Design, development and testing of a low-cost electric powered wheelchair for India

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Design, development and testing of a low-cost electric powered wheelchair forIndiaJon Pearlman ab; Rory Cooper ab; H. S. Chhabra c; Alexandra Jefferds ab

a Human Engineering Research Laboratories, VA Pittsburgh Healthcare System, Pittsburgh, PA, USA b

Department of Rehabilitation Science and Technology, University of Pittsburgh, Pittsburgh, PA, USA c IndianSpinal Injuries Center, New Delhi, India

Online Publication Date: 01 January 2009

To cite this Article Pearlman, Jon, Cooper, Rory, Chhabra, H. S. and Jefferds, Alexandra(2009)'Design, development and testing of alow-cost electric powered wheelchair for India',Disability and Rehabilitation: Assistive Technology,4:1,42 — 57

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PRODUCTS AND DEVICES

Design, development and testing of a low-cost electric poweredwheelchair for India

JON PEARLMAN1,2, RORY COOPER1,2, H. S. CHHABRA3 & ALEXANDRA JEFFERDS1,2

1Human Engineering Research Laboratories, VA Pittsburgh Healthcare System, Pittsburgh, PA, USA, 2Department of

Rehabilitation Science and Technology, University of Pittsburgh, Pittsburgh, PA, USA, and 3Indian Spinal Injuries Center,

New Delhi, India

Accepted July 2008

AbstractPurpose. To design and develop an appropriate, low-cost electric powered wheelchair (EPW) for the Indian subcontinent.Method. We performed the following multi-phase design process: (1) Conceptual design; (2) System design, Prototype Ifabrication, focus group testing with Indian stakeholders (n¼ 29); (3) System re-design, Prototype II fabrication and usertrials with US (n¼ 5) and Indian (n¼ 25) subjects.Results. (1) Preliminary investigations revealed that a conventional EPW design was infeasible due to the high componentcost. Instead, we constrained our design to incorporate a single drive motor and manual steering, with the option ofupgrading to power steering where economically feasible. (2) The first prototype was fabricated out of easily available, low-cost materials. Focus group testing demonstrated feasibility of the design and revealed differences between stakeholdergroups. (3) Prototype II incorporated feedback from the first focus group and a needs assessment. US subjects providedvaluable design advice prior to the India trials. Indian subjects travelled further in the SIMPL-EPW than their own manualwheelchair (MWC). Depending on spinal injury level, Indian subjects found the entire (tetraplegia) or outdoor portion(paraplegia) of the obstacle course significantly less challenging in the SIMPL-EPW compared with their own MWC.Conclusions. We demonstrated a useful and successful multi-phase design approach for developing assistive technology fordeveloping regions.

Introduction

There is a tremendous need for assistive technologies

(ATs) to improve the quality of life for people with

disabilities (PWD) in developing countries. The need

for wheelchairs (WC), for example, is estimated to be

anywhere between 20 million [1] and 100 million [2].

The World Health Organisation (WHO) estimates that

10% of any population has a disability, and 10% of these

individuals could benefit from a WC [3]. Using these

values, there are approximately 66 million potential WC

users world-wide. In India, a large and developing

country, the WHO estimate suggests that there are

approximately 10 million potential WC users, which is

corroborated by India’s most recent country-wide

census [4]. Unfortunately, because of factors including

an underdeveloped healthcare system, stigmas and

stereotypes associated with disability, and the below-

average income of most PWD in India [5], the need for

suitable WC is unmet [6].

There have been promising developments to help

equalise the rights of PWD by improving their access

to healthcare and AT, as well as reducing the stigma

associated with their disability. The most encoura-

ging development was the recent passage of the

United Nations (UN) Convention on the Rights of

PWD (UN-CRPD) [7], and the ratification of the

document by several countries (including India).

Personal Mobility (Article 20), of the UN-CRPD

mandates that countries provide a choice of high-

quality, affordable devices for PWD. Although

Article 20 is a necessary step to provide PWD the

devices they need, in the WC industry, it represents a

significant challenge.

Considering the tremendous unmet need for

WCs, as well as evidence of poor performance of

Correspondence: Jon Pearlman, PhD, Human Engineering Research Laboratories, VA Pittsburgh Healthcare System, 7180 Highland Drive Building 4, 151R-

1H, Pittsburgh, Pennsylvania, 15206 USA. Tel: þ412-365-4850. Fax: þ412-365-4858. E-mail: [email protected]

Disability and Rehabilitation: Assistive Technology, January 2009; 4(1): 42–57

ISSN 1748-3107 print/ISSN 1748-3115 online ª 2009 Informa Healthcare USA, Inc.

DOI: 10.1080/17483100802338440

Downloaded By: [University of Pittsburgh] At: 18:49 29 June 2009

WCs in developing countries, the WC designs and

supply mechanisms in place are insufficient to

provide the variety, quality or volume of WCs

mandated by the UN-CRPD. Unfortunately, there

is little guidance on how to move beyond the current

situation due in large part to the scarcity of reliable

information on the topic. What has been published

are mostly descriptive accounts of what types of WC

do not meet the needs of individuals in developing

countries, and basic guidance on design methods to

avoid poor quality designs (namely, that the designs

be ‘user-centred’). The majority of this evidence is

anecdotal, and suggests that hospital style WC fail

rapidly in the rough terrains of developing countries

[1,8–15]. We have located three research studies in

the literature. Saha and co-authors [16] surveyed

individuals who received their WCs from two

District Rehabilitation Centres (DRC) in India.

Each DRC provided a hospital-style WC from two

local manufacturers. Remarkably, only 14% of the

subjects propelled their manual wheelchair (MWC)

independently. Between 50% and 70% were exclu-

sively propelled by an attendant. The subjects

complained of frequent caster failures, size problems

and stability issues. The second study, by Mukherjee

and Samataa [17] investigated the outcome of 162

individuals who received their hospital-style WCs

through non-governmental organisations in West

Bengal. Of the 162 WCs distributed, 7.4% were

regularly used, 10.5% were occasionally used, 14%

were sold, 57.4% were abandoned and 10.5% were

attendant propelled. When asked why the chairs were

not used, subjects reported ‘habitat adaptability’

(34%) and ‘pain, fatigue and discomfort’ (29%),

and frequent damage (15%) as the primary reasons.

Armstrong and co-authors [18] reported the only

longitudinal study that we have located in the

literature. One hundred adjustable WCs, which were

specifically designed for the rugged terrain and use

were fitted by trained personnel from Kabul,

Afghanistan. An assessment and fitting was followed

by WC skills training. Subjects rated their newly

provided chair superior in all factors (usability,

comfort and appearance) to their original chair.

Subjects also generally improved their WC skills over

the two follow-up sessions (at 3 and 10 weeks) with

their new WC. This study demonstrates the im-

proved usability and value of training when providing

appropriate WCs. Objective comparisons between

mobility characteristics in the subject’s original

versus new WC were not made, however, so the

impact of an appropriately designed and fitted chair

on mobility characteristics is still unclear.

The anecdotal and research studies strongly

suggest that hospital-style WCs are difficult to

manoeuvre independently in the terrain of develop-

ing countries, do not fit the user well and have

maintenance problems. Although from our own

experience we believe these results are accurate, they

are difficult to interpret relative to the performance of

other WC designs in these countries: Hospital-style

WCs are, by a large margin, the most common

designs distributed [6], which increases the chances

that product failures will be noticed and reported. In

addition, the only outcomes that have been reported

with appropriately designed and fit WC were by

Armstrong et al. [18], discussed above, who pro-

vided results from 10 weeks beyond delivery

(although all were positive). Without longer-term

comparative outcome studies, an evidence-based

argument about which design(s) perform better

cannot be made. To remedy this, it is critical that

comparison studies be performed.

Despite the lack of comparative evidence, the

reported failures of the hospital-style designs suggest

that the key factors in the design process should be to

ensure that the WC provides safe, low-maintenance

independent mobility in the terrain of developing

countries. The question is how to proceed through

the design process and to assure whether these

requirements are met.

Rigorous product design requires a multi-step

process where a faithful description of the customer’s

needs are developed, and those needs are addressed

with a product [19]. When designing a product for a

foreign customer, the economic, cultural, physical

and social gulf between the product designer and

customer can impose a significant barrier to generat-

ing this faithful needs assessment; in addition, the

distance complicates all portions of the design

process: concept development, system-level design,

detail design, testing and refinement and production

ramp up [19]. If these barriers are not adequately

addressed, they can impact the success of the product

in the foreign market, which is likely the cause of the

high failure rate of WCs in developing countries.

Although several organisations have designed

WCs for developing countries, descriptions of the

design process are nearly non-existent. Conse-

quently, there are no guides to help steer future

efforts in WC designs. Overviews of the process used

by some organisations have been discussed in the

literature, but not step-by-step methods. These

approaches include open-source methods [10,12,

20], traditional industrial design methods where

designers are collocated with users, and ‘remote’

design methods where designers have limited or no

contact with the users during the design process

[21]. The traditional approach of collocating de-

signers with the user population has yielded several

appropriate WC designs, but it requires a high

financial and personal commitment. If design meth-

ods can be augmented to facilitate remote design

without sacrificing the appropriateness of the device,

Low cost EPW for India 43

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then presumably more design professionals would be

willing to address the overwhelming need for

appropriate WCs. Advances in communication

technology, as well as a surge of interest in socially

responsible engineering may help make this a reality.

Remote design methods for WCs are best devel-

oped based on the successes and failures of past

projects. Unfortunately, while WC designs have been

described and provide useful design examples

[13,22–24], the design process has not been well

described. Mulholland and colleagues published the

most comprehensive series of articles on the R&D of

a mobility device for developing countries. In their

first study, assessments were performed in India [25]

to understand the needs of Indian women with

disabilities. Their second study [26] details the

design of a mobility device to meet the needs of the

Indian women. In their final study, Mulholland

describes the focus groups that were performed with

the device [27] in India. Although she performed a

thorough needs assessment, she found that there

were mixed responses to the device. This result

could be for several reasons, including the few focus

group participants (n¼ 8), and the fact that other

stakeholders such as clinicians and manufacturers

where not part of the focus groups. These efforts

mark a first step toward evidence-based practice of

design and development of mobility devices for

developing countries.

The goal of this study was to build on the work of

Mulholland and colleagues by describing our ap-

proach to and our experience with a research and

design project to develop an electric powered wheel-

chair (EPW) for Indian users. We augmented a

traditional design strategy in several ways to

accommodate the physical distance between the

designers and customers to ensure faithful needs

assessment were performed. We hope that our work

provides guidance for others and encourages design

projects to be documented and the information

disseminated.

Methods

Phase I: concept generation

As an initial step, we worked with an Indian native

who was a visiting researcher in our laboratories, and

asked him to develop a preliminary design brief for

an EPW for Indian users. The brief included several

aspects of the product, including engineering speci-

fications such as geometric size, obstacle climbing

ability and price point. Based on the results of this

brief, we performed several short research projects to

better understand the implications of some the

design specifications, especially related to the re-

quirement that the EPW be very cost effective

(5US$1000), highly manoeuvrable in rough terrain

and highly durable.

Project I.A: motor component-level and system-level

testing. To maintain a low cost for the device, we

planned to use locally available hub motors as the

propulsion source – these are low-cost and widely

available in India. The goal of this project was to

subject a hub-motor supplied by an Indian colla-

borator to international WC durability standards

[28] to assess its performance (Figure 1, Left). After

durability testing was completed, we adapted the

motors to an existing low-cost, highly manoeuvrable

EPW sold in the US to test the feasibility of the

motors (Figure 1, Right).

Project I.B: price-point analysis based on Indian income

levels. To approximate the sensitivity of the EPW

market size to price, we performed an analysis using

the most recent Indian census data [4] to determine

the approximate market share for three prices (in

US$): $500, $750, $1000. We made several assump-

tions. First, we used relative percentage of EPW

users in the US population [29] to predict the

expected overall market size. Second, we assumed

that a family would purchase an EPW if they could

Figure 1. Candidate Motor for EPW being durability tested (left) Hub motor adapted to an Invacare M50 (right).

44 J. Pearlman et al.

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afford financing the device over a 3 year period with

their disposable income. Finally, we assumed that

families eligible for a government subsidy for WCs

[30] would use it to offset the price of the EPW.

Project I.C: material testing of Indian low-carbon steel.

The structural integrity of a WC depends on the

strength and durability of the underlying material.

Engineers typically refer to published material

properties to determine which failure modes are

most likely so they can design accordingly. When

fabricating a prototype for a remote region, it is

important to determine if these published material

properties reflect the properties of the indigenous

materials [31]. To investigate whether these differ-

ences exist, we performed elongation-to-failure and

indentation tests on US and Indian low-carbon steel.

Dog-bone specimens were cut from 2.54 cm tubular

steel and secured to custom clamps fixed to a

uniaxial Instron materials testing machine. Load-

displacement curves were generated with three

specimens of the metal from each country (Figure

2). Indentation tests as well as images of the

microstructure were also recorded. We used de-

scriptive statistics to report the results of this work.

Our design was brief and the results from the

above projects persuaded us to move away from

current EPW designs due to their high component

costs and the unsatisfactory trade-off between dur-

ability and price [32]. Instead, we focused on designs

that would reduce these component costs and still

meet the performance specifications. These costs,

especially in regions where metal fabrication, up-

holstery and assembly are inexpensive, are heavily

weighted toward the electrical components: the

controller, two drive-motors and two batteries. To

limit these expenditures, we constrained our design

to use a single drive motor and require manual

steering, with the option of upgrading to a power

steering system when economically feasible. We also

emphasised locally available components and mate-

rials, when possible, and limited the manufacturing

techniques to those widely available in India. We

named the device the single motor propelled EPW,

or SIMPL-EPW.

Phase II: system-level design, prototype fabrication and

testing

A single engineer (the first author) led the design

process, which was reviewed and discussed in several

informal personal and group meetings with engi-

neers, technicians and clinicians in the US. The

design process was largely unstructured, and the final

design evolved from use of informal sketches, small

mock-ups of the frame and suspension system, and

use of Solidworks to model more complicated

structures of the EPW (such as the steering system).

Several graduate and undergraduate students from

the engineering and rehabilitation sciences assisted

with aspects of the work. The final design was

modelled in Solidworks, and the SIMPL-EPW(1.0)

prototype was fabricated as an operational proof-of-

concept device (rather than a pre-production

model).

To gather feedback about the device, we shipped

the SIMPL-EPW(1.0) to India and performed IRB-

approved focus groups with stakeholders: potential

users, clinicians and manufacturers. These focus

groups were held in New Delhi at the Indian Spinal

Injury Centre during the International Spine &

Spinal Injuries Conference in 2006, and in Kanpur,

at the headquarters of the Artificial Limbs Manu-

facturing Corporation of India. After subjects pro-

vided informed consent for this IRB-approved

protocol, the SIMPL-EPW(1.0) features were de-

scribed and subjects were asked if they would like to

test-drive the device (all agreed). After test-driving

the device, the subjects filled out a questionnaire and

ranked the SIMPL-EPW(1.0) on several factors.

Finally, the subjects answered open-ended questions

in a video-taped interview. We used descriptive

statistics to analyse the results. Based on the mostly

positive feedback, we adopted the basic design, and

advanced to the next design stage.

Phase III: detailed design, prototype II development and

testing

III.A Design upgrades. Two sources of information

were used to guide the design modifications for the

second prototype. First, we catalogued the feedback

from the focus groups held in India which suggestedFigure 2. Dogbone specimen and clamp used for load-deflection

testing of Indian and US steel.

Low cost EPW for India 45

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a redesign of the steering interface, improvements in

the aesthetics and improvements in the performance.

Second, we integrated results from an ethnographic

study we performed in parallel [33], where Indian

WC users took photographs in and around their

homes with disposable cameras and the photos were

incorporated into an online questionnaire. We

recruited WC experts from around the world to

gauge the accessibility barriers, which were portrayed

in a random selection of the (*500) photos. Subjects

were also asked to provide advice on the design

features and specifications necessary for the EPW to

overcome the accessibility barriers portrayed in the

photos. Results from this study were used to guide

design modifications for the second prototype. In

contrast to the first prototype, we fabricated all of the

non-electrical SIMPL-EPW(2.0) components in our

machine shop. We restricted the fabrication tools to

those would be readily available in India to ensure

that the design could be manufactured in low-

volume workshops in India.

III.B Testing. We tested the SIMPL-EPW(2.0) with

users in the US to gather final design feedback before

the India-based testing. We recruited subjects with

EPW experience to use the SIMPL-EPW(2.0) to

perform a series of tasks: enter/exit/operate an

elevator; approach and use a computer at a desk;

approach and use a kitchen sink; enter and leave a

bathroom and drive over rough terrain. After each

task, subjects were asked a series of questions about

the difficulty of completing the task and what design

upgrades could improve the performance of the

SIMPL-EPW(2.0). A final questionnaire was com-

pleted by each subject to rank the SIMPL-EPW(2.0)

on several different features and performance dimen-

sions. The trial was audio-recorded and transcribed

to document all design ideas.

Final design upgrades were performed on the

SIMPL-EPW(2.0) before it was transported to New

Delhi, India. Testing of the device was performed at

ISIC in February – April 2007. We recruited

potential EPW users in an IRB approved comparison

study. After informed consent was given, demo-

graphic information was collected from each subject.

After completing the enrolment, the subject was

scheduled to participate in the study for 2 days within

the span of 1 week. During the first day, we attached

a datalogger [34] to the subject’s manual WC which

non-invasively recorded the distance they traversed

for 3–4 h during their typical daily activities around

ISIC. After the datalogging was completed, the

subject was asked to complete a 100 m obstacle

course (Figure 3), which included both indoor and

outdoor tasks.

Each subject was asked to perform the obstacle

course three times, and the duration of each trial was

recorded using a stopwatch. The researcher provided

assistance to the subjects when requested, and

recorded the number of times assistance was

provided in each trial. After the first and third trial,

the subject completed a questionnaire which had a

series of 14 cm horizontal lines for each task in the

obstacle course. The subject was asked to place a

mark along each line according to how difficult the

task was to accomplish (the left margin being ‘easy’).

The identical protocols were followed for the

second day, although the subject used the SIMPL-

EPW(2.0) rather than their own manual WC for their

daily activity tasks and the obstacle course trials.

Figure 3. Obstacle course layout at ISIC.

46 J. Pearlman et al.

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Most commonly, the researcher met the subject in

the morning and demonstrated the SIMPL-EPW(2.0)

controls and other features. The subject then

transferred into the device and the seating system

was adjusted for comfort. The datalogger was fixed

to the wheel of the SIMPL-EPW(2.0) and the user

was allowed to carry out their daily activity tasks in

the device. In the afternoon (typically after lunch),

the subject would return and navigate through the

obstacle course three times. After completing the

third trial of the obstacle course and required

questionnaires, a final questionnaire was adminis-

tered to gather directed and open-ended feedback

about the SIMPL-EPW(2.0).

We used a two-tailed paired-sample t-test to

determine if the distance the subject travelled during

their daily activities was sensitive to the device used

(SIMPL-EPW(2.0) or their own MWC). Because

normality requirements were not satisfied, we used a

non-parametric Wilcoxon rank-sum [35] to test if

trial duration was sensitive to repeated trials, injury

level or device.

A single researcher used a ruler to measure the

location (in millimeters) of the marks placed by the

user along each of the horizontal lines of the

questionnaire to gauge course difficulty. The data

were digitised and three cumulative ‘difficulty’ scores

were calculated: indoor, outdoor and complete

course. Because of non-normality, we used a

Wilcoxon rank-sum test to determine if there were

significant differences in the perceived difficulty of

the obstacle course between the first and third trials,

which would indicate a learning effect. We also used

a Wilcoxon rank-sum test to determine if the

cumulative scores (total, indoor and outdoor) were

sensitive to the device used and injury level. Finally,

we used Wilcoxon rank-sum tests to determine if the

frequency of required assistance was sensitive to the

device used, injury level, or trial number. In all cases,

if trial number was significant we interpreted it as a

learning effect, and discarded the data from the first

trial, which we considered less reliable.

Results

Phase I: conceptual generation

The preliminary design brief, developed by an Indian

native who is familiar with both EPWs and the built

and un-built environments in India is presented

below (Table II).

Project I.A: motor component-level and system-level

testing. When we performed simulated ISO durability

testing on the same motors, we found that the axle-

strength was not sufficient to sustain the abuse from

ISO testing (Figure 1, Left). We found that the hub

motors were a sufficient replacement for higher-cost

gear motors when we adapted them to an EPW

frame (Figure 1, Right).

Project I.B: price-point analysis based on Indian income

levels. Using target prices of $500, $750 and $1000,

our market analysis predicted the size of the EPW

market in India would be would be 152, 68 and 36

thousand units, respectively. Using the number of

units and sales price, these values indicate the market

could be worth $76, $51 and $36 million US dollars,

respectively.

Project I.C: material testing on Indian low-carbon steel.

We found that Indian steel was significantly weaker

than US steel, and its failure properties were less

predictable (Figure 4). When indentation tests were

performed on the materials, the Indian steel indenta-

tion size was larger than could be classified on

traditional tables. The larger grain size of the Indian

Table II. Initial design brief.

Feature Value Comments

Climbing

angle (min)

128 Ramp angle common

to Indian hospitals

Turning radius 2000 Traditional Indian

House spacing

Ground

clearance

400 Height of road

obstacle

Overall

dimensions

3500 long 2000 wide

Obstacle

climbing

height

500 Sidewalks/

footpath height

Weight capacity 230 lb

Caster size 900 To improve

maneuverability

in rough terrain

Drive wheel size 1600 deep-tread

pneumatic

or gel-filled

To allow for

rough terrain

maneuverability

and traction

Cost $800

Other features Suspension,

modular design

Table I. Drive and control system estimated costs for a scooter,

and an EPW.

Device

Scooter EPW

Controller $50 DC R series $220 DC A series

Drive system $440 Fr PoV

trans-axle and motor

$450 DC EPW motors

Total cost $490 $670

DC, dynamic control; Fr, Fracmo.

Low cost EPW for India 47

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material is the cause of the increased ductility and

reduced strength send in the load-deflection curves.

Phase II: system-level design, prototype I

fabrication and testing

System-level design. A drawback of using a single

motor is that maintaining traction, especially in rough

terrain, requires a unique suspension design. In the

case of a ‘scooter’ design the propulsive force from

the single drive-motor is distributed using a transaxle,

which is a costly component that is not efficient at

distributing propulsive forces. We addressed the

traction problem by using a hub motor as the main

propulsive, braking and turning source, and mount-

ing it on a suspension system which enforces a force-

balance between free-wheeling casters and the hub

motor. As the caster displaces when encountering

rough terrain, force is transferred to the hub-motor

which maintains or increases traction (Figure 5). A

250-watt hub motor (model #280-1342M, Xti Hub

Motor, Rogers, AK, USA) was mounted to a swing-

arm system in the mid-line of the EPW. One end of

the swing-arm pivoted about the large free-wheeling

(back) wheels. The second end of the swing-arm

attached to caster links through a captive spring

system. The caster links pivoted about the uni-strut

frame using a shackle system, and 600 casters where

bolted to caster forks. Load from the user was distri-

buted between the casters and the hub motor nearly

equally. Furthermore, since the force balance must be

maintained, the caster constantly tracks over rough

terrain, maintaining contact with the ground, as well

as applying downward force to the hub motor. The

steering arm projected from one armrest in front of

the user and was operated by either pushing or pulling

the handle. A wigwag throttle was incorporated into

the bottom of the steering arm as the throttle. The

steering arm swung away to allow for transfers.

The frame was built primarily from uni-strut, a

low-carbon steel channel used in commercial build-

ing construction. The seat was borrowed from an old

EPW that we had in our laboratory, and the

controller was adapted from a scooter we had readily

available. The SIMPL-EPW(1.0) (Figure 6) was

completed in January 2006 and shipped to New

Delhi, India. Because of the use of spare parts (seat

and controller), the cost of the prototype was below

$500.

Testing. Twenty-nine subjects (10 consumers, 10

clinicians, 9 manufacturers) participated in the focus

groups and tested the device. User and clinician

feedback was mostly positive about the device

Figure 4. Load-deflection curve of Indian (dashed line) and US steel (solid line), and images of the microstructure and indentation tests

(above).

48 J. Pearlman et al.

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(Figure 7) except for the steering system, which

most consumers found was too stiff. Open-ended

discussions about the steering system suggested it

would be difficult for many users who had trunk-

instability, since they would not be able to both push

and pull the steering arm to turn. Users and clinicians

did not have any strong opinions regarding the

comfort of the EPW and how it compared with other

EPWs they had tried. Manufacturer’s had mixed,

and in some cases, conflicting opinions about the

EPW (Figure 7, horizontal bars). Although the

manufacturers were confident that they could

fabricate and sell the device in India, they thought

the overall price and the components would be

expensive and many would need to be imported.

Manufacturers were generally neutral about whether

they could fabricate the steering system and whether

the EPW had a pleasing appearance and was

comfortable.

Phase III: detailed design, prototype II development and

testing

Using feedback the feedback from Phase II, as well as

information gathered from our camera study [33],

we re-designed and fabricated all parts of the second

prototype (Figure 8). Based on the clinician and user

feedback (Figure 7), we completely redesigned the

steering system to use a handlebar control. This

allows the SIMPL-EPW2.0 to be steered with two

hands (one pulling, one pushing) which helps the

user maintain trunk balance. The mechanism uses

two bicycle brake cables to transmit direction from

the user to the steered hub-motor. A fully retractable

steering arm and armrests allow for unencumbered

Figure 5. System design and free body diagram of SIMPL-EPW suspension system.

Figure 6. Photo of the SIMPL-EPW(1.0).

Low cost EPW for India 49

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transferring into the device, and also provides the

user clear access in front of them when not driving

(Figure 8).

Based on the feedback from the camera study, we

narrowed the base of the WC and reoriented the seat

so that the larger wheels were in the front of the

Figure 7. Median clinician, user and manufacturer responses to final questionnaire during the first set of focus groups.

Figure 8. SIMPL-EPW(2.0) features.

50 J. Pearlman et al.

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device, allowing for better obstacle climbing ability.

Design specifications and performance values are

listed in Table III. A tilting seating system was also

incorporated into the device based on camera study

feedback (Figure 9).

Testing

The five subjects (2 male, 3 female) recruited for the

US focus groups in January 2007, had an average of

14.5 (+16.0) years of experience with wheeled

mobility products. Based on the open-ended feed-

back during each trial, design upgrades were

performed prior to the subsequent testing of the

device. Four primary design adjustments were made

based on subject feedback: the seat was moved

forward relative to the base to increase rearward

stability, the handlebars were extended to increase

the user’s leverage on the steering mechanism, an

optional twist-throttle was added, and a stop was

integrated into the steering arm to limit the travel

when it is flipped out of the way. Feedback on the

final questionnaire from the US subjects (Figure 10,

US Trials) was positive except related to the ease of

steering, the appearance and how intuitive it was to

drive.

Twenty-seven subjects were recruited to partici-

pate in the trials at the Indian Spinal Injuries Center

(ISIC) in New Delhi, India (Table IV).

A total of twenty five subjects completed the study;

after enrolling, two subjects found it difficult to take

time out of their work schedule to visit ISIC for 2

days.) Of the subjects, the majority were inpatients

(19) and the rest were split among outpatients,

employees and non-affiliated individuals. A sum-

mary of the statistical findings is below (Table V).

We found that subjects drove significantly further

when using the EPW for 3–4 h of their daily activities

compared with driving their MWC. We also found

that subjects with tetraplegia needed significantly less

assistance when using the EPW compared with their

MWC; this was not the case for subjects with

paraplegia.

When comparing trial times for the three

repeated trials (with a repeated measures ANO-

VA), and questionnaire responses between the first

and third trial (with a Wilcoxon rank-sum), we

found most variables significantly different regard-

less of the mobility device used (SIMPL-EPW2.0/

MWC) or impairment level (Tetra/Para), suggest-

ing a learning effect. Thus, we performed statistical

analysis only on the results from the third trial,

assuming that the data were approaching a steady

state. When testing the third trial, we found that

subjects with tetraplegia rated the entire obstacle

course as significantly easier with the SIMPL-

EPW2.0 compared with the MWC. Subjects with

paraplegia only found the outdoor portion of the

course significantly easier. Both of these results are

consistent with our hypotheses. We found that

subjects with paraplegia took significantly longer to

complete the obstacle course with the EPW

compared with their MWC.

Final questionnaire results from subjects in India

were in many cases consistent with US subjects

(Figure 10, Indian Trials), although responses from

Indian subject were generally more positive than

their US counterparts. Indian subjects notably rated

the device higher in ‘appearance’ and ‘intuitiveness’

to drive. The open-ended question at the end of the

questionnaire provided insightful design advice.

The most common suggestion was to shorten the

wheelbase to reduce the swinging arc of the rear

casters. Only three of the subjects noted the stiff

steering as an issue. The simple seating system was

well received – 15 of the 25 subjects had no

suggested changes, or praised how comfortable the

seat was. Several subjects suggested a more

supportive footrest. Subjects were generally pleased

with the appearance; 7 subjects suggested different

colours for the frame, and many subjects suggested

add-on features such as a cup holder, cane-holder

and shrouds over the wheels. One subject gener-

ically stated that the ‘style of the WC’ needed to be

improved, and another stated that the steering arm

was ‘ugly’.

Table III. Specifications of the SIMPL-EPW 2.0.

Spec Value Notes

Length, width,

height (cm)

130, 57, 89 Overall dimensions

Mass (kg) 77

Distance on full

charge (km)

43.1

Max speed (m/s) 1.65

Max obstacle climbing

ability (cm)

7.6, 2.5 Forward, rearward

Figure 9. Tilt feature on the SIMPL-EPW2.0.

Low cost EPW for India 51

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Discussion

Phase I: preliminary work

Our preliminary design brief provided a valuable

design goal. Based on this design brief, we

identified the Invacare M50 as our test-bed and

adapted Indian hub motors to the frame for initial

testing. Although there are distinct differences, the

SureStep traction system on the M50 was also an

inspiration for the traction system developed on

our EPW.

Durability issues are prevalent with low-cost

mobility devices in both developed [36–38] and

developing [8,15–17,38] countries. This literature,

and our experience with Indian steel [39] led us to

perform simulated ISO testing on candidate

motors, which revealed premature failure. This

testing helped us rule out particular motors, and

has also become our standard testing approach for

WC components. With the wide range of product

quality of devices being manufactured in China,

Taiwan and other countries, it is important to set

objective standards to ensure quality is met.

Although ISO WC Standards are in place [40],

they do not prescribe component-wise testing

procedures – which are important in the initial

design stages. Because we adapted ISO Section 8

durability testing procedures to component-wise

testing, we believe failures at the component-

level will faithfully reproduce failures at the device

level.

Our preliminary market analysis demonstrated

the price-sensitivity of the market. Although we

made several assumptions to reach our market size,

it is highly likely that our findings are conservative.

First, the census and income values we used [4]

were from 2002. Based on World Bank

(www.worldbank.org) data, India’s population con-

tinues to grow (1.4% in 2005), the economy is

expanding at a rapid rate (8.5% in 2005) and

inflation is kept to relatively low levels (4.2% in

2005) [41]. This indicates that the growing popula-

tion is slowly becoming wealthier, making devices

such as the EPW more affordable, which will

increase the size of the EPW market. In parallel

with population and economic growth, India is

becoming more accessible due to the Persons With

Disabilities (Equal Opportunities, Protection Of

Rights And Full Participation) Act of 1995 (PDA)

[42] and the UN-CRPD. Public and private

transportation such as railway stations, subway

stations and airlines are slowly becoming accessible

to PWD. This increased accessibility will likely

broaden the mobility device market, as more PWD

can become active members of society.

Figure 10. Median responses of subjects to Likert questionnaire in the US and India for Phase III trails.

Table IV. Demographics from phase III India trials.

Parameter Value

Age: mean+SD 20.5 (8.1)

Gender: M, F 20, 7

Impairment: Tetra, Para 9, 18

Months post-injury:

mean+SD

42.5+64.9

Months of experience

with MWC: mean+SD

19+ 28.9

52 J. Pearlman et al.

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Phase II: first-generation design and prototyping and

testing

We designed a unique, low-cost proof-of-concept

design during Phase II. Although costs were kept to a

minimum, there were several drawbacks to using

low-cost uni-strut and parts available EPWs to

develop the first prototype. First, use of uni-strut

required fasteners to secure parts of the frame

together. The fasteners added to the weight of the

device and made it less aesthetically appealing in

comparison to a fully customised welded frame and

seating system. Likewise, the frame and suspension

system were not as structurally stiff as they would

have been if welded, reducing overall performance

(manoeuvrability and obstacle climbing ability).

These effects bias the focus group feedback.

Subject responses to our focus groups in India

were important to evaluate the feasibility of the

device, and reveal important design changes. Most

importantly, we identified the steering system as a

critical design shortcoming. Our initial design was

focused on developing a non-invasive steering

system that could be easily flipped behind the user.

Our first design accomplished this, but also

required the user to steer by pushing (right turn)

or pulling (left turn) on the steering arm. For

individuals with spinal cord injury, depending on

the injury level, there are trunk stability deficits and

reduced function of the triceps muscles; this limits

the individuals ability to pull (due to trunk

instability) and push (due to reduced triceps

function), making it nearly impossible for many

individuals with higher level spinal cord injuries to

drive our first prototype. We rectified this problem

by using a balanced steering system in the second

phase, where users can push and pull simulta-

neously on the handlebar to turn in a single

direction.

We held focus groups with potential manufac-

turers to gauge the manufacturing feasibility.

Although other projects of this type have not

addressed manufacturability directly [26,27], we felt

feedback was necessary with a multi-component

device such as an SIMPL-EPW. The results were

mixed (Figure 7) – although manufacturers agreed

that they could fabricate and sell the EPW, they felt

the components were expensive and would need to

be imported, and that the overall device would not

be affordable. The focus group for manufacturers

was held at the Artificial Limbs Manufacturing

Corporation of India (ALIMCO), a large-scale

manufacturing facility in India, which specialises in

making low-cost AT for the poor in India. Although

the company had initially made overtures about

introducing an EPW in their product line, their focus

is on extremely low cost devices that are built at costs

below government subsidy levels (USD125) [30].

Thus, their response, especially related to afford-

ability, may reflect their company’s bias toward

selling inexpensive, low-tech AT. What was most

important and revealing was their confidence in

being able to fabricate the device using available

materials. Based on more recent information, we

know of several importers of the parts that are not

manufactured domestically (specifically the motor

and controller), which can be purchased, in bulk, for

low costs in India.

Table V. Summary of statistical findings from Phase III India trials.

Parameter MWC EPW Notes

Casual driving* 193.0+98.9 651.4+346.3 Mean+SD m/h

Assists

Tetra* 11 (2,14) 2 (2,4) Median (min, max) averaged values for trial 1& 3

Para 1.5 (0,5) 2.0 (0,3) Median (min, max) averaged values for trial 1& 3

Total course score

Tetra* 815 (69,1194) 206 (29,554) Median (min, max) mm for Trial 3

Para 237.5 (14,720) 200.5 (11,738) Median (min, max) mm for Trial 3

Indoor score

Tetra* 258 (20,495) 152 (16,341) Median (min, max) mm for Trial 3

Para 75.5 (5,371) 139.5 (9,450) Median (min, max) mm for Trial 3

Outdoor score

Tetra* 412 (49,814) 106 (13,213) Median (min, max) mm for Trial 3

Para* 189.5 (4,420) 41 (2,288) Median (min, max) mm for Trial 3

Course time

Tetra 317 (125) 227 (65) Mean+SD seconds for Trial 3

Para* 179 (75) 294 (97) Mean+SD seconds for Trial 3

A * denotes statistical differences between MWC and EPW values. Course scores were normalised from the full range from 0 to 2100 mm to

a scale of 0–100 for clarity. Indoor and outdoor scores do not necessarily add to total scores because medians are reported rather than

averages.

Low cost EPW for India 53

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Phase III: second-generation design, prototyping and

testing

Phase II results and our camera study [33] informed

our design changes, guiding us to improve the

steering and seating and also the dimensions of the

device. Our second device was custom-fabricated,

reducing the number of fasteners and weight. Apart

from the re-designed steering and seating system, we

simplified the suspension system by using leaf

springs in place of the rigid suspension links and

captive spring system on the first prototype. This

design change increased rigidity of the suspension

system, significantly reduced the number of compo-

nents, and was simple and low-cost to fabricate. We

demonstrated the device to two local manufacturers

during focus group testing, and both suggested they

could build the device for approximately $450, and

make a profit if they sold it priced at $550, closely

achieving our goal of a $500 device. Several of the

specifications of the SIMPL-EPW were measured

based on ISO 7176 standards [40] and are shown in

Table III. Specifications of the SIMPL-EPW 2.0

Based on energy consumption tests (ISO 7176

Section 4 [40]), the SIMPL-EPW2.0 can travel a

total of 43.1 km on a single charge (Table III). This

value suggests the SIMPL-EPW can travel, on

average, 48% and 31% further than low-cost [38]

and higher-cost [43] EPWs, respectively. We did not

perform several pertinent tests, such as static stability

(ISO 7176 Section 1) or Static Strength, Impact and

Durability (ISO 7176 Section 8) although this is the

subject of future work.

We had a large subject population in comparison

to similar studies [27,44,45] (n¼ 8–15). Our

breakdown between men and women (Table IV)

(m¼ 74%, w¼ 26%) is similar to the breakdown in

the population of PWD in India (m¼ 62%,

w¼ 38%). A majority of our subjects were inpa-

tients at ISIC, and had recently been injured.

Although all were out of acute care, many had

little experience with MWCs and were propelled

by assistants (regardless of injury level). Although

this is atypical for users in the US and European

countries, data suggests the majority of individuals

do not self-propel their manual WCs [16,17]. This

is due to several reasons, inclusive of, but not

limited to, the poor quality MWCs in India, the

lack of user training, and the low-cost of a personal

assistant (*$2.50/day). We agree that with proper

training and improvements in WC quality (as

suggested by the WHO [3], Chapter 1), MWC

users could be more functionally independent, but

these improvements are likely far in the future.

Meanwhile, the market for WCs is dominated by

low-cost, low-quality hospital style WCs which

limit independent mobility.

The summary of our statistical findings (Table V)

demonstrate several relative improvements when

subjects used the SIMPL-EPW2.0 compared with

their MWC. First, subjects travelled significantly

further, per-hour, when they were driving the

SIMPL-EPW2.0, compared with their MWC. We

attribute a portion of the relative increase (*450 m/

h) on a ‘novelty’ effect of driving a new device.

Regardless, each subject had a daily schedule of tasks

to accomplish (whether it was physical therapy or job-

related tasks), and so drove the EPW more during

their free time. In many cases, the subject would roam

outside, up and down ramps and socialise in wards

that otherwise were difficult to access because they

were not independently mobile in their MWC. In

many cases, their assistant would accompany them

initially during their EPW driving walking behind the

EPW (it cannot be pushed), but in many cases, the

assistant would leave, allowing the subjects to move

unencumbered. Although the comparison between

the distance travelled in the EPW and MWC is

telling, even more telling were the qualitative

observations of the users in the EPW – they seemed

excited to roam outside and speak with others; they

generally seemed happy to be independently mobile,

made positive remarks about the device and com-

monly asked when it would be available for sale.

Comparison between the obstacle course assists,

difficulty ratings and course times were similarly

telling of the EPW performance (Table V). Indivi-

duals with tetraplegia required significantly less

assistance during completion of the obstacle course

and found the course significantly easier to accom-

plish when using the SIMPL-EPW2.0. There were no

significant differences between the course times with

the SIMPL-EPW2.0 and MWC for subject with

tetraplegia. Taken in the context of the significant

reduction in assistance for individuals with tetraplegia

in the SIMPL-EPW2.0 over their MWC, these results

suggest the SIMPL-EPW2.0 effectively replaces a paid

assistant, and makes tasks significantly easier.

We found that subjects with paraplegia felt the

outdoor portion of the obstacle course was signifi-

cantly easier to accomplish with the SIMPL-EPW2.0

compared with their MWC. Although this result may

be surprising, the poor quality of MWCs available in

India and the lack of WC skills training significantly

limit outdoor mobility. This is troubling, considering

nearly 75% of individuals with disabilities live in the

rural environments [4]. We also found that subject

with paraplegia took significantly longer to complete

the course in the SIMPL-EPW2.0 than in their

MWC. The reason for this is likely the indoor speed

at which individuals with paraplegia can complete

the obstacle course in their MWC. The course was

setup in the physiotherapy lab, which is ideally

accessible (except for the bathroom doors, which

54 J. Pearlman et al.

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have spring-closing systems). Most subjects were

very familiar with approaching the desk, sink and

table; and entering the bathroom in their MWC, so

the individual tasks themselves were not demanding.

When using the EPW, the front-wheel drive man-

oeuvrability of the device slowed many subjects

indoors.

Subject feedback on the Likert portion of the final

questionnaire was revealing especially when com-

pared with feedback by the US subjects (Figure 10).

In general, Indian subjects rated the EPW higher

than their US counterparts. All responses from

Indian subjects were positive except for the question

related to ease of steering and attractiveness, which

were rated as ‘neutral’ (neither agree nor disagree).

Despite the issues Indian subjects conveyed with

steering the device (discussed more below), they

found the EPW substantially more intuitive to drive

than the US subjects. The steering system on the

EPW mimics a motorcycle, with a twist throttle and

handlebars. Although motorcycle use is relatively

uncommon in the US, motorcycles and mopeds are

ubiquitous in India. Similarly, low-cost taxis (‘auto-

rickshaws’) are driven with an identical steering and

throttle control system. This is an example of how

the societal differences have a significant effect in the

response to product design [46].

During the Phase II focus groups, the small casters

were located in front of the device. Based on trials

with the seat reversed, we found obstacle-climbing

ability to be much improved when the seat was

reversed, and so the Phase III prototype was

fabricated with the large diameter wheels at the front

of the device. The consequence of this design change

is reflected in the open-ended comments from

subjects on the final questionnaire. By switching

the orientation of the seat, the device manoeuvres

like a front wheel drive EPW, where the device

rotates about a point approximately between the

user’s knees. This gives the sense that the EPW is

very long, since the rear portion of the device swings

in a wide arc during a turn. Given that few of the

subjects had driven an EPW before, especially a

front-wheel drive design, they were more comforta-

ble with how an automobile steers (which is similar

to how a rear wheel drive EPW steers). Thus, the

feedback that the wheelbase should be shortened

from many of the subjects (which was not given when

the seat was reversed), indicates that possibly the seat

should be oriented in its original position. This

original orientation (Figure) also allows for the users’

feet to be placed between the suspension links,

effectively shortening the overall length of the device.

The SIMPL-EPW was designed for an adult

population although there is a tremendous need for

pediatric mobility devices world-wide. Bias towards

the adult population stems the fact that a parallel

design effort is being made to develop a low-cost

pediatric WC for Indian users. Since the SIMPL-

EPW is a ‘power-base’ EPW [47,48] the design does

not prohibit placing a seating system appropriate for

pediatric clients. Adapting the product for pediatric

clients is the subject of future work.

Conclusions

PWD deserve high quality mobility devices so they

can be more independent and participate more fully

in society. Already implemented [42] and upcoming

[7] policies in developing countries will help in this

vein, but there are still substantial technological

challenges to overcome that will ensure devices meet

the social, economic and technical constraints in

developing countries. To leverage the skills of

rehabilitation specialist and engineers world-wide,

along with the growing interest among students to

participate in international development projects, it

is important to build a wider body of published

experience-based knowledge of the research and

design approaches that are successful and unsuccess-

ful in these countries; this will help avoid situations

like the repeated failures of MWCs technology

transfer to meet the needs in developing countries

[1,8,38].

The project described here has been successful in

developing a low-cost appropriate EPW for indivi-

duals in India. The device will likely be appropriate

in many developing countries, with slight design

changes to accommodate the parts and materials,

which are locally available. Despite the strong

performance of our design, a more comprehensive

engineering analysis could have been performed to

optimise the steering and obstacle climbing ability of

the device prior to user trials. We plan to perform

this analysis for the next prototype.

To complete the project, we plan to perform in-

home trials of the SIMPL-EPW2.0 after design

modifications have been integrated based on our

Phase III results. We may perform these trials

independently, although we feel that it is best to

collaborate with a manufacturer to fabricate the

prototype device so that user-feedback can be

integrated directly into the product design cycle.

Acknowledgements

This work was supported by the grants from the

National Science Foundation (EEC 0552351 and

DGE0333420). We gratefully acknowledge the

clinical staff (Annmarie Kelleher, Emily Teodorski,

Rosemarie Cooper), technical staff (Jeremy Puhl-

man, Mark McCartney) past students (Neil Stegall,

Low cost EPW for India 55

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Mary Wu, Amy McNeal and Jaideep Karnawat)

and our India-based support (Nekram Upadhyay

and Jyoti Vidhani) who helped make this project

successful.

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