Many years ago, I was lucky enough to work in “Launch Pad” in the science museum. There were lots of wonderful activities and the following blog posts are about the activities. Launch Pad has been replaced by the equally wonderful “Wonderlab”
The grain pit
The grain pit consisted of a number of machines which were arranged together so that grain and feed wheat could be moved around the exhibit by turning the handles.
The prototype ‘Grain Pit’ under test. This exhibit required visitors to cooperate in shifting grain around an endless circuit using lifting and transportation mechanisms found in industry. This was a popular exhibit which children operated with great determination and intense concentration.
What did it show?
The grain pit demonstrated the operation of machinery that is commonly used to move things in farms, factories etc. The slides and funnels moved things down, the conveyor belt, vibro-conveyor and horizontal auger moved things along and the bucket conveyor and auger moved things up. The technology represented by these machines varies from the modern to that which has been around for thousands of years.
How does it work?
There are two augers on the grain pit: one to lift the grain and one to move it along horizontally. These work on the principle of Archimedes screw, which is said to have been invented by the Greek mathematician, Archimedes’, over two thousand years ago. Although primarily used for raising water, the Archimedes’ screw is quite effective with grain and other material in small pieces.
Archimedes of Syracuse (c. 287 – c. 212 BC) was a Greek mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity. Considered to be the greatest mathematician of ancient history, and one of the greatest of all time, Archimedes anticipated modern calculus and analysis by applying concepts of infinitesimals and the method of exhaustion to derive and rigorously prove a range of geometrical theorems, including: the area of a circle; the surface area and volume of a sphere; area of an ellipse; the area under a parabola; the volume of a segment of a paraboloid of revolution; the volume of a segment of a hyperboloid of revolution; and the area of a spiral.
Archimedes’ screw is a machine primarily used for raising water. It may consist of a tube wound spirally round a cylindrical axis or a cylinder enclosing a screw so as to form a spiral chamber from end to end. The lowest portion of the screw just dips into the water, and as the cylinder is turned a small quantity of water is scooped up. The inclination of the cylinder is such that at the next revolution the water is raised above the next thread, whilst the lowest thread scoops up another quantity. The successive revolutions, therefore, raise the water thread scoops up another quantity. The successive revolutions, therefore, raise the water thread by thread until it emerges at the top of the cylinder.
Unsurprisingly this piece of equipment was not invented by Archimedes. The first records of a water screw, or screw pump, date back to Ancient Egypt before the 3rd century BC and it has been widely used over the centuries to raise irrigation water and for land drainage. Of robust and simple construction, it has the advantage of being able to shift water which contains mud, sand, gravel, and even larger debris. The machine is in use today in the Middle East and the Netherlands.
The conveyor belt is a long narrow rubber sheet joined up to itself to form a continuous belt, which is turned by a handle. The direction in which the handle is turned is the same as that in which the grain travels.
This is unlike the vibro-conveyor, where the handle must be turned slowly and in the “wrong” direction. The principle behind the vibro-conveyor is rather complicated: basically, what happens is that the grain is thrown and caught by the trough as a result of its movement. The grain thus bounces along slowly, and “backwards” in a series of throws and catches by the trough.
The Synchro-Shear conveyor consists of a trough in which material is carried, a base for mounting the conveyor and its machinery, stabilizer links which support the conveyor trough above the base, a reactor system, plus an eccentric drive which imparts a controlled motion to the trough.
Material moves ahead in the conveyor in a series of gentle “throws and catches” as a result of the controlled linear motion produced by the eccentric drive and stabilised by the stabilizer links, or legs, as they are sometimes called.
The Synchro-Shear reactor system is designed so that its resonant frequency matches the eccentric speed. This is then a tuned or synchronised frequency system where all of the forces required to decelerate and accelerate the trough balanced by the forces developed by deflection of the rubber shear reactors.
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of a periodically applied force is equal or close to a natural frequency of the system on which it acts. When an oscillating force is applied at a resonant frequency of a dynamical system, the system will oscillate at a higher amplitude than when the same force is applied at other, non-resonant frequencies.
The eccentric drive provided only the additional energy lost because of friction. All forces are uniformly distributed along the unit and no large destructive stresses appear at the drive connections since each shear spring functions as an individual drive. Power requirements are kept to a minimum.
The bucket conveyor is similar to the conveyor belt, except that attached to the belt are small buckets, which scoop up the grain at the bottom of the turn and drop it into a funnel at the top. This enables the grain to be carried up the slope – without the buckets, it would slip down faster than the handle could be turned.
Funnels and slides are convenient ways of getting the grain down to a lower level. There are several on the grain pit. The funnel that leads down to the conveyor belt has a metal plate at the bottom, which can be moved backwards and forwards to control the flow of grain.