Investigation - Puppetry- Case Study- BackgroundPuppetry has a way of bringing communities together. In ancient Mali an animal horn would call the community together for a puppet show. The puppet show, created by the youth, would be the highlight of a day of festivities such as sporting competitions, drumming, and singing, dancing and feasting. Giant puppets are often featured in opening ceremonies of international sporting events such as the Olympic Games. A South African rural youth development programme called “The Seven Passes Initiative” were involved in the creation and performance of Roger Titley’s giant dung beetle that featured in the opening ceremony of the 2010 FIFA soccer world-cup.
Today this ancient Malian tradition is kept alive by The Sogolon Puppet Troupe who does not stop with African tradition only, but combines European and Asian traditions as well. The Sogolon Puppet Troupe collaborated with The Handspring Puppet Company of South Africa on a production called “Tall Horse”. Handspring Puppets have designed and developed a life-sized horse puppet which appears on stage in the award-winning play, “War Horse. This puppet’s movements are so real that one could easily think it was a real horse on stage. The life-like movements of the puppets are created by a series of levers and pulleys. Handspring Puppets have designed and developed a life-sized horse puppet which appears on stage in the play, War Horse. This puppet’s movements are so real and one could easily think it was a real horse on stage. Mechanisms used by such puppets include hinges and pivots and levers and linkages. These puppets could be automated through incorporating other mechanisms such as cranks which are a different form of wheels and axles, pulleys and belt drives and/or pneumatics or hydraulics. Another well-known South Africa puppetry company is Roger Titley’s Creatures. Both South African companies are internationally known and are well-respected in International Art circles. Roger Titley’s Creatures was responsible for the elephant puppets which formed part of the closing ceremony of the 2010 FIFA Soccer World Cup, held in South Africa. This company also created the giant dung beetle puppet that was used in the opening ceremony of the same tournament. A feature of the puppets designed and developed by both of these enterprises is that the puppeteers become an integral part of the puppets. Often more than one puppeteer is involved in the movements. This means that the way the puppet moves and the people creating that movement must become a complete unit and each move must be practised to perfection. Mechanisms used by such puppets include hinges and pivots and levers and linkages. These puppets could be automated through incorporating other mechanisms such as cranks which are a different form of wheels and axles, pulleys and belt drives and/or pneumatics or hydraulics. With a little imagination a hydraulic excavator could be transformed into a giraffe with a moving neck or an elephant with a moving trunk. Wheels could make a puppet mobile and cranks could create movement similar to walking. |
Investigation - Content KnowledgeTypes of Movement
Rotary movement is movement around a central point, in a circle. An example is a wheel on an axle,e.g. a moving bicycle. (Image source: www.examiner.com) Linear movement is movement of any object in a straight line e.g. train moving straight on a railway line, a ball kicked, hit or thrown in a straight line. Reciprocating movement is movement that goes up and down or forwards and backwards, e.g. a saw cutting wood. This is to and fro movement but has a linear nature. |
Changing the direction of Movement
Changing the direction of movement means that the direction of an input movement is altered to a different direction in the output movement. The direction of movement can be changed by using various mechanisms, e.g levers and linkages, gears, pulleys, cams and followers, cranks and cranks with followers and finally pneumatics and hydraulics. In this section we will focus on cranks and cranks and followers, pulleys and belt drives.
Mechanisms to change the direction of movementCranks
Cranks normally consist of a metal bar that is bent at right angles to form a handle or pedal. Cranks are used as mechanisms that change rotary movement to linear movement when a follower is connected to them, e.g. lifting a bucket at a well. They can convert circular movement into reciprocal movement. Cranks cause the pumping motion in windmills. Two main functions of a crank: To turn a shaft more easily e.g. the crank on a hand drill transfers movement to the drill bit. To help change the direction of the movement e.g. a bicycle crank(pedal) rotates causing the wheels to rotate. As the wheels rotate the bicycle moves in a linear manner. The crank has the following: handle, central shaft and the connecting rod (follower). When you turn the handle it creates rotary (circular) movement. Rotary movement is a turning movement that takes place around the central shaft. By connecting a rod to the central shaft it will create the reciprocating movement. Advantages of a crank system A longer crank has larger output. This means that less work will be done, e.g. when lifting a bucket from a well. A larger crank will lift more rope with each turn, easing the work done. Disadvantages of a crank system Shorter cranks have a smaller output. This means that more work must be done to obtain the same result as with a longer crank. Heavy objects may cause the rope to stretch and or slip. The result of which is more work will be done for the same result. |
Pulleys
Pulleys may have been invented by Archimedes in ancient Sicily, about 250 BC.
A pulley is a wheel with a groove in the rim (edge), in which a belt or rope can run. Pulleys can transfer rotary motion from one shaft (axle) to another or can be used to lift heavy loads vertically. This second set up of pulleys is known as a block and tackle. In a block and tackle system rotary movement is changed to linear movement. If you have ever looked at the end of a crane, or if you have ever used an engine hoist or looked at the rigging on a sailboat, then you have seen a block and tackle at work. A block and tackle is an arrangement of rope and pulleys that allows you to trade force for distance. With each additional pulley you require twice the amount of rope but the work you do is much less. Belt drive systems are pulley systems that use a belt to transmit motion and force from the driver shaft (axle) to the driven shaft (axle). Both these axles rotate in the same direction. For example, cars use a pulley system with V-belts running in grooves on the pulley wheels to rotate the fan belt for the cooling system. Speed changes are made by using different sizes of pulleys on the driver and driven shafts (axles) respectively. A small driver and a larger driven pulley will result in the driven pulley rotating slower. Direction changes are brought about by twisting the belt, this causes the driven axle to rotate in the opposite direction. Pulleys are very flexible because they use ropes or chains to transfer force rather than a rigid object such as a rod. Ropes can be routed through virtually any path. For example as used in cranes on building sites for the lifting of heavy objects. An example of a manual system like this is when we lift a bucket filled with water from the well to the surface. A compound pulley system 'trades' force for distance. This means that with each additional pulley twice the amount of rope is required. Advantages of pulleys and belts ● Belts are not noisy ● Belts can be stretched for fitting and for removal ● Crossed belts can change the direction of rotation The disadvantages of pulleys ● Slipping and stretching are disadvantages of both belt drives and pulley systems. A rope will permanently stretch under tension, which may affect the future performance of a device. If a line becomes slack, then the operation of a machine may change entirely. ● Ropes will slip and stick along pulley wheels just like belts. This can be prevented by using a chain instead of a rope. The chain will not stretch as the links are strong in tension (pulling forces). Slipping can be avoided by exchanging the pulleys for gears and chains may also be made to fit on gears so that slipping is avoided. |