Cranks have many uses and they can be found in some toys as part of a mechanism or in serious machinery such as car engines. Some cranks are attached to mechanisms that are difficult to turn or rotate.



The crank acts like a lever, increasing mechanical advantage (the distance between the handle and the central shaft is increased - this makes it easier to turn).

http://www.technologystudent.com/cams/cam10.htm
check out this website. it tells you more about cams!

An eccentric cam is a disc with its centre of rotation positioned ‘off centre’. This means as the cam rotates the flat follower rises and falls at a constant rate. This type of cam is the easiest to make and yet it is one of the most useful.
A mechanical toy based on a series of eccentric cams is seen below. As the handle is turned the shaft and the cams fixed to it rotate. Placed above the cams are a number of segments representing a ‘snake’. As the cams rotate some of the flat followers are pushed upwards whilst others drop down. This gives the impression that the snake is moving.

Instructions to Build a Rubber Band Gun

Introduction
This rubber band gun is made out of a couple of pieces of wood and fires a single rubber band. I used to have a commercial rubber band gun that you could load with four or more rubber bands and shoot them off semi-automatic style. That's pretty groovy. Mine melted and warped after I left it on the back seat of my car on a hot day. The rubber-band gun that I describe here is more like a muzzle-loading flint lock. But it works and it is fun.
What You Will Need
A piece of 18 mm thick wood. It is alright to use particle board but the trigger has to be solid wood.
A drawing pin.
A thick rubber band that will stretch to 200 mm.
A small rubber to shoot with and that will also stretch to 200 mm.
You will need the following tools:
A coping saw (you can get away with a hacksaw).
A flat file.
How To Build It

Cut out a gun shape from the wood as shown in the diagram above. The length is not critical but the 6mm step at the back is fairly important. Otherwise the shape of the gun does not matter - do whatever is comfortable.
Cut out a 5 mm thick strip of solid wood. This is the trigger.
With the file, smooth all corners of the gun except for the corner marked "A" (this must remain a sharp edge).
Push a drawing pin through the trigger. It should poke through the trigger. The point of the drawing pin must fit under the edge at the back of the gun when the top of the trigger is flush with the top of the gun. See the diagram.
Place the trigger against the back of the gun and hold it in place with the thick rubber band as shown in the diagram.
The rubber band gun is finished. To load the gun take one of the small rubber bands, squeeze the trigger and push a small loop of the rubber band into the opening between the trigger and the gun. Release the trigger, then stretch the rubber band over the nose of the gun. Then Aim and Fire!

Instructions to Build a Mouse-Trap Car

Introduction
The energy for a mouse-trap powered cars is stored in the mouse trap spring and it drives a wheel by some arrangement such as a string connected from the trap's jaws. There was a competition among the mechanical engineers at my University to build a mouse trap car that could travel the furthest. There were plenty of different designs. The winners had a design that released energy from the spring slowly and had only two wheels! The mouse trap hung from the axle. There are endless variations of designs for mouse-trap cars. The design I describe here is not a record breaker, but it can be made easily at home. If you do want to see some record breakers try Mike Flamino and Kevin McHale's Ultimate Mouse Trap Car Home Page. Actually, I don't think it really is the ultimate mouse trap car but it has a cute animated gif of a hopping mouse.
What You Will Need
One wooden mouse trap or rat trap.
Two lengths of 4 mm metal rod that are each about 15 mm longer than the width of the mouse trap. An engineering firm should be able to give or sell some scraps of steel rod and it can probably be bought at hobby stores too..
Four small eye-hole screws. These are like cup hooks but the hook part makes a circle. The eye must be large enough to put the rod through.
Some pieces of 3-ply plywood for the wheels.
Two rubber bands.
Some string.
A stack of small washers with a 4 mm inside diameter
You will need the following tools:

a drill with a 3.7 mm bit,
a jigsaw or coping saw,
a compass,
a hammer,
a vice,
a hacksaw,
a flat file,
some super glue,
two-part epoxy glue,
a pair of pliers, and
a flat jeweller's file.
How To Build It
With the pliers pull the wire catch that holds the trap open and the bait holder out of the wooden mouse trap. Pull out the wire staples that hold these parts in place, too. Keep the wire catch.
Take one of the eye hooks and screw it into one end of the mouse trap about 8 mm from one of the edges. Leave the eye hook in a position where the eye of the hook looks towards the sides of the mouse trap. Do this gently so that the wood of the mouse trap does not split. If splitting is a problem drill a small hole first.
Screw the other three eye hooks into the other three corners of the mouse trap.
Using a compass, mark out four 75 mm diameter circles on the plywood.
Drill the centres of the four circles with the 3.7 mm drill bit. Make sure that the metal rod will require some force to be inserted into the holes.
Cut out the circles from the plywood with the jigsaw or coping saw.
File the plywood circles smooth with the flat file.
Holding the rods in a vice cut each of them to a length equal to the width of the mouse trap plus two times the thickness of the plywood plus 5 mm.
File the ends of the rods smooth and put a small chamfer on them.
Hold one of the rods in the vice and use the hacksaw to make a small cut across the rod about one-third of its length from the end. The cut should go about half way through the rod.
Using the jeweller's file widen the slot so that the wire catch that you removed in the first step can fit snugly into it.
With the pliers cut a 7 mm piece of the wire catch.
File the ends of the piece of wire so that there are no burrs.
With the two-part epoxy glue, glue the wire piece into the slot in the axle. The wire piece should overhang the rod on one side only. Let the glue dry overnight.
Take the rod with the wire piece in it and put it through the eye hooks at the rear of the mouse trap. The rear is the end where the trap jaws lie when it is set.
Put a number of washers on the axle at either end. There should be enough of the rod left at either side to accomodate the wheels but not too much rod or the wheels will rub against the mouse trap.
With the vice, push a wheel onto each end of the axle.
Assemble the front axle in the same way as the rear axle.
Take the piece of string and tie it to the middle of the mouse-trap jaws.
Tie a small loop in the string so that the tip of the loop ends at the rear axle. Cut the loose ends off the string.
Take the rubber bands and put one around each of the rear wheels. The rubber bands will give the wheels traction on smooth surfaces. Use some drops of super glue to hold the rubber bands in place.
The mouse-trap car is complete! To use it start by raising the jaw of the mouse trap slightly. Take the loop at the end of the string and slip it over the wire piece on the rear axle. Turn the rear wheels in reverse so that the string winds onto the axle. This will pull the trap jaws open. When the trap jaws have been fully opened put the mouse trap car on the ground and release it.
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What is a simple machine?

Machines are used to reduce the amount of force required to do work, such as lift a load, but the trade off is that you must apply this force over a greater distance.

Man has learned to use machines to help him do work - which in our case means to move things. Some machines, such as bicycles, are complex because they involve more than one simple machine.


What are the two basic families of simple machines?

All simple machines are derived from either the inclined plane or the lever.

The six types of simple machines are:

the inclined plane
the wedge
the screw
the lever
the wheel and axle
the pulley
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Which machines belong to the inclined plane family?

The inclined plane

The word "inclined" means "at an angle". The word "plane" means "a flat surface". An inclined plane is a slope or a ramp. It can be any slanted surface used to raise a load from a lower level to a higher level. Examples of an inclined plane include: a ramp used by a workman to push a heavy load on wheels up into a truck, ramps for wheel chairs, ramps to load luggage onto a plane, an escalator. An inclined plane was used to move huge stones to build the Egyptian Pyramids.

Notice that all these inclined planes are stationary (with the exception of the stairs moving on an escalator). Inclined planes don't move! An inclined plane helps a person to move or raise heavy objects. An inclined plane enables a load to be lifted with less force, but the distance over which it moves is greater.

In other words, when an inclined plane is used, less force is required to move the resisting weight up the slanted surface than to lift it up vertically. However the amount of work remains the same since:

Work = Force x distance.

W = Fd
The wedge - two inclined planes put back to back.

It is not really a separate type of machine, as the principle involved is identical to that of the inclined plane.

Some examples of wedges include: chisels, axes, knives, saws (small wedges), a splitting wedge, a doorstop, a plow, the hull of a boat






The screw - the circular version of the inclined plane, though it must move to work.

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Which machines belong to the lever family?

The lever - a bar that turns on a point, called a fulcrum.

The wheel and axle - a circular lever, whose fulcrum (pivot point) is an axle.

The pulley - another circular lever, but the pulley wheel rotates freely on the axle.

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Why does an inclined plane make work easier?

Principle of the Inclined Plane

W = Fd (Force x distance)
As with all simple machines, the inclined plane can be used to trade increased distance for decreased force or effort. The force is applied in a different direction to that in which movement takes place.

Can you get something for nothing?

No!

The steepness of the inclined plane is a key factor. If a person uses a longer board to make the inclined plane, he or she will need less force to move the object up the ramp. If a shorter board is used (the angle of the slope is steeper), more force is required but the distance over which it must be applied is less.

For an object resting on an inclined plane, the vertical force of gravity acting on it is split into two smaller forces; one perpendicular to the plane, and one parallel to the plane. It is only the parallel force which needs to be counteracted by pushing (and, of course, friction, though we are ignoring that for this exercise). The slope provides "mechanical advantage" as a simple machine.


Principles of the lever family

With levers, the force is applied at a different point from the load.

The closer the fulcrum to the load, the less force needed to lift the load. The force will move a greater distance, and the load will move a shorter distance.

The closer the fulcrum to the force, the greater the force needed to lift the load. The force will move a shorter distance, and the load will move a greater distance.

At GCSE level, the two year course requires all students to produce one piece of coursework. This coursework must consist of a product that the student has manufactured in the workshop plus a folder including research and analysis about the problem being solved. It should also include a specification based on the research and analysis which should in turn inform the sketched or modelled ideas. As these ideas are developed into workable solutions the students are required to evaluate them as they evolve. As well as a detailed plan of the making process to be undertaken in manufacturing a prototype product the product must take into account the various industrial practices necessary if the product were to be mass produced commercially. On completion the course teacher awards marks for finish of the final product, creativity, complexity, and how well the project itself was made. 60% of the final mark is given for the coursework and 40% for an examination of general knowledge in the subject (AQA). Of the 60% coursework 60% is based on the making and 40% design work. There is a similar split within the 40% examination where 60% is based on making and 40% is based on designing.

A and AS level examinations are rigorous and demanding. The subject is a Human Science and as such many universities[who?] like the examination because it prepares students for individualised learning and problem solving, which is essential in business and industry. Time management is a key factor to candidates success within the coursework elements of the qualification. The examinations are as rigorous as any other subject. Indeed, due to the complexity and variety of tasks and organisational skills required this examination and course is very demanding. The subject covers activities from control technology to aesthetic product design. Students have to use all types of computer software including computer-aided design and manufacture, spreadsheets and presentations. Outputs from such work are often sent to CNC machines for manufacture.

Name : YIHPIN(:
Age : THIRTEEN
D.O.B : 230994
School: HUAYI
Class : 1e5'07, 2e3'08
Gender: MALE

December 2007

April 2008

:D ANDY
:D JINXIA
:D GEKNIAN
:D HUIMIN
:D KAHHWEE
:D IVAN
:D NATASHA
:D SHUJUAN
:D SOONGIT
:D SULING
:D TOMMY

Designer: XOXO
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