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Controller & modification of a light hub-motor propelled electric wheelchair
Matthews, Alistair Marc
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Due to the complex design of existing electric mobility vehicles in South Africa and their imported parts, make them unaffordable to the majority of disabled people in South Africa. The traditional electric units are also not practical for use in rural areas due to the heavy, bulky design. The scope of this study was to investigate various designs using existing wheelchair frame designs, low cost three phase hub motors and various electronic techniques to achieve the desired functionality. An attempt was be made to remove inefficient and expensive DC brush motors and the gear boxes associated with the traditional design of wheelchairs, while still allowing the unit to fold like the traditional manual chair design. One of the aims for this electric wheelchair was to utilise existing large radius wheels, typical of manual wheelchairs and a modified traditional frame design, providing the clearance often necessary to overcome rough terrain whilst enabling the chair to be used as a manual wheelchair should the battery fail. One of the primary aims of the project was to develop a method for an electric assist feature built into the modified electric wheelchair, whereby the force applied to the manual pushrims on the wheels would be measured and the electric component would proportionally assist the user. This option suits the users who are weak but not physically disabled. One of the many focal points here would be on HIV/AIDS patients, which is prevalent in South Africa, who may require a wheelchair when debilitated with this disease. The electric assist portion of the design would act similarly to a wireless self-powered torque sensor, allowing for an array of applications besides the electric assist portion of this project. A recent survey by National Government indicated that over 85% of wheelchair users only generated an income of between R0 – R500 per month. Low state disability grants and wage figures for disabled and HIV/AIDS patients mean that electric mobility vehicles have become a luxury rather than an essential commodity in South Africa. The need for cheap electric wheelchairs that could cope with the rural terrain and could be fitted onto existing manual wheelchairs offering the full manual operation should the batteries go flat, was clearly apparent. The cost of an electric wheelchair ranges from R18 000 with more advanced models escalating in price to well over R150 000. These prices were typically the result of the complexity of the unit and local wheelchair manufacturers having to import 80% of their parts from abroad. The largest local manufacturer is CE Mobility which is the dominant mobility vehicle supplier in Southern Africa and has the only SABS approved units for sale. Our complete redesigned wheelchair including the manual frame supplied by an existing supplier would only cost R9 000. A prototype demonstrated that is was possible to build a wheelchair that meets all these criteria. A cost effective unit could provide a solution to assist and enable economically challenged and disabled people in rural areas of Southern Africa.