world
M. BOLLINIa,1
aDepartment of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02142
Abstract. The Figure-Eight Drive is a novel handcycle drivetrain designed specifically for the developing world. Utilizing a retro-direct chain configuration, the system offers users two forward motion gear ratios that can be switched between by changing the direction of pedaling. Movement in the reverse direction can be achieved by rotating the steering column 180 degrees. The drivetrain was designed at the Massachusetts of Institute of Technology and was successfully implemented and tested during the summer of 2007 at the Association for the Physically Disabled of Kenya in Nairobi, Kenya, where it is now in production.
The Figure-Eight Drive can be constructed entirely out of conventional bicycle components already found on handcycles across the developing world. It has been well received by handcycle users and manufacturers because of its simplicity, low-cost, and significant improvement in mobility and usability compared to current single speed and derailleur handcycles currently in production.
Keywords. handcycles, developing countries, mobility.
1. Introduction
While wheelchairs are ubiquitous in the western world, they are biomechanically inefficient [1] and are difficult to operate over rough terrain and long distances. Instead of wheelchairs, the disabled in developing countries frequently use locally designed and manufactured handcycles as their primary means of ambulation. While these handcycles offer a significant biomechanical advantage over wheelchairs, they are frequently available only in single-speed configurations. This single gear makes it impossible for users to navigate hilly terrain. While multi-geared systems that make use of bicycle derailleurs are available, these systems are uncommon because they are expensive, fragile, and difficult to use while using the arms to pedal and steer. The Figure-Eight Drive is an implementation of a retro-direct bicycle drivetrain that allows users to change between two gears, one high and one low, simply by changing the direction of their pedaling. Both directions result in forward motion, providing users with a simple and robust two-speed drivetrain.
1 Corresponding Author: Mario Bollini, [email protected] Rehabilitation: Mobility, Exercise and Sports
L.H.V. van der Woude et al. (Eds.) IOS Press, 2010
© 2010 The authors and IOS Press. All rights reserved.
doi:10.3233/978-1-60750-080-3-91
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2. Design
The Figure-Eight Drive was designed during the spring of 2007 at the Massachusetts Institute of Technology by the biomechanics group of the class Wheelchair Design for Developing Countries. The system utilizes two bicycle chains, one in a loop such as a chain found on standard single speed handcycles and another in a figure-eight loop on the opposite side of the steering column. The chain in the standard loop (henceforth to be referred to as the O-side chain) is looped around a bicycle crank at the top of drivetrain, and around a standard freewheel at the bottom wheel hub. The figure-eight chain (henceforth to be referred to as the 8-side chain) is looped around a reverse-mounted freewheel at the top of the drivetrain near the pedals, and around a forwards-mounted freewheel at the bottom wheel hub. The slack side of the 8-side chain is passed through a steel tube to prevent it from grinding against the return chain. Figure 1 shows the chain and freewheel configurations.
Figure 1. The freewheel mounted at the top of the 8-side chain near the pedals is in the reverse direction, while both freewheels near the wheel are in the forwards direction. The chain on the right hand side of the image, the 8-side chain, is in a figure-eight loop.
When pedaling forwards, the O-side chain engages, driving the tricycle forwards just as it would on a single-speed handcycle. The freewheel at the top of the 8-side chain ratchets and does not engage, leaving the 8-side chain stationary. This is the high gear of the Figure-Eight Drive. When pedaling backwards, the O-side chain freewheels, just as one’s bicycle chain freewheels when one pedals backwards on bicycle. The freewheel on the top of the 8-side chain, however, engages and drives the 8-side chain backwards. Because this chain is in a figure-eight loop, the backwards motion of the chain drives the handcycle forwards. This is the low gear of the Figure-Eight Drive. Thus the drivetrain offers users one high and one low gear, switch able between simply by changing the direction of pedaling.
While the two chain solution allows users to ambulate and coast in the forward direction, the chains lock when the drive wheel rotates backwards, meaning that users cannot move in the reverse direction. Though this is convenient in that one can remove one’s hands from the pedals while climbing without fear of rolling backwards down the hill, it dramatically reduces the mobility of the handcycle. In order to allow users to
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move their handcycles in reverse, the fork was designed to allow the steering column to be rotated 180 degrees, allowing users to both freewheel and ambulate backwards.
3. Development and testing
A proof-of-concept prototype was constructed at MIT in order to validate the design.
During the summer of 2007, the author traveled to Nairobi, Kenya to implement and test the drivetrain at the Association of the Physically Disabled of Kenya (APDK). The prototype was developed through four generations. The final version of the prototype was constructed entirely out of stock bicycle components and required no machined parts, adding approximately $3 to the $200 cost APDK’s existing single-speed handcycle.
The prototype was tested by numerous handcycle users on and around the APDK campus. It was preferred over existing single and multiple speed derailleur based handcycles for its ease of use and its wide gear ratio range, which allowed users to both travel quickly over flat terrain and to climb hills easily. The ability of the handcycle to move in reverse via the pedal-drivetrain was also appreciated by handcycle users. In addition on on-site testing, four models of the final Figure Eight Drive prototype were constructed and given to handcycle users for long duration usability and durability testing. After over six months of use, no negative feedback was received.
4. Results and conclusion
In September of 2007, APDK presented the Figure-Eight Drive at the Pan African Wheelchair Congress in Arusha, Tanzania. It was extremely well received; over 100 compact disks containing manufacturing instructions were distributed to interested African wheelchair and handcycle manufacturers. The Figure-Eight Drive has also been manufactured locally Tanzania and the Philippines. The Figure-Eight Drive is currently being produced and sold in Kenya by APDK.
The Figure-Eight Drive has proven to be an effective replacement for both single and multi geared handcycle systems. It allows users to travel over terrain that is impossible to traverse with single speed handcycles. It is cheaper to manufacture, easier to use, and significantly more robust than current derailleur based handcycles.
User feedback continues to be extremely positive, demonstrating the system’s ability to meet user needs better than current systems. The Figure-Eight Drive is constructed using materials and manufacturing techniques that are ubiquitous across the developing world, making it an accessible mobility solution for handcycle users worldwide.
References
[1] L.H.V. van der Woude et al., Wheelchair ergonomics and physiological testing of prototypes, Ergonomics 12 (1986), 1561-1573.
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