PEDAL POWER selections from: Understanding Pedal Power , by David Gordon Wilson Published by Volunteers in Technical Assistance: "VITA is a private, nonprofit organization that supports people working on technical problems in developing countries. VITA offers information and assistance aimed at helping individuals and groups to select and implement technologies appropriate to their situations. VITA maintains an international Inquiry Service, a specialized documentation center, and a computerized roster of volunteer technical consultants; manages long-term field projects; and publishes a variety of technical manuals and papers." "The power levels that a human being can produce through pedaling depend on how strong the pedaler is and on how long he or she needs to pedal. If the task to be powered will continue for hours at a time, 75 watts mechanical power is generally considered the limit for a larger, healthy non-athlete. A healthy athletic person of the same build might produce up to twice this amount. A person who is smaller and less well nourished, but not ill, would produce less; the estimate for such a person should probably be 50 watts for the same kind of power production over an extended period. A simple rule is that most people engaged in delivering power continuously for an hour or more will be most efficient when pedaling in the range of 50 to 70 revolutions per minute (rpm). For simplicity's sake, we will use 60 rpm, or one revolution of the pedal cranks per second, as an easy reference value for estimates of the gear ratios required to drive a given load. Broadly speaking, applications of pedal power are possible when the power level required is below a quarter of a horsepower (that is, below about 200 watts). Common applications of stationary pedal power include pumping water, grinding grains or metals, shredding, or threshing. Pedal power can also be used to generate electricity for individual uses--to operate room lights, a television set, or a projector, for example. Surplus power could be diverted to a battery-charging circuit. The easiest way to do this is simply to drive either a DC generator or an AC alternator through a circuit feeding a battery in parallel with the load. The same circuit could be used for an alternator of higher power, chain-driven from the cranks, through an appropriate gear ratio. Other pedal power applications include: o Cassava graters The Dynapod Bicycles can sometimes be adapted to drive the devices mentioned above, but the result is often inefficient. It is frequently cheaper in initial and maintenance costs to use a properly designed and constructed dynapod. There are three kinds of dynapods: 1) A one-person dynapod that utilizes belt drive. It can be built either with or without chain drive. 2) A two-person dynapod that can be pedaled either by one person at a time, or by two people together. It is also possible to fit a special adaptor so that a direct shaft drive leads off the unit and powers a flour mill or other machine. (When this is done, only one person can pedal at a time.) 3) A one-person dynapod that has belt drive, chain drive, and direct drive. It is very similar to the two-person dynapod. The two-person dynapod ... has been attached to a grain mill, but the unit can be adapted to a wide variety of uses. The dynapod frame can be made of wood or welded steel, depending on cost and availability of materials.A heavily weighted flywheel provides extra power and smoothes out the pedal stroke, reducing operator fatigue. A similar device, designed to draw irrigation water from shallow wells in Bangladesh, consists of a welded steel frame with a drive wheel attached to the plunger of a handpump." |