasked to operate the repeating crossbow.

 
Table 10: Integrated System Test Plan  

1.2.2.1 System Level Test Results under Operation Environment

The team put the repeating crossbow through the tests listed in Table 11 and the test results are listed below. For safety reasons, all tests other than the penetration tests were carried out with the fully wooden projectile.

 
Tests Measure of Performance Achieved results Operational Requirements Results  

Projectile will be launched down a long hallway 10 times and maximum distance travelled will be recorded. Projectile must travel at least 10m in range consistently 14m 10m Passed

Projectile will be launched 20 times at a 30cm x 30cm target at a range of 10m. Projectile must hit the target at least

90% of the time 20 projectiles on target 18 shots on target Passed

Repeating crossbow will fire off 5 shots as fast as possible. Time taken will be recorded. Time taken per projectile to be launched will be calculated. The number of shots able to be fired off in a minute will then be extrapolated 18.75 projectiles per minute 10 projectiles per minute Passed

Projectile will be Projectiles must 3.5cm 2cm Passed  

launched at a penetrate at least

polystyrene target 5 times at a distance of 10m. Penetration of the projectile into the target will then be measured. 2cm into the target.

 Repeating Projectile must be 10s 20s Passed  

crossbow will be launched off in

operated to launch a projectile from an unloaded state and the time taken will be measured. under 20s

 
Repeating Bowstring must not No observable No Passed  

crossbow will launch 50 projectiles and the conditions of the repeating crossbow will be observed after. snap after testing.

  change

  abnormalities  

 Bow must still be able to launch projectile after testing. No observable change No abnormalities Passed  

Repeating Repeating crossbow No observable No Passed

crossbow will must be able to change abnormalities

launch 10 launch projectiles

projectiles in a rainy and windy environment. without misfires.

Right handed, Left handed, male and female adult users will be tasked to operate the repeating crossbow. All users must be able to fire off a projectile with the repeating crossbow Projectile successfully launched for all users Projectile successfully launched for all users Passed

 
Table 11: Results Under Operation Environment  

 
If all the tests were carried out with the projectile with a metal arrowhead, the results would be even better than those recorded in Table 11. The metal arrowhead provides a better weight distribution for the projectile. This allows it to have a better flight path and thus fly further and more accurately.  

 2. Cost Breakdown  

 
The total cost incurred to build the scaled model is $25.992. Refer to the cost breakdown in Table 12.  

 
Component Raw Material(s) Cost  

Body and Feeding system Balsa wood $20

Bow 2 x Steel ruler $5

Projectiles 5 x Wooden chopstick $0.04

Trigger/ Safety switch Ice cream stick,

2 x Rubber band,

Paper clip $0.04 +

$0.012 +

$0.9

Table 12: Cost Breakdown

3. Challenges and Lessons Learnt

 
One of the major challenges that the team faced was to get the projectile to travel in a trajectory path like an actual arrow. Various experiments had been conducted with different types of chopsticks. However, all of them were not able to travel in the intended path. The team then considered making several modifications to the chopsticks to make it more head-heavy, such as taping the front part of the chopstick. The final modification that was made was to saw off the front portion of the chopstick and attached a nail to it. With this modification made, the projectile can achieve a high degree of accuracy that is specified in the performance requirement.