Off-Road Wheelchair Helps People with Disabilities Get Off-Road and On With Their Lives (Op-Ed)

The Leveraged Freedom Chair, technology — The Leveraged Freedom Chair serving an early adopter of the technology.

(Image credit: MIT.)

Amos Winter is an assistant professor in the Department of Mechanical Engineering at the Massachusetts Institute of Technology, a member of the American Society of Mechanical Engineers (ASME), and a participant in ASME's Engineering for Global Development Committee. This Op-Ed was adapted from an article that originally appeared in Demand, a publication of ASME. ASME contributed this article to LiveScience's Expert Voices: Op-Ed & Insights.

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 with curb cuts. The goal is for people with mobility-based disabilities to have as much independent access to those 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 for people with disabilities, their ability to support themselves is restricted.

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The idea behind the Leveraged Freedom Chair (LFC) that my colleagues and I developed 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 the solution.

The technology evolved into a tractable and viable product because our team engaged stakeholders who 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, manufacturers 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. Stakeholders 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. [NIH Funds Robotics Projects To Help Disabled ]

Many currently available mobility 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 each purchase. Our team also made the LFC's seat and footrest adjustable and offer the chair in three different widths to accommodate varying user size and meets World Health Organization standards. Another important aspect of the design is that all of the LFC's moving parts are from bicycle components, so the chair can be repaired by local bicycle technicians familiar in rural and urban communities in developing countries.

The LFC is a three-wheeled wheelchair propelled through a lever-powered drivetrain. Instead of using multiple gears to change speed, a 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. Our team used human power and force output capabilitiesto determine a lever size and drivetrain geometry that enables the users 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, means the LFC drivetrain can 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 $20 and are commonly found in the developing world. To put this performance/cost ratio 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 USD.

The LFC weighs 21.4 kg (47 lbs.), which is within 2.3 kg (5 lbs.) 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 5 kg (11 lbs.). Our team reduced the weight through judicious use of steel in the frame, optimizing strength to weight of the components, making the seat subframe a fully triangular-trussed structure, and using lightweight clamps to connect the seat to the lower subframe.

The lever pivots are built directly into the seat pan to support the greater than 204 kg (450 lbs.) peak chain tension, the highest loads we expect the chair to experience. The LFC frame was designed to support over 600 kg (1,300 lbs.) in the seat, corresponding to a 6X factor of safety compared to static loading. We chose this safety factor because the front tube of the frame could bend and fail, potentially resulting 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 wobbly table with one short leg.

These initial 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 the original design was that the user could climb over obstacles with 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 to put the big wheels in back for indoor use, similar to a conventional wheelchair.

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, because the rear wheel would tend to swing around to the front, and on side slopes, the uphill drive wheel tended to lose traction. This prototype was a failure, but it did provide 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.

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 (65 lbs.), it was at least 9.1 kg (20 lbs.) heavier than other developing world wheelchairs on the market.

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 8.9 cm (3.5 in.), making it 68.6 cm (27 in.) wide, which is approximately 1.3 cm (0.5 in) 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 we used on the East African LFC. Backwards tipping stability was improved by lowering the center of gravity by 12.7 cm (5 in). A back pad 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 20.4 kg (45 lbs.), 9.1 kg (20 lbs.) 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 (2.55 mph), 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 them 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 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 providing assistive devices. 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 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 12.7 cm (5 in) 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, our team implemented an LFC training program. 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 2.7 km (1.7 mi.) 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 (2.04 mph) 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. We have since incorporated a storage bag that hangs behind the seat into the product.

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 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, we might have needed many more iterations to achieve the necessary performance, manufacture, repairability and cost specifications for the LFC.

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.