A transistor is a semiconductor used as a high-speed switch or amplifier with three connections: base, collector and emitter. A ‘Darlington Pair’ enables a larger current gain. To calculate dc current gain (hfe): hfe = Ic / Ib
Mechanisms
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A mechanism changes a given input motion or force into a desired output motion or force. There are four types of motion: linear, rotary, reciprocating and oscillating.
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A Mechanical Advantage (MA) is gained when the effort applied is further from the fulcrum than the load. MA = Load / Effort
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Moments are the product of force (N) x distance (m) and are measured in Newton meter’s (Nm).
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The Gear or Velocity Ratio (VR) is the relationship between the input speed (driver) and the output speed (driven) and can be calculated using the number of gear teeth or the diameter of the pulleys. The VR for compound gears and pulleys is worked out by multiplying the velocity ratio of each pair.
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Levers and linkages transmit motion and amplify or apply forces.
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Spur gears transmit rotary motion, together they form a gear train, an idler gear enables motion in the same direction. Bevel gears transmit motion through 90º. Worm and wheel gears produce a large speed reduction through 90º. Crown wheels produce a large speed increase through 90º.
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Flat belts and pulleys transmit rotary motion, toothed and vee belts provide a more positive drive. Cone pulleys produce adjustable speeds. Chain and sprocket drives transmit a more positive rotary motion. A jockey wheel maintains tension in drive belts and twisting drive belts changes the direction of rotation.
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A Crank and slider, a cam and follower and a rack and pinion transmit/convert motion. Terms used for a cam are rise, fall, stroke and dwell. A Crank has a mechanical advantage away from the centre of rotation. Crankshafts convert multiple linear motions to a single rotary motion. Camshafts convert a single rotary motion to multiple linear motions. Ratchet and pawl allows rotary motion in one direction only. Eccentrics are circular cams producing a simple harmonic motion.
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Bearings support shafts and cope with radial (rotating) and axial (along shaft) loads and can be plain or bush, split, ball or roller bearings. To reduce friction moving parts are lubricated using oil or grease.
Promotional Displays
Use a range of sources, photographs/pictures and some text to show:
- three different types of promotional displays (e.g. a film, a CD and sportswear)
- how each promotional display works (i.e. show input, process and output)
- how each promotional display was made (i.e. materials, components and processes used)
- where the information came from (e.g. a book, the Internet, a magazine)
Tip: The following web site will help get you started:
Questionnaire
In my survey I asked the following questions:
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Do you believe there is a need for promotional displays? • Yes • No
- Which type of display do you prefer?
• Static • Interactive
- Which of the following outputs do you prefer?
• Light • Sound • Movement
- Do you prefer to buy traditional or contemporary designs?
• Traditional • Contemporary
- How much would you be willing to pay for a promotional display?
Less than £5 • £5 - £10 • £10 - £15 • more than £15 •
Thank you for your time
Tip: Use this questionnaire to find out what the user wants. Ask family and friends do not ask people that you do not know! To achieve a higher level you will need to include some questions of your own. The following web site will help get you started:
Research
From my research it is apparent that my design must:
Tip: In this section you must write about how your research relates to your design (e.g. the majority of people asked said they prefer contemporary designs. My designs will need to be contemporary. I will need to carry out some further research into this type of design.)
Design Specification
To be successful my design must:
- promote the item concerned
- attract the attention of potential customers
- not weigh more than two kilograms
- be easy for sales assistance to maintain
- cost no more than five pounds per unit to mass produce
- be easy for sales assistance to assemble
- comply with BS EN 50088 – electronic products
- include a simple mechanical system e.g. lever/linkage, crank and slider, pulley system
- make use of a 741 op amp or a 555 timer
Tip: To achieve a higher level you will need to add a few more items to your specification (e.g. reliability, safety or appearance). Remember what you write down must be measurable.
Idea 1
Use labelled sketches, comments and photographs/pictures to show:
- three different ideas for your promotional display design
- discussions that you have had about your promotional display design
- models that you have made to test your ideas for your promotional display design
- materials, components and processes that you might use to make your promotional display
Tip: Sketch or model your ideas in 2D and 3D and then discuss them with the user. Draw your three best ideas on an A3 page. Add notes and a border use pencil crayons and if possible a fine liner pen.
Final Idea
Use labelled sketches, comments and photographs/pictures to show:
- the reasons for choosing your final promotional display (refer to your specification)
- discussions that you have had about making your final promotional display
- models that you have made to help you decide how to make your final promotional display
- materials, components and processes that you will use to make your promotional display
Tip: Sketch or model your development in 2D and 3D and then discuss your decisions with the user. Draw your development on an A3 page. Add notes and a border use pencil crayons and if possible a fine liner pen.
Final Design
Use orthographic and isometric drawings to show:
- final dimensions/sizes, materials and components
- assembly details
- cutting lists for materials
- order list for components with order numbers and prices
Tip: Use graph paper, drawing boards or ICT to produce an orthographic view of your final design include a front and side elevation, a plan and final dimensions. If possible produce a fully rendered view of the final idea. Draw your final idea on an A3 or A4 page.
How to make my promotional display
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Circuit Assembly. Collect PCB and components. Use PCB drill to drill holes for component legs and drill 1mm holes for leads, wear safety goggles. In a well-ventilated area, tin circuit pads leaving holes open and tin components as required. Use the circuit diagram and locate components, heat the component leg/pad producing a ‘volcano’ shaped joint. Solder resistors, flying leads and battery snaps first, then polarised components. Check for dry-joints, broken tracks and loose or damaged components.
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Measuring and marking out. Collect materials. Measure and mark out MDF using spray mounted picture, bradawl and compass to mark centres and circles. Use steel rule, pencil and try square, marking gauge and marking knife, to mark out squares and rectangles. Clear and tidy workshop.
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Cutting and shaping. Cut MDF using Hegner saw set at a 5°-draw/draft angle. Wear safety goggles. Hold MDF in woodworkers vice and cut using coping saw, cross-file, draw file and finish with glass paper. Use glass paper to round edges. Clamp work and use pillar drill to drill holes. Wear safety goggles. Clear and tidy workshop.
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Joining. Attach 3mm MDF using PVA glue and panel pins and use a damp cloth to remove excess adhesive. Clear and tidy workshop.
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Forming. Place pattern on platen and lower, remove protective cover from polystyrene and clamp in position, pull heater into position and turn on, when polystyrene is soft, remove heater, raise and lock platen and evacuate air. Switch former off and remove polystyrene when cold. Clear and tidy workshop.
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Cutting and shaping. Ask teacher to cut mould, leave pattern in mould, clamp and use pillar drill to drill holes. Wear safety goggles. Clear and tidy workshop.
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Joining. Attach PCB and components. Print graphic image on self-adhesive paper or use spray adhesive in a well-ventilated area and attach to mould. Clear and tidy workshop.
Tip: Use this guide with advice from your teacher to help you write a plan for your own project, this can be a simple flowchart or a sequence diagram (comic strip). Include quality control, health and safety points and say how long you think each stage will take.
The Final Product
Use photographs/pictures, text and comments to show:
- your final promotional display
- how well the promotional display worked (refer to the specification)
- how you could improve the promotional display (e.g. more features, colour or greater movement)
Also write about improvements that you could make to:
- your approach to the research
- your approach to the design work
- your approach to the planning
- your work in class
- your homework
Tip: Keep the evaluation simple. Do not give excuses but state facts. Explain any problems that you may have had and how you overcame them. Say what the users think about your work.