The Cam Drive in the Exclusive Models of Keith Newstead

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.

1. Survey 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. Newstead was born in 1956, has studied art and technology and for 10 years he has earned his money as a motorcycle despatch rider in London. A TV-film inspired him to construct mechanical sculptures - in Great Britain known as "automata". Some of them are from metal, many from cardboard. Many of his mechanical paper models Newstead has designed exclusively for touristic attractions in London. The construction kits are printed on strong cardboard, partly diecutted and packed in very costly shaped cardboard covers. Arcturus Publications who sells many of Newstead's constructions kits writes about him: "Keith Newstead is the UK´s leading automata artist". The four models I've brought with me today are all driven by cams which are attached to the input shaft. That's the reason for my lecture's subject: "The cam drive in the paper mechanical exclusive models of Keith Newstead."

2. Cam Drive Eccentric Disc 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:

Lobed Cam 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. Snail Cam By a snail cam the push rod is lifted slowly to the highest radius, and then it drops down abruptly to the smallest radius. Cam and Lever 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 lever. The more the lever juts out beyond the cam the bigger is the oscillating movement which the end of the lever carries out. Newstead often uses a combination of cam, oscillating lever and push rod. By putting in between a lever he can vary the stroke of the push rod respect to the stroke of the cam. Moreover he can use steep curves of the cam because the cam follower of an oscillating lever doesn't jam so easliy like a push rod. Now let's have a look at the models and their mechanisms.

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. This model shows two movements, the opening bridge and the going bus. The bridge is opened by a cam which resembles a flattened eccentric disc. The bus is attached to a holder which is pushed on the crankshaft and turns round and round with it. b. The Sculptor 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. There are four movements in this model: the blowing of the hammer, the breaking of the arm, the expression on the statue's face and the retraction of the sculpture's head. The sculpture's arm with the hammer is driven by a cam with four lobes which make the hammer blow four times. In the first half of the crank rotation nothing happens, the hammer is in a waiting position. The arm and the expression on the statue's face are driven by a lobed cam. Most of the time nothing happens, the radius remains the same. That's the phase, when the sculptor is hammering. Then the arm breaks off abruptly - the cam follower falls from its highest point to the lowest. Then the curve of the cam increases again quickly which achieves a repair of the statue, the arm goes up again. For both cams Newstead uses a lever-push- rod-combination and makes use of the longer load arms to increase the movement. On the arm lever he fastens a second push rod which carries the head of the sculptor.

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.

c. Tippoo´s Tiger "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's musical box Newstead's cardboard model

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 Justice 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.

Book of the Dead - Papyrus Newstead's Cardboard 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.

     top