Job S. Ebenezer, Ph.D.
President, Technology for the Poor,
877 PELHAM COURT, WESTERVILLE, OHIO - 43081
The original Savonius design called
for a 7 to 8 inch overlap of the buckets. Research at Sandia Laboratories,
however, suggested an overlap of 10 to 15% of the bucket diameter or in this
case 3 inches (the bucket diameter=23 inches).
The second modification was the use of an automobile differential at the bottom of the machine to convert the vertical shaft power of the rotor to horizontal shaft power. A water pump or grain grinder could then be connected to the horizontal shaft either directly or via chain or V belt arrangements. The vertical main shaft of the wind machine was connected to the driveshaft of the differential., and one axle shaft of the differential became the horizontal power take off shaft for the wind machine. The other axle shaft was removed and the slip gears were locked. The gear ratio offered by this arrangement was 3:1, i.e. for every three turns of the wind machine's main shaft, the horizontal shaft turned once. This arrangement provided a high torque, low speed power to run a chain pump and a grain mill. A simple brake mechanism was provided to stop the machine in high winds.
A chain pump was constructed using a design proposed by Volunteers in Technical Assistance (VITA). A drawing of the chain pump constructed is shown below. In order to prevent corrosion of the metal chain, short lengths of nylon ropes were substituted for the lengths of chain between each leather washer. This substitution;. however, proved to be unsatisfactory
as there was much binding and
misalignment of the washers as they ascended the pipe. It is suggested that the
metal links should not be replaced by light weight ropes as the weight of the
links keep the washers taught and aligned well. Aside from these alignment
problems, the Savonius machine performed well. The Brace Research Institute in
Canada has successfully operated a diaphragm pump made of a tire with a Savonius
windmill. It is suggested that a diaphragm pump may be better suited for
Savonius windmill than a chain pump. Although the Village Technology Program did
not construct and test a chain bucket pump (shown below), it is believed that it
might perform very well with a Savonius windmill. Conventional piston pumps can
also be used with a Savonius windmill.
The Savonius windmill was also used to grind grain. A small grain mill known as "Corona Convertible" manufactured in Columbia, South America, was fitted with a hopper and sprocket.
The hopper holds a large amount of grain and can feed the mill automatically. A s shown below, the horizontal shaft of the windmill is connected to the grain mill via a roller chain and sprocket drive. The overall ratio between the wind machine and the grain mill was 5:1. The mill turned once for every five turns of the rotor.
This wind machine and mill combination successfully ground grain into fine flour. However, the rate of production and wind speed are not known with any accuracy, as this set up was not instrumented. Also unknown is the eventual durability of the mill's simple cast iron journal bearings. Perhaps the use of higher quality mills with better bearings will be required.
All factors considered, the Savonius design affords a very simple, stable machine requiring little maintenance. The Savonius' power output is relatively low (about 1 2 hp), but so is the initial investment for its construction (about $250 of materials). We highly recommend this machine for use in Third World countries.