Hello there, my name is Mrs. Dhami.

Thank you for joining me for your "Design and Technology," lesson today.

Now, the big question for today is what are cams and what are pulleys? Well, we're gonna work this out together and we're going to use lots of examples as we go through.

So seat belts on, hope you're ready.

Let's get started.

Our Outcome for today is that we will be able to describe the function of cams and pulleys using specific examples.

Our Keywords are cam, follower, friction and pulley.

And we will go through each of these words as we meet them through today's lesson.

Our Lesson Outline starts with exploring cams and then goes on to explore pulleys.

So let's get started with exploring cams. For the start of our lesson today, it will be really useful to recap the types of motion.

So take a minute with the person next to you.

Have a think, what are the types of motion for A, B, C, and D? Pop back to me when you've got an answer.

So hopefully for A, this is motion going around in a continuous circle and we call that rotary.

For B, hopefully you got oscillating.

Oscillating motion is motion which goes in the shape of an arc.

For C, that is linear motion in a straight line, and then D is reciprocating.

Now reciprocating can be forwards and backwards, but it can also be up and down.

Our first check-in.

Which image below represents reciprocating motion? Let's have a little look.

Take a minute and remember what the definition of reciprocating is.

Come back to when you're ready.

Fantastic, if you got the sewing machine needle.

Just like the last slide, reciprocating can be either up and down or backwards and forwards motion.

If you're unsure at all, pop back to my last slide and have a little look at those again.

Cams convert rotary motion into reciprocating motion.

Take a little look at the gif on the right hand side.

The green part is the follower, and you can see that moving up and then down.

Obviously that's reciprocating motion, but it only moves up and down due to the cam.

Now the cam, as you can see, is moving around and around.

Therefore, that is rotary motion.

When the follower moves up, we describe the motion as rising.

When it moves down, we describe it as falling.

Try and remember these two words.

They're gonna help us over the next few slides.

Time for our first check.

Rotary motion in cams is changed into which type of motion in followers? Is it A, linear, B reciprocating, or C, oscillating? Come back to me when you've got an answer.

Well done, if you got reciprocating.

Remember that green follower, moving up and then down and repeating that, that is obviously reciprocating.

The shape of a cam determines the speed and magnitude, otherwise known as height of the motion.

Sofia says, "How can you describe the motion by the different shaped cams?" To do that, you need to be looking at the effect of the follower.

So the green part, again is the follower.

And watch how with this pear shaped cam, it moves gradually up, gradually down, and then rests.

Let's take a look at the snail shaped cam.

Notice how it gradually goes up, then all of a sudden has a drop.

And lastly, the eccentric cam.

Notice how it gradually goes up and gradually goes down with no rest.

We're gonna look at these in a little bit more detail in a minute.

We've just looked at three different shaped cams. Can you remember what they are? I'd like you to match the name of the cam, eccentric, pear or snail, to its shape.

Come back to me when you're done.

Okay, well done for having a go at that.

Hopefully A, you got pear shaped.

Does look a little bit like a pear.

B snail, again, it shows it with its shape.

And lastly, C, eccentric.

That's where the centre of the circle is off set.

With a pear shaped cam, the motion of the follower gradually rises, gradually falls, and then enters a rest phase.

Let's look at this a bit more closer.

So first of all, as it moves up the side of the pear shaped cam, it gradually rises until it reaches its top point.

It then comes down the other side and gradually falls.

When it gets to the bottom of the pear, the radius is at equal distance all the way round to the other side.

This means that it enters a rest phase, where it doesn't move the follower at all.

Pear shaped cams can be used in car engines to open and close valves.

The motion of the follower using an eccentric cam gives a smooth continuous movement.

Let's look at that in a little bit more detail.

As the cam moves around, notice the follower getting higher and higher and higher as it gradually rises until its top point.

When it gets to its top point, it gradually falls until it becomes at its lowest point.

Notice though, the difference between the eccentric and the pear is that the eccentric cam does not rest.

It's always moving that continuous movement.

Eccentric shaped cams can be used in fuel pumps to maintain steady pressure and flow.

The motion of the follower using a snail shaped cam, gradually rises and then suddenly falls.

Let's take a closer look.

As you can see, the cam is moving round, and the follower gradually rises slowly until it gets to its top point.

Notice what happens next.

All of a sudden it falls.

Now, notice that follower has not gone gradually down, it's done that sudden drop.

Now, snail shaped cams can be used in punches or machines that require a sudden drop and a sudden amount of force, and that's why snail cams are great at their job.

Next check, which description fits the motion of the pear shaped cam? Is it A, gradually rises and suddenly falls, B, smooth continuous movement, or C, gradually rises, falls, and then appears to rest? Come back to me when you have an answer.

Well done, if you got C.

It gradually rises, falls, and then it's the only shaped cam that we've seen so far that appears to rest.

Aisha says, "I have used cams in my D&T work." You can see she's made a spider surprise with a cam and then a mechanical toy.

Think back to your design and technology education.

Have you made anything using cams? Here's Aisha's mechanical toy.

Which shape cam is this mechanical toy using? Is it A, eccentric, B, snail, or C, pear? Come back to me when you've got an answer.

Well done, if you got snail.

You can see that cam making the follower gradually rise and then of course doing that sudden drop, which are the features of a snail shaped cam.

Friction is one of our Keywords today, so let's define it.

Friction is resistance, which is encountered when two things rub together.

When the edge of the cam moves against the follower, friction occurs.

This can affect the mechanism's performance.

The shape of the follower can be changed to counter this.

Below are three types of followers.

We have the flat follower, which has a large surface area, so lots of friction and wear.

We have the roller, which moves around.

This reduces friction, so wears well and spins smoothly.

And lastly, we have the knife-edge follower.

The friction here is concentrated on one point, so often wears quite quickly.

The shapes differ depending on the application, because of the amount of friction produced.

Which follower will encounter the most friction from the cams edge? Would it be the flat, roller or knife-edge? Come back to me when you've got an answer.

Fantastic, well done, if you got flat.

It's the largest surface area, which therefore produces the most amount of friction.

On to Task A.

Number one, sketch the shape of the following cams. A, pear, B, eccentric, and C snail.

Then moving on to part two, label the different stages of motion that the follower goes through with the pear shaped cam.

Now you might find it useful to try and remember the words rise and fall, as you label this diagram.

Good luck, come back to me when you're done.

So let's take a little look at your answers.

Part A, the pear shaped cam looks a little bit, ironically, like a pear or an egg.

Part B is the eccentric, which is circular, with the offset centre.

It's a difficult phrase to say.

And then part C is the snail shaped cam that looks a little bit like a snail's shell.

Hopefully you got those right.

Moving onto part B, sorry, part two.

I asked you to describe the motion of the follower.

So as the pear shape cam moves round, you'll see the follower, the green part, gradually rises, it then gradually falls, and then as it comes to the bottom part of the egg or pear shaped cam, the radius between the centre and the edge of the circle is the same.

And this means that it enters the rest phase, until it continues back into the loop of gradually rising, gradually falling, and the rest phase again.

Hopefully you got that right.

If you didn't, just try and adjust your answers before we move on.

Let's now apply that wonderful knowledge.

So a mechanical toy has been designed that requires a cartoon character to rise gradually and then suddenly drop.

So for part three, please can you suggest a suitable cam shape? And then part four, explain how the cam and follower work together to produce this motion using sketches and annotations.

Come back to me when you're done.

Let's take a look at what your answers could include.

So part three, that has to be the snail shaped cam, because obviously that's the one that gives us that sudden drop for the cartoon character to suddenly drop down.

Part four, as the cam rotates, its shape moves the follower slowly upwards, which moves the character up slowly.

When the follower gets to the highest position, the cam then drops it suddenly to the lowest position.

And let's take a little look at that diagram.

You can see as the snail shaped cam is moving around, it's gradually moving up to the top, top point, and then all of a sudden, it suddenly falls.

Well done, if you got that right.

So we move on to our second and final learning cycle, where we are going to be exploring pulleys.

A pulley system transmits rotary motion from a driver pulley wheel, starts the motion to a driven pulley wheel through a belt.

Let's take a little look at the diagram.

So on the left, we have the driver pulley wheel.

That is where the motion starts.

That might be manually by maybe turning a handle or that might be through a machine.

Then that motion is transferred to the driven pulley wheel, which today is on our right, and that is transferred through the belt.

And you can see that orange belt going around both pulley wheels.

Now the belt fits into a groove on the pulley wheel and motion is transferred through friction.

Quick check, which type of motion do pulleys transmit? Is it A, linear, B, reciprocating, C, oscillating, or D, rotary? Come back to me when you've got an answer.

Well done, if you got rotary as your answer.

That is correct.

Have a little look at the gif on the left hand side.

What do you notice about the direction that the birds are moving in? Tell the person next to you and come back to me.

Andeep says, "They both move in the same direction as each other." Fantastic, well done, Andeep.

Take a little look at the next gif.

Which direction do the birds move in, in this one? Come back to me when you've got an answer.

Laura says, "They move in opposite directions." She's absolutely right.

Both of them are right.

So what is the one thing that is different about these two gifs? Have a little look.

Chat with the person next to me and come back once you've worked it out.

Hopefully you've worked it out.

Laura says, "The pulley belt is crossed." Take a little closer look, if you haven't yet noticed that.

A pulley belt in this instance is yellow and you can see it's been crossed over between the two pulley wheels.

Crossing the belt makes the driver and driven pulley wheels turn in opposite directions to each other.

Let's test that knowledge out then.

Which diagram is not correct? Look at them closely, but look at the direction of those arrows.

Come back to me when you've got an answer.

Fantastic, if you got C right.

As you can see, the arrows on C are both moving in the same direction as each other.

Whereas, crossing the belt enables the two pulley wheels to move in opposite directions to each other.

I have two spanners here.

Imagine each spanner is turned at the same speed as each other.

Which spanner will complete a full turn first? Have a little think.

Tell me or tell your partner what you think, and come back to me when you're done.

Jacob says, "The smallest spanner, as it has less distance to travel." Jacob's absolutely right.

And it's the same with a pulley system.

The smaller the pulley wheel, the quicker it will complete a rotation in a given amount of time.

So let's apply that information to a real life product.

Now, this is my pillar drill in one of my workshops.

You might have a pillar drill like this in one of your workshops, and perhaps if you ask your technician or your teacher, they might be able to show you the insides too.

So the inside of the pillar drill uses a pulley system to change the speed that the drill spins.

The pulley wheels have multiple diameter grooves, allowing quick and easy speed adjustments to be made.

And you'll see I put a bit of a zoom in on that pulley wheel.

You can really notice on that pulley wheel, the grooves where that belt slots into, so that the belt doesn't slip out.

And again, we use that to change the speed that the drill spins at.

So I hear you asking the question, "Why would we need to change the speed of our pillar drill?" Well, let me explain.

Timbers can handle fast drill speeds without damaging the drill bit or causing overheating.

Therefore, the belt can be placed on a smaller diameter pulley wheel.

However, we can move that belt down, and that's what I'm trying to show here in this second picture.

I've moved the belt down here, to the larger diameter groove on the driven pulley wheel.

The reason I've done that is that drilling through different materials such as metals, generates more heat.

So slower speeds reduce the heat buildup and extend the drill bit life.

Something that you might never have noticed, something that perhaps your technician normally sorts out for you.

Let's have a quick check.

Decreasing the size of the driven pulley wheel has what effect on the output? Does it decrease the speed, increase the speed, or does it make no difference? Think back to the pillar drill.

Come back to me when you've got an answer.

Well done if you got, increases the speed.

Now this is a common misconception.

Lots of people think if you increase the size of a wheel, it's going to increase the speed, when actually, it's the opposite.

Remember that spanner, the smaller the spanner, the quicker it manages to get around the circle in comparison to the larger spanner.

So decreasing the size of the driven pulley wheel will actually increase the output speed.

Well done, if you got that right.

On to Task B.

First activity, I would like you to label my pillar drill.

And please can you label it with the following, motor, belt, driver pulley wheel, and driven pulley wheel.

Have a go.

So hopefully, you've got these answers.

A, is of course, the driver pulley wheel, because actually that's attached to D, which is the motor.

B, is of course, your driven pulley wheel.

And we know that, because you can see the drill bit underneath that.

Part C, is the belt, and then Part D, is the motor, because it's underneath the driver pulley wheel.

Well done, if you got those right.

Next part, have a little look at the diagram below, and please note the wheel on the left is the driver pulley wheel, and the wheel on the right is the driven pulley wheel.

Remember that the motion starts with the driver pulley wheel.

So for part two, I would like you to describe what you could do to change the direction of the driven pulley.

Part three, describe what you could do to decrease the speed of the driven pulley wheel.

And then part four, name a product that uses a pulley system and explain why it is used.

Good luck, have a go.

Let's take a little look at your answers.

For part two, crossing the belt makes the driver and driven pulley wheels turn in opposite directions.

Part three, you were asked what you could do to decrease the speed of the driven wheel.

And to do that you could increase the diameter of the driven wheel, because that means that the driven wheel has further to go around in a set amount of time.

Number four, you were asked for an example that uses a pulley system.

So obviously, the pillar drill, just like the one in my classroom, uses a pulley system to change the speed of rotation of the drill bit depending on the material required for drilling.

So for example, when we're drilling through metal, it requires a slower drilling speed, in comparison to timber.

So that enables me or my technician to be able to quickly and efficiently change the speed of the pillar drill.

Well done, for all of your efforts.

Wow, that brings us to the end of cams and pulleys.

Let's recap what we have learned today.

So cams convert rotary motion into reciprocating motion.

The shape of a cam determines the speed and magnitude of the motion.

Remember, magnitude means height.

The shape of the bottom of the follower changes the accuracy of the motion.

However, this does affect wear and friction.

Pulley systems transmit rotary motion from a driver pulley wheel to a driven pulley wheel through a belt.

And crossing the belt makes the driver and driven pulley wheels turn in opposite directions.

A massive well done, with all your hard work and efforts today.

And I look forward to seeing you soon for another lesson.

Take good care.

Bye, bye, bye.