Leaving Certificate Engineering Design Portfolio 2009

Examination Number: 132465

Analysis of BriefMy personal analysis of the brief is as follows:

Design a model of a fairground carousel.

The carousel should have the following specifications:

Its circular motion must be controlled by an ON/OFF switch so therefore it must be electrically operated. Possible switches I could use are push buttons or a toggle switch.

It must incorporate mechanisms which will sequentially animate four figures. This means that it must animate four figures in a consecutive manner. Possible animations I could use are rotating the figures or making them move up and down.

Include an electronic indication to signal the carousel is in operation for example a light or small speaker.

Furthermore:

All main operating features must be clearly visible without dismantling. This can be done through the use of transparent windows or by leaving open spaces for spectators to view the mechanisms in the model.

The longest dimension of the carousel cannot exceed 350MM .I believe this shouldn’t be a problem as 350mm is quite a large size.

Electric power must not exceed 9 volts. This could be a problem depending on the mechanism I choose to use. I will have to use one that doesn’t require too much power.

IntroductionA carousel (from French carrousel, from Italian carosello), or merry-go-round, is an amusement ride consisting of a rotating platform with seats for passengers. The "seats" are traditionally in the form of wooden horses or animals, which are often moved mechanically up and down to simulate galloping, to the accompaniment of looped circus music. This leads to one of the alternative names, the galloper. Other popular names are roundabout and flying horses. Both "carousel" and "merry-go-round" are used with equal frequency in North America while the latter is usually used elsewhere and "roundabout" is quite common in the United Kingdom. In practice, all the terms would generally be understood throughout the English-speaking world.

Any rotating platform may also be called a carousel. In a playground, a roundabout or merry-go-round is usually a simple, child-powered rotating platform with bars or handles to which children can cling while riding. At an airport, rotating conveyors in the baggage claim area are often called carousels.

History of the fairground carouselThe earliest carousel is known from a Byzantine Empire bas-relief dating to around 500 A.D., which depicts riders in baskets suspended from a central pole. The word carousel originates from the Italian garosello and Spanish carosella ("little war"), used by crusaders to describe a combat preparation exercise and game played by Turkish and Arabian horsemen in the 1100s. In a sense this early device could be considered a cavalry training mechanism; it prepared and strengthened the riders for actual combat as they wielded their swords at the mock enemies.

Early carousels had no platforms: the animals would hang on poles or chains and fly out from the centrifugal force of the spinning mechanism; these are called "flying horses" carousels. They were often powered by animals walking in a circle or people pulling a rope or cranking. By the mid-1800s the platform carousel was developed where the animals and chariots would travel around in a circle sitting on a suspended circular floor which was hanging from the centre pole; these machines were then steam-powered. Eventually, with the technological advances of the industrial revolution, bevel gears and offset cranks were installed on these platform carousels, thus giving the animals their well-known up and down motion as they travelled around the centre pole. The platform served as a position guide for the bottom of the pole and as a place for people to walk or other stationary animals or chariots to be placed. Fairground organs (band organs) were often present (if not built in) when these machines operated. Eventually electric motors were installed and electric lights added, giving the carousel its classic look.

Many carousel connoisseurs consider the golden age of the carousel to be early 20th century America. Very large machines were being built, elaborate animals, chariots, and decorations were superbly made by skilled old-world craftsmen taking advantage of their new freedoms in America. Large amounts of excellent and cheap carving wood were available such as Appalachian white pine, basswood, and yellow poplar. Whereas most European carousel figures are relatively static in posture, American figures are more representative of active beasts - tossed manes, expressive eyes and postures of movement are their hallmarks.

Investigation of solutionsFor my research I mostly browsed the internet searching for solutions that would satisfy the brief. I also read through my engineering notes and discussed the project with my teacher. The following are the individual headings that I investigated:

Function

The carousel must move in a circular motion and sequentially animate four figures and must also include an electronic indication to show that it is in operation.

Firstly I had to think of a way to cause a circular motion. There were certain considerations I had to keep in mind while thinking of one such as the fact that it must operate on a 9V battery.

I came across some interesting solutions:

Worm Wheel Mechanism :To make the model rotate I could use a worm-wheel mechanism .This would be a simple enough solution as I would attach the worm-wheel to a motor and have a gear attached to a centre pole on my

piece. When the motor is switched on it would cause the worm-wheel to rotate and that would cause the centre pole to rotate. See the below diagram.

Worm Wheel Mechanism

Belt drive mechanism: The motor could be attached to a small pulley (see B on below diagram). This pulley is then attached to a larger pulley (see A on below diagram) by means of a belt. When the motor is turned on it will cause the pulley to rotate and thereby causing the larger pulley to rotate as well. The larger pulley could be placed underneath the carousel to cause the rotation.

Belt Drive Mechanism

Crank Mechanism: Another way of causing a circular motion would be by using a crank mechanism. A motor could cause Part (i) seen on diagram to move from A to B repeatedly, this movement would cause part (ii) to rotate due to the bar connecting the two of them. Part (ii) could be connected to the underneath of the carousel.

Crank Mechanism

Materials to use

For researching materials I looked up the properties of all the materials that were available in the engineering room and then decided which was best for each part.

I decided to use aluminium for my central disc/platform on which the figures would be supported, I chose aluminium due to it being light-weight and therefore would not slow down the rotational speed. Using aluminium would also mean that I wouldn’t need to have a very large support to keep it stable. Aluminium also has a very high strength to weight ratio making it perfect for the job.

I will most likely be using windows in my project so as to satisfy the brief where it says all operating features must be visible. The material I would use for these windows would be Polymethylmethacrylate (Acrylic). Acrylic is a rigid plastic with a high degree of transparency making it perfect for the windows. An alternative to acrylic would be Perspex which is also transparent.

For my mechanism I will most likely use brass to make the majority of the parts as my research has provided me with a lot of information about it such as its easy to machine and produces a high quality finish as well as being durable making it a perfect selection for the mechanism.

Shape and dimensions

The brief states that the longest dimension of the model must not exceed 350mm so I must try to keep all parts of my model under that size. I researched the typical size for model carousels and found a shop that deals in models and that had a large selection of model carousels. I noted that the majority of the model carousels fit the sizes allowed by the brief and so it made me realise that it should be possible to build a model that satisfied the dimensions outlined by the brief. I planned to not exceed 300mm on any dimension, never mind 350mm.

Joining and fitting

The design brief says to avoid adhesives where possible so I researched the following joining and fitting methods:

Screws: I will most likely be using screws as a joining method for the majority of my project. The reason for this is that screws can be used to assemble parts and then dismantled with damaging the piece and there is no need for repair. I researched screws and my investigation showed me exactly how screws work. I researched them on the internet and had a discussion about the different types and advantages of screws with my engineering teacher. Screws work by exerting a strong force and pulling the joint faces tightly together. The load is then taken by the head of the screw. In the previous work I did with screws I found them to be very useful and didn’t experience a problem with using them so I don’t expect to find any this time around.

Rivets: Using rivets is another option to me in terms of joining methods. Riveting is a fairly simple process, it is where a riveted joint is made by drilling the plates and inserting the rivet. A second head is then formed on the shank of the rivet by applying pressure, usually by hammering. The rivet head is supported on a bolster and the end of the shank is formed into a second head suing a special former of the required shape. Riveting machines are used on large rivets, but won’t be necessary for my project as I just require small rivets. I found out my information on rivets through my engineering textbook and off the internet.

Soldering: Soldering is another joining method I could use for my carousel model. Soldering is a process by which two or more metal parts are united by an alloy. The alloy melts at a lower temperature than either of the pieces of metal. The liquefied solder does not adhere to the surface of the metal. Instead, the molten solder passes into (permeates) the molecular structure of each of the metals. An alloy is formed at the boundary of the two metals to a depth of about 0.1 millimetres (mm). On cooling, the alloy forms a common bond, uniting the metals. Soldering operations can be performed with hand tools, one joint at a time, or en masse on a production line. Hand soldering is typically performed with a soldering iron, soldering gun, or a torch, or occasionally a hot-air pencil. I gained this information on soldering through reading my engineering textbook.

Surface finish

If I decide to use wood in my project, I will most definitely be using varnish as a surface finish. The reason I will be doing this is that varnish provides a protective layer for the wood and also gives it a nice glossy look. I found out this information by visiting my local hardware store and reading a leaflet I received which was all about varnish.

For surface finishing on metal i use in my project I will most likely coat it with a layer of paint as this will give it protection against corrosion as well as giving it a nice colour adding to the attractiveness of the piece. I found information on metal finishes from my engineering teacher.

Safety

Manufacturing:

I will most likely be using the lathe to manufacture the majority of the pieces for my project so I looked up the safety rules to abide by when using the lathe. The guidelines were pretty basic such as roll your sleeves up and wear eye protection.

The same applies to the majority of the machinery I will be using, to roll up sleeves and wear eye protection. It is also a good idea to be careful when using equipment such as a saw and to concentrate on the project at all times.

Actual project:

Seeing as the piece will run on electrical power I will need to make sure to not use any defective equipment. I will also be careful to make sure the piece doesn’t get wet. I will also try to conceal the electrical wiring as much as possible so as to avoid contact and injury. I will also have to be careful so as to not overload any of the circuits.

Also seeing the piece will be rotating I will have to make sure that I don’t have any very sharp edges on the piece as it will lead to someone getting cut.

Special Factors

Mechanism to animate figures:

Bevel gear system: There could be four bevel gears at the top of the centre shaft (seen at A on the diagram). As the centre shaft rotates it would cause the bevel gears to rotate causing B to move up and down. This would cause an animation of a figure suspended on B.

Cam system: As the four cams move around the piece seen in the diagram, the ramp causes them to lift up. A figure could be suspended on top of the cams causing them to move up and down.

Best solution

In the end I decided to go with the Tea cup ride themed carousel as my project for the following reasons:

It satisfies the design brief perfectly as it has a solution for each aspect of it outlined in the brief. I also believe it is the most innovative of the solutions that I came up with.

I prefer the whole concept of it to the other solutions I came up with. I think it will be the most enjoyable to manufacture, and when it’s completed will bring me the most satisfaction compared to the other solutions

It isn’t as complicated as the other solutions, as it has a simple yet satisfactory mechanism. It will also be the least time consuming solution to the brief, leaving me with time to perfect it.

I believe it is a unique idea as the majority of people will opt for more commonly used mechanisms such as the cam’s moving over the ramps seen in the boat themed carousel.

This solution brings the most room for customisation so I can customise it as I go along slightly if I feel it benefits the project.

It is the solution which will showcase my engineering skills the most in my opinion as it involves the biggest range of production methods.

This solution will look the most attractive when it is completed.