The crank is one of humankind’s most useful inventions. It is defined as a right-angled arm attached to a rotating shaft that converts circular motion into reciprocal motion or vice versa.
The crank is one of humankind’s most useful inventions. It is defined as a right-angled arm attached to a rotating shaft that converts circular motion into reciprocal motion or vice versa.
Cranks are commonly found on treadle sewing machines, pencil sharpeners, fishing reels and internal combustion engines. Simple cranks were used by the Romans in hand mills and by the Greeks in Archimedes screws nearly 2 000 years ago.
About 1 000 years ago, Muslim engineers, such as the three Banu Musa brothers and al-Jazari, were probably the first to use them in complex machines, such as water clocks and pumps. One of the commonest uses of the crank is in the crankset of a bicycle, which converts the reciprocal motion of the rider’s legs into circular motion, which rotates the chain and rear wheel.
Hand and foot cranks have also been used in many other machines. One of the best, invented by Helmuth Redinger of Dalton and Brian Servant of Pietermaritzburg in 1998, is the revolutionary EEZE Water Pump.
The EEZE is a free-flow suction water pump that is operated by people riding a bicycle or turning a crank with their hands. The power unit can comprise a single bicycle for a man, a crank handle for use by two women, or a tandem bicycle for use by two children.
The pedalling and cranking mechanisms consist of standard BMX bicycle parts that are readily available. The shaft of the pump is rotated by means of a belt-driven pulley that is attached to the pedals. The shaft rotates at 270 revolutions a minute – slow for a water pump – which means that wear and tear is minimised.
At the top of the shaft, a patented rotating head is fitted, complete with 15mm nozzles that are shut off by spring-loaded boots that face in opposite directions. The rotation of the shaft causes the water to be thrown out by centrifugal force, which actuates the opening of the boots and directs jets of water in opposite directions. This principle assists in the rotation of the shaft.
The EEZE Water Pump is able to pump three litres of water a second on the level and two litres a second to 6m in height. It can fill four 25-litre containers simultaneously on the level. A later version of the EEZE Water Pump, developed in 2001, includes a number of improvements to the original prototype. For instance, the height and weight of the rotating head have been reduced, which makes the unit lighter and easier to move.
The moving parts in the upgraded unit have also been minimised, and it is far more robust. Furthermore, pumping volumes have been increased substantially by improving the centrifugal pump mechanism. A variety of hand- and foot-powered crank-driven machines invented by South Africans was displayed in the Great South African Inventions exhibition mounted by the MTN Sciencentre, now the Cape Town Science Centre, in 2004.
These included crank-driven band saws, water pumps, water filters, meat saws, air pumps, mielie grinders, electricity generators, wood drills and knife sharpeners – but, as far as I know, none of them has ever been commercialised.
The simple crank still holds a great deal of promise as the mechanism behind simple alternative technologies that could be used in post-industrial, green homes, gardens and farms of the future. There is surely no good reason why small scale, hand- or foot-driven cranks could not be used to mix cement, charge cellphones, open cans, squash grapes, lacerate compost, water the lawn, juice fruit, saw wood or dig a hole in the ground.
Perhaps we should all have an exercise bicycle in the back yard linked up to these gadgets, so that we can do useful work while enjoying healthy exercise and reducing our carbon footprint at the same time.
* The Turning over Logs column, on South African inventions, appears in Grocott's Mail every second Tuesday.
