Lecture during the 14. International
Cardboard Modelers Convention
in Bremerhaven/Germany on April the 28th 2002
|Since 1989 the Deutsche Schifffahrtsmuseum (German Maritime Museum) in Bremerhaven organizes International Cardboard Modelers Conventions every year. There the friends of cardboard modelling can exchange their experiences, listen to interesting lectures and present their made-up models. Peter J. Visser from Holland has made a lot of pictures for a report about the last three meetings (please click on "Pictures: Fairs and exhibitions" on his website). The theme of my lecture was "The Cam Drive in the Exclusive Models of Keith Newstead", you can see the manuscript and the shown transparencies below.
Last year I have shown you two pneumatic driven paper
automata of the English designer and constructor of automata, Paul Spooner:
the Wedding Cake and the Museum of the Mind. Now I want to show you
four paper mechanical models designed by another English artist. His name
is Keith Newstead. These are the models: Tower Bridge, The Sculptor, Tippoo's
Tiger and The Scales of Justice.
Basically a cam is an asymmetrical bulbe of a crankshaft. The simplest shape of a cam is a disc which shaft is not located in the centre but off-centre or "eccentric". So the eccentric disc gets two radii, a big radius and a small one. When the shaft is rotating the disc so to speak wobbles, alternately the small or the big radius is up. The difference between both radii is called the stroke.
When you fix a movable rod above the eccentric disc, a push rod, it follows the alteration of the radii and lifts and drops regularly during a revolution of the crank. The extent of the movement of the push rod corresponds to the stroke. An effective guiding is very important to prevent the push rod from jamming. So a cam in connection witht a push rod can transform a rotary motion into a linear up and down movement.
Different shapes of the cam can cause different rhythms in the up and down movement of the push rod. You can say that in the outline of the cam a movement programme is stored. About this two examples:
While the eccentric disc causes a regular raising and
lowering the lobed cam has a completey different rhythm. The raising occurs
quickly, the lowering as well, then there is a pause because the radius doesn't
change during half the rotation.
By a snail cam the push rod is lifted slowly to the
highest radius, and then it drops down abruptly to the smallest
When you combine a cam and a lever you will convert
the rotation of the crank into an oscillating movement of the lever. The
shape of the disc cam is feeled by a cam follower which is fastened to the
|3. The Models
a. The Tower Bridge
Newstead has designed the model "Tower Bridge" for
the show "Tower Bridge Experience". It describes a real event which happened
in December 1952. Then the driver of a public service bus no. 78 missed the
red traffic lights, broke through the chain and raced towards the opening
bridge. Miraculously the bus jumped over the gap and made a soft landing
on the other side.
The model "The Sculptor" has been designed exlucsively
for the Tate Gallery. It tells a story that could be a traumatic situation
for each artist. The sculptor has nearly finished a female statue and puts
the finishing touches to the shaping of the arm. Just a few hammer blows
- and then he has a little accident: the arm of the statue breaks off, the
expression on the face of the statue turns into pain and horror and the sculptor
frightened ducks his head.
|When the arm of the statue falls the head of the sculptor sinks at the same time downwards. Because the load arm that belongs to it is much shorter than the moment arm the movement is decreased. So the head sinks only a little bit downwards.
"Tippoo´s Tiger" is an exclusive model for the Victoria and Albert Museum. It describes a dramatic situation: A man in an English uniform is attacked by a tiger, and it looks very bad for the man. The historical example for this model is a sculpture from coloured wood which had been made for Tipu Sultan, the sovereign of Mysore in South India in the 18th century. The sculpture contains a musical box produced in France which simulated the tiger's roaring and the victims's moaning. At that time musician automata were very popular in Europe and were esteemed in India too. The sculture has a political background. At the end of the 18th century the British East India Company ruled large parts of India as a private possession and plundered the country.
|Tipu Sultan showed militarian skill and for a long time fought successfully the armies of the East India Company. He got the title "Tiger of Mysore." So the sculpture symbolizes the war of independence against the colonial power. The tiger is driven by a cam with four lobes, one of them is a little bigger. This makes the tiger set upright and causes a fourfold biting. With each biting the victim moves, right arm and neck plus head are driven. The movements are coordinated with the tiger's. The tiger's roaring is simulated by a rattle which is moved by a cam with teeth.
|d. The Scales of
Newstead's model "Scales of Justice" was designed for the British Museum which possesses one of the greatest collections of the Egyptian art. It includes a papyrus which shows a scene from the Egyptian Book of the Dead. According to the ancient Egyptian religion the soul of a dead person - symbolized by its heart - is weighed against the feather of truth. The god of the death Anubis takes the weighing. If the soul is lighter than the feather the deceased had been a good person and may live an everlasting life. But if the heart is heavier than the feather, then the monster Ammut snaps at him and eats it up. The monster is a mixed creature from different animals like crocodile, hippo and hyena. This papyrus is the pattern for Newstead's model.
|The scales, the dead person and the monster are driven by cams. At first the matter looks very good for the deceased. His heart is lighter, and he loughs happily. Then the situation alters: the scales lowers, the monster snaps and the expression of his face changes to dismay. The rotating crank decides the fate of the deceased - so it is in our hands.