Trishuli River

MECH 2412: Design Project 2018

Trishuli River Crossing

Final Report

Lab 4: Group 4

Members: Anthony Reyes:

214261341

Kishon Webb:

215076730

Mahgoub Mohamed:

214717235

Constantinos Kandias: 215181928

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Table of Contents

Team Statement of Participation Executive Summary ​Planning and Clarification ​Conceptual Design ​Embodiment Design ​Design Implementation

2 2 3 6 11 12

Figure Index Figure 1: Functional Structure Diagram

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Figure 2: Design Concept 1

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Figure 3: Design Concept 2

7

Figure 4: Design Concept 3

8

Figure 5: Design Concept 4

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Figure 6: Preliminary Design Top View

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Figure 7: Preliminary Design Side View

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Figure 8: Prototype Design Full View

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Figure 9: Prototype Design Side View

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Figure 10: Final CAD Model

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Figure 11: Final Left View

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Figure 12: Final Right View 16 Figure 13: Bill of Materials

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Table Index Table 1: Requirements

3

Table 2: Morphological Chat

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Table 3: Concept Ranking

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I.

Team Statement of Participation All four members of the team, mentioned below, offered some contributions to

the completion of this project. Signed by: Kishon Webb Constantinos Kandias Mahgoub Mohamed Anthony Reyes

II.

Executive Summary Every day, countless Nepalese people risk their lives crossing the Trishuli river. Due to the absence of a bridge system, they are forced to use nothing more than a rope and pulley to cross the river, dangling above the raging waters. Our project, inspired by the challenges these people face on a daily basis, was to create a fully automated, cost effective device, which is capable of carrying a load across an existing cable system. Given limited time and resources, we were tasked with providing an alternative solution which can transport a mass of 4 kg across a 15 foot long inclined rope. Our design was required to function on a variety of rope conditions; an incline of 2°, a steeper cable inclined at 20°, and a simulated dirty cable, inclined at 10° with obstructions spaced apart by 6 inches. We were constrained to a total budget of $45, which we can use to purchase the provided materials from a shop in order to create our prototype and final design, which must fit within a 50*50*50 cm box. In order to be considered successful, each of the three challenges must be completed within 10 minutes.

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III.

Planning and Clarification A. Background In Nepal, the Trishuli River acts as a barrier for the residents of the highland region of Nepal; it separates them from a market of goods, education, healthcare facilities, and other institutions. With the sparse population and the surrounding mountainous terrain, it would prove difficult and costly to create bridges to cross the river. As a result, the residents of Nepal relied on large cables and their own strength to cross the river. Our design was created in an attempt to address the Trishuli River crossing in Nepal. Our goal is to provide the local residents a method of transportation that is safe, reliable and affordable to cross the Trishuli River. B. Design Specifications Listed in Table 1 below are the requirements and constraints we specified in the Needs Assessment and Conceptual Design reports.

Table 1: Requirements Requirement

Constraint

Priority

Yes(Y)

(1-5)

Total

Rank

No(N) Safety

Y

4

8

2

Easy of use

N

4

4

3

Inexpensive

N

2

2

5

Easy Implementation

N

3

3

4

Versatility

Y

5

10

1

Speed

N

1

1

6

Autonomous (after activation)

Y

4

8

2

Compact

N

3

3

4

4

Objectives ● Safety ● Efficiency ○ Speed ○ Strength ● Ease of implementation ● Low cost ● Autonomous ● Compact Constraints 1. Only materials available from the MECH 2412 shop may be used 2. Glue and batteries are exempt from the material and budget restrictions 3. The budget is limited to $30 for the prototyping phase, and an additional $15 for the construction of the final design 4. The design can only incorporate a single motor 5. 3D printed parts must have a volume less than 5 cm^3 6. The design must allow for easy mounting onto the cables 7. The design must be smaller than 50cmx50cmx50cm Reflection In our objectives and requirements, we did not place enough emphasis on the speed of our design. We emphasized safety and reliability over speed, and this impacted the performance of our initial prototype. Part way through our design process, our requirements were reworked to accommodate the problems we saw during the prototyping phase. In the end our design did meet all of our requirements. It functioned consistently well, and fell within the budget and other restrictions. Our design also satisfies all of our design objectives, such as its reliability, efficiency, ease of use, cost and size.

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C. Functional Structure Diagram Another aspect of our design process to look back on is our functional structure diagram as shown below. Figure 1.

Figure 1: Functional Structure Diagram Figure 1

Reflection Our functional structure diagram was missing one key aspect of our design. A method of torque conversion was not included in the diagram. In our final design, we added a multi ratio gearbox, allowing the gear ratio to be adjusted without the need to disassemble and replace parts. This is one of the most crucial parts of the design, allowing it to perform as efficiently and powerfully as possible across all the necessary conditions. All of the functions we did include in our functional structure diagram were present in our final design.

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IV.

Conceptual Design A. Morphological Analysis Below is the morphological chart included in our Conceptual Design Report,

showing all the proposed concepts we discussed during the ideation phase of the design process. Table 2: Morphological Chart Option 1 Housing

Load Carrier

Option 2

Option 3

Option 4

N/A

N/A

Type of Motor

Type of Wheel

N/A

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Powertrain

N/A

Wheel configuration

Design Concepts

Design 1: Housing: No housing Load Carrier: Hook Motor: Geared 150 RPM Wheels: Grooved Powertrain: Gearbox (1:1 ratio) Wheel configuration: two wheels above cable ​ Figure 2: Design 2: Housing: Square Load Carrier: Basket Motor: Geared 150 RPM Wheels: Spoked Powertrain: Pulley Wheel Configuration: Two above

Figure 3:

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Design 3: Housing: Circular Load Carrier: Hook Motor: Geared 90 degree Wheels: Grooved Powertrain: Direct Wheel Configuration: Two above, two below

Figure 4: Design 4: Housing: Triangular Load Carrier: basket Motor: Geared 300 RPM Wheels: Smooth Powertrain: Pulley Wheel Configuration: Three wheels above cable ​ Figure 5:

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B. Conceptual Design Selection In the table below are the weights given previously based on design criteria devised in the same report. Table 3: Concept Ranking Design Criteria

Weighting

Design 1

Design 2

Design 3

Design 4

Safety

0.05

2

3

1

4

Efficiency

0.28

3

2

2

4

Easy Implementation

0.23

4

3

2

3

Inexpensive

0.10

4

2

3

1

Autonomous

0.14

3

3

3

3

Compact

0.2

4

2

3

1

3.48

2.42

2.39

2.73

Total

Reflection Based on what we have learned from our design process, it appears that none of our conceptual designs would have performed acceptably. We can determine this by examining the various aspects of each design, and comparing it to our current design and past prototypes.

Design 1​: The most significant shortcoming of design 1 is its lack of structural rigidity. It relied on a steel rod to connect the wheels, which would have made it very difficult to assemble and prone to damage. Gluing multiple steel rods together would have likely resulted in a poor, weak bond with very little rigidity. The powertrain would have likely not provided enough torque to complete the 20 degree incline, while not having enough speed on the 2 degree incline.

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Design 2​: This conceptual design addresses some of the issues with the previous design, but is not without flaw. The pulley, while allowing for some torque multiplication, would have required very precise manufacturing to ensure the right balance between friction and clearance between the pulley and the belt. The pulleys themselves would likely have to have been 3d printed to ensure the proper tolerances. Given the 5 cm^3 material limit associated with 3d printing, manufacturing the pulleys was not the most feasible option. Design 3​: Our third design was deemed to be unnecessarily complex, the addition of two wheels below the rope to aid in overcoming the obstacles was not an effective use of materials and we felt the budget could have been better spent elsewhere. Attaching the motor directly to the wheels, using it in effect as half of an axle, was a poor design decision. It adds unnecessary stress to the motor shaft, which could have potentially caused damage to the motor, and would have likely resulted in a larger than acceptable deflection of the wheel due to its inadequate support. Design 4​: Our final conceptual design fell short for many of the same reasons as the previous designs. The third wheel added more cost and complexity without any improvement in performance. The pulley system, although an option worth considering, was overall not the most effective way to transmit power from the motor to the wheels. The smooth wheels would have been an excessive use of material, either requiring many laminated layers of HDF board, or the use of 3d printing, which we decided to keep to a minimum due to the added cost and restrictions.

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V.

Embodiment Design A. Preliminary Layout Below are sketches of the preliminary layout, complete with dimensions taken

from the Embodiment Design Report. Preliminary Design Top View

Figure 6: ​

Side View Figure 7:

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B. Design Analysis Reflecting on our final design, the most important components to analyze are the shafts, body structure and powertrain. The shafts must be rigid enough to resist deflections, keeping all the components aligned and in place. The body structure needs to be rigid enough to prevent bending or torsional deflection, and designed for easy assembly and use, with adequate clearance between each component, and secure fit between joining parts. The powertrain must be able to provide adequate torque and speed, allowing the design to perform reasonably. Before beginning the manufacturing process, we performed a variety of calculations analyzing the strength of our design, which proved to be accurate. Our predictions that our design would withstand the load required were correct. Despite nothing breaking, there is some slight wear on the gear teeth within our gearbox from repeated use. The gears are mostly constructed from laser cut HDF, and some slight wear was expected. The stresses within the gear teeth were low enough that no major damage occured. To prevent this, the only option would be to choose a more suitable material for the construction of the gears, but given the constraints of the project and what we wanted to achieve, this was not possible.

VI.

Design Implementation A. Manufacturing The main structural materials we used are HDF board, and the provided 4mm

diameter Carbon steel rods. HDF board is very strong material made from wood compressed wood fibers, with an added resin. Because of this it is relatively inexpensive, which led us to use this material for the bulk of our design. Carbon steel on the other hand is much stronger, but also more expensive. We used it sparingly where necessary, for the axles. 3D printed PLA plastic was used due to its resistance to wear and the relative ease and accuracy associated to 3d printing. We used laser cut HDF board to construct the frame of our design, as well as most of the gears, and the wheels. Laser cutting proved to be a fast manufacturing process that was accurate enough for our needs. The individual pieces were designed to be slotted together and then permanently attached using super glue.

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Some joints remained unglued which allows for partial disassembly, and easy mounting onto the rope. When designing the gear which attaches to the motor, we initially used layers of HDF board glued together to create one thicker gear. This proved to be inaccurate as some of the gear teeth were not perfectly aligned, causing issues with gear meshing. To resolve this, we used 3D printed PLA to make this gear, resulting in a much greater precision and smoother operation. The steel rods were cut to length using a hacksaw, and the ends were smoothed and beveled by hand with a file. Our design did require some modifications after experiencing the strengths and limitations of each manufacturing method, particularly as outlined above with the 3d printed gear. We also included some additional support beams to prevent our design from deforming during operation. B. Prototype Analysis In ​figures 8 and ​9 below, images of the prototype from our Prototyping report. Prototyping Design:

​ Figure 8:​ Full View of Prototype design

​Figure 9:​ Side View of Prototype design

Testing Analysis After manufacturing, we were finally ready to test our prototype. During initial testing of the design, it was surprisingly faster than we expected. Problems that we did not forsee however, was the wobble caused by lack of balance in our design.

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Another problem was the lack of rigidity in our design. This, we suspect caused our other problems such as the frame shifting and gears popping out during operation. Increase time modeling would probably have not make us notice these problems, since other factors were not present in solidworks, like gravity, tolerances, dynamic movements (swing) and other things.Testing was an integral part of the team understanding the strengths, weaknesses and limits of our design. Test 1 Gear ratio: 5:1 Distance:15ft Time: 1:08 Problems: The body was visibly deforming due to the combination of the weight and high rotational speed Test 2 Gear ratio: 1:1 Distance: 10ft Time: 1:40 Problems: The gears disengaged during the trial and therefore it was not able to cross the entire length of the rope.

Test 3 Gear ratio: 1:2 Distance 15ft Time: 2:57 Problems: The weight shifted and caused the prototype to tilt as it was moving.

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C. Final Design In the figures 10, 11 and 12 the final design is shown, both in a CAD model and photographs.

Figure 10: ​CAD model

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Figure 11: ​Final Design Right View

Figure 12: ​Final Design Left View

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Our prototype performed fairly well, given it was the first testing iteration. Although the speed was in line with what we predicted in our calculations, we encountered some issues with balance and engagement of the gear train that caused it to fail. Before beginning the process of making the parts for our design, a complete CAD model was created. This was done to ensure that all the parts fit together properly and to serve as a guide for the assembly process, ensuring all the parts were put together correctly. The prototype was extensively modelled and analyzed before the first piece was sent to the laser cutter, and despite this, we still encountered some issues. These issues were not flaws with the planning of the prototype, they were due to the tolerances associated to the manufacturing of our design. Due to these tolerances, particularly the thickness of the HDF board and the glue attaching the pieces, some slight deviations from the CAD model dimensions was observed. This discrepancy caused the issues we experienced during testing. In our final design, we made several changes to the model we had in our prototyping phase. The gear attached to the motor was 3d printed instead of being laser cut to ensure accuracy and smooth operation. A second battery pack was added in a parallel circuit along with the original battery pack. This kept the voltage constant at 6V, but doubled the potential power output. This allowed our design to successfully complete all the challenges, giving it enough torque to overcome the steep incline and obstacles in its way, without putting excessive voltage on the motor which could have potentially damaged it. Due to a lack of shop materials, the second battery pack had to be manufactured from HDF board and was wired in along with the original circuit. Relative to the other designs created by our peers, we believe that our design will perform very well. We have had only minor issues completing the obstacles, which will surely be fixed by the test date. We anticipate that we will complete each of the three tasks with a competitive speed relative to the other designs. Our design’s cost is low, considering its performance. We relied heavily on HDF board which was very inexpensive and avoided the more expensive components such as the bearings.

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Parts

Cost

HDF board ● Volume = 584564.69 cubic millimeters

0.20 * 2.097 = ​$0.42

○

Area = Volume/Height = 584564.69 / 3 =194855mm​2 =2.097 ft​2

●

DPDT Slide Switch

$0.78

●

Tight-Tolerance 12L14 Carbon Steel Rod Ultra-Machinable, 4 mm

2 * $3.25 * 0.246 =

Diameter, 1 Foot Long

$1.60

○

Two of them cut to 0.246ft

●

N20 Micrometal Gear Motor (150 RPM)

$6.00

●

4xAA Battery holder (wire leads)

$2.54

●

Super Glue The Original Super Glue 15187, .07 Ounce, 12-pack

$0.97

Total :

Figure 13: ​Bill of Materials

$12.31