MESA - Charles County, Maryland

Henry E. Lackey High School

Prosthetic Arm

6/3/2014

Team Members:

George Jenkins, Cody Rogers, Shade Jenifer, &

Christian Warren

Abstract

The Prosthetic Arm Challenge detailed design criteria and testing specifications for a

trans-radial prosthetic device. Devices are scored based on the distance accuracy relay, the object

relocation task, the dexterity task, and design efficiency. This report details the efforts of the

second Henry E. Lackey Prosthetic Arm Team to meet the goals of the challenge up to June

3rd, 2014. It includes a discussion of research, material choice, and other components of the

design evolution, along with STEM influence and principles, and an analysis of preliminary

tests. This design is a cost effective, efficient, and effective trans-radial prosthetic device. The

tension created by straightening the user's arm and the force created by the spring of the spring

clamp is enough to hold and relocate relatively heavy objects. The device can be used to thread

nuts onto bolts and throw ping pong balls, albeit with some difficulty. Additionally, the design is

composed of highly cost-efficient materials. The design can be improved by focusing on the

hand mechanism and the direct tension mechanism. If the direct tension method of design was

maintained, possible re-design concepts would include using simple machines or a pulley system

to enable an increase of the spring tension of the clamp but allow the force produced by

straightening the arm to remain the same. Even without these advancements the current design

remains an effective trans-radial prosthetic device and could be effective in a real life

application.

Table of Contents

Title Page1

Abstract...2

Table of Contents3

Introduction.4

Discussion...5-12

Conclusion.12

Recommendations..........13

References13-14

Acknowledgements15

Appendix A...16-18

Appendix B...19-20

Appendix C...21-22

Appendix D...22-23

Appendix E24

Appendix F.25

Appendix G...26-31

Introduction

Prosthetic devices have been mentioned throughout history. Early models were created

out of wood and metal and were often uncomfortable and had limited ranges of movement. At

the end of world war two, the National Academy of Sciences began to advocate better research

and development of prosthetics. The use of stronger, lighter materials like plastic, aluminum, and

composite materials, alongside the advent of microprocessors, computer chips, and robotics,

allows amputees to function with increasing efficiency.

The Prosthetic Arm Challenge detailed design criteria and testing specifications for a

trans-radial prosthetic device. The device could not utilize the elbow, forearm, wrist, hand, or

fingers of each arm to control the prosthetic device, must have had "fingers" that could open at

least ten centimeters, could not be modified mid-challenge, and could not exceed a monetary cost

of forty dollars and needed to be as light as possible. Devices were scored based on the distance

accuracy relay, the object relocation task, the dexterity task, and design efficiency. The distance

accuracy relay measured the distance and accuracy achieved by tossing balls of three different

sizes into target containers located at three different distances. The object relocation task

measured the mass-to-time ratio achieved by placing objects of varying weight into the specific

container. The dexterity task measured the number of bolts and nuts correctly placed and secured

onto the testing device. Design efficiency measured the greatest ratio of device performance to

device mass. Additionally, the team was scored based on its technical paper, academic display,

and oral presentation. This report details the efforts of the second Henry E. Lackey Prosthetic

Arm Team to meet the goals of the challenge up to June 3rd, 2014. It includes a discussion of

research, material choice, and other components of the design evolution, along with STEM

influence and principles, and an analysis of preliminary tests.

Discussion

The team started the project back in November and like in any successful engineering

project, followed the design process. The team started by defining the problem of having to

design and construct a low cost prosthetic that could be used in application of everyday life to

perform various tasks. The team also evaluated the given constraints of the challenge and knew

exactly what criteria the arm had to meet and the expectations in terms of the performance. Once

the team had the problem clearly defined, the team moved into the research stages of the process.

In order to begin the preliminary research to find the particular solution desired, the team began

concept development by defining the purposes of four subsystems of the device: tension

mechanism, hand configuration, harness, and fastenings (Appendix A, Figure 1). The team

brainstormed possible implications of the enumerated criteria especially relevant to design: the

forty dollar budget, the inability to use the wrist, hand, or fingers in any way, and the necessity of

having at least two moving fingers. The team then met once a week to move thoroughly through

the design process.

The tension mechanism needed to open and close a device wide enough to pick up a two

liter bottle, which is the largest object in the competition being approximately 10cm, without

using the wrist, hand, fingers, or forearm of the arm equipped with the trans-radial prosthetic

device or any part of the other arm. Once the concept development was complete the team was

able to conduct preliminary research to find the types of prosthetics on market and options for

the project. Four options were explored, and extensive research was completed on each: direct

tension (Appendix B, Figure 1), pneumatics (Appendix B, Figure 2), hydraulics (Appendix B,

Figure 3), and mechanical devices (Appendix B, Figure 4). Direct tension involved stretching the

entire arm out to pull a string taut and to close the hand mechanism. For this to work as efficiently

as possible, research had to be conducted into how to gain the highest possible mechanical

advantage of the system in order for the arm to produce the most torque via the less human force

applied. Pneumatics and hydraulics both involved using a series of tubes with air and fluid,

respectively, to achieve the same result. Using the Pascal's Principle and the ideal gas law, the

team could have used either system which would have great efficiency since a system could have

been built which had a great change in area, resulting in a great output force to the arm.

Mechanical devices involved creating a switch mechanism that would turn a motor on and off,

again achieving the same result. This last idea involved potentially costly and heavy mechanical

motors and may have hindered the user's ability to time the opening and closing of the hand

mechanism to grasp objects effectively. Hydraulics involved potentially heavy quantities of

fluids, promised to be complicated to design and build, and raised concerns about leakage.

Pneumatics did not involve potentially heavy fluids, but did promise to be complicated to design

and build and also raised concerns about air leakage. Direct tension used only human muscle

power and would not be as efficient as the other options, but was the cheapest, lightest, and

simplest option. For these reasons, the team decided to pursue a direct tension trans-radial

prosthetic system design.

Once the preliminary research was conducted and the team had the main concept of a

direct tension prosthetic, further research was conducted in order for the team to have complete

understanding on the concepts behind direct tension. Online research indicated that a common

direct tension prosthetic system design involves running a string from the center of the user's

back (Appendix A, Figure 2), through a hook near the user's elbow, and to a gripping device.

The next topic of research was the natural state of the prosthetic. In a naturally closed direct

tension device, the user's naturally relaxed state would ensure the lack of tension in the string

and a spring or spring-like device would force the device's fingers together. The user could

extend his or her shoulder and elbow to create tension in the string, thereby opening the device's

fingers and grabbing the intended object before relaxing, letting the force of the spring pull the

fingers back together with enough force to continue holding onto said object. There are several

potential issues with this design. If the force created by the spring is not large enough, the fingers

may slide open and let the object fall out, but if the force created by the spring is too large, it

may be difficult to provide enough force using only your arm and shoulder to open the fingers

wide enough to grasp the object in question. These problems are somewhat alleviated by running

the string from the center of the back to the hand mechanism, thereby increasing the string length

and allowing the user to utilize the combined force of back, shoulder, and arm muscles to create

tension. This increased tension potential would allow for stronger spring devices and stronger

grips.

The other researched natural state is known as naturally open direct tension devices.

Naturally open direct tension devices are much like the naturally open devices, except the spring

is not in compression, yet tension. The spring actually presses out on the fingers and by the user's

motion of the extension of the user's arm, would compress the spring and the fingers would

come to. The team found this option very viable considering the user has complete control

over the forces compared to the spring having the control in the naturally closed device. The

major problem with this came when analyzing how a device such as this would perform in the

challenges given and if someone in real world would have to use the arm. The problem is user

fatigue while using the device, since in order to pick up an object the user would have the arm

fully extended for long periods of time since the extension of the arm is what holds the fingers

shut. Because of the fatigue issue and knowing the device is being made for real life application,

the team chose a naturally closed arm since the device would function and only a proper spring size

would be needed.

The performance tasks provided several distinct challenges. The prosthetic device had to

open at least two fingers at least ten centimeters apart, pick up objects of various shapes, sizes,

and weights, throw three sizes of balls different distances, and thread nuts onto bolts. Now that

the research had been conducted the team moved into the brainstorming and design portions of

the design process. The team chose to go through each aspect of the design; claw, mounting

apparatus, harness, and cable respectively, separately, and for each brainstorm possible solutions

to chose the best component rather than focus operations on one main device. The hand was a

spring clamp that was naturally closed and opened with the application of tension from the

string. One spring clamp design (Appendix B, Figure 5) had a wide, circular opening directly

between each finger that can hold larger balls and two pieces of rubber attached laterally to the

tips of the fingers. The opening allowed it to pick up, and subsequently release and throw, balls,

and the laterally-attached rubber squares moved with the shape of the targeted object, increasing

the likelihood of successfully picking that object up. A flat piece of plywood provided a stable

base for the clamp, but several challenges remained: mounting the device on a stable surface and

holding everything in place. Particular attention was paid to the kinetic friction of the constantly-

moving string and the force required opening the clamp.

Two different team members had to attempt each task. The system, in order to fit more

than one person, could not rely on any singular set of measurements. A t-shirt seemed a likely

solution. Velcro straps could be used to secure the plywood platform and the elbow hook for the

string in place in addition to fastening the t-shirt securely onto the user's arm. Additionally, long

sleeves could prevent any harmful abrasion on the user's skin during testing. Another hook could

be added to the back of the t-shirt to extend the length of the string and allow the user to fully

utilize his or her back, shoulder, and arm muscles to create tension. Unfortunately, a t-shirt

would not provide enough stability for the overall system, as the Velcro straps would not prevent

rotational sliding on the arm or slippage on the back hook. The team used a free body diagram

which showed that the shirt did not provide sufficient horizontal support to prevent such motion.

A leather "8" harness looped around both shoulders could secure the back hook in place and

multiple hooks around the upper arm, elbow joint, and wrist could prevent rotational slippage on

the arm. In order to limit the amount of materials required, however, a looped dog leash

(Appendix B, Figure 6) was incorporated into the design instead of a leather harness, eliminating

the need for attaching an additional hook on the back, and PVC pipe was used in place of several

Velcro straps and a long-sleeve t-shirt to hold the hand mechanism.

Originally the team was going to use a cardboard shipping tube, but overall, less wear

could be done with the PVC, and the team needed the device to be as durable as possible. The

string began at the loop already on the secured dog leash loop in the back, ran through the PVC

pipe and a loop located above the wrist, and through each of the handles of the spring clamp. The

string, however, chafed against both the user's forearm and the edges of the PVC pipe. Original

designs called for latex tubing to act as the string, but its relative weakness made it difficult to

create enough tension to force the spring clamp open, and so it was replaced with the stronger,

more durable butcher's twine. During testing, however, friction from the constant fraying on the

edges of the PVC frayed the twine, causing it to snap. The butcher's twine was then replaced with

the much-more-durable trimmer line and a hole was drilled into the side of the PVC pipe, allowing

the trimmer line to be fed in around the area where the user's fist rested, preventing any harmful

chafing.

The spring clamp was connected to a plywood rectangle of wood by the use of two bolts

(Appendix A, Figure 3). It was further held in place by a doubled rubber band attached to

the center of gravity of the clamp and the two screws. The top half of approximately five inches

was cut off of the PVC pipe so the plywood could be placed inside. The plywood was secured

via wood screws. Foam padding was placed behind the end of the plywood in order to minimize

user discomfort. The trimmer line was tied to the looped dog leash, run through a hole in the side

of the PVC pipe, the wrist hook, and a hole pre-drilled into one of the spring clamp handles

before being tied to the pre-drilled hole in the other handle. Now the build of the prosthetic

device was complete.

Further modifications were made to the prosthetic build after competing in the state

competition on May 1st. The changes made were to increase design efficiency since the main

weakness of the device was the weight. The PVC pipe of the arm was cut down two inches, now

being the ideal length for arms of members (Rogers and Jenifer) who will be competing in the

National event. Additionally, the piece of plywood used initially was longer than needed, so the

wood was cut to proper length. Lastly, to reduce the weight of the device even further, a series of

holes were drilled in rows around the arm to reduce the weight as much as possible. These

changes increase the design efficiency and overall quality of the device since at a lighter weight

the prosthetic is easier to operate.

Three preliminary tests were designed. First, various objects were placed on a table to be

picked up and moved to a designated zone via use of the trans-radial prosthetic device (Appendix

C, Figure 1). These objects were chosen from the list of given objects (e.g. 2 liters, soup cans,

and notebooks) and based on their particular weights or ergonomic shapes (e.g. power drill,

coffee mug) in order to determine whether or not the prosthetic device could perform the

challenge adequately and the relative ease with which it was possible to pick up heavier or oddly

shaped objects. During testing, it was noticed that the laterally-attached rubber rectangles did not

have significant gripping properties. Electrical tape was added to the rubber to provide extra

friction between the device and objects. This increased the grip tremendously. The device was

able to move every single object the user attempted to move. During a timed test, one team

member moved fifteen items from a table to a designated location two meters away in forty six

seconds (Appendix D, Graph 1). These results clearly suggest that the prosthetic device can pick

up, move, and drop items of various shapes, sizes, and weights.

Secondly, balls of various diameters as defined in the testing challenge were collected

and thrown into buckets (Appendix C, figure 2) of the specified meters away fifty times. Fifty

ping pong balls were thrown in a bucket two meters away, three-and-a-half meters away, and five

meters away. Trials were conducted for each type of ball. The results (Appendix D, Graph 2)

show a significant downward trend in accuracy as the distance of the buckets increases. A ping

pong ball successfully thrown into the closest target earns twenty-five points.

Landing in the next target earns thirty points. A successful landing in the farthest bucket earns

forty points. If all fifteen ping pong balls are thrown into the nearest bucket, approximately six of

them will get in, earning a total of one hundred and fifty points. If they are all thrown into the

bucket after that, approximately four of them will get in, earning a total of one hundred and

twenty points. If they are all thrown into the farthest bucket, approximately one of them will get

in, earning a total of forty points. These results show that all balls should be thrown into the

nearest bucket unless accuracy can be significantly improved at three-and-a-half meters.

Lastly, the prosthetic was used to thread a nut through a bolt (Appendix C, figure 3). The

team constructed a replica of the actual board and was able to get the same nuts and bolts as the

competition would provide. The team member would go exactly as if in the competition and put

the bolt in the hole then fasten the nut onto the bolt. It took approximately twenty seconds to

thread a nut completely on the bolt (Appendix D, Graph 3). The indentations on the bolt guided

the nut up the shaft. Although the non-equipped hand could hold the head of the bolt in place, the

bolt had to be repositioned several times during some trials. Overall the device was very

successful with the challenge proving the device could be implemented in terms of use for fine

motor control tasks.

As stated previously, the Lackey Prosthetic arm team has been meeting every Monday

since November. An estimated time worked on the project would be approximately 114 hours,

including work done in school and then the various outside practices and work done on the

project (Appendix E). The team is committed to the success of the arm and has gone above all

expectations now having acquired much practice time for the challenges and looks very

promising. Team members worked together through every aspect of the design process. The

members did everything together, no one person in control, everyone working together to do

everything to the highest potential. Everyone had the same role, all important. During testing the

two performers (Rogers & Jennifer) performed the tasks, while the other two members (Jenkins

& Warren) helped to set-up and record data. Teamwork helped the success and in the end, made

the team what it is.

Conclusion

This design is a cheap (Appendices F & G), efficient, and effective trans-radial prosthetic

device. The PVC pipe and dog leash adequately constrain the trimmer line and the single wrist

hook adequately aligns it with the spring clamp. The tension created by straightening the user's

arm and the force created by the spring of the spring clamp is enough to hold and relocate

relatively heavy objects. The device can be used to thread nuts onto bolts and throw ping pong

balls, albeit with some difficulty. The data collected through the ball tossing challenge indicates

the device has accuracy up to the two meter line, which is where the teams focus will be and the

device has relatively acceptable fine motor control. Additionally, the design is composed of

highly cost-efficient materials. The design has much room for improvement, but is an effective

trans-radial prosthetic device.

Recommendations

As of writing this report, the device would perform better if the user did not have to apply

as much force to open the clamp because great strength is needed to open the device all the way,

but the same amount of spring force is necessary to grasp the provided objects. The team needs

to look into alternate direct force applications, such as simple machines. The design needs to

hold more objects, no matter their shapes, and be more easily utilized. This can be achieved by

focusing on the hand mechanism and the direct tension mechanism, respectively. Additional

testing should be done to see how the device can handle more delicate objects, such as a fish

bowl, to see the true real life application of the device.

References

Norton, K. M. (n.d.). inMotion: A Brief History of Prosthetics. Amputee Coalition - Resources

for amputees, amputation, limb loss, caregivers and healthcare providers. Retrieved March 15,

2014, from http://www.amputee-coalition.org/inmotion/nov_dec_07/history_prost

Burck, J., Zeher, M. J., Armiger, R., Beaty, J. D., & Laboratory, J. H. (n.d.). Developing the

World's Most Advanced Prosthetic Arm Using Model-Based Design - MathWorks News &

Notes - 2009. MathWorks - MATLAB and Simulink for Technical Computing. Retrieved March

15, 2014, from http://www.mathworks.com/company/newsletters/news_notes/2009/jhu-model-

based-design.html

Scott, D. (n.d.). University of Illinois Students Design $300 Prosthetic Arm | Complex. Complex

| Style, Music, Sneakers, Entertainment, Girls, Technology. Retrieved March 15, 2014, from

http://www.complex.com/tech/2012/11/university-of-illinois-students-design-300-prosthetic-arm

Chorost, M. (n.d.). A True Bionic Limb Remains Far Out of Reach | Wired Science | Wired.com.

wired.com . Retrieved March 15, 2014, from http://www.wired.com/wiredscience/2012/03

AMO Arm pneumatic prosthetic does mind-control on the cheap. (n.d.). Engadget. Retrieved

March 15, 2014, from http://www.engadget.com/2011/04/05/amo-arm-pneumatic-prosthetic-

does-mind-control-on-the-cheap/

Nylon Dog Traffic Leash 1-inch x 2 foot Blue - Dog Leashes Nylon. (n.d.). Arcata Pet Supplies -

Online pet shop for all your supply needs. Retrieved March 15, 2014, from

http://www.arcatapet.com/item.cfm?cat=794

Magellan self-actuated prosthetic device can be operated with your smartphone | The geek's

guide to awesomeness | DamnGeeky. (n.d.). The geek's guide to awesomeness. Retrieved March

15, 2014, from http://www.damngeeky.com/2012/08/15/4071/magellan-self-actuated-prosthetic-

device-can-be-operated-with-your-smartphone.html

Alfred Mann Foundation » Limb Loss. (n.d.). Alfred Mann Foundation. Retrieved March 15,

2014, from http://aemf.org/our-research/current-focus/limb-loss/

spring clamp. (n.d.). plastic spring clamp for hundreds of uses. Retrieved March 15, 2014, from

http://www.alibaba.com/product-gs/341861413/plastic_spring_clamp_for_hundred

Acknowledgements

The Henry E. Lackey Prosthetic Arm team would like to thank our sponsors;

Mr. Crawford and Mr. Liston, for helping us flush out our design ideas and their continuous

support through our entire design process and as we have advanced through numerous

competitions to the National level. Also special thanks go out to Dr. Warren for his constant

support of the team and allowing the team to use his tools for construction and also to be there for

the team for assistance when needed in the construction portion of the design. The team would

like to recognize Michael Laury who aided in the training of the competition portion of the

challenge. Mike served as an outside observer, helping us refine our techniques for the

performance. Thomas DeLoache is very fluent in Inventor, our 3-D modeling program, and

answered any questions the team had while utilizing the CAD program. The team would also like

to recognize Mai-Lin Quinto and Melissa Nelson who helped in the layout of the backboard.

Thank you to Henry E. Lackey High School, Charles County Public Schools, and Maryland

MESA for supporting the team as the team represents Charles County and the State of Maryland at the

National level.

Appendix A: Design Notebook Photocopies

Figure 1: 4 subsystems of design

Figure 2: Team's Direct Tension Method

Figure 3: Plywood Layout

Appendix B: Design Ideas

Figure One: Direct Tension Prosthetic Device

Figure Two: Pneumatics Prosthetic Device

Figure Three: Hydraulics Prosthetic Device

Figure Four: Motorized Prosthetic Device

Figure Five: Spring Clamp

Figure Six: Looped Dog Leash

Appendix C: Testing

Figure 1: Object Relocation Test Set-up

Figure 2: Distance Accuracy Relay Test Set-up

Figure 3: Block used for dexterity challenge practice

Appendix D: Testing Data

Trial # Items Relocated Time (Sec)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Average

15

15

15

15

15

15

15

15

15

15

15

15

15

15

15

15

51

47

42

46

41

51

48

43

45

48

46

52

45

46

47

46.533 Graph 1: Chart of Time to relocate all objects.

80

70

60

50

Successes 40

30

20

10

0

Arm Throws

Tennis Ball

Kick Ball

Ping Pong Ball

2 meters 3.5 meters 5 meters

Distance

Graph two: Chart of the number of balls that landed in buckets of varying distances

Trial #

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Average

Bolts Secured

3

3

3

3

3

3

3

3

3

3

3

3

3

3

3

3

Time (Sec)

63

57

69

59

72

64

67

59

62

54

63

57

59

61

63

61.933

Graph three: Chart of time to secure all nuts on bolts

Appendix E: Cost-Labor Summary

Cost - Labor Summary

Component Time per Session Number of Sessions Total Time

Device - In School

Meetings/ Practice

Device - Out of School

Meetings/ Practice

Paper

Academic Display

Presentation

Additional Time -

Build with Volunteer

1 Hour

2 Hours

2 Hours

1 Hour 2

Hours

5 Hours

35

10

6

10

8

1

35 Hours

20 Hours

12 Hours

10 Hours

16 Hours

5 Hours

Support

Additional Time -

Research Conducted 2 Hours 8 16 Hours

for Project

Total Time 114 Hours

*In school meeting consisted of the group going through the design process and coming up with

ideas. All research was split in between the group members to be done outside of school

individually. Out of school practice was when the group meet up most of the time after school on

our free time to do additional work on the arm and also to practice the challenges. Then on a

single day, the group meet together at a members house (Warren) and constructed the arm, using

the tools and time volunteered by the member's father (Dr. Warren). Above is the chart

reflecting the average time spent on each one of these sessions and also the exact values of

sessions had for each component. The total time is an estimate, but is very close to the actual

time spent.

Appendix F: Itemized Budget Sheet

Part Unit Dimensions Retail Price Price per Unit Quantity Used Total Cost Retail Source

PVC PipeCharlotte Pipe 6- in x 10 ft

Sch 40 PVC DWV Pipe$42.48 $0.354/inch 15.5 Inches $5.49 Lowes.com

Hardwood Oak, Red 3/4" x 4" x 48" $15.75 $0.08/inch^2 18 Inches^2 $1.44 Woodcraft.com

Leash Large, 6ft $6.49 $6.49/Leash 1 Leash $6.49 Chewy.com

Trimmer

Line

Husqvarna 639 00 51-05

230 ft Titanium Force

Premium

$15.99 $0.08/foot 3 Feet $0.24 vminnovations.com

Wood

Screws75 Pack, 1-3/4" $3.14 $0.042/screw 8 Screws $0.33 midlandhardware.com

Spring

Clamp

Jaw Opening Capacity

(Inch): 3 Overall Length

(Inch): 9

$8.36 $8.36/clamp 1 Clamp $5.85 use-enco.com

Sponge 9" x 5" $1.79 $1.79/sponge 1/2 Sponge $0.90 Amazon.com

Bolts100 Pack, Width: 3/8",

Length: 1-1/2"$165.50 $1.655/bolt 2 Bolts $3.31 Lowes.com

Nuts 25 Count, 3/8" $2.74 $0.1096/nut 2 Nuts $0.23 Lowes.com

Washers 50 Count, 3/8" $3.99 $0.0798/washer 2 Washers $0.16 Amazon.com

Butt

Conector50 Count, 12-10 Gauge $7.15

$0.143/Butt

connector

1 Butt

connector$0.14 protelecomsupply.com

Total $24.58

Documentation of Retail Prices – Print screens of Retail Prices

- Highlights Price of Material

PVC Pipe:

Hardwood:

Leash:

Trimmer Line:

Wood Screws:

Spring Clamp:

Sponge:

Bolts:

Nuts:

Flat Washers:

Butt connector: