In the United States and other developed nations, much of the built environment is designed to accommodate people in wheelchairs. Most locations in urban areas are accessible via modest-grade ramps and smooth sidewalks possessing curb cuts. The goal is for people with mobility-based disabilities to have as much independent access to these locations as possible.
The reality is much different for the 20 million to 40 million people in the developing world who require the use of a wheelchair. Paved roads and sidewalks are often non-existent, and in many cases locations are linked only by a network of rough or muddy footpaths. In such conditions, a conventional wheelchair provides only limited mobility and the ability for people with disabilities to help support themselves is restricted.
The idea behind the Leveraged Freedom Chair (LFC) was conceived—and the technology evolved—through field trials in East Africa, Vietnam, Guatemala, and India. The LFC project is an example of stakeholder-driven innovation. That is, our partners in developing countries did not simply articulate their needs, but they participated in the entire design process in order to identify and then create solutions as well.
The technology was directed towards a tractable and viable product by engaging stakeholders that represent each link in the chain from inception of an idea to its implementation in the real world. These included end users of course, but also part suppliers, manufactures, and distributors of wheelchairs in developing countries. Stakeholders were integral in identifying design failures, such as our first prototype, which was heavy, unstable and awkward to get into. They also deserve credit for many of the design elements that make the current LFC a viable product, such as its low center of gravity and compact/maneuverable form.
When conceiving the project, we started with the notion of creating a product that could meet the mobility needs—both indoor and outdoor—of people with disabilities in the developing world. There is great demand for a device like the LFC because many people living in rural areas must traverse rough roads and muddy walking paths to find connections to community, employment and education.
The LFC fills an important niche in the developing world mobility aid market because many currently available products are limited in their capability. The most common mobility aids in the developing world are conventional, pushrim-propelled wheelchairs and hand-powered tricycles. Pushrim-propelled wheelchairs are inefficient to propel and are exhausting to use for long distances on rough roads. Hand-powered tricycles, which are often preferred by users if they have adequate torso stability, are more efficient to propel than a wheelchair, but are difficult to maneuver on soft ground and up steep hills. They are also much too large to use inside the home.
The LFC combines the salient features of chairs currently on the market with multiple features modified or added as the result of field trials, such as a back pad to improve tipping stability, Velcro straps for extra security, and instructional lessons on how to use the chair that are included with purchase. We also made the LFC’s seat and footrest adjustable and offer the chair in three different widths to accommodate varying user size and meet World Health Organization Standards. One important aspect of the design was the decision to make all of the LFC’s moving parts from bicycle components, so that the chair can be repaired by local bicycle technicians commonly found in rural and urban areas of developing countries.
Form and Function
The LFC is a three-wheeled wheelchair that is propelled through a lever-powered drivetrain. Instead of using multiple gears to change speed, the LFC user varies mechanical advantage by sliding his or her hands up and down the levers. Pushing forward on the levers propels the chair through a single-speed assembly of bicycle components; pulling back ratchets the drivetrain and resets it for the next stroke. Pulling all the way back engages the brakes, which are the small bars that protrude from the levers and rub against the tires. Human power and force output capabilities were used to determine a lever size and drivetrain geometry that enables the user to efficiently travel on smooth surfaces and gentle grades, and produce enough torque to overcome harsh terrain.
Varying mechanical advantage by changing the user’s geometry (i.e., hand position on the levers), rather than the machine’s geometry, allows the LFC drivetrain to be built from a lightweight, single-gear ratio chain drive made from bicycle components. These components provide a 3:1 change in mechanical advantage, cost less than US$20 and are commonly found in the developing world. To put this performance/cost ration into perspective, top-of-the-line Shimano XTR mountain bike components provide a 6:1 change in mechanical advantage, but cost more than $1,500.
The price of the LFC, when produced in India and sold in bulk, is $200, while a single LFC is $250. This price point is within the same range of the most commonly distributed wheelchairs in developing countries and is 25 to 30 times less expensive than off-road wheelchairs with similar capabilities offered in the developed world.
The LFC weighs 21.4kg , which is within 2.3kg of other manual wheelchairs available in the developing world. Achieving this weight was a challenge, as the drivetrain alone (which includes the levers, chainrings/couplings, freewheels, chains, axles and bearings) weighs 5kg. The weight was reduced through judicious use of steel in the frame by optimizing strength to weight of the members, making the seat sub-frame a fully triangular-trussed structure, and using lightweight clamps to connect the seat to the lower sub-frame.
The lever pivots are built directly into the seat pan to support the greater than 204kg peak chain tension, the highest loads commonly experienced by the chair. The LFC frame was designed to support over 600kg in the seat, corresponding to a 6x factor of safety compared to static loading. This safety factor was chosen by taking into consideration the fact that the front tube would principally fail in bending; that failure could result in injury to the rider; and that 6x static loading on the front wheel is conservative, as impacts, such as drops off curbs, are absorbed primarily by the rear wheels.
The LFC was built on a three-wheeled platform to enhance its mobility on rough terrain. This layout was inspired by a three-wheel model developed by the international disability charity, Motivation. The long wheelbase reduces load on the front wheel, which combined with its large diameter enables it to roll over obstacles more easily than smaller casters placed closer to the rear wheels—such a layout is found on conventional four-wheeled wheelchairs. The LFC’s three-wheeled layout makes it kinematically constrained with the ground. That means that no matter how rugged the terrain may be the three wheels provide three points of contact. On rough ground, four-wheeled chairs can be less stable than those with three wheels as one of the wheels can lift off the ground, similar to a tippy table with one short leg.
For indoor use, the levers on the LFC can be removed and stowed in the frame, which converts the chair to a regular, pushrim-propelled wheelchair.
Driven by Feedback
The first field trial of a prototype LFC was conducted during the summer of 2008 with the chair. These LFCs were made and tested with the Association for the Physically Disabled of Kenya (APDK) in Nairobi; Mobility Care in Arusha, Tanzania; and Kien Tuong in Ho Chi Minh City, Vietnam. The tests were informal. They lasted only a few minutes and were performed by technicians on the terrain surrounding the wheelchair workshops where the prototypes were built. The intent behind this design was that the user could climb over obstacles with the large front wheels and maintain a stable position with a low center of gravity. Our thought was that future iterations would have a swiveling seat and to put the big wheels in back for indoor use, similar to a conventional wheelchair.
The first prototype was a failure, but by engaging stakeholders, we were able to discover flaws early and to iterate to improve the design.
We knew going in that the prototype would need some improvements. The consensus from the testing showed that the prototype would not work—it was awkward to transfer into and was much too heavy to be viable in the field. The chair would become unstable when going downhill, plus because the rear wheel would tend to swing around to the front. On side slopes, the uphill drive wheel tended to lose traction. This prototype was a failure, but it did provided a valuable lesson to the design team. We learned that by engaging stakeholders we were able to discover flaws early and were able to iterate to improve the design.
Together with partners in East Africa, our team designed the next iteration of the LFC. Six of these prototypes were produced with the Association for the Physically Disabled of Kenya (APDK). One chair was tested in Tanzania, one in Uganda, and the remaining four in Kenya. The trial ran from August 2009 to January 2010.
Although the chair received positive reviews on rough terrain, the six subjects felt the LFC was too wide to be used indoors. This feedback made our team realize that the chair had to be a viable conventional wheelchair when the levers are removed, as the levers would typically be used only for an hour or two per day during long distance travel. The second concern, which was raised by five of the East African test subjects, was that the LFC tipped backwards too easily and felt precarious when going up hills. The final problem was that the LFC was too heavy. At 30kg, it was at least 9.1kg heavier than other developing world wheelchairs on the market.
Changes Were Made
The Guatemala LFC was designed in collaboration with our East African partners and the Transitions Foundation of Guatemala. Changes were implemented to rectify the issues raised in the East African trial. The width of the chair was reduced by 8.9cm, making it 68.6cm wide, which is approximately 1.3cm narrower than a hospital chair of the same seat size. This was accomplished by tapering the seat, putting jogs in the levers and using narrower tires than were used on the East African LFC. Backwards tipping stability was improved by lowering the center of gravity by 12.7cm. A back pad behind the user's shoulder blades was also added to improve tipping stability. This pad acts like a bench-press bench, providing a reaction force against the user’s spinal column when he or she pushes on the levers, and thus preventing the user’s torso from bending backwards over the seat. The mass of the Guatemala LFC was 20.4kg—9.1kg lower than that of the East African chair.
Twelve Guatemala LFC prototypes built by Transitions were tested around Antigua, Guatemala, from November 2010 to January 2011. The test subjects rated the chair’s indoor performance nearly as highly as conventional wheelchairs. On an average daily commute on a rough village road the LFC averaged 1.14 m/s—81 percent faster than a conventional wheelchair. Qualitative feedback about the LFC’s comparable performance was not as compelling, presumably due to shortcomings in the design. Many subjects in the trial, particularly those who had sustained spinal cord injuries, wanted to be secured to the chair with straps to prevent from being pulled out of the seat when pulling back on the levers to apply the brakes while rolling downhill. Three of the 12 subjects requested that straps be standard in future versions of the chair. Five subjects suggested that the parking brakes be moved to a new position because the levers could hit them when propelling vigorously.
The most common suggestion from the Guatemala trial, which was voiced by six subjects, was that recipients should be trained on how to use it.
The Final Trial
The LFC was brought to India for its final trial, which was run in collaboration with Bhagwan Mahaveer Viklang Sahayata Samiti (BMVSS—commonly known as Jaipur Foot), the largest disability organization in the world in terms of assistive devices provision BMVSS, was chosen as a partner because of its ability to scale up distribution of the LFC as well as its reputation as a leader in assistive device provision in the developing world. BMVSS facilitated a relationship with a production partner, Pinnacle Industries, an original equipment manufacturer of truck and bus seats—products similar in construction to a wheelchair.
The most common suggestion from the Guatemala trial was that recipients should be trained on how to use the chair.
The India LFC design addresses the critical feedback expressed by subjects in the Guatemala trial. Chest, waist and foot straps made of Velcro were added as standard features to the chair. The parking brakes were lowered by 12.7cm to allow for a larger stroke while still preventing the levers from hitting the ground in the event they were dropped by the user. Additionally, a training program was implemented on how to use the LFC. Each subject received more than two hours of instruction, including skills to cope with obstacles, before he or she took the chair home. The World Health Organization’s “Guidelines for the Provision of Manual Wheelchairs in Less-Resourced Settings” includes training as a critical part of appropriate wheelchair provision.
Twenty-four India LFC prototypes were tested throughout the country from May to October 2011. Data from these tests showed that the LFC performed nearly as well as conventional wheelchairs indoors, and provided drastic advantages on rough terrains. Eleven of the trial subjects were full-time wheelchair users, and 10 of them switched to the LFC as their primary mobility aid. These people traveled an average of 2.7km per day using the LFC. Conversely, using a conventional wheelchair, none were able to leave their home without the assistance of a family member. Four of these people were able to gain employment because of their newfound mobility.
Seven of the full-time wheelchair users in the trial underwent biomechanical testing and were able to average 0.91 m/s using an LFC during a common daily commute on their home terrain. This was 50 percent faster than what they could achieve with a conventional wheelchair.
The most common feedback following the India trial, voiced by seven of the subjects, was that the LFC should have cargo space. A storage bag that hangs behind the seat has since been incorporated into the product.
The Power of the Customer
Stakeholder input drove the evolution of the LFC, and with each design iteration performance was improved. Furthermore, the number and complexity of requested design revisions decreased with every trial. The relatively minor requests for upgrades following the India trial indicated that the LFC design was sound and perhaps even ready for commercialization.
The importance of the active participation of all the stakeholders cannot be overemphasized in the development of the LFC. The stakeholders represent each link in the chain from inception of an idea to its implementation in the real world. The diagram above illustrates the importance of stakeholder involvement. The inner circle of the diagram shows the stages through which a technology matures; the outer circle represents the stakeholders best positioned to advance the technology through each stage.
The LFC successfully came to market because the outer stakeholder circle was fully represented in the project; each group had the opportunity to express requirements, constraints, and insight for driving the technology towards implementation in the real world. This design process, including identifying customer and stakeholder needs, is similar to commonly accepted product design practices, as well as
methods aimed specifically at creating developing world technologies, with a few notable exceptions.
Representatives from the various stakeholder groups in the outer ring of the diagram were engaged concurrently during the development of the LFC. This approach enabled our team to understand the most important constraints and requirements associated with an improved rural area mobility aid. End users expressed a desire to travel long distances on rough terrain and navigate tight, indoor confines. Manufacturers such as Pinnacle, as well as APDK and Transitions, added design elements to improve production and identified that custom parts are difficult to repair or replace in the field—which we solved with the use of bicycle components. Wheelchair distributors, represented by APDK, Transitions, and BMVSS, set the price point of approximately $200, which makes the LFC competitively priced and the same cost to donors as other wheelchairs on the market.
If these requirements were revealed in a linear fashion, as the technology moved from prototype to product, many more iterations may have been required to achieve the necessary performance, manufacture, repairability and cost specifications for the LFC.
The importance of active stakeholder participation cannot be overemphasized. The stakeholders represent each link in the chain from inception of an idea to its implementation in the real world.
Also unique in the design process are the positions of academics and technology transfer firms. With the support of the Massachusetts Institute of Technology, the Singapore University of Technology and Design, and the Indian Institute of Technology Delhi, our team had the resources to innovate, test and iterate quickly. But the outputs of academic projects are typically proof-of-concept prototypes, not products ready for commercialization.
To bridge the gap between academia and industry, it was necessary to form a start-up, Global Research Innovation and Technology (GRIT), and engage the help of the Boston-based product development firm Continuum. These stakeholders were able to perform functions critical to bringing a product to market, such as design for manufacturing, quality control, and packaging. Our team also received frequent and valuable mentorship from Whirlwind Wheelchair International, an organization that has been designing and distributing developing-world wheelchairs for more than 30 years.
The LFC shows that the development and implementation cycle starts and ends with end users—the people best positioned to articulate a need and validate a solution. Navigating differences in culture, demographics and geography can be tricky, but it is critical for those of us creating technologies for developing countries and emerging markets to utilize stakeholder-driven innovation. We need to recognize end users—as well as all the other stakeholders of a technology—as part of our team in order to create a product that truly works on the ground.
This case study was written by Amos Winter. Amos is the Robert N. Noyce Career Development Assistant Professor in the Department of Mechanical Engineering at MIT. His work focuses on the marriage of mechanical design theory and user-centered product design for emerging markets and developing countries. He is the principal inventor of the Leveraged Freedom Chair. He is also a founder of Global Research Innovation and Technology.