Redesign of a human powered battery charger for use in Mali

Abstract

The design for a human powered battery charger was analyzed and a redesign was proposed. The original product was designed in the MIT ME course 2.009 to power a LED projector that will be used to teach literacy classes in Mali. The goals of the new design are to decrease the cost and usability of the alpha prototype, producing a minimum of 60W that is required to provide a 10:1 use to charge ratio for the 6W projector. The alpha prototype utilizes a modified rowing motion to move a device produces power through a constant force spring, a small motor. A voltage regulator safely charges the battery using the voltage output of the motor. The rowing motion requires a number of moving parts and expensive components and although the complex motion combines the power available from the leg and arm muscles, the movement is not simple to understand or particularly comfortable to use. A model was created to test a proposed redesign that simplifies the product in several areas. The new design will use the arm muscles only to provide the necessary power and will avoid costs by making the charger a stationary product. The model is made of a recoil spring and pulley mechanism mounted to a freewheel, which turns a shaft and flywheel. The shaft would then be connected to a motor to charge the battery in a similar manner to that of the alpha prototype.

(cont.) The experiments performed and calculations on the model provided information that suggests that a flywheel based design does provide sufficient power for a 60W output. Further research will be needed to accurately ascertain the cost of a product and whether it can be manufactured for under $50. Preliminary analysis suggests that it is possible to meet both the cost and power requirements of the product.