Lesson video

Hello and welcome to today's Design and Technology lesson.

My name's Mrs. Fletcher and I'm really excited to be able to help and guide you through today's lesson.

Today's lesson is called Bell Crank and Lazy Tong Linkages, and it's part of the Levers and Linkages Interactive Books unit.

Let's have a look at what we are learning about today.

So the outcome for today's lesson is I can make bell crank and lazy-tong linkages.

Now that means by the end of today's lesson, we will not only have looked at what are bell crank linkages, what are lazy-tong linkages and where you might find them, but we'll also look at how they work and you'll even get to make your own version, so you can see how they really work in real life.

So there are some key words that we're going to need in today's lesson.

It's really important that we understand what these words mean because they are important to today's learning.

You may already recognize a few of them, but we'll go through them together and make sure we all know what they mean.

So we'll start with the word linkage.

Can you repeat that after me?

Linkage.

Well done.

Now, linkage is a mechanism connecting levers together.

So wherever we've got levers that are connected together, we refer to that as a linkage.

The second word is the word input.

Can you repeat that after me?

Input.

Well done.

The input refers to the motion or the movement that's used to get a mechanism started.

So a mechanism that moves needs to be started and the input is the movement that starts that mechanism.

The third word is the word output.

Can you repeat that?

Output.

Well done.

And the word output is the opposite of the word input.

It's the movement or motion that's created by the input.

So the next one is a phrase, loose pivot.

Loose pivot.

Well done.

A loose pivot is a free moving point that connects two levers together so it connects the levers together, but allows them to move because the pivot is loose.

And the last one is a fixed pivot.

Can you repeat that?

Fixed pivot.

Well done.

A fixed pivot is a point that connects a lever to one place.

So if a levers are connected or a lever is connected to a base with a fixed pivot, they are fixed to that one place.

They're not free to move.

Okay, so now we've got our keywords and phrases.

Let's have a look at what we're going to be learning today.

So the lesson is broken down into four parts today.

We'll start by looking at the key features of a bell crank linkage, how it works, what it looks like, and where you might find it in real life.

Then we'll move on to actually making a bell crank linkage so you can see for yourself how it works.

The third part of the lesson, we will look at the key features of a lazy-tong linkage where we find them, what it looks like and how it works.

And then in the last part of the lesson, you'll get to make a lazy-tong linkage as well.

So you'll get to see for yourself how that linkage works in real life.

So we'll get started with the key features of a bell crank linkage.

Now a lever you may already know is a rigid, which just means hard to bend, bar or beam that moves around a pivot.

And there's one of our key words that pivot.

We have a loose pivot and a fixed pivot, but a lever is connected via a pivot point, and you see simple levers in lots of everyday objects.

So you might see them in a seesaw where we've got a lever that moves up and down on each side on that pivot point in the center.

You might see it in a pair of scissors, which is actually two levers connected together by a loose pivot in the center, which allows them to both to move, making that cutting movement of a pair of scissors and you find them in door handles.

That's the mechanism that allows you to open and close the handle, push and pull the handle to open and close the door.

Now a linkage, as we said earlier, is a mechanism that connects one or more levers together.

So that's our key word linkage.

It's a series of levers connected together and they're connected via those pivot points.

So those two key words are very important today.

There's different ways to connect levers depending on what we want them to do and how we want them to move.

So we'll connect them differently depending on the type of movement we want them to make.

Okay, time for a quick check.

Now we've been learning about the word linkage today, but what does a linkage connect together?

Does it connect mechanisms?

Does it connect pivot points or does it connect levers?

Pause the video.

Have a think.

Well done if you said levers.

When a series of levers are connected together, we call that a linkage.

So let's have a look at a bell crank linkage.

So here's a diagram of a bell crank linkage.

You can see the three main parts that make up this linkage.

We've got the central piece looks a little bit like a triangle in the middle, and then we've got the input and the output which are levers connected to that central piece.

Now the input movement, so that's the movement that gets the mechanism started, causes an output movement at a set angle in a bell crank linkage.

And that angle is usually 90 degrees, which you might know as a right angle.

So that angle is set, the input and the output move in those same, in that same set direction, might look in be a different angle, but it moves at that same set angle in a bell crank linkage.

Now the two levers in this linkage connected to that central piece using loose pivots.

Now remember that was one of our key phrases.

The loose pivots are the ones that allow the lever to move independently, but it's not fixed to anything.

The two levers are connected to that central piece by the loose pivots.

So that's our key phrase of loose pivots.

So that means that the levers connected to that central piece in a way that allows it to move freely.

It's not fixed in one place.

Loose pivots also allow the levers to move in different directions as well.

There is a fixed pivot in a bell crank linkage and that is on the central piece and that means that that central piece can move around, but it's fixed to that one spot and it's connected to that base so it can stay in one place.

Now you can see here how the bell crank linkage works.

We've got that central fixed pivot holding the central piece to the background piece of car.

And there there are two levers attached on loose pivots, which means that they can move freely in different directions.

Now the angle usually stays at that 90 degree or right angle, but it can move, those levers can move independently of each other.

So time for another quick check now.

What connects the levers to the central piece in that bell crank linkage?

Is it loose pivots?

Is it fixed pivots or is it right angle pivots?

Pause the video, have a think.

Okay, well done if you said loose pivots.

In order for them to move freely, they need to be attached by loose pivots.

Okay, so where might you find a bell crank linkage?

Well, one place you might find one are on the brakes of a bicycle.

So if we have a look here, we can see the input of the bell crank linkage and bicycle brakes is the brake on the handlebar and the output are the brake pads themselves pushing against the wheel in order to stop it from moving.

So the brake handle is pulled vertically, so upwards by the rider and that's the input.

So that squeezing of the brake handle is the input that sets off this bell crank linkage mechanism in the bicycle brakes.

This moves the brake pads horizontally, pressing them together and that's what stops the wheel from moving.

So that's the output.

So we've got the input movement, which is pulling the handle brake, the brake handle, and then we've got the output movement, the brake pads pushing together against the wheel.

And that output we've got a vertical and a horizontal is at a 90 degree angle.

So that's how it works in the brakes of a bicycle.

Now we would use a bell crank linkage if we wanted a moving part, which would be the output to move at a set angle such as 90 degrees from the input.

So if we wanted to set this specific angle that the output was moving, then we could use a bell crank linkage, particularly if it was around 90 degrees.

So it doesn't matter which way around that would be, it's still working the same way.

So the input and the output would be at that fixed angle of around 90 degrees.

Here we've got a bell crank linkage being used to make a dinosaur's mouth moved in this moving picture.

You can see the input is moving the dinosaur's tail and the output is the dinosaur's mouth moving.

And if you have a look at the second image, you can see how that bell crank linkage is making that happen.

So the bottom lever is actually the dinosaur's tail and the top lever is connected to the jaw of the dinosaur, which is allowing it to move up and down.

So we've got that 90 degree angle of the bell crank linkage, allowing that movement in that moving picture.

Okay, time for your tasks now.

So first of all, I would like you to use the template on the worksheet and label the bell crank linkage with the correct pivot points.

So we've been looking at where those fix and loose pivot points are on a bell crank linkage, but can you label them now in the correct place and make sure you check that you've labeled three pivot points, because we've learned that a bell crank linkage has three pivot points when you've done that.

Task number two is to use this word bank and explain how a bell crank linkage works.

So using some of these keywords and phrases, can you explain what you've learned today about how it works?

So you might need to use the words fixed pivot, loose pivot, lever, 90 degrees or right angle, input and output.

Use those words, explain how the bell crank linkage works.

Pause the video, come back when you've had a go.

Okay, welcome back.

So let's have a look at what you have done for task number one.

So you needed to place the fixed and lose pivots on the bell crank linkage and this is how it should look.

So you should have one fixed pivot in that central piece of the bell crank linkage and you should have two loose pivots connecting the two levers to that central piece.

Have a quick check if that's where you've got them.

Well done if you did that correctly.

The second task then you were asked to do was to explain how a bell crank linkage works.

And I wanted to see you using some of those keywords and phrases that we've been learning in today's lesson.

And your answer might have been something a little bit like this.

A bell crank linkage has a central part with a fixed pivot.

It has two levers attached to the central piece using loose pivots.

The levers move at a fixed angle from each other.

This angle is usually 90 or a right angle.

So if you've got some of those keywords and phrase in there and you've explained it a little bit like this, then well done.

You can explain how a bell crank linkage works.

Okay, so it's time to move on to the second part of our lesson now where you get to make a bell crank linkage yourself and see how it actually works.

So we can make a bell crank linkage using the following tools and materials.

So these are things you'll need to get ready for this task.

You'll need a piece of recycled card for the background.

Now a cereal box is really good for this.

That kind of recycled card would work really well.

You will need some card templates of the three main parts of the bell crank linkage.

So you can either photocopy those onto card or you can cut them out and stick them onto card and cut them out again on the card.

You'll need a sharp pencil, a pair of scissors, three split pins and some sticky tack.

So quick check before we get started.

Which of these do you think we will use to make the pivot points on our bell crank linkage?

Will we use safety pins, split pins or drawing pins?

Which of those are we using to make the pivot points on our bell crank linkage?

Well done if you said split pins, those were on our list of tools and materials that we will need for today's lesson.

So these are the steps to making your own bell crank linkage and we'll go through them together and then you can pause the video and have a go at making it and then come back when you're finished.

So step number one, you'll need to use a pencil and sticky tack to safely make the holes in the levers and in that central piece.

The holes are marked on the templates for you.

You just need to make sure you use your pencil and your sticky tack to make those holes in the correct place.

Step number two, you'll need to attach the two levers to that central piece using the split pins and these will be loose pivots.

So the levers are connected to the central piece and they can move independently because they are loose pivots.

And then for step number three, you will need to attach that central piece to the background piece of card using another split pin, and this will be a fixed pivot.

So that central piece will be attached to the background card as a fixed pivot and the two levers will be attached as loose pivots.

So they will only be attached to the central piece, not to the background card.

Okay, so quick recap on how you can safely make those holes in your card templates.

Make sure that the sticky tack is underneath the hole guide on your card templates on the levers and that central piece before you pierce the hole with your pencil.

And make sure your pencil is sharp so that it makes the hole, the sticky tack will protect the table, protect your fingers and stop your pencil from breaking as well.

So task one then is for you to go away and have a go at making your own bell crank linkage.

So to make sure you get it right, you'll need to make sure you've got two levers at a 90 degree angle from each other.

So whichever way you've got it in front of you, make sure those levers are at a 90 degree angle or a right angle that you've got loose pivots connecting the levers to the central piece and you've got a fixed pivot connecting the central piece to the background piece of card.

So check you've got those three things to make your bell crank linkage work correctly, come back when you've had a go.

Okay, so hopefully you've finished and your bell crank linkage looks a little bit like this.

So did you check that you had two levers at a 90 degree angle or a right angle from each other?

So they're roughly at that kind of angle from each other whichever way you've attached it to your card.

You've got loose pivots connected to the central piece.

So the levers are connected with loose pivots to that central piece and you've got a fixed pivot connecting the central piece to the background card.

If you've got all those three things in the right place, then well done.

You've made yourself a bell crank linkage.

Okay, so part two of your task now is to use that success criteria that you've just used to evaluate your own linkage to evaluate your partner's linkage.

So I want you to swap your linkage with somebody else and have a look at your partner's linkage and have a look does it move in the correct way?

Is everything in the correct place?

If not, how could they improve it?

Which parts of the linkage have they not quite done right?

And I want you to feedback what you find and what you think about their linkage to your partner.

Remember to be positive.

Giving feedback should be positive and if there's something you can do to help them, then offer that as help as well.

Come back when you've had a go at evaluating your partner's linkage.

Okay, so hopefully your partner's linkage was made correctly.

If it wasn't, you were able to help them to fix it.

Now you may have given some feedback, something like this.

Remember we said it's important to be positive with feedback and to offer some help if it's needed.

So you might have said something like this, you have the correct number of levers and they are connected to the central piece with loose pivots.

Your levers are at a right angle, are 90 degrees from each other, but you've forgotten to attach the central piece to the background card to make a fixed pivot.

So in that feedback, I was being positive about what my partner had done, but I was also pointing out something that could be improved and then I would then offer to help them improve it if they needed some help.

So feedback can be very important, which should be done in a positive way.

Okay, time to move on to the third part of our lesson now.

So this is where we're going to look at the key features of a lazy-tong linkage.

So a different type of linkage to the bell crank.

We're going to look at how it works, where you might find it and what it looks like in real life.

So this is a lazy-tong linkage.

You can have a look at those two diagrams.

Now a lazy-tong linkage is made of levers which lengthen and shorten when one end is pushed or pulled.

So you can see in that top image that the linkage is contracted together in the middle and if they are pulled apart, if either end is pulled apart, then it lengthens.

If they're pushed back together, it shortens.

So either end of the linkage is moving in opposite directions.

So if the either end is pulled or pushed, they move in opposite directions.

Now the levers are connected together with loose pivots.

So because we want those levers to move, they are connected with loose pivots, and the pivots must be in a very specific place on a lazy-tong linkage, they must be in the center of the lever and they must be at each end of the lever as well.

Fixed pivots can be used but they can only be used in the center of the lever.

So you can see one on the diagram in the pink color is a fixed pivot, but it has to be in one of those central pivot points.

Each lever must have the same pivot points, so that they make the same movement at the same time.

So when we had a look at that diagram of the linkage moving in and out, all of the levers were moving in the same way and at the same time.

And that's what allows that lazy-tong linkage to move the way it does.

Have a look at these two images here.

So on the left we've got a lazy-tong linkage with all loose pivots.

So you can see it's being extended and contracted.

It's being lengthened and shortened and all of those pivots are loose, so they're all moving at the same point.

And if you look in the second image, there is one fixed pivot point in the center.

So it's on the left in the center and the effect that's having is when the linkage is extended, it's all moving away from that fixed pivot point, so that that side of the linkage can't move because it has a fixed pivot keeping it in place.

All the other pivots are loose.

So they are all moving in the same way as they did in the first image.

Quick check, a lazy-tong linkage needs three pivot points on each lever to work.

Is that true or false?

Does it need three pivot points in order to work?

Well done if you said true, but why did we say it needs three pivot points?

Well it's because the pivot points must be in that those same location on each lever to make the save movement at the same time.

So they need to be connected together in the middle and connected to each other at the top, so that they can all make that same movement at the same time.

Okay, so have you ever seen a lazy-tong linkage in real life?

You may be thinking of somewhere where you might have spotted it.

Now Jacob's seen one, he's seen some tools that use a lazy-tong linkage including this one here, which is a riveter, and the tool is on one end of the lazy-tong linkage and the handle is on the other.

And that allows the tool to be extended and shortened.

So it can work away from the hand and it also allows it to reach a bit further than the hand could as well.

So the lazy-tong linkage is used in tools quite often to extend the tool to make it longer.

You might also find a lazy-tong linkage in expanding garden fences.

So you can get fences that you can change the size and of by expanding or contracting the linkage mechanism.

We see them in trellis, which plants can climb up.

So you can extend and shorten those as well depending on the height of the plant.

You can see them in scissor lifts, which are often used to reach heights on buildings and you find them in some toys as well.

So they're not as commonly seen as some linkages, but you might be thinking of some places you have seen one.

Okay, another quick check now.

Why does the lazy-tong linkage need loose pivots?

So why does it specifically need all those loose pivots?

Is it to hold the lever in place?

Is it to make some of the levers move or is it to make all of the levers move?

Pause the video.

Have a think.

Well done if you said it's to make all the levers move.

So remember we said all the levers need to make the same movement at the same time to allow the lazy-tong linkage to make that movement that it makes.

Okay, it's time for your tasks now.

So first of all, task number one, I want you to use the template on the worksheet to draw and label the pivot points in the correct place for a lazy-tong linkage.

So just like we did earlier for the bell crank linkage, this time you're going to do it for the lazy-tong linkage.

So think about what type of pivot points you will need to label and where they need to be on a lazy-tong linkage.

When you've done that, task number two is to explain in your own words how a lazy-tong linkage works.

So we've looked at how it works, we've looked at where the pivot points go, and we've looked at how that allows it to move.

But can you explain using some of those keywords and phrases in your own words, how it works.

Pause the video and come back when you've had a go at those two tasks.

Okay, welcome back.

So hopefully you've got those two tasks completed.

Let's have a look at what you should have done.

So there should be a pivot point on your diagram at the end of each lever and in the center of each pair of levers.

So where the levers cross over, there should be a pivot point in the center and at the end of each lever, there should be a pivot point as well.

So there's three pivot points on each lever in a lazy-tong linkage.

If you included a fixed pivot, then that should just be in one of the central pivot points.

Okay, and then for part two of your tasks, you were asked to use your own words to explain how that lazy-tong linkage works.

So you may have answered something like this.

A lazy-tong linkage has several levers that are connected by loose pivots.

There must be an even number of levers.

The loose pivots allow all of the levers to move in the same way so the linkage can lengthen or shorten when it's pushed or pulled.

So we've got some of the key words in there of the linkage, the loose pivots, the fixed pivots you might have used as well to explain how it works.

So it's the lengthening and shortening of this linkage, which is the key feature.

And the three pivot points that they have on each lever, the position of those as well.

So if you've answered something like that, then you've correctly explained how a lazy-tong linkage works.

Well done.

So time to move on to the last part of our lesson now, and this is where you get to make your own lazy-tong linkage.

So you're going to have a look at how to make it and then you can have a go by yourself.

So we can make a lazy-tong linkage using the following tools and materials.

So you're going to need the card templates like we did for the bell crank linkage, either photocopied onto card or cut out and stuck onto some thin card.

You're going to need seven split pins for this task.

Some sticky tack, some scissors, some recycled card again for the background.

So something like the cereal box and a sharp pencil.

So again, I'm gonna go through the steps of how to make your own lazy-tong linkage.

We'll go through them together and then you can pause the video and have a go at making it by yourself.

So step number one of making a lazy-tong linkage, you're going to use your sharp pencil and your sticky tack again to safely make holes in all of the templates.

So you've got six levers and there are three pivot points on each one of those levers.

So safely make a hole in each of those hole guidelines.

Step number two, you're going to connect each pair of levers by the central holes using a split pin.

So you're gonna make like an X out of two levers and you're gonna do that three times.

So you've got three pairs of levers connected together in their central pivot points.

And then you're going to connect each of those pairs for step number three by the ends of the levers using another split pin.

So each end of a lever will be connected to another pair of levers using the holes at the ends of each lever.

So it should look like something like this in this diagram.

So you can add a fixed pivot point at this point once you've done those three steps to secure your linkage to the background to that background piece of card.

One of the central pivot points should be used for this.

So you might need to undo one of the split pins from a central pivot point and push it through the background card as well as the linkage.

On the left you can see what it looks like with no fixed pivot.

So you'll just have a free moving linkage that can be extended and short, lengthened and shortened like so.

But if you fix it with one of the central pivots, it will look something like the diagram on the right.

So where you put that central pivot point can change the way that your linkage moves.

If you attach your fixed pivot on the left side of your linkage, then everything will extend to the right.

If you fix it in the center, then the linkage will extend to both sides.

Both sides will move away from that central point.

And if you fix it on the right, then the linkage will extend to the left.

So the linkage will always extend away from that fixed pivot point.

You could have a go at trying all three fixed pivots and seeing the difference that it makes to the movement of the linkage.

So quick check before you go and make your linkage, which two things will you need to use to safely make the holes for the pivot points?

Will you need sticky tack, scissors or a pencil?

Which two of those things will you need to safely make holes for the pivot points?

Pause the video, have a think.

Okay, well done if you said sticky tack and a pencil.

So remember you need to use your sharp pencil to push through the card and the sticky tack underneath the card will protect the table and your fingers and the pencil as well.

So to safely pierce those holes, you need some sticky tack and a sharp pencil.

Okay, so that's your first task then is to go and make your lazy-tong linkage for yourself.

Make sure you follow those steps and that you have an even number of levers, because you need to make pairs of levers and pairs mean that we'll always need an even number of levers.

Make sure that your pairs of levers are connected with a loose pivot in the center and that the ends of the levers are connected to another pair using loose pivots as well.

You can have a go at exchanging some of those central loose pivots for a fixed pivot and attaching your linkage to the background card.

But make sure you've at least got those three points and you'll have a working lazy-tong linkage.

Pause the video and come back when you've done.

Okay, so hopefully you've done and your linkage looks something like this and it's moving something like this.

So just check that you have an even number of levers, so 2, 4, 6, 8, 10, all even numbers, because you need to make pairs of levers to connect together to make this linkage.

Make sure that each of the pairs of levers are connected with a loose pivot in the center and that the ends of each pair of levers are connected with a loose pivot to another pair.

You may have a fixed pivot in the center connecting to that background card, but if not, then you'll just have a free moving lazy-tong linkage.

If you've got all those three things then well done.

You've made yourself a working lazy-tong linkage.

Okay, so part two of your tasks today is to use the success criteria that we've just used to evaluate your own linkage, to evaluate your partner's linkage just like we did earlier on in the lesson.

So you're going to swap your linkage with somebody else and you're going to have a look.

Does it move in the right way?

Is everything in the correct place?

If it's not quite working, then how could it be improved?

How could it be fixed?

Can you help your partner with that?

And I want you to feed back what you found to your partner, remember to be positive and to help them if they need that help to make their linkage work properly.

So swap your linkages and come back when you've done.

Okay, welcome back.

So hopefully you've managed to have a good look at your partner's linkage and you've given them some positive feedback.

So your feedback might look something like this, it might have sounded something like this.

You have an even number of levers in your linkage.

You have connected all the pairs together using loose pivots on the end of each lever.

Each pair of levers are connected with a loose pivot, but they're not all in the center.

So the linkage does not move correctly.

So there was something to improve on that feedback.

Maybe your partner didn't have anything to improve, but if they did, hopefully you gave that feedback in a positive way and then offered some help for them to fix that problem in their linkage.

Well done if you did that.

Okay, so we have come to the end of today's lesson.

I've had so much fun learning about bell crank and lazy-tong linkages, and hopefully you've had fun making your own linkages as well.

So let's have a quick summary of what we've been learning in today's lesson.

So we learned that a bell crank linkage moves levers at set angles from each other.

So we saw that they were quite often in that right angle or 90 degree angle from each other.

A lazy-tong linkage was a little bit different, and that was made of levers which lengthen and shorten when one end is pushed or pulled.

The moving pivot points are those loose pivot points on a lazy-tong linkage must be in the correct place to allow those levers to move.

So they had to be three pivot points in the very specific places of the center and the ends of the lever in order for that linkage to make that very specific extending and contracting movement that it makes.

If they were not in the right place, then the levers cannot move together and it would not make that movement.

So thank you for joining me for this lesson.

Hopefully I'll see you again for another lesson.

But for now, this is goodbye from me.

I'll see you again soon.