Cam Toy
Learning Objective
I will be abe to explain how cams change the direction of motion and how they are used in everyday life.
Task
On the worksheet, explain what a cam does, then explain the type of motion produced by each cam.
Cams are found in lots of different places, they are a mechanical device used to change the direction of motion from rotational to linear, or linear to rotational. For example they are used in engines to transform the linear motion of the piston going up and down to the rotation of an axle that turns the wheels and propels the vehicle forwards.
Types of Cam
Cams come in variety of shapes that will define the type motion they produce.
Off Set Cam
An offset cam has a smooth profile which causes the follower to rise and fall at a constant rate, this is type of cam used in conjunction with a piston as it produces a constant velocity or steady speed of rotation.
Pear Shaped Cam
These cams produce no motion for 75% of it's rotation, then they produce a quick rise and fall. This is useful when wanting to open and shut something, they are found on cylinder heads in engines where they are used to open and shut the valves that let the fuel and air in and out of the piston head.
Snail Cam
A snail cam produces the same sort of motion that a pear shaped cam does, but it can only turn in one direction, this is useful when you want to make sure you can only turn the axle in one direction. It also produces a slow rise and a sudden drop when being turned.
Cam Toy from Tom Watson on Vimeo.
Cam Toy 2 from Tom Watson on Vimeo.
The Engine
Link the following statements to the parts of diagram.
Lets the air and fuel into the cylinder head.
Spins or rotates when pushed up and down by the piston and connecting rod.
Connects the piston to the crank shaft
Lets the air and fuel out once they have been used.
Creates and electrical spark to ignite the fuel and air, which as it explodes pushes the piston down.
A very strong metal casing that contains all the engines components.
Moves up and down as the air and fuel explode when ignited by the spark plug.
Engine Firing Sequence
Learnng Objective
I will be abe to explain how fuel and air are used to push a piston that turns a cam, changing linear motion into rotational motion.
Task
On the worksheet add the position of the piston and explain in your own words what ishappening at each stage.
Intake
Fuel and air are mixed together in the carbertor, producing a highly explosive gas. The intake valve opens to allow the mixture into the cyclinder head.
Compression
The intake valve closes trapping the gas in the cyclinder head, as the piston continues to travel upwards compressing the air and fuel making the mixture more explosive.
Power
With both valves still shut, electricity generated by the alternator in the car engine causes an electrical spark. This ignites the fuel and air, the subsequent explosion forces the piston downwards.
Exhaust
The exhaust valve now opens to allow the fumes left over from the expoded air and fuel out of the engine, before the process can start all over again.
