Ph 2 Report NOTT Spiderman Suit (3)

8/10/2019 Ph 2 Report NOTT Spiderman Suit (3)

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Ascend Consulting Ltd4-9 Mechanical Engineering Building

University of Alberta Edmonton

AB, T6G 2G8

March 9th, 2012

Dr. Dan Sameoto

Assistant Professor5-01LMechanical Engineering,University of Alberta

Dear Dr. Sameoto;

Subject: Spiderman Climbing GearProject Phase 2 Deliverables

Ascend Consulting is pleased to submit the Phase 2 Conceptual Design Report for the SpidermanClimbing Gear project. This report includes the following:

Conceptual Design Description Preliminary Design Costs

Conceptual Design Evaluation Matrix

Revised Project Schedule

Detailed Conceptual Design Drawings

Macro-scale Test Results

Further to your approval and review of the Phase 1 report detailing project deliverables and scope,Ascend Consulting has designed three different conceptual solutions. A detailed description of eachconceptual design, relevant design calculations and drawings are included in the enclosed report.

To date, the conceptual design phase has required a total of 227 hours and a total project cost of $58,000.

This includes labour costs of $56,850 and prototyping costs of $1050 and material testing costs of $100.Phase 3 is estimated to require 179 hours. The final Phase 3 report detailing the chosen design will besubmitted by April 5th, 2012.

Please review the package and do not hesitate to contact me by email [email protected] you forconsidering Ascend Consulting for this project.

Sincerely,

Darren TingCc:

Dr. Ben Jar, University of AlbertaDr. Yongsheng Ma, University of AlbertaDr. Kajsa Duke, University of AlbertaDr. Jin-Oh Hahn, University of AlbertaDr. Larry W Kostiuk, University of AlbertaDr. Roger W Toogood, University of AlbertaMr. Joel Tannas, Ascend ConsultingMr. Calvin Ng, Ascend ConsultingMr. Ooi Kai Wen, Ascend Consulting
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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Phase II Report Page 2

Gecko Climbing Gear Concepts

Executive Summary

The objective of this project is to design a set of climbing gear that uses a dry adhesive provided

by the client to adhere to the wall. The design should be capable of supporting a 150 pound climber and

allow the climber to ascend and descend a 20ft smooth plexiglass wall.

Three conceptual designs were developed:

Concept A: A design which uses a lever mechanism to provide mechanical advantage when

initiating peel (by pulling on flaps).

Concept B: A design that initiates peeling using a user-actuated rod. The rod is constrained

such that it pulls on the flap only when in a certain position.

Concept C: A design that uses segmented plates for increased flexibility when peeling.

The three design concepts were evaluated utilizing a design matrix that may be found in

Appendix I.Ascend Consulting recommends concept B for future development. A macro-scale materialtest of the adhesive was performed to better understand its material properties. An attached report on

the material testing may be found inAppendix VI.

The main determining factors for choosing Concept B were simplicity, cost, and ease of

manufacturing. Very few parts are required for this design, and the ease of fabricating replacement

parts for Concept B was also contributed to its overall score. Additionally, the design of the device

makes premature peel less likely.

For phase 3, detailed calculations will be performed for the chosen design. Design details (such

as exact part sizing and tolerances) will be finalized in Phase 3. This includes a study of deflection and

stress distributions. Prototype construction and testing will be conducted if time permits.The Phase schedule was updated to incorporate a more detailed breakdown of remaining tasks

(found inAppendix IV). The updated estimated hours for Phase 3 are 179 hours, while the total

estimated project cost is $58,000. This includes a labor cost of $56,850, prototyping costs of $1,050, and

material testing costs of $100.


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Table of Contents

Executive Summary ....................................................................................................................................... 2

Table of Contents .......................................................................................................................................... 3

Table of Figures ............................................................................................................................................. 5

Table of Tables .............................................................................................................................................. 6

1.0 Introduction ...................................................................................................................................... 7

2.0 Concept Design A-Lever mechanism ................................................................................................ 8

2.1 Concept A- Hand Gear Application ............................................................................................. 11

2.2 Concept A- Hand Gear Removal ................................................................................................. 12

2.3 Concept A- Foot Gear Application .............................................................................................. 13

2.4 Concept A- Foot Gear Removal ................................................................................................... 143.0 Concept design B-Flap design ......................................................................................................... 15

3.1 Concept B- Hand Gear Application ............................................................................................. 17

3.2 Concept A- Hand Gear Removal ................................................................................................. 18

3.3 Concept B- Foot Gear Application............................................................................................... 19

3.4 Concept B- Foot Gear Removal ................................................................................................... 20

4.0 Concept Design C: Slotted L Bracket ............................................................................................... 21

4.1 Concept C- Hand/Foot Gear Application .................................................................................... 24

4.2 Concept C- Hand/Foot Gear Removal ......................................................................................... 25

5.0 Feasibility Analysis .......................................................................................................................... 26

5.1 Adhesion Ability .......................................................................................................................... 26

5.1.1 Hand Gear ............................................................................................................................... 26

5.1.2 Feet Gear ................................................................................................................................. 26

5.2 Peel Prevention ........................................................................................................................... 26

5.2.1 Hand Gear ............................................................................................................................... 27

5.2.2 Feet Gear ................................................................................................................................. 27

5.3 Peeling initiation ......................................................................................................................... 27

5.3.1 Hand Gear ............................................................................................................................... 27

5.3.2 Feet Gear ................................................................................................................................. 27

5.4 Ergonomics .................................................................................................................................. 28

5.5 Replacing Adhesives .................................................................................................................... 28


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5.6 Manufacturing and Cost ............................................................................................................. 28

5.7 Safety harness ............................................................................................................................. 28

6.0 Project management....................................................................................................................... 29

7.0 Recommendations .......................................................................................................................... 31

References .................................................................................................................................................. 32

Appendix I Updated Design Specification Matrix ............................................................................... I-1

Appendix II Concept Drawings ............................................................................................................ II-1

Appendix III Manufacturing and Cost Estimates ................................................................................. III-1

Appendix IV Project Schedule ............................................................................................................ IV-1

Appendix V Calculations ..................................................................................................................... V-1

Appendix VI Material Testing Procedure ........................................................................................ VII-26


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Table of Figures

Figure 1: Assembly of Concept A hand component. ..................................................................................... 8

Figure 2: Assembly of Concept A foot component ....................................................................................... 9

Figure 3: Application of concept A hand component ................................................................................. 11

Figure 4: Detachment of concept A hand component ............................................................................... 12

Figure 5: Application of concept A foot component ................................................................................... 13

Figure 6: Detachment of concept A foot component ................................................................................. 14

Figure 7: Assembly of concept B hand component .................................................................................... 16

Figure 8: Assembly of concept B foot component ...................................................................................... 16

Figure 9: Application of concept B hand component ................................................................................. 17

Figure 10: Detachment of concept B hand component.............................................................................. 18

Figure 11: Application of concept B foot component ................................................................................. 19

Figure 12: Removal of Concept B foot component ..................................................................................... 20

Figure 13: Assembly of concept C hand component .................................................................................. 21

Figure 14: Assembly of concept C foot component .................................................................................... 22

Figure 15: Application of concept C ............................................................................................................ 24

Figure 16: Detachment of concept C .......................................................................................................... 25

Figure 17: Foam backing for peel prevention ............................................................................................. 27

Figure 18: Man hours distribution by phase ............................................................................................... 29

Figure 19: Project cost by phase ................................................................................................................. 30

Figure III-1: General assembly for replaceable adhesive .......................................................................... III-2

Figure IV-1: Phase 1 project timeline ....................................................................................................... IV-2

Figure IV-2: Phase 2 project timeline ....................................................................................................... IV-3

Figure IV-3: Phase 3 project timeline ....................................................................................................... IV-4Figure V-1: Free body diagram of climber ................................................................................................ V-1

Figure V-2: Equivalent body postures Avalues of (a) 180 (b) 90and (c) 0.......................................... V-2

Figure V-3: Free body diagram of Rod E ................................................................................................... V-4

Figure V-4: Free body diagram of Rod D ................................................................................................... V-4

Figure V-5: Plot of Fayforces versus A...................................................................................................... V-5

Figure V-6: Plot of Faxforces versus A ...................................................................................................... V-6

Figure V-7: Plot of Fbyforces versus A...................................................................................................... V-6

Figure V-8: Plot of Fbxforces versus A ...................................................................................................... V-7

Figure V-9: Plot of Fresultantforces versus ................................................................................................ V-7

Figure V-10: Free body diagram of analysis model ................................................................................... V-9Figure V-11: Plot of LFZ versus A ........................................................................................................... V-11

Figure V-12: Plot of LHZ versus A ........................................................................................................... V-12

Figure V-13: Free body diagram for concept A ....................................................................................... V-16

Figure V-14: Free body diagram for concept B ....................................................................................... V-18

Figure V-15: Free body diagram for concept C ....................................................................................... V-20

Figure V-16: Free body diagram for concept C after peel initiation ....................................................... V-21


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Figure VI-1: SEM image of a typical micro-structured synthetic adhesive ........................................... VII-26

Figure VI-2: General setup of experiment ............................................................................................ VII-27

Figure VI-3: Side view of backed adhesive strip .................................................................................... VII-28

Figure VI-4: Side view of unbacked adhesive strip ............................................................................... VII-28

Figure VI-5: Shear strength versus micro-scale feature size ................................................................. VII-33

Figure VI-6: General experimental setup .............................................................................................. VII-38

Figure VI-7: Peel test sample specimen ................................................................................................ VII-39

Figure VI-8: Shear and normal test sample specimen .......................................................................... VII-39

Figure VI-9: Peel test configuration ...................................................................................................... VII-40

Figure VI-10: Shear test configuration .................................................................................................. VII-40

Table of Tables

Table 1: Manufacturing and cost details for concept designs .................................................................... 28

Table 2: Project time and resource allocation ............................................................................................ 29

Table I-1: Design Matrix Revision Table ...................................................................................................... I-1

Table I-2: Design Importance Legend ......................................................................................................... I-1

Table I-3: Updated Design Specification Matrix ......................................................................................... I-2

Table I-4: Design Matrix Additional Notes .................................................................................................. I-3

Table I-5: Design matrix score reasoning .................................................................................................... I-3

Table III-1: Manufacturing cost breakdown for concept designs ............................................................. III-4

Table III-2: Estimated cost of design component ..................................................................................... III-5

Table VI-1: Adhesive strengths ............................................................................................................. VII-31

Table VI-2: Raw shear test results ......................................................................................................... VII-35

Table VI-3: Raw peel test results ........................................................................................................... VII-35

Word Count : 2447


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1.0Introduction

The clients research on micro-fabrication has resulted in a dry adhesive that can withstand up

to 1MPa in normal force under ideal conditions. Ascend Consulting was requested to develop a design

that can utilize this material to scale a smooth wall and demonstrate its adhesive properties on a largerscale.

The objective is to design a set of climbing gear that allows a 150lbs climber to scale up and

down a 20 feet smooth wall using the provided dry adhesive. The greatest challenge when approaching

this design problem is that the climbing gear should both adhere strongly and detach easily whenever

required. These conflicting requirements serve as the focus for developing feasible conceptual designs.

The dry is strong against normal forces but significantly less so for shear forces. With this in

mind, the client has requested design values of 100kPa normal strength and 20kPa shear strength. The

adhesive is very prone to peeling at the edges. Once peeling is initiated, the adhesive can be removed

with minimal force due to peel propagation.The material properties of this adhesive were translated into several criteria for the design of

the climbing gear. The design should minimize the probability of unwanted peeling.

To detach the climbing gear from the wall, the design should take advantage of the adhesives

weak peel strength. The design should initiate a peeling action when desired to allow premature

detachment of adhesives from the surface. Also, a rigid backing is also required for the climber to apply

a preload to the adhesives. Therefore it is important to note that the design should have the means to

be flexible or rigid when required.


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2.0Concept Design A: Lever Mechanism

Figure 1: Assembly of Concept A hand component.


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Figure 2: Assembly of Concept A foot component


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The following concept design (seeFigure 1)provides the user with a mechanical advantage using

a lever. By using a lever, the force required to initiate peeling of the adhesive can be greatly reduced by

adjusting the levers pivot point. A unique feature of this design is that the user of this design would

push into the wall to initiate peeling and pull out to prevent peeling.

The feet gear design utilizes a simple fixed plate and an angled. This design has a strip offrictional material at the bottom end of the flat plate to initiate peeling. The reason behind this is that

the feet would generate a moment which applies the most inward normal force at the bottom end of

the plate which results in a high frictional resistance. Dry adhesives on the remaining areas of the plate

would resist any remaining shear force and prevent the design from peeling at the top of the plate due

to moment. The friction material at the bottom of section of the feet gear resists shear and provides a

peel interface.


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2.1 Concept A- Hand Gear Application

1

Flaps unlocked

2

Pivot point

3

Figure 3: Application of Concept A Hand Component

Step 1: Initially, the flaps are locked in angled position. The climber applies the main plate to the glass

and pushes into wall to pre-load the adhesives.Step 2: The climber gives the handle a quarter turn twist.

Step 3: The climber pulls away from wall. The pulling motion of the handle causes the lever to push the

flap against the wall. This would apply a pre-load on the flaps dry adhesive fixing the flaps to the wall.


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2.2 Concept A- Hand Gear Removal

2Flaps locked

1

3

Figure 4: Detachment of concept A hand component

Step 1: To detach design, climber gives handle a quarter turn twist and pushes into wallStep 2: Lever would cause flaps to pull away from wall to initiate peeling and the flaps will be locked in

angled position.

Step 3: Climber then pulls away from wall to remove rigid plate and entire design from wall.


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2.3 Concept A- Foot Gear Application

Figure 5: Application of concept A foot component

Step 1: Climber pushes plate against wall to apply a preload.

Step 2: Climber presses heel downwards on platform. Moment is generated on design. Dry adhesives

resist any normal forces at the top generated by the moment (orange arrow). Strong inward normal

force applied by moment onto frictional material for maximum shear resistance (blue arrow). Design isnow fixed to wall. The inward normal force generated by the moment prevents peeling.

1 2


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2.4 Concept A- Foot Gear Removal

Peel Initiation

Figure 6: Detachment of concept A foot component

Step 1: To detach, the climber lifts their heel. The resulting moment pulls frictional material from wall

easily as they dont resist any normal force. Dry adhesives will peel from bottom as plate is removed.


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3.0Concept design B-Flap design


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Figure 7: Assembly of concept B hand component

Figure 8: Assembly of concept B foot component


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Concept design B uses two plates attached via a hinge that allows the user to initiate peeling at

the lower section when removing the gear from the wall. This design uses a slide-able rod that can be

engaged in two positions. One position only loads the main plate, while the other loads the peel plate.

The leg gear comprises a hinged plate and a knee pad for preloading purposes. Similar to the

concept B, The climber will lift his feet to initiate peeling.

3.1 Concept B- Hand Gear Application

1A

1B

View

B

Rod in Engage

Position

Figure 9: Application of concept B hand component

Step 1: Ensure that the slide-able rod is fixed in the position shown in Figure 9.This avoids the climber

from applying a moment that initiates peeling at the lower plate once climber is fully supported.

Step 2 Apply pushes gear into wall to preload adhesives.


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3.2 Concept A- Hand Gear Removal

Figure 10: Detachment of concept B hand component

Step 1: Slide the rod through the sliding slot as shown in 2A ofFigure 10.Step 2: Pull on handle to initiate peeling of lower plate as shown in 2B ofFigure 10.


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3.3 Concept B- Foot Gear Application

Figure 11: Application of concept B foot component

Step 1: The climber pushes against the wall. Initial contact will be between the lower plate and the wall

Step 2: Climber applies preload through the knee pad by pushing leg against the wall. Design is now

fixed to wall.


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3.4 Concept B- Foot Gear Removal

Figure 12: Removal of Concept B foot component

Step 1: To initiate peeling, the climber will lift his heel and generate a moment to pull the frictionalmaterial on the lower plate from the wall. The dry adhesives will peel from the bottom as the plate is

gradually removed.


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4.0Concept Design C: Slotted L Bracket

Figure 13: Assembly of concept C hand component


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Figure 14: Assembly of concept C foot component


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The L-bracket designs main feature is its segmented plates that allow for greater flexibility

during peeling motion. A block acts as a backing to the plates when rigidity is required. The staggered L-

brackets provide users with a mechanical advantage by facilitating a gradual peel. Since this design only

requires an up-down motion, the same concept can be applied for the feet of the climber.

T L bracket peeling design uses segmentation of the gecko material. Separation of the sections

reduces the amount of normal force needed to disengage with the wall, but increases the number of

peel locations.

The different sized L bracket causes the shorter segments to apply a normal force first to

remove each section one at a time. Each individual set of L brackets essentially concentrates the load at

each individual segment before moving onto the next segment.

The drawback to this design is it will only work under almost ideal conditions. With the amount

of moving parts and complexity it is likely that a section will be exposed to an accidental peel.

Thankfully, accidental peeling of one section will not cause the entire device to be removed.


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4.1 Concept C- Hand/Foot Gear Application

1 2

Figure 15: Application of concept C

Step 1: Climber pushes block into wall with their forearm to apply required preload.

Step 2: Climber slides block downwards to lock studs in L-brackets. Note that segmented plate is now

rigid and design is fixed to wall.


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4.2 Concept C- Hand/Foot Gear Removal

1 2

Figure 16: Detachment of concept C

Step 1: Climber slides block upwards.

Step 2: Climber pulls block away from wall. Pulling force is concentrated at the edge and removal of

segmented plate is initiated. This continues along the length of the entire design until entire segmentedplate is separated from wall.


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5.0Feasibility Analysis

A free body diagram force analysis of a climber on the wall was performed (calculations in

7.0Appendix V). Although the existing dimensions for the design are not fixed, the surface area of the

dry adhesive for each design is sufficient to resist the forces exerted by the climber was found to be

0.12m2. All designs were scaled accordingly to reach this value.

5.1 Adhesion Ability

5.1.1 Hand Gear

For the hand component of concept A the two step process of force application could be an

advantage for the climber as a smaller force is required for sufficient preload. However, depending on

the size of the rigid plate and the flaps, this advantage could be miniscule.

For concept B, the climber has to apply a preload to the entire surface area of the adhesive

(including the flap) which could mean a higher force requirement. Higher stress concentrations are

speculated for this design as load application occurs at the edges and not the center of the adhesive

sheet.

For concept C, a similar preload force to concept B is estimated as the force is applied to the

entire adhesive area. Force is applied using the forearm which could be hard for the climber. Stress

concentrations can be minimized provided tolerances on the L-brackets are sufficiently tight.

5.1.2 Feet Gear

The angled design of concept A allows the climber to use their body weight to apply the

required preload to the adhesives. On the other hand, concepts B & C require the climber to apply a

load using their shins which could be potentially awkward or hard to do.

5.2 Peel Prevention

A good measure of the design its ability to apply a preload for the adhesives to stick to the

surface. Although load concentrations cannot be avoided, a rigid backing for all designs can minimize

this effect. Currently, all concept designs can be easily modified to achieve the needed rigidity (which

will be determined in Phase 3).

The size of the rigid plate gives rise to a concern that air pockets might be trapped between the

adhesive and the glass surface during application. These air pockets should be avoided as they provide

an interface for peeling. Therefore an initial force should be applied to the edge of the adhesive before

pushing the gear into the wall.

A feature to prevent peeling is to have the thin layer of soft foam that is countersunk into the

edges of adhesive plates in spots where peeling is not wanted. When applying a preload to the adhesive,

the foam will compress first, applying a preload to the foam before the rest of the plate. When pulling


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outward, the low stiffness of the foam means that less force will be transmitted to the adhesive on the

foam than on the rest of the plate. This ensures that loading is kept to the center of the plate.

Figure 17: Foam backing for peel prevention

5.2.1 Hand Gear

Concept B and C both initiate peeling from the bottom of the design which is ideal as accidental

peel is more likely from the top. Concept A initiates peeling from both sides and peeling could happen

prematurely at the top hinge corners (since the flaps push in).

5.2.2 Feet Gear

Concept A is least likely to peel since the foot placement reduces moment. Concept B does not

avoid moment generation but the lack of edge of loading avoids accidental peel. Concept C is likely to

peel if rigidity is not maintained.

5.3 Peeling initiation

5.3.1 Hand Gear

Concept A uses a lever to give the climber a mechanical advantage. Also, the peel interface is

doubled due to flaps on both sides. Concept B does not have mechanical advantages, but the flaps can

be sized to a desired removal force

Concept Design C would require the climber to exert a relatively high initiation force on each

individual plate to initiate peeling requiring additional effort for gear removal. However, the segmented

plates would reduce the probability of adhesion failure by avoiding unintentional peeling from one plate

from propagating throughout the entire adhesive sheet.

5.3.2 Feet Gear

Depending on the rigidity of Concept A, peeling can be difficult but the ratio between adhesives

and frictional material can be tailored to a specified removal force. Concept B better facilitates removal

as it allows the material to flex. Concept C has a very similar removing system but peeling initiation is

required for each plate making it the hardest to peel.


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5.4 Ergonomics

Concept Cs hand component is strapped to the users forearm, forcing the climbers body to be

closer to the wall increases the application of shear force in the hands. Concept B requires lateral

movement of the forearm to initiate peeling. Concept A however requires more delicate hand control.

Feet components for both concept B and C require the climber to apply a preload using the

shins. This can be difficult when the climber is trying to maintain a distance from the wall surface to

maximize inward force on the feet.

5.5 Replacing Adhesives

Deterioration of the adhesives strength is unavoidable due to contamination and

microstructural damage. Therefore all designs would use detachable metal plates to replace the

adhesives. Details regarding replaceable plates (applicable to all three designs) may be found in

Appendix sectionIII.2.

5.6 Manufacturing and Cost

Concept B has the least components and is simple to assemble. Concept C requires many parts

with tighter tolerances, leading to higher costs. The hand component for Concept A involves many

moving parts. However, the feet component is much simpler.

An analysis of the estimated manufacturing costs of all designs was performed. The

methodology and detailed breakdown are found in Appendix sectionIII.6.Weight estimates were taken

from solid modeling of the concepts (drawing inAppendix II). The final cost and weight estimates are

shown inTable 1.

Table 1: Manufacturing and cost details for concept designs

Design Number of Parts Est. Mass (kg) Est. Mfg. Cost

Hand-A 33 7.9 $700

Hand-B 10 4.6 $325

Hand-C 38 3.0 $650

Feet-A 4 6.9 $200

Feet-B 12 5.5 $200

Feet-C 38 3.5 $650

5.7 Safety harness

From initial inspection, no interference between the designs and standard climbing harness is

anticipated.


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6.0Project management

Actual hours spent for Phase 2 were overestimated by approximately 50 hours. The allocation of

hours on each individual item is where discrepancies occurred. Three items that had significant

discrepancies occurred at Conceptual Design Calculations, Test Material and Conceptual BrainStorming.

The time required for material testing was underestimated due to technical difficulties and

apparatus preparation. Other unexpected issues such as smoothness of the test surface and epoxy

failures extended the time required to successfully complete the material testing process.

Table 2: Project time and resource allocation

Phase Number Baseline Hours Baseline Cost Real Hours Real Cost

Phase 1 90 $8,400 92 $8,280

Phase 2 286 $3,1740 227 $20,430Phase 3 179 $16,710 TBD TBD

Figure 18: Man hours distribution by phase

0 50 100 150 200 250 300 350

Phase 1

Phase 2

Phase 3

Design Poster

Design Conference

Hours

Real Hours

Baseline Hours


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Figure 19: Project cost by phase

The hours spent on the design conference and posters are not billed to the client and therefore

are not included in the cost estimates.

From the issues found in Phase 2, Phase 3 was updated with more detail to determine a more

realistic date of completion. Significant changes include more time to further develop our final design

with the client and the intermediate engineer, to complete calculations, to prepare manufacturing

drawings, and to review final costs. Refer to6.0 for both the most recent schedule and the original

baseline schedule made in phase 1.

0 5000 10000 15000 20000 25000 30000 35000

Phase 1

Phase 2

Phase 3

Hours

Real Cost

Baseline Cost


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7.0Recommendations

Three design concepts were compared in the design evaluation matrix inAppendix I.The Must

Have design conditions were checked on a pass/fail basis to ensure that critical conditions are met

before any further design evaluation is performed. It was found that design concept B best fit the

desired specifications, followed by concept design A and C. Ascend Consulting recommends Design

Concept B for the final design.


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References

[1] K. Ono, "Contact Mechanics Anlaysis of a rubber on a smooth plate," Proceedings of the ASME/STLE

2009 International Joint Tribology Conference, 2009.

[2] "ANTHROPOMETRY AND BIOMECHANICS," 5th July 2008. [Online]. Available:

http://msis.jsc.nasa.gov/sections/section03.htm. [Accessed 20th February 2012].

[3] D. Sameoto, "Spider-Man" Climbing Gear Project Proposal, Edmonton, Alberta: University of Alberta,

Department of Mechanical Engineering, 2012.

[4] "Ace Hardware," Ace Hardware Corporation, 2012. [Online]. Available:

http://www.acehardware.com/home/index.jsp. [Accessed 13th Fenbruary 2012].

[5] Biomimetic Systems Lab, Dept. of EECS, UC Berkley, 2012. [Online]. Available:

http://robotics.eecs.berkeley.edu/~ronf/Gecko/gecko-compare.html.

[6] M. S. I. Inc., "Metal Supermarkets," 2012. [Online]. Available: http://www.metalsupermarkets.com/.

[Accessed 20th February 2012].


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Phase II Report Appendix I-

Gecko Climbing Gear

Appendix I Updated Design Specification Matrix

This appendix outlines the design specification matrix for the Gecko Climbing Gear Design Project. The matrix presented here has been updated with updated criteria that were found as more was learned about the project. Each

specification is accompanied by a number that describes how important it is to fulfill each criterion. This appendix consists of the following tables:

A legend of the design importance meanings

Table I-2

A design evaluation matrix (Table I-3)

A table of additional notes concerning the design specifications

A table of additional notes concerning the ranking scheme

A revision table of design matrix changes (Table I-1)

Table I-1: Design Matrix Revision TableRev Comments

0 Initial Version

1 Edited to clarify certain requirements

Table I-2: Design Importance Legend

Number Significance

9 to 10 Must meet requirement to the letter, non-negotiable

7 to 8 Must meet the spirit of the requirement

5 to 6 Highly Suggested

3 to 4 Recommended

1 to 2 Nice-to-have

0 Not Significant


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Gecko Climbing Gear

Table I-3: Updated Design Specification MatrixItem Specifications/Requirements Design

ImportanceDesign ALever

Rank Design BRod & Hinge

Rank Design CL-bracket

Rank

Compliance 0-10 Value Compliance 0-10 Value Compliance 0-10 Value

1 Adhesion Ability1.1 Design must support the weight of a 150 lbs climber. Must Have 1.2 Designs adhesive strength should achieve a minimum safety factor of 10. Must Have

1.3* Adhesive normal adhesion strength will be taken as 100kPa for design purposes. Must Have 1.4* Maximum normal force to remove climbing device from a smooth surface should be no more than 15lbf (70N). 9 9.6 86.4 7.3 65.7 1.8 16.21.5* Maximum force to attach climbing device to a smooth surface should be no more than 15lbf (70N). 9 8 72 8 72 5 451.6 3 point contact during climbing is assumed. Weight of climber should be fully supported by 3 individual climbing

gear components.Must Have

1.7 Adhesive shear strength will be taken as a 20kPa unless material testing confirms otherwise. Must Have

2 Material2.1* Design must use the dry adhesive supplied by the client (composed of specially molded ST-1060 polyurethane)

as the sole means of adhering to the wall.Must Have

2.2* Bonding between adhesives and replaceable parts should not fail in normal operation. Must Have

3 Design3.1* Design should not incorporate any external power sources. Must Have 3.2* The design should be easy to clean by the climber while on the wall. 2 3 6 5 10 3.4 6.83.3* Design should have means to change the parts the adhesive material. 0 0 A

a) Hand Gear 6 5 30 5 30 7 42b) Foot Gear 6 8 48 5 30 7 42

3.4 Replacement parts for design should be easy to fabricate and easy to install with basic hand tools.a) Hand Gear 2 3 6 7 14 4 8b) Foot Gear 2 3 6 9 18 4 8

4 Ergonomics4.1 The climbing gear should be easy to grip and control while on the wall 5 5 25 7 35 8 404.2 Design should be easy for the wearer to put on and take off 5 7 35 7 35 7 35

4.3* Maximum width of climbing gear should not exceed 26. Must Have

5 Weight5.1 Total weight should be no more than 11 kg. 6 3.7 22.2 5.4 32.4 8.5 515.2 Heaviest individual climbing gear component should be no more than 3kg. 5 3.8 19 5.4 27 8.6 43

6 Manufacturing6.1 Ease of manufacturing with standard machine shop tools 5 6 30 8 40 3 156.2 Labour hours to attain design prototype shall not exceed 1 week 4 4 16 8 32 3 12

7 Additional Features7.1 Compatibility with climbing harnesses Must Have

8 Costs8.1 Funds for prototype and experimental testing should not exceed $1,000. 4 5.1 20.4 9.4 37.6 3.9 15.6

Totals 422 478.7 379.6


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Table I-4: Design Matrix Additional Notes

*Additional Notes:

1.3 The adhesion strength of 100 KPa does nothave the safety factor of 10 incorporated.

1.4 & 1.5 15 lbs. is the speculated force that the climber can comfortably exert with one hand while climbing.

2.1 The adhesive material has the greatest adhesive strength in the normal direction, and significantly reduced adhesive strength in shear loading. The client has agreed

that a non-adhesive material with a high friction coefficient may be used for resisting shear forces.

2.2 Material testing found that a chemical bond between adhesive sheets and an acrylic plate will be necessary.

3.1 The design must not require any external power sources such as batteries, power cords, compressed air, motors, etc

3.2 The client has communicated that the adhesive materials adhesive strength deteriorates with use due to dust and damage to the microstructures on the materials

surface. It is preferred that the design incorporate away to easily cl ean the material when needed and lengthen the useful life of the material.

3.3 The client has warned that the once the material is chemically bonded to a surface, it is almost impossible to remove it and therefore the surface would have to be

changed out as well.

4.3 This value is based on the humans average shoulder width.

Table I-5: Design matrix score reasoning

Item Design Notes3.3a A Replacing the adhesive means replacing pieces in both the adhesive plate and peel plate.3.3b A The simple foot design with no moving parts makes replacement backings easy to manufacture and install3.3a B Replacing the adhesive means replacing pieces in both the adhesive plate and peel plate.3.3b B Replacing the adhesive means replacing pieces in both the adhesive plate and peel plate.3.3a C The lack of connection between the adhesive plates means that replacement parts are small, simple, and interchangeable.3.3b C The lack of connection between the adhesive plates means that replacement parts are small, simple, and interchangeable.3.2 A The rotating handle and the weight may make the lever design difficult to maneuver. This will make cleaning difficult3.2 B The weight will make the rod & hinge design difficult to maneuver.3.2 C The smaller plates and lower weight make this design easier to maneuver. This makes it easier to clean while on the wall.3.4 A The number of pins and their critical alignment makes maintenance difficult.3.4 B All parts on this design are low precision and have easily accessible bolts. The requirement for a water-jet machine makes replacement parts difficult to obtain.3.4 C The critical alignment of the pins and slots in this design make maintenance tricky. However, many parts are used repeatedly, so replacement parts can be made ahead of

time.4.2 A The rotating handle of this design may make it difficult to hold on to.4.2 B This design is relatively easy to hold on to, but the weight prevents it from getting a higher score.4.3 C The additional arm slot in this design makes it very easy to maintain a grip on.

6.1& 6.2 A The care required when welding aluminum and the slots required in thin bars make this design tricky to manufacture, however the loose tolerances make the overall difficultyaverage.

6.1 & 6.2 B The loose tolerances and simple construction of this design make it very easy to manufacture. The requirement for the use of a water-jet machine prevents it from getting ahigher score.

6.1 & 6.2 C The tight tolerances for the slot profiles and for the plate thickness on this design make it difficult to manufacture, probably requiring advanced techniques.8.1 All Score = 1000$ / Cost * 10; refer toAppendix III for source

1.4 All Score = 70N / Force; refer toAppendix V for source5.1 All Score = 11kg / Total Weight * 10; referAppendix II for source5.2 All Score = 3kg / Total Weight * 10; refer toAppendix II for source


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Phase II Report Appendix II-

Gecko Climbing Gear

Appendix II Concept Drawings

II.1 Concept A Drawings


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II.2 Concept B Drawings


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II.3 Concept C Drawings


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Phase II Report Appendix II-1

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Phase II Report Appendix II-1

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Phase II Report Appendix III-1

Gecko Climbing Gear

Appendix III Manufacturing and Cost Estimates

III.1 Method

The concept drawings focus on communicating function, not on making manufacturable designs. For cost estimates, rough estimates of

the required material profiles were made, and then costs for these base materials were sourced from materials suppliers [1] [2]For certain

suppliers, these costs included the cost of cutting it to the proper size, eliminating the need for labor estimates. For pieces that needed extra

machining, the Mec E machine shop internal labor cost of 20$/hr was used (since the client is a professor at the U of A). Labor hour estimates

were based off group member experience in machining, carpentry, and woodworking. Economies of scale for manufacturing a part repeatedly

were not considered, since this requires a more detailed consideration of manufacturing methods. Supplier quotes were for machining deemed

not necessary until the detailed design stage. Plastics were avoided since these designs are one-off constructions and making plastic molding is

a high-volume manufacturing method.

III.2Adhesive Plates

The adhesive backing plate on al l designs was chosen to be thick aluminum plate. This is so that the adhesive will have a rigid backing.

The thickness of the plate will be revised in the final design, but the plate provides a consistent reference for cost and weight estimates.

Additionally, the adhesive plate will be a combination of a replaceable acrylic plate that the adhesive is bonded to and the rigid backing for extra

stiffness (see [ref: figure]). An area of 0.12m of adhesive was used for sizing the designs. Any design that uses a hinged plate will require milling

in order to countersink the hinge into the plate.


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Figure III-1: General assembly for replaceable adhesive

III.3 Design Concept A

The cost estimate for the two feet components was found to be $400, and the cost of two hand components was found to $1600. The

simple design of the feet and extremely loose tolerances mean that they can be manufactured with a cut-and-weld approach. Extra labor time

was allocated given the challenges of welding aluminum. The hand design manufacturing is significantly more involved, requiring milling on all

pieces. Though all the parts are manufacturable from common shapes (plate, round, and angle metal profiles), they all require significant

customization (a.k.a. labor cost).

III.4 Design Concept B

The cost estimate for the two feet components was found to be $400, and the cost of two hand components was found to $650. These

components are built from common metal profiles, with final machining being possible with a drill press or vertical milling machine. The hand

design currently requires square slots, meaning a laser cutter or water-jet machine will be needed. If these slots are not possible, round slots will

be substituted so that a milling machine can be used. This will require the substitution of the square bar with a round bar and some changes to

the handle design. For the feet design, the main challenge is to make sure that both the main adhesive plate and peel plate engage evenly with

the wall (to ensure even loading and to prevent premature peeling). This means that the design will require a way of tuning the range of

motion. This will probably be by using a steel cable and turnbuckle.


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III.5 Design Concept C

The cost estimate for the two feet components was found to be $1300, and the cost of two hand components was found to $1300.This

design has a relatively complex set of slots and tabs to initiate peeling. Because of the way they are designed, they will require smaller

tolerances in order to function. This means more engineering time, higher labor costs, and more scrapped parts. Additionally, the segmentation

of the adhesive plates means there are far more parts than the other designs. Although no special tooling is required for the manufacturing

process, this design has a very labor (and cost) intensive manufacturing process.


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III.6 Cost Tables

Table III-1: Manufacturing cost breakdown for concept designs

Concept Description Mfg. Process Mfg.

Cost

Material Profile Material QTY. $/Unit QTY. Cost

Feet-a Adhesive Plate N/A $0 6061 Aluminum 0.25" Plate 260mm x 500mm $52 2 $104

Feet-a Foot Plate Water-Jet $10 6061 Aluminum 0.25" Plate 320mm x 500mm $54 2 $128

Feet-a Support Strips Saw + Weld $30 6061 Aluminum 0.25" x 1" Flat Bar 220mm $10 4 $159

Feet-b Adhesive Plate Milling $20 6061 Aluminum 0.25" Plate 400mm x 350mm $49 2 $138

Feet-b Piano Hinge N/A $2 Stainless Steel N/A 400mm $3 2 $10

Feet-b Peel Plate Milling $20 6061 Aluminum 0.25" Plate 400mm x 125mm $29 2 $99

Feet-b Stop Braces Sawing $5 6061 Aluminum 1"x1"x0.125" Angle 100mm $9 4 $57

Feet-b Foot Blocks Sawing $2 Spruce 2"x4" 1 foot $3 6 $30

Feet-b Wire Brackets Sawing + Drilling $5 6061 Aluminum 1"x1"x0.125" Angle 1" $2 4 $29

Feet-b Steel Cable Cutting & Looping $10 Steel 0.125" Diameter 12" $2 4 $50

Hand-a Adhesive Plate Milling $20 6061 Aluminum 0.25" Plate 400mm x 300mm $49 2 $138

Hand-a Peel Plate Milling $20 6061 Aluminum 0.25" Plate 400mm x 50mm $21 4 $163

Hand-a Pins N/A $1 1018 Steel 3/8" Round 2" $6 16 $112

Hand-a Lever Cross Bar N/A $1 1018 Steel 3/8" Round 10" $10 4 $44

Hand-a Handle Grip Milling $50 6061 Aluminum 0.25" Plate 4" x 3" $21 2 $141

Hand-a Handle Shaft Milling $120 6061 Aluminum 1" Round 4" $13 2 $266

Hand-a Handle Pins Gluing $10 1018 Steel 3/8" Round 4" $6 4 $64

Hand-a Bracket Milling $10 6061 Aluminum 2" x 3" x 0.25" Angle 1" $10 32 $654

Hand-b Main Plate Milling $20 6061 Aluminum 0.25" Plate 340mm x 380mm $52 2 $144

Hand-b Peel Plate Milling $20 6061 Aluminum 0.25" Plate 340mm x 100mm $26 2 $92

Hand-b Slot Bracket Water-Jet $15 6061 Aluminum 3" x 3" x 0.25" 150mm $17 6 $192

Hand-b Handle Water-Jet $15 6061 Aluminum 0.25" Plate 150mm x 120mm $27 2 $84

Hand-b Rod Drilling & Cutting $20 CREW Steel 3/4" x 0.065"

Square Tube

500mm $13 2 $66

Hand-b Stop Pins N/A $10 1018 Steel 1/2" Round 2" $6 4 $64

Hand-b Piano Hinge N/A $2 Stainless Steel N/A 400mm $3 2 $10


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Concept Description Mfg. Process Mfg.

Cost

Material Profile Material QTY. $/Unit QTY. Cost

Feet-c Foot Plate Sawing $20 Pine 2"x6" 1ft $5 2 $50

Feet-c Hard Plate Woodworking $30 Pine 1"x6" 8" $4 2 $68

Feet-c Slot Brackets Water-Jet $10 6061 Aluminum 0.25" Plate 2"x3" $5 24 $370

Feet-c Pegs N/A $0 6061 Aluminum 0.5" Round 1" $6 24 $141

Feet-c Piano Hinge N/A $2 Stainless Steel N/A 400mm $3 10 $50

Feet-c Adhesive Plate Water-Jet $15 6061 Aluminum 2" x 0.25" Flat Bar 480mm $18 12 $395

Feet-c Knee Brace Sawing $10 Pine 2"x6" 1ft $5 2 $30

Hand-c Hard Plate Woodworking $30 Pine 1"x6" 8" $4 2 $68

Hand-c Slot Brackets Water-Jet $10 6061 Aluminum 0.25" Plate 2"x3" $5 24 $370

Hand-c Pegs N/A $0 6061 Aluminum 0.5" Round 1" $6 24 $141

Hand-c Piano Hinge N/A $2 Stainless Steel N/A 400mm $3 10 $50

Hand-c Adhesive Plate Water-Jet $15 6061 Aluminum 2" x 0.25" Flat Bar 480mm $18 12 $395

Hand-c Handle Bought $0 Brass Door-Handle 1 $10 2 $20

Hand-c Arm Slot Water-jet $10 6061 Aluminum 0.25" Plate 150mm x 120mm $27 2 $74

Table III-2: Estimated cost of design component

Design # of Parts Estimated CostFeet-a 8 $391

Feet-b 24 $412

Feet-c 76 $1104

Hand-a 66 $1581

Hand-b 20 $652

Hand-c 76 $1118


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Phase II Report Appendix IV-1

Gecko Climbing Gear

Appendix IV Project Schedule

Ascend Consulting has developed a baseline schedule plan and to track project progress. A commercial project planning software (Liquid

Planner 2011) is being used to monitor project progress and allocate tasks to team members. A timeline was proposed with the aim of having a

functional prototype built within 4 months as the best case scenario. The schedule is accessible by all team members and a project supervisor

(Dr. Ben Jar) for tracking project progress.


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Figure IV-1: Phase 1 project timeline

No items are shown as no items

remain to be completed


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No items are shown as no items

remain to be completed


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Phase II Report Appendix V-1

Gecko Climbing Gear

Appendix V Calculations

V.1 Free body analysis of climber

For this analysis, the human body is approximated as a two rigid member linkage with the hands

and feet of the climber modeled as pin connections to a rigid vertical wall. The client has agreed that

performing a quasi-static analysis is reasonable for this design. Therefore this analysis assumes that

climbing movements are performed as sufficiently slow speeds such that inertial forces are negligible.

The objective is to determine the vertical and normal forces exerted by the climbers hands and feet

during climbing.

A

B

C

Fax

Fw

Fby

Fbx

L1

L2

L3

L4

Fay

G

x

y

Rod D

Rod E

Vertical

Normal

Figure V-1: Free body diagram of climber


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V.1.1 Assumptions

1. The human body can be approximated as a two rigid member linkage pivoted at points A and B

which corresponds to the climbers wrist and ankles respectively. Point C is equivalent to the

shoulder of the climber.

2. The weight of the average male climber is approximately 700N.

3. The coefficient of friction for rubber on glass is 2 [1].

4. The model is quasi-static, i.e. inertial effects are negligible.

5. Length of rigid members is equal to body measurements of an average human male. Values are

obtained from the NASA website for anthropometry and biomechanics [2].

6. The comfortable working range for is 45

0

to90

0

. Further explanation as follows.

A

B

C

A

B

C

A

B

C

Rod D

Rod E Rod E Rod E

Rod D

Rod D

(a) (b) (c)

Figure V-2: Equivalent body postures Avalues of (a) 180 (b) 90and (c) 0

Figure 2 is a clear depiction of how affects the free body model of the analysis. By initial

speculation, it was clear that case (a) and case (b) are both unrealistic models and therefore excluded

from further analysis. Preliminary calculations have also proved that values above 450resulted in

large shear forces that cannot be resisted by adhesives of a practical area size.


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V.1.2 Calculations

General dimensions (refer toFigure V-1)


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Fby

Fbx

Fw

L3

L2

c

Fint

B

Rod E

Figure V-3: Free body diagram of Rod E

Figure V-4: Free body diagram of Rod D


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V.1.3 Result

Fay(N)

A (radians)0.8 1 1.2 1.4

0

50

100

150

200

Figure V-5: Plot of Fayforces versus A


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Fax(N)

A (radians)0.8 1 1.2 1.4

400

300

200

100

0

100

Figure V-6: Plot of Faxforces versus A

Fby (N)

A (radians)

0.8 1 1.2 1.4500

600

700

Figure V-7: Plot of Fbyforces versus A


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Fbx (N)

A (radians)0.8 1 1.2 1.4

10 0

0

10 0

20 0

30 0

40 0

Figure V-8: Plot of Fbxforces versus A

A portion of shear force is resisted by frictional material (assumption 3):

= 2

Fresultant (N)

A (radians)

0.8 1 1 .2 1.40

50 0

1 103

1.5 103

Figure V-9: Plot of Fresultantforces versus


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V.1.4 Conclusion

This analysis has revealed that the climbers hands exert a considerably smaller magnitude of

force than the feet. FromFigure V-5 andFigure V-6,the maximum force exerted by the hands in positive

normal direction is found to be slightly above 300 N. A maximum downward vertical force was

determined to be 150 N. On the other hand, the climbers feet exert a maximum of 150 N normal forceinto the wall and a downward shear force of 700 N. Fortunately, a portion of the feets shear force is

resisted by friction due to the normal force acting into the wall.

A general trend was observed from this analysis. Shear force was found to increase at the hands

but decrease at the feet as the overall distance of the climbers body from the wall surface was

increased. However the reverse was noticed for the feet. Since in a typical climbing situation, the pushes

for vertical ascend is mostly fueled by the feet, shear should be avoided in the hands and maximized at

the feet. This is also consistent with the clients request. Therefore it can be concluded that the climber

should try to maintain a maximum distance from the wall to achieve this ideal scenario.

It is also very important to note that shear resistance due to friction played an immense role in

supporting the climber. Without it, the size of required adhesives would be immense and unrealistic due

to its size. The possibility of the design impeding the movement of the climber and interfering with

standard climbing safety equipment would also be incredibly high. Similarly, the climber should try to

maintain a maximum distance from the wall to maximize normal force (and therefore friction force) on

the feet.


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V.2 Force equilibrium for three point contact

This analysis aims to determine the magnitude of lateral forces (z-direction) as shown inFigure

V-10.As soon as a climber detaches one component of the climbing gear, lateral forces would develop

as the remaining gears re-balance the moment of the climber. The objective is to investigate the

significance of lateral forces and their effects on the loading of the design and the adhesive.

V.2.1 Assumptions

1. The climber is modeled as a rigid body supported by a maximum of four pin connections.

2. Lateral load is distributed evenly between hands and feet.

3. The weight of the average male climber is approximately 700N.

4. The model is quasi-static, i.e. inertial effects are negligible.

5. Dimensions for model correspond to body measurements of the average human male [2].

6. Climbers hands are at equal height. Similarly, climbers feet are at equal height.

Figure V-10: Free body diagram of analysis model


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V.2.2 Calculations


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Scenario 1: Climber releases right foot.

Conditions: No loading on the right foot, i.e.: RFX=RFY=RFZ=0

V.2.3 Results

LFZ(N)

A (radians)

0.8 1 1.2 1.40

100

200

Figure V-11: Plot of LFZ versus A


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Scenario 2: Climber releases right hand.

Conditions: No loading on the right hand, i.e.: RHX=RHY=RHZ=0. Conditions below were inputted into

MathCad to simulate the climbers right foot being not attached to the wall.

V.2.4 Results

LHZ(N)

A (radians)

0.8 1 1.2 1.4

40

20

0

20

Figure V-12: Plot of LHZ versus A


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V.2.5 Conclusion

The maximum lateral forces acting at the climbers hands and feet are 20 N and 150 N

respectively. These forces are significantly smaller than forces found in the x- and y- direction. The gain

from counteracting this force is minimal and therefore it is negligible. A higher lateral force was found

for the legs and therefore greater adhesive strength could be required for the feets climbing gear.


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V.3 Minimum required contact area

The aim of this analysis is to determine the minimum area of adhesives required for the design.

This analysis was performd for the feet as it exerts the largest and therefore the critical load in the

design.. This calculation includes rubber as a high frictional material to utilize the climbers normal

reaction force to minimize the total load experienced by the feet.

V.3.1 Assumptions

1. Material properties used are obtained from material tests and are as follows:

Peel strength = 0.2

Initiation Force per length of adhesive = 1

Normal strength of adhesive = 100

Shear strength of adhesive = 20

V.3.2 Calculations

The maximum force resisted by adhesives was found to be:

V.3.3 Conclusion

The minimum adhesive area required for the feet is 0.1252. Note that this value is obtained by

assuming the adhesive will be loaded entirely in shear which was considered the worst case scenario.


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V.4 Concept Design Calculations

The aim is to estimate the force required to initiate peeling relative to the three concept

designs.

V.4.1 Assumptions

1. The initiation force required to initiate peeling is linearly dependent on the adhesives

peel length

2. Peel initiation strength, = 1

(estimated from material testing found in

Appendix VI)

3. The peel strength of the adhesive after initiation has occurred is linearly dependent on

the adhesive peel length.

4. Peel strength, = 0.2

(estimated from material testing found inAppendix VI )

5. The normal and shear strength of the adhesives are taken to be 100 kPa and 20 kPa

respectively.

6. Dimensions for concept design are equal to preliminary dimensions from design concept

models.


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V.5 Concept Design A: Lever concept calculations

La

Fremoval

Pivoted rod

member

hinged flap plate

Lb

Adhesive layer

Fflap

Om

Finitiation

Figure V-13: Free body diagram for concept A

General Dimensions (Refer toFigure V-13)

Pivoted rod member angle

Length of flap plate

Peel length

M 0:=

Lpeel 5c:=

Lflap 25c:=


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V.5.1 Calculations


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V.5.2 Concept Design B- Rod and hinge calculation

Figure V-14: Free body diagram for concept B


X

La Lb Lc

Finitiation

Fflap

Fremoval /2 Fremoval /2


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V.5.3 Calculations


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V.6 Concept Design C- L-bracket design

Figure V-15: Free body diagram for concept C



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V.6.1 Calculations

Figure V-16: Free body diagram for concept C after peel initiation


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V.7 Concept Design Conclusion

Concept Design A

Lever Mechanism

Concept Design B

Rod and Hinge

Concept Design C

L-bracket

Maximum removal

force (N)7.31 9.56 65.22

These forces contribute to relevant scorings for each design in the design matrix found inAppendix I.


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Phase II Report Appendix VI-23

Gecko Climbing Gear

Appendix VIAverage human body lengths

The 50thpercentile was taken to be a reasonable measure of an average male climbers body

proportions. All of the following body size charts came from reference [2].


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Phase II Report Appendix VII-26

Gecko Climbing Gear

Appendix VIIMaterial Testing Procedure

VII.1Introduction

As part of the design project for a set of climbing gear, the adhesive properties of the

employed biomimetic material are required. The adhesive properties of this material change

significantly with the direction of applied forces. Also, the adhesive strength of the material

degrades as it picks up contaminants and with repeated usage. In order to gain a better

understanding of how the material will behave when it is used in the climbing gear, the following

tests were designed to test the adhesive strength of the material in normal, shear, and peel loading

when they have been applied under less than ideal conditions.

Objective:To determine the normal, shear, and peel strengths of an adhesive sheet under

non-ideal conditions after repeated usage.

Figure VI-1: SEM image of a typical micro-structured synthetic adhesive

VII.2Required Materials

A set of laboratory weights (ranging from 10g to 3kg)

Acrylic block as shown in AppendixVI.9 A bubble level or equivalent

Two C-clamps

Metallic bar as a spacer

Selected samples of the adhesive sheets with and without acrylic backing in rectangular strips of

2cm x 1cm


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VII.3Assembly

Adhesive Backing

Block

C-Clamps

Table

Acrylic

Block

Metal bar

Weights

Table Vise

Figure VI-2: General setup of experiment


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Weight

Adhesive Pad

Acrylic layer (pre-

attached, 1mm thick)

Glue ( epoxy or

alternative)

Aluminium Backing Block

Figure VI-3: Side view of backed adhesive strip

Unbacked

Adhesive PadSquare Tubing

2cm

Epoxy

Figure VI-4: Side view of unbacked adhesive strip

VII.4Procedure

Although the design construction of the adhesive material is an advanced and delicate

process, the macroscale testing ignores much of the finer detail. This is to more closely approximate

the experience of the climber, who will not have the opportunity to ensure exact conditions are

followed.


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VII.4.1General Setup

1. The Polyethylene (PE) film that is attached to the acrylic backed samples was removed.

This step is crucial as the PE film has a low bonding surface energy which prevents

epoxy from properly bonding to the surface.

2. Epoxy was applied to backed samples and aluminum blocks were attached. Epoxy was

applied to one end of un-backed samples and square tubing was attached. The epoxy

was then left to dry for one hour to ensure maximum strength.

3. The samples were trimmed to obtain desired 2cm x 1cm test samples.

4. Thirty pound test fishing lines were run through the aluminum blocks and square

tubing. Figure VI-7 shows samples ready for testing.

VII.4.2Shear Loading Test

5. Acrylic surface was wiped down with ethanol and left to dry.

6. A backed sample was attached to the vertical side (A) of the acrylic block. The sample

was preloaded with a 5 kg weight.

7. Acrylic block was clamped to metal bar with c-clamps and a bubble level was used to

ensure that the acrylic block is properly aligned.

8. Weights were attached to the string slowly to avoid impulse loading.

9. Applied weight was increased until adhesive separates from acrylic block. This final

weight was recorded.

10.Steps 4 through 8 were repeated for remaining samples.

VII.4.3Normal Loading Test11.Acrylic surface was wiped down with ethanol and left to dry.

12.A backed sample was attached to the normal side (B) of the acrylic block. The sample

was preloaded with a 5 kg weight.


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13.Acrylic block was clamped to metal bar with c-clamps and a bubble level was used to


14.Weights were attached to the string slowly to avoid impulse loading.

15.Applied weight was increased until adhesive separates from acrylic block. This final

weight was recorded.


VII.4.4Peel Test

17.Acrylic surface was wiped down with ethanol and left to dry.

18.An unbacked sample was attached to the inclined side (C) of the acrylic block with the

orientation shown inFigure VI-4.The sample was then preloaded manually.

19.Acrylic block was clamped to metal bar with c-clamps and a bubble level was used to


20.Weights were attached to the string slowly to avoid impulse loading.

21.Applied weight was increased until sample begins peeling. This weight was recorded.

22.Weight was removed and reapplied slowly. Weight was increased until a peeling

interface of constant velocity is achieved. This weight was recorded.


VII.4.5Normal Preload Test

24.Gently place the aluminum block backed adhesive specimen on the appropriate surface

of the acrylic block.

25.Gently place a 5g weight on the aluminum block and wait for approximately 30 s or until

adhesives are evenly preloaded.

26.Gently attach the acrylic block to the metal spacer and ensure that it is leveled using a C-

clamp.


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27.Gently attach weights to the string attached to the aluminum block until failure. Record

the weight at failure.

28.Repeat the test with increasing preload weights with an initial increment and doubling

the weight increment for each subsequent test to determine the maximum preload for

which no further increase in normal stress is observed.

VII.5Results and Discussion

Table VI-1: Adhesive strengths

Microscale

Feature Size (m)Average 45

o

Peel Force (N)Average fai lu re

shear stress (kPa)

16 0.22 88.3

24 0.20 119.732 0.15 102.8

40 0.20 90.3

Table VI-1 summarizes macroscale test results for pure shear and 45opeel tests conducted.

VII.5.1Peel Test

Table 1 summarizes the force required for continuous peeling from an existing peel interface. It

was observed that for all samples an initial force of 1N was required to initiate the peeling of the

adhesive strip. The test results indicate that there is no significant variation in the normal and tangential

peeling strength of the adhesive with the microscale feature sizes tested. This was expected by the

client as the adhesive was tested on a flat surface, and smaller features are only more helpful on curved

surfaces. However, the experiment used weights with a smallest increment of 10g, and this may have

been too large to accurately test the peel strength. A smaller weight with a finer resolution may have

given better results. Alternately, the materials engineering department has recently acquired a peel

strength testing machine. Though access to the machine is very limited right now, later tests may be

able to make use of this device.

VII.5.2Shear Test

Table VI-1 summarizes pure shear test results with varying microscale feature size. On average all

adhesive samples exceeded the initialed assumed shear strength value of 20kPa. Dry adhesives with

microscale feature size of 24 microns displayed higher failure shear stress values in comparison to the

other adhesives. However, no conclusions on the samples shear strength should be drawn due to the

low precision of shear strength obtained. Even so, it can be concluded that shear strength of 20 kPa for

the adhesive is a valid assumption as none of the samples failed below that threshold.


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One major setback was discovered which jeopardized the performance of this test. During the

test, many of the samples separated from the aluminum backing either before or during the test. It was

later discovered that the polyethylene protective sheet on the acrylic backing of the adhesive was not

removed before epoxy was applied. Therefore the shear test for many of the samples could not be

performed.

VII.6Normal Test

A normal test was attempted but no results were obtained due to failure of the epoxy. From the

shear test, it was speculated that the aluminum backings would be separated from the adhesive backing

before a maximum supported weight can be obtained. However, the assumed value of 100 kPa for

normal strength can be considered safe as this value was provided based on extensive normal strength

tests performed by the client.

VII.7Improvements

It was found that just removing the protective polyethylene layer was insufficient in preventing

the epoxy between the backed adhesive and the aluminum blocks from yielding. The client suggestedreplacing the aluminum backing blocks with acrylic ones. These acrylic blocks can then be strongly

bonded to the adhesive backing using acetone as a solvent. The client warned that a white residue could

remain but should not have any impact on the experiment. Another suggested method was to use a hot

gun to melt the block and the adhesive backing together. This method however raises concern of how

the heat would affect the adhesive.

Due to the environment in which this experiment was performed, the samples were exposed to a

lot of handling and dust. A lint roller proved somewhat effective but still does not remove all

accumulated contaminants on the adhesive. It was noted that further test should require greater

caution in handling the adhesives. The adhesives could always be attached to a clean sheet of

polyethylene until tests are ready to be performed.

The use of epoxy in this experiment could have also impacted the results of this experiment. Due

to the small size of the adhesive samples, epoxy frequently overran the edges of the sample and

contaminated the edges of the adhesive samples. Therefore for future experiments, care must be taken

to ensure that any bonding agent used does not contaminate the sample.

Another problem noticed during the experiment was the roughness of the test surface. The acrylic

block was machined for surfaces of different orientations and this process left the test surfaces

extremely rough. Initial attempts revealed that the adhesives were not sticking to the rough surfaces at

all. These surfaces were ground down to a 0.5 micrometer surface roughness (native acrylic has aroughness of 0.3 micrometers). Even so, there was concern that constant roughness cannot be assured

for all surfaces which might lead to deviations between strengths obtained from different surfaces. It

was therefore suggested that glass slides should be acquired and attached to the test surfaces of the

acrylic block as a solution to this problem.


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Figure VI-5: Shear strength versus micro-scale feature size

0

20

40

60

80

100

120

140

16 24 32 40

FailureS

tress

(k

Pa)

Micro-scale Feature Size (m)

Average of Failure

StressStdDev of Failure Stress


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VII.8Calculations

VII.8.1Nomenclature

Cross sectional area of adhesive strip (2)

Failure shear load ()

Failure shear stress (kPa)

, Normal peeling force ()

, Tangential peeling force (kPa)

Total peeling force ()

Peel angle (degrees)

Mass of weight required for constant peeling (kg)

g gravitational acceleration (9.81

)

VII.8.2Sample Shear Test Calculations

For sample 1, the failure weight when the adhesives are loaded in pure shear was 1820g.

Failure shear stress, =

=1.820 9.81

(0.01 0.02)1

1

1

1000

= 89.27


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VII.8.3Results

Table VI-2: Raw shear test results

Sample

#

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