Engineering

instructions.docx

So I’m just responsible for the chair and the rod that is under the chair which will support the chair , I need you to do the needed engineering calculations for those two parts like shear and moment diagrams the force distributions the diameter needed for the shaft the size of the chair, depth , bearings for rotation ,spring shocks and so on …… I have the course book, its

You can find what you need in this book please try to use the book equations, tables as much as you can chapter (6-7-8-9-10-11-12): Shigley’s Mechanical Engineering Design, 10th edition, Budynas, R.G., and Nisbett, K, McGraw Hill, 10th Edition, 2014.

So you will do for me the calculations based on machine design and stress analysis concepts for the chair and the parts under the chair like shaft and Bearing and the type of shaft and bearings and used diameters ,screws, spring shocks , materials needed to be used , like everything needed for those two parts , moments ,shears , forces ,load , width of the chair, factors of safety calculations , seat post and all the forces and calculations needed to attach it to the chair , later when you are done i will assemble this on solid works so make sure all the dimensions are correct the height for the chair and the seat post together should be 1.1 m .

Please look at the file(Two jpeg files) that I attached you can make some assumptions, but not everything I need to see machine design calculations and the hole mobility scooter will weight 160 kg so the chair and the part under the chair should not be high weighted because I have to account that for other parts too , please search the book online.

Imp: I am attaching a pdf file as well, it’s kind of helping sample. Please check page18-28

a1.jpeg

a2.jpeg

sample-see-page-18to28.pdf

Table of Contents

1.0 Problem Analysis …………………………………………………………………………………………………………………… 1

1.1 Current Situation ………………………………………………………………………………………………………………… 1

1.2 User Groups ………………………………………………………………………………………………………………………. 1

1.3 Deliverables ………………………………………………………………………………………………………………………. 2

1.4 Existing Designs ………………………………………………………………………………………………………………… 2

2.0 Product Requirements …………………………………………………………………………………………………………….. 4

3.0 Embodiment ………………………………………………………………………………………………………………………….. 5

3.1 Morphological Chart …………………………………………………………………………………………………………… 5

3.2 Evaluation of the Initial Concept ………………………………………………………………………………………… 12

3.3 Revising the Concept ………………………………………………………………………………………………………… 14

4.0 Final Analysis and Recommendations …………………………………………………………………………………….. 16

5.0 References …………………………………………………………………………………………………………………………… 17

6.0 Appendix …………………………………………………………………………………………………………………………….. 18

6.1 Selection and Justification of Parts ……………………………………………………………………………………… 18

6.1.1 Selected Motor …………………………………………………………………………………………………………… 20

6.1.2 Stresses on Base Frame ……………………………………………………………………………………………….. 24

6.1.3 Stresses on Welded Parts …………………………………………………………………………………………….. 26

6.1.4 Deflection of Shaft ……………………………………………………………………………………………………… 27

6.1.5 Critical Speed …………………………………………………………………………………………………………….. 28

LIST OF FIGURES

Figure 1 – Trailer Valet XL [2].……………………………………….……………………………2

Figure 2 – Force 10K Electric Powered Trailer Dolly [3].………………………………………..3

Figure 3 – Ergo PowerCart [4]…………………………………………………………………….3

Figure 4 – Morphological Chart for Trailer Dolly Design………………………………………..7

Figure 5 – Initial Concept Design………………………………………………………………..12

Figure 6 – Revised Concept Design………………………………………………………………14

Figure 7 – FBD of the Hitch……………………………………………………………………..18

Figure 8 – Cross-Section to Show Gearing………………………………………………………19

Figure 9 – Shear Diagram of Shaft [z-y plane]…………………………………………………..20

Figure 10 – Moment Diagram of Shaft [z-y plane]………………………………………..…….21

Figure 11 – Shear Diagram of Shaft [x-y plane]………………………………………………….21

Figure 12 – Moment Diagram of Shaft [x-y plane]………………………………………………21

Figure 13 – Critical Speed Forces…………………………………………………………..……28

LIST OF TABLES

Table 1 – Method of movement system concept scoring…………………………………………8

Table 2 – Braking system concept scoring………………………………………………………..8

Table 3 – Control system concept scoring…………………………………………………………9

Table 4 – Safety system concept scoring…………………………………………………………10

Table 5 – Transmission system concept scoring…………………………………………………10

Table 6 – Weighted concept scoring matrix……………………………………………………..11

Table 7 – Assessment of design requirements……………………………………………………15

1.0 Problem Analysis Under commission from ABC Trailer and Co., a prototype trailer dolly is to be designed in order to be sold in conjunction with the company’s trailers. The Fast Design process [1] is to be utilized in order to accomplish this task in a timely, efficient manner. The current situation of trailer dollies with respect to user groups and existing designs, including other relevant information, will be discussed in this following section.

1.1 Current Situation • Individuals want to move their trailers themselves • Trailers are difficult to move in tight spaces using conventional towing vehicles • Trailer dollies are usually purchased in conjunction with trailers • Physically-weak individuals may have difficulties using conventional dollies • Dollies can take up considerable space for storage • Most trailer dollies are quite costly

1.2 User Groups Users that benefit from current situation:

• Healthy, middle-class adults • Towing companies • Individuals that own towing vehicles • Trailers in easily-reachable locations

Users that suffer from current situation:

• Physically-disabled adults • Elderly • Low-income individuals • Trailers in hard-to-reach locations

Possible improvements:

• Decreasing the weight and size of the dolly can enable weaker people to use it • Less space should be required when the dolly is put into storage • Reducing the price will help accommodate individuals with lower budgets • Incorporating safety and stability mechanisms

In any new design, the users that benefit from the current situation should not be adversely affected while the users that currently suffer should notice new benefits. The overall usability of the trailer dolly with respect to all the user groups should be maintained or increased with any design alteration.

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1.3 Deliverables The design of a suitable trailer dolly that meets the requirements set out in the original design brief should be achieved. It should satisfactorily address the challenges introduced in the Problem Analysis section and provide the same or an increased level of usability for the users that suffer from current in-market products, without sacrificing any features that provide benefits to some other users. The overall design methodology carried out in this project should follow the Fast Design process [1]. Detailed calculations and diagrams are also expected for all of the custom parts of the design in order to justify the functionality and safety features. Furthermore, a formal analysis and critique of the design should be made. Possible future improvements pertaining to the design will be suggested and expanded upon. Finally, a full set of engineering drawings must be produced for the dolly and any major components that interact with it.

1.4 Existing Designs

Vendor: Trailer Valet

Price: $600.00 USD

Reference Design: Trailer Valet XL [2]*

Specifications:

Product Specifications

Figure 1: The Trailer Valet XL trailer dolly [2].

• Uses cordless drill to spin protruding shaft connected to internal gears in order to move dolly

• Quickly attaches and locks ball hitches in place

• 300 hours of corrosion resistance • Weighs 54 lbs • Automatic braking when handle

lever is released

*This model was used as the main benchmark design for this project.

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Vendor: Parkit360

Price: $2324.00 CAD [1 CAD = 0.77 USD as of April 11, 2016]

Reference Design: Force 10K Electric Powered Trailer Dolly (Base Version) – P360HD-Base [3]

Specifications:

Product Specifications

Figure 2: The Force Electric Powered Trailer Dolly [3].

• Uses external battery (e.g. from trailer, stand-alone unit, etc.) to power itself [not included in base pricing]

• Powerful 1.5 hp motor • Fast, secure-locking ball

mount • Optional battery charger

and monitor, and “smart” brakes [add-ons, extra costs]

Vendor: DJ Products Inc.

Price: $1995.00 (base) + $995.00 (add-on) = $2990.00 USD (total)

Reference Design: Ergo PowerCart with Trailer Pulling Kit option [4]

Specifications:

Product Specifications

Figure 3: The Ergo PowerCart trailer dolly [4].

• 0-3 mph variable speed forward and backward with hand twist control

• Automatic battery charger • Multipurpose use: can be used to

move boxes, laundry, building supplies, etc. on its flatbed

• Handles at comfortable arm level to reduce the need to bend

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2.0 Product Requirements Several requirements were determined for the trailer dolly design to be met, as per the supplied design brief and other logical considerations. The trailer dolly must satisfy these requirements in order to be a successful design:

Attributes:

• Accommodates individuals of different physiques • Takes up the least amount of space as possible, while in use and in storage • Must be intuitive to use • The weight and cost of the dolly needs to be minimized while its usability, functionality,

and safety are maintained

Functions:

• Supports the weight of the trailer when in motion and at rest • Must be easy to maneuver around, with a tight turning radius • Applies sufficient torque to move trailer • Withstands wear-and-tear from the environment over time • Stops in emergency situations

Constraints:

• Must use standard, interchangeable hitch ball • Must lift the trailer from 12 in at rest to a minimum height of 20 in off the ground • Inhibits speeds above 2 mph • Must be powered by motor and/or human force • Must be able to be manually operated by a sufficient number of people • Includes appropriate factors of safety in the design • Allows trailer to be functional even when dolly is attached • Must function on any common surface (e.g. gravel, asphalt, hard packed dirt) • Must be relatively simple to manufacture • Minimal cost (as long as all other requirements are met)

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3.0 Embodiment It was determined that the design of the trailer dolly would be divided into five main subsystems: method of movement, braking, controls, safety, and transmission (with the motor).

3.1 Morphological Chart The basic role of the movement subsystem is to allow for the trailer dolly to move around on a variety of surfaces and terrains, whether it is loaded with a trailer or not. The first ideation was the implementation of pneumatic tires. These tires can travel on a variety of surfaces such as gravel, dirt, and grass with ease and can act to absorb excessive perturbations that may be experienced when rolling. They are also able to support large forces due to the strong material they are fabricated out of. Furthermore, they are widely available in many different sizes and configurations in many retail locations, which would therefore reduce the overall costs of manufacturing the whole dolly. The second ideation was the use of a balanced ball tire. Like pneumatic tires, it can also handle relatively large forces well and would always keep the dolly balanced upright. It is a round sphere with actuators surrounding its surface, with the actuators making adjustments to the ball’s rotation every time it moves. The ball wheel would require an additional control system to maintain upright stability, but would allow for very easy and durable movement on most terrain. The third ideation was of using treads. This would provide the most stability and most reliable ability to work on a variety of surfaces. Treads would be implemented on the underside of the dolly, such that with a sufficient transmission system the tracks would move in the direction the user was steering very accurately.

The braking system makes sure the dolly stops when the user wants it to. The first ideation was of mechanical disk brakes. These would essentially suppress the rotation of the wheels or some part of the transmission in order to stop the movement of the dolly quickly. The user would deploy the mechanical brakes through the control system. The second and third ideations were pneumatic and hydraulic-powered brakes, respectively. These would use an air or water-based source to power the suppression system that counters the rotation of the wheels or internal transmission of the dolly. The fourth ideation for the braking system is the use of magnetic brakes. This ensures that the trailer dolly stops when controlled to do so by the user. It uses a powerful electromagnetic system that stops the wheels from rotating without actually making contact with them. This requires little maintenance is reliable for a lengthy time. Implementation of magnetic brakes would also increase the overall lifespan of the dolly.

The control system enables the user to maneuver the trailer dolly the way they want. It encompasses the deployment of the braking and safety systems, and is a direct interface for the method of movement. The first ideation is a Rudder system. It would provide a smooth method for the user to direct the dolly to a desired position. The second ideation is the use of a handle bar. This presents a very familiar and simple method to move the dolly around. The third ideation was the implementation of a steering wheel. This would also provide the user with a familiar control method and would allow for them to effectively maneuver in any direction. The fourth ideation is the use of a lever system. The user would push or pull a lever arm to direct the dolly and trailer in their desired direction to move forward or backward. The fifth and sixth

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ideation uses a remote control and an onboard button system, respectively. For the remote control method, the dolly would be wired up so that at the tap of a button or lever on the remote control the dolly moves accordingly. This would enable the user to move the trailer and dolly at a distance, therefore maximizing safety and comfort. The onboard buttons would provide a similar experience, except that the user will be required to be within reaching distance of the buttons while the dolly is in operation. The seventh ideation is the use of direct manipulation of the dolly. The user will have to adjust the orientation of the dolly themselves using their own hands.

The safety subsystem of the trailer dolly encompasses the mechanisms that help prevent the user and everyone else around them from getting injured during the use of the trailer dolly. The first ideation was the implementation of a dead-man switch fail-safe system. This method activates when the user lets go of a lever or handle bar mechanism for any reason, and immediately stops the movement of the dolly through the braking system. The second ideation is the use of lighting around placed around the dolly and the trailer it is moving to alert everyone near it. This would be especially effective in dimly-lit locations such as dark alleys or between buildings. The third ideation is to have warning sounds be activated while the dolly is in operation, as to alert all nearby people in order to ensure they are aware of the moving trailer. The fourth ideation is to make sure that the outer surface of the dolly has all dull edges to prevent anyone from being injured if accidental contact is made with the dolly. The fifth ideation for safety is a pin-in-hole locking interface for the hitch. A strong pin is inserted into a slot between the hitch and hitch ball to lock the two parts in place. This ensures that the hitch and hitch ball stay securely connected when the dolly is loaded. This prevents the hitch connection to the trailer from collapsing and potentially causing any injuries to anyone nearby. The sixth ideation is the use of a screw cap hitch locking mechanism. The bottom end of the hitch is threaded in this situation and screws into a geared locking mechanism. When the user wants to adjust the height of the hitch, they can just use a control to make the hitch shaft screw upwards or downwards, and then the gear-hitch mechanism will lock into place. This enables the user to easily adjust the height of the trailer and keeps it secure while in use. The seventh and final ideation for the safety subsystem is to implement a blind spot camera interface between the back of the trailer and the front of the dolly. This allows the user to have a full view of their surroundings when they are using the dolly to prevent any incidents from occurring.

The transmission system is the interface between the motor and the method of movement. Ideally, it should enhance the effect of the motor and help to drive the wheels so that the user can move the dolly with ease. The first ideation was the implementation of gears in the transmission. With an effective gearing system, the gears can transmit large amounts of force from the motor to apply to the shaft of the wheels, resulting in a large mechanical advantage to enable the user to move the dolly with ease. The second ideation was the use of a belt drive system. Similar to the gearing transmission, this method transmits force from the motor to the axle of the dolly to spin the wheels. However, friction bands or belts are used rather than gears to transmit the forces.

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Figure 4: The morphological chart developed for the trailer dolly.

After the morphological chart was created, each individual ideation was assessed based on the requirements set forth earlier in the design process. For the most part, most requirements depended on every subsystem to be functioning correctly for optimal effectiveness. From the morphological chart, each ideation within their respective subsystems was then scored in a series of Pugh screening matrices to evaluate their feasibility against a number of screening criteria.

The selection criteria was chosen because they all contribute to the processes involved in the use of the system. The durability comes into mind because a longer lifespan of the machine is desired. Weight is a factor in the system as a whole because if it weighs too much, it requires more energy to power the system, whether it be for more rotations due to a smaller gear ratio or more power for a motor. Simplicity of the design is relative to how easy it is to perform maintenance on the system, which means more people will be able to service it, without the need of an expert. The size is a factor because it is desired for the machine to be small and be able to get into difficult-to-reach places that towing trucks cannot. Reliability is the measure of how frequently the machine can be used without needing to make modifications to it. This is important because it is wanted for the users to not feel like using the tool is a must in order move the trailer, but rather a tool to assist in it. The jamming frequency refers to how often a

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component will malfunction while in use: the lower the better. The amount of noise it makes is also examined, with the less sound produced the better, because excessive noise can be damaging to the human ear. Since the system will use a motor, and the user will need to stand beside it, it may get really loud for the user. The cost of production is taken into account because the machine is to be sold alongside the trailer. If the cost is too high, the consumer may think that ABC Trailer and Co. is selling them an incomplete item, and is asking for more money to be “unlock” the full features of the trailer system. Also, too high of a cost would deter individuals with lower incomes from purchasing the product.

Table 1: The concept scoring for the selection of the method of movement.

Selection Criteria Concepts

Pneumatic Tires

Ball Wheel Treads

Durability 0 -1 1 Weight 1 1 -1

Ease of use/Simplicity of design

1 1 0

Ease of manufacturing 1 1 -1 Safety 0 0 0 Size 0 1 -1

Reliability 0 0 1 Jamming frequency 0 -1 1

Noise 1 1 -1 Cost of production 1 1 -1

Sum +s 5 6 3 Sum 0s 5 2 2 Sum –s 0 2 5

Net score 5 4 -2 Rank 1 2 3

Continue? Yes Yes No

Table 2: The concept scoring for the selection of the braking system.

Selection Criteria Concepts

Mechanical Disk Brakes

Pneumatic Brakes

Hydraulic Brakes

Magnetic Brakes

Durability 1 -1 0 1 Weight 0 1 -1 -1

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Ease of use/Simplicity of design 1 -1 0 -1 Ease of manufacturing 1 -1 -1 0

Safety 0 0 0 0 Size 0 -1 1 1

Reliability 1 -1 0 1 Jamming frequency 0 1 1 0

Noise -1 0 1 1 Cost of production 1 -1 0 -1

Sum +s 5 2 3 4 Sum 0s 4 2 5 3 Sum –s 1 6 2 3

Net score 4 -4 1 1 Rank 1 4 2 2

Continue? Yes No Combine Combine

Table 3: The concept scoring for the selection of the control system.

Selection Criteria Concepts

Rudder System

Handle Bar

Steering Wheels Lever

Remote Control Buttons

Direct Manipulation

Durability 0 1 1 1 -1 0 1 Weight 1 0 0 1 1 1 1

Ease of use/Simplicity of design 1 1 1 1 0 1 1

Ease of manufacturing 0 1 0 1 -1 0 1 Safety 1 0 1 -1 1 -1 -1 Size 1 0 0 1 1 1 1

Reliability 1 1 0 1 0 0 1 Jamming frequency 0 1 0 0 0 0 1

Noise 1 1 1 1 1 1 1 Cost of production 0 0 -1 0 -1 -1 1

Sum +s 6 6 4 7 4 4 9 Sum 0s 4 4 5 2 3 4 0 Sum –s 0 0 1 1 3 2 1

Net score 6 6 3 6 1 2 8 Rank 2 2 5 2 7 6 1

Continue? Yes Yes No Combine No No Yes

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Table 4: The concept scoring for the selection of the safety system.

Selection Criteria

Concepts

Dead-man System Lighting

Warning Sounds

Dull Edges

(no sharp edges)

Pin- in-

hole to

secure hitch

Screw- cap

hitch locking

Blind Spot Camera

Durability 1 1 1 1 0 1 0 Weight 1 0 0 1 1 0 -1

Ease of use/Simplicity of design 1 1 1 1 1 1 1

Ease of manufacturing 1 1 1 0 1 0 1 Safety 1 1 1 1 0 1 1 Size 1 0 0 1 1 1 -1

Reliability 1 0 0 0 0 1 0 Jamming frequency 1 1 1 1 -1 -1 1

Noise 1 1 -1 1 1 1 1 Cost of production -1 -1 -1 -1 0 1 -1

Sum +s 9 6 5 7 5 7 5 Sum 0s 0 3 3 2 4 2 2 Sum –s 1 1 2 1 1 1 3

Net score 8 5 3 6 4 6 2 Rank 1 4 6 2 5 2 7

Continue? Yes Adapt Adapt Yes No Yes No

Table 5: The concept scoring for the selection of the transmission system.

Selection Criteria Concepts

Gears Belts Durability 1 0

Weight -1 1 Ease of use/Simplicity of design 1 1

Ease of manufacturing 0 1 Safety 1 0 Size 1 0

Reliability 1 0 Jamming frequency 1 0

Noise 1 0 Cost of production -1 1

Sum +s 7 4 Sum 0s 1 6

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Sum –s 2 0 Net score 5 4

Rank 1 2 Continue? Yes No

After all the scoring was completed, the highest ranked ideations of each subsystem were chosen to create a complete concept. Eventually, three possible concepts were initially brainstormed before one initial concept was accepted as the main design to move forward with for this project. Each design consisted of either one or a combination of multiple ideations from each of the five subsystem categories, and were ultimately combined to form a complete concept for a trailer dolly.

Design 1 consisted of: pneumatic tires for the method of movement, mechanical disk brakes for the braking system, direct manipulation of the dolly for the control system, a dead-man switch mechanism for the safety system, and the use of gears for the transmission system.

Design 2 included the use of: the ball wheel for movement, hydraulically-powered mechanical disk brakes for the braking system, handle bars for easy steering in the control system, a pin-in- hole mechanism to secure the hitch and a dead-man switch fail-safe for the safety system, and a belt-driven transmission system.

Design 3 used: pneumatic tires to provide smooth movement, permanent magnetic brakes for an effective braking system, a handle bar-based control system to guide the dolly, a dead-man switch fail-safe for the safety system, and a gearing transmission system.

After the three concepts were generated, they were evaluated based on a weighted concept scoring system, as outlined in the following table.

Table 6. The weighted concept scoring matrix.

Concept Scoring D1 D2 D3

Factors Concept Weight (%) Raw net raw net raw net

Durability 10 4 0.4 2 0.2 4 0.4 Weight 5 2 0.1 4 0.2 3 0.15

Ease of Use 12 3 0.36 5 0.6 4 0.48 Safety 25 5 1.25 5 1.25 5 1.25

Reliability 8 4 0.32 2 0.16 4 0.32 Jamming

Frequency 8 3 0.24 2 0.16 3 0.24

Noise 5 4 0.2 5 0.25 4 0.2 Cost of Production 12 4 0.48 2 0.24 3 0.36

Total 100 3.95 3.81 4

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Design 3 was ultimately chosen as the concept design to move forward with. The final result of the concept with all of its components attached was then sketched.

3.2 Evaluation of the Initial Concept

Figure 5: The initial concept design of the trailer dolly.

The pneumatic wheels were chosen as the method of movement due to their reliable and secure ability to undergo large loads and smoothly move vehicles. Additionally, their wide availability in the markets and affordability makes these wheels in line with the requirement of simple manufacturability as they can be bought off-shelf. They are designed to allow for maximum

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freedom of movement in all directions, and offer a tight turning radius. Also, they are able to move on many different surfaces such as asphalt, gravel, and grass, which meets another requirement set out in the design process.

The gearing mechanism was decided as the concept for the transmission system due to its ability to transmit a large mechanical advantage to the pneumatic wheels once the motor is running. A sufficient gear ratio allows the dolly to move easily with the help of the motor, but physically limits the speed of the wheels to ensure that the 2 mph speed limit is met. It also allows for the manual movement of the dolly by several people if the motor does not work. The gearing is very reliable, and can be integrated into the safety and braking subsystems of the dolly.

The magnetic brakes were chosen as the concept for the braking system due to their reliability of stopping the dolly quickly. They are designed to stop the wheels of the dolly immediately once activated by the user or through a safety mechanism. Although they usually do cost a fair amount greater than the other ideations, in the long term they can cost less due to their very low maintenance requirements and longer lifespans.

The handle bar was chosen for the control system, with the addition of a crank mechanism to increase the ability to actually maneuver the dolly. The handle bar is attached to the back of the dolly, as illustrated in the initial concept sketch. This allows the user full control over where the dolly will be guided when it is under load. The addition of the crank mechanism with a pedal- like handle combines with the gear transmission system. As the crank is rotated, the wheels move even more. The pedal arm helps the user to rotate the crank even easier and provides extra leverage too. This is especially helpful in situations where the motor is not being used, so that the dolly can still be relatively easy to maneuver with the hand crank system manually being operated by one or several people.

Finally, the dead-man switch fail-safe was chosen as the main safety subsystem concept in the trailer dolly design. It was designed to be integrated with the handle bar system, so that once the handle bar is released for whatever reason the dead-man switch activates and stops the dolly immediately. This ensures the safety of the user and others around them. This, along with the actual braking system, fulfills the requirement to stop during emergency situations.

The overall frame of the trailer dolly design was based off of the benchmark design, the Trailer Valet XL [2]. It was realized that the benchmark offered a very compact, lightweight design but was still able to meet all its functionalities, most notably the ability to move a 10,000 lb trailer. Its low price was also very alluring. Although the Trailer Valet XL met many of the requirements that were determined earlier in this report, it did have some shortcomings that were improved on in this trailer dolly design concept.

Although this initial design meets the most important requirements of the design and is therefore deemed acceptable, some changes were required in order to optimize the design further and make it a truly successful, preferred design.

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3.3 Revising the Concept Upon more research and closer examinations, the magnetic brakes in the initial concept design were changed to the mechanical disk brakes due to the realization of the large initial price of the trailer dolly if magnetic brakes were actually implemented. Although they do boast a great ability to quickly stop the wheels, the long-term costs take very long to balance out compared with a dolly implemented with simple mechanical brakes. It was deemed that the longer lifespan that the magnetic brakes offered did not heavily outweigh the lifespan of mechanical disk brakes because of the low frequency of use by most users. Many users will not use the dolly more than a few times each year. Therefore, it was determined that the costs associated with installing magnetic brakes were deemed to be too high and did not meet the requirement of having a minimized cost (since all other requirements have been met through the rest of the design). Having a lower-costing dolly will only expand the user groups, and allow more individuals with limited budgets to afford this product.

Figure 6: The final revised concept design of the trailer dolly.

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The revised concept design was deemed to be the preferred design. It was able to satisfy all the requirements set out in the beginning of this report, as summarized in Table 7.

Table 7. An assessment of all the design requirements.

Requirements Revised Concept The dolly must allow forward and reverse movement, as well as steering to the tightest possible turning radius.

8 in diameter pneumatic wheels allow for efficient movement and tight, steady turning.

A motor, to be selected by the designers, will nominally power the dolly.

A sufficiently powerful motor was chosen based on reasonable transmission power requirements (see calculations in Appendix).

In emergencies, it must be possible for the dolly to be operated (pushed, pulled, turned) manually by a sufficient number of people.

An efficient gearing transmission system allows for the manual operation of the dolly (see calculations for gearing).

Suitable, justified factors of safety must be embedded in the design.

This is satisfied for all components, as shown in the engineering calculations (Appendix).

The dolly must use a standard trailer hitch ball, and be interchangeable.

Standard hitch ball sizes can mount onto the hitch of the dolly.

The dolly must keep the fully loaded (10,000 lbs) trailer stable without external forces applied by the user, both when in motion and when at rest.

The motor and gearing transmission system keeps the dolly steadily moving and locks into place when not in motion.

The dolly must lift the trailer receiver to a minimum height of 20” off the ground.

The height-adjustable hitch and locking bolts possess satisfactory safety factors, as evaluated in the engineering analysis).

The dolly must inhibit trailer movements at speeds beyond 2 mph.

The selection of the motor and gearing transmission system satisfy this, as per the engineering calculations (in the Appendix).

The design must maximize safety of anyone near the trailer during operation.

The fast-acting braking and safety mechanisms produce dependable safety.

The trailer must remain functional throughout any use of the dolly.

Reasonable factors of safety were determined to allow for extra loads and movements on the dolly, as part of the engineering analysis.

The dolly must be able to stop itself in emergency situations once properly activated by the user.

This is satisfied through the mechanical brakes and dead-man switch fail-safe of the braking and safety systems of the design.

The dolly must function on any surface the trailer may move on: gravel, asphalt, and hard packed dirt.

The pneumatic tires chosen in the movement system accomplishes this.

Operation of the dolly must require minimal training.

A simplified user interface with basic steering and braking controls reasonably satisfy this.

Since this is a prototype, manufacturing must be as simple as possible.

The use of standard, in-market components such as bolts and wheels achieves this.

Overall cost must be minimized so long as no other requirements are violated.

Very reasonably-strong materials and simple manufacturing allow for low costs if product is produced in mass.

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4.0 Final Analysis and Recommendations

A final revised design was successfully completed for the prototype trailer dolly using the Fast Design process [1]. A profile of the final concept can be seen in Figure 6, and the detailed drawings of the design can be located in the Appendix of this report. This design meets all the specified requirements given in the original project brief as well as in the Product Requirements stage of this design process. Although the preferred design met all the requirements, several items could have still been addressed and possibly be further improved upon. Considering the limited amount of time that was allotted for this complete design process though, this trailer dolly design was deemed to be very satisfactory.

Several recommendations could be made for future improvements on the trailer dolly design if more time was available. Firstly, as seen in the engineering drawings, the actual shape of the shell of the dolly contained an extended hood to cover the internal gears and motor. The original revised concept did not consider that the motor and gear transmission combination would require more space to fit properly in a slim profile. Ideally, a smaller motor and a better gear layout could have resolved this issue so that the slim frame of the dolly could still be realized. Due to limited time for detailed planning, however, this was not achievable in this iteration of the Fast Design process [1]. Another recommendation would be to possibly choose more suitable materials to be used in the design. Although the materials that were chosen accomplish their tasks just fine, if more time was available to spend on investigating a wider variety of materials, alternative materials could have been found to reduce the overall costs of the design and still achieve all requirements. A third recommendation would be to combine additional features onto the dolly if the costs would not be too high. Having optional add-ons such as blind spot detection, warning sounds, and safety lighting could be relatively inexpensive methods to increase the safety of the users significantly depending on the environmental conditions. These additional items, along with others, could have all been integrated together and could have offered possibly significant improvements for many users.

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5.0 References

[1] Salustri, F. A. & Neumann, W. P., A Fast Design Process, Toronto: Department of Mechanical and Industrial Engineering, Ryerson University, 2015.

[2] Trailer Valet XL – Trailer Valet. (n.d.). Retrieved April 11, 2016, from

Trailer Valet XL

[3] Force 10K. (n.d.). Retrieved April 11, 2016, from http://parkit360.ca/products/trailer- mover-10000lbs-capacity-base

[4] Felker, D. Ergo PowerCart Brochure. [Email correspondence on April 7, 2016].

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[7] MTGR-P14-1L077 DC GEARMOTOR RT-ANG 1/7HP 90VDC 77RPM 97in-lb 23:1 RATIO. (n.d.). Retrieved April 11, 2016, from http://www.automationdirect.com/adc/Shopping/Catalog/Motors/DC_Gearmotors_- _IronHorse_(up_to_.25HP)/90_VDC_Right_Angle_Gearmotors/MTGR-P14-1L077

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