WEBVTT - TechStuff Tidbits: How do Cams work?

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<v Speaker 1>Welcome to tex Stuff, a production from my Heart Radio.

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<v Speaker 1>He there, and welcome to tech Stuff. I'm your host,

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<v Speaker 1>Jonathan Strickland, and I'm an executive producer right here at

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<v Speaker 1>the Heart Radio. And how the tech are you. I've

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<v Speaker 1>got an upcoming episode with a special guest that I'm

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<v Speaker 1>really excited about. And in that episode, I'm probably gonna

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<v Speaker 1>talk a little bit about a system that uses cams.

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<v Speaker 1>So I thought today's Tech Stuff Tidbits, I would actually

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<v Speaker 1>talk about cams, what they are, what they do. This

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<v Speaker 1>will be a true tidbits episode. It will not be

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<v Speaker 1>a fifty minute tidbits episode. So we're just gonna look

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<v Speaker 1>at cams and what they do. Now. And now, first

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<v Speaker 1>of all, I am talking about mechanical cams mechanical systems,

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<v Speaker 1>So when I say cams, I am not talking about cameras.

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<v Speaker 1>So this is not about webcams or anything like that.

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<v Speaker 1>That's a totally different thing. Instead, we're talking about components

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<v Speaker 1>used in some mechanical systems for the purposes of generating

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<v Speaker 1>a particular motion at a specific timing. So, to put

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<v Speaker 1>it simply, cams are components in a mechanical system that

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<v Speaker 1>convert ordinary rotational motion into something else typically into a

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<v Speaker 1>reciprocating motion, a linear reciprocating motion, so it and up

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<v Speaker 1>and down or in and out motion, if you want

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<v Speaker 1>to think of it that way. Now, to talk about

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<v Speaker 1>cams and how they work, let's let's really consider mechanical systems,

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<v Speaker 1>and I'm going to really look at, you know, electro

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<v Speaker 1>mechanical systems in particular. So first let's let's think about

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<v Speaker 1>motors and electro magnets. And I know I talk about

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<v Speaker 1>electro magnets a lot on this show, but as it

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<v Speaker 1>turns out, there at the heart of a lot of

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<v Speaker 1>different mechanical and electrical systems. So it comes with the territory, right.

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<v Speaker 1>I'm sure most of us know that if you wrap

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<v Speaker 1>a conductive wire around, say a core of iron, like

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<v Speaker 1>a little iron rod, or the very simple version an

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<v Speaker 1>iron nail. So you get some copper wire and you

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<v Speaker 1>wrap several coils around a copper nail, and then you

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<v Speaker 1>connect that wire to something that generates a current, like

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<v Speaker 1>a battery. Then you get yourself an electro magnet. The

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<v Speaker 1>electro magnet will have its own magnetic field, with its

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<v Speaker 1>own magnetic north and magnetic south pole, and it will

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<v Speaker 1>behave just like a permanent magnet would, which means if

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<v Speaker 1>you bring the north end of your electro magnet near

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<v Speaker 1>the south end of a permanent magnet, the two magnets

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<v Speaker 1>will attract each other. If you bring the north end

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<v Speaker 1>of your electro magnet near the north end of a

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<v Speaker 1>permanent magnet, they will repel each other because opposite magnetic

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<v Speaker 1>charges attract, and like magnetic charges or poles, if you

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<v Speaker 1>prefer repel. Now, let's make things a bit more complicated.

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<v Speaker 1>Let's say that we connect our electromagnet not to a

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<v Speaker 1>battery which supplies direct current, meaning the current always flows

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<v Speaker 1>in the same direction, but to a source of alternating current.

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<v Speaker 1>So now the direction of current switches from one direction

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<v Speaker 1>to the other, often at very high frequencies, and each

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<v Speaker 1>time it switches, the magnetic field switches as well. So

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<v Speaker 1>when the current flows in one direction, the north poles

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<v Speaker 1>on one side of the electromagnet the south poles on

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<v Speaker 1>the other, current switches directions those poles flip. So what

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<v Speaker 1>was the north pole of the electromagnet is now the

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<v Speaker 1>south pole, and vice versa. Now, if you brought this

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<v Speaker 1>kind of electro magnet near a permanent magnets, poll doesn't

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<v Speaker 1>matter which of the poles we're talking about. Your electro

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<v Speaker 1>magnet would alternately attract and repel the permanent magnet because

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<v Speaker 1>the poll would be flipping on your electromagnet. So some

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<v Speaker 1>times it would be north to north and sometimes it

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<v Speaker 1>would be north to south. All right, Now, let's imagine

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<v Speaker 1>that we've got a permanent magnet. Let's say it's in

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<v Speaker 1>the shape of a U. Okay, and the north pole

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<v Speaker 1>is on the left tip of the U from our perspective,

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<v Speaker 1>and the south pole is on the right tip of

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<v Speaker 1>the U. This magnet does not move. It's in a

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<v Speaker 1>fixed position. We call it a statter. It is stationary,

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<v Speaker 1>so statters s T A T O R. In between

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<v Speaker 1>these poles. In the center between the two we mount

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<v Speaker 1>our electro magnet, which has no magnetic field. If we're

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<v Speaker 1>not running a current through those coils, right, and our

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<v Speaker 1>electro magnet is on an axle that can rotate, so

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<v Speaker 1>the electromagnet can spin freely between the two poles of

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<v Speaker 1>the permanent magnet. Now, if we run alternating current through

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<v Speaker 1>our electro magnet at the right frequency, we can cause

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<v Speaker 1>this electro magnet to rotate and keep rotating by flipping

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<v Speaker 1>the direction of the current and thus the electro magnets

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<v Speaker 1>magnetic field, and it will consistently push against the permanent

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<v Speaker 1>magnets magnetic field on either side, because that field is

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<v Speaker 1>not going to move right. The permanent magnets field is fixed.

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<v Speaker 1>It's a statu our rotor the electro magnet. It's poles

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<v Speaker 1>keep flipping so that it's consistently pushing against these magnetic fields,

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<v Speaker 1>causing the electro magnet to rotate. So if you just

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<v Speaker 1>time this perfectly, you can create this source of rotational force. Now,

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<v Speaker 1>if we want to use a direct current, we could.

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<v Speaker 1>You know, the problem with the direct current is unless

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<v Speaker 1>you have a way of flipping the poles of your

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<v Speaker 1>electro magnet, your electro magnet is just going to orient

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<v Speaker 1>itself so that the opposite poles are attracted to the

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<v Speaker 1>permanent magnet. Right, it'll move in a horizontal plane relative

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<v Speaker 1>to our our permanent magnet's polls, and it won't go

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<v Speaker 1>any further than that because it will be held in

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<v Speaker 1>place by magnetic force. But if we use a structure

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<v Speaker 1>called a commutator, which effectively flips the polarity of the

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<v Speaker 1>electro magnets magnetic field, by changing how the electromagnet connects

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<v Speaker 1>to the circuit that's providing the current as the electromagnet rotates,

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<v Speaker 1>then you have essentially the same effect as if you

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<v Speaker 1>had connected the electro magnet to an alternating current. There's

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<v Speaker 1>more to it than that, but we've already spent enough

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<v Speaker 1>time here, and I've done other episodes where I've talked

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<v Speaker 1>about commutators and how they work. Now, the point is

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<v Speaker 1>that these motors, these electric motors, generate rotational force. But

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<v Speaker 1>that's all they do, right. They can't they can't generate

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<v Speaker 1>a different kind of force there. The way that they

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<v Speaker 1>are designed mechanically means that they make things spin. They

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<v Speaker 1>don't make things go up and down or anything like that.

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<v Speaker 1>But rotational force can be useful for a lot of stuff.

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<v Speaker 1>Like you know, a relatively simple use would be to

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<v Speaker 1>drive an electric drill. The rotational force from the motor

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<v Speaker 1>provides the drilling action you need. It's providing the rotational

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<v Speaker 1>force to your drill. Bit. So there are legit uses,

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<v Speaker 1>simple uses for the electric motor, but a lot of

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<v Speaker 1>mechanical systems often require other types of motion, not just rotational.

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<v Speaker 1>So to accomplish that we have to get a little creative.

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<v Speaker 1>We have to think of ways to convert rotational force

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<v Speaker 1>generated by the electric motor into something else, and that's

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<v Speaker 1>kind of where cams can come in. So a cam

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<v Speaker 1>rotates on the axis of a shaft that could be

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<v Speaker 1>driven by something like an electric motor, So it's getting

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<v Speaker 1>rotational force from some part of the mechanical system. And

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<v Speaker 1>a cam on a shaft is frequently and a regularly

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<v Speaker 1>shaped object. It can be sort of like an eccentric

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<v Speaker 1>wheel is a very frequent example. So imagine you have

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<v Speaker 1>a wheel. Let's start with a perfect circle. Just imagine

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<v Speaker 1>a perfect circle on your mind. Now imagine deforming this

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<v Speaker 1>perfect circle a bit. Maybe parts along the circumference bulge out,

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<v Speaker 1>making it a little more oblong, or maybe they dip

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<v Speaker 1>inward a bit, so that you have still generally a

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<v Speaker 1>circular shape, but it's not perfect anymore. There are parts

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<v Speaker 1>of the circumference where it's a different shape. So by

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<v Speaker 1>positioning cams at specific points along a shaft where they

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<v Speaker 1>will make contact with other mechanical elements such as levers,

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<v Speaker 1>you can translate rotational motion into something else, like reciprocating

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<v Speaker 1>linear motion. So let me give you an example imagine

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<v Speaker 1>you have a horizontal shaft that can rotate in a

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<v Speaker 1>particular way. And this shaft, and in this example, we'll

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<v Speaker 1>say it connects to an electric motor. So the electric

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<v Speaker 1>motor is providing the rotational force turning the shaft, and

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<v Speaker 1>you know, let's say it's a clockwise direction from our perspective.

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<v Speaker 1>And then let's say that we have a cam positioned

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<v Speaker 1>midway down the length of this shaft. It is permanently

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<v Speaker 1>attached to the shaft. It will rotate along with the shaft.

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<v Speaker 1>It is as as far as we're concerned, part of

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<v Speaker 1>that shaft. This cam, let's say his egg shaped, so

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<v Speaker 1>one side of the cam bulges outward compared to the

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<v Speaker 1>rest of it. And positioned above this cam is a

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<v Speaker 1>type of lever that will call a cam follower. So

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<v Speaker 1>this follower is actually making contact with the surface of

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<v Speaker 1>the cam itself. So if you're thinking about let's say

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<v Speaker 1>a vinyl record or a wheel, it's making contact with

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<v Speaker 1>the the outer surface of this wheel, like the edge

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<v Speaker 1>of it. In other words, and the lever is attached

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<v Speaker 1>to something else in this mechanical system. So let's say

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<v Speaker 1>in our example, this lever which can move up and

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<v Speaker 1>down is connected to a little mechanical gopher, and this

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<v Speaker 1>gopher will pop out of a hole that's in some

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<v Speaker 1>rundown and yet still vaguely charming theme park attraction at

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<v Speaker 1>your local amusement park. So as the shaft rotates, the

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<v Speaker 1>cam rotates too, because it's attached to the shaft, it's

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<v Speaker 1>part of the shaft, and the bulging bit of this

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<v Speaker 1>oblong cam's surface rises up to meet the lever, which

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<v Speaker 1>means it pushes against the lever, pushing it upward. So

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<v Speaker 1>the lever goes up, which in turn pushes our little

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<v Speaker 1>mechanical gopher up out of the hole. The cam continues

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<v Speaker 1>to rotate with the shaft, and so the bulging bit

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<v Speaker 1>of this part of the cam is now sloping away

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<v Speaker 1>from the lever, so the lever can actually start to

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<v Speaker 1>come back down again. It's sliding along the surface of

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<v Speaker 1>the cam as the cam rotates away, and you know,

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<v Speaker 1>gravity just pulls our little gopher back down the hole.

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<v Speaker 1>The full distance that the lever is able to travel

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<v Speaker 1>due to how it connects to this cam is called

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<v Speaker 1>the throw. That is the throw of our cam follower.

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<v Speaker 1>Now the cam followers don't have to rely purely on

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<v Speaker 1>gravity to move back down. In fact, that would be

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<v Speaker 1>a very bad design because over time the leaver could

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<v Speaker 1>start to stick in the up position. Our gopher might

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<v Speaker 1>not ever go back down into its hole. It just

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<v Speaker 1>stays up there, which is just another reminder of how

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<v Speaker 1>this park isn't the same as it was when you

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<v Speaker 1>were a kid. No, I made myself sad. We'll tell

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<v Speaker 1>you what. We're gonna take a quick break. When it

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<v Speaker 1>come back, we'll get happy again. Okay, let's get back

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<v Speaker 1>to our discussion about cams and and the example we

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<v Speaker 1>were thinking about with the little gopher that can pop

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<v Speaker 1>up and down based upon the rotation of this cam

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<v Speaker 1>pushing against a lever. Again, you probably wouldn't just rely

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<v Speaker 1>on gravity on these systems. You would probably have some

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<v Speaker 1>other form of device that would ensure that the lever

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<v Speaker 1>would return to uh it's full down position in this case,

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<v Speaker 1>so we would probably have something like maybe a spring

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<v Speaker 1>connected to this lever, so that when the cam is

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<v Speaker 1>pushing against the lever, pushing it up, you know, moving

0:12:46.520 --> 0:12:49.280
<v Speaker 1>the gopher up out of the whole. In the process,

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<v Speaker 1>the lever is also compressing a spring, and as the

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<v Speaker 1>cam's edge slopes away from the lever, allowing it to

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<v Speaker 1>move back down again. The spring actually forces the lever

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<v Speaker 1>to move back down towards the cams surface, so that

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<v Speaker 1>you don't just have a gopher stuck out of its hole.

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<v Speaker 1>Internal combustion engine cars use cams. In fact, they have

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<v Speaker 1>a special shaft called the cam shaft that uses these

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<v Speaker 1>to govern the intake and exhaust valves in the combustion engine.

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<v Speaker 1>That's why I specifically say internal combustion engine cars. The

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<v Speaker 1>cams in this case are used to to govern, or

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<v Speaker 1>to control when an intake valve is open and when

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<v Speaker 1>it's closed, and when the exhaust valve is open and

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<v Speaker 1>when it's closed. You don't need those in an electric

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<v Speaker 1>vehicle because you don't have the combustion uh cylinders. So

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<v Speaker 1>let's talk about internal combustion engines and cams in those

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<v Speaker 1>really quickly to kind of understand how cams are used

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<v Speaker 1>in modern mechanical systems. So, an internal combustion engine burns

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<v Speaker 1>a mixture of fuel and air inside fix cylinders. The

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<v Speaker 1>energy generated from this combustion it's really an explosion, is

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<v Speaker 1>used to push a piston outward. The piston, in turn

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<v Speaker 1>provides power to the car's power train. Via a crankshaft

0:14:14.920 --> 0:14:17.880
<v Speaker 1>and then in turn provides power to the wheels. The

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<v Speaker 1>crankscheft also, by the way, provides rotational power for the

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<v Speaker 1>actual camshaft. That's part of this system too. Will get

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<v Speaker 1>to that. And all of this means that you can

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<v Speaker 1>have your car go without having to do the flintstones

0:14:30.360 --> 0:14:33.880
<v Speaker 1>thing and just use your feets. So the pistons connect

0:14:33.920 --> 0:14:37.000
<v Speaker 1>to a crank cheft via piston rods. It's that connection

0:14:37.040 --> 0:14:39.920
<v Speaker 1>that allows the reciprocating motion of the pistons, the in

0:14:40.080 --> 0:14:43.800
<v Speaker 1>and out motion of the pistons as they move relative

0:14:43.880 --> 0:14:48.640
<v Speaker 1>to the cylinders, into rotational motion for the shaft itself.

0:14:49.200 --> 0:14:51.840
<v Speaker 1>These are really tricky things to talk about without the

0:14:51.960 --> 0:14:54.960
<v Speaker 1>use of visual aids, but you know, just think that

0:14:55.000 --> 0:14:58.040
<v Speaker 1>the up and down motion of the piston is connected

0:14:58.200 --> 0:15:02.200
<v Speaker 1>via this rod to a shaft that can then rotate

0:15:02.800 --> 0:15:04.840
<v Speaker 1>due to the up and down motion of the piston.

0:15:05.640 --> 0:15:08.600
<v Speaker 1>All right, Now, let's talk about a four stroke engine

0:15:08.640 --> 0:15:12.720
<v Speaker 1>because that will illustrate how this is all working and

0:15:12.840 --> 0:15:16.040
<v Speaker 1>where the cams come involved. So when we say stroke,

0:15:16.560 --> 0:15:20.600
<v Speaker 1>what we mean is one full travel of a piston,

0:15:20.800 --> 0:15:26.240
<v Speaker 1>either inward into the cylinder or outward relative to the cylinder.

0:15:26.600 --> 0:15:30.720
<v Speaker 1>So in is one stroke, out is another stroke, and

0:15:31.560 --> 0:15:36.640
<v Speaker 1>internal combustion engines traditionally use four strokes, so those four

0:15:36.640 --> 0:15:41.080
<v Speaker 1>strokes are intake. This is where a cylinder pulls in air,

0:15:41.240 --> 0:15:45.000
<v Speaker 1>and it does this by opening the intake valve. As

0:15:45.040 --> 0:15:49.920
<v Speaker 1>the piston is traveling outward from the cylinder, This draws

0:15:50.000 --> 0:15:53.240
<v Speaker 1>air into the cylinder, kind of like if you were

0:15:53.240 --> 0:15:56.960
<v Speaker 1>pulling the plunger back on a syringe. At the end

0:15:57.000 --> 0:16:01.360
<v Speaker 1>of the stroke, the intake valve closes, which is absolutely critical.

0:16:01.400 --> 0:16:05.360
<v Speaker 1>It has to close, and that seals the cylinder. You

0:16:05.400 --> 0:16:07.640
<v Speaker 1>also get a mix of fuel that enters into the

0:16:07.680 --> 0:16:09.960
<v Speaker 1>cylinder at this point, so in older cars that would

0:16:10.000 --> 0:16:13.320
<v Speaker 1>come from a carburetor, in modern vehicles from the fuel

0:16:13.320 --> 0:16:17.680
<v Speaker 1>injection system. The next stroke, the piston is moving back

0:16:17.920 --> 0:16:22.080
<v Speaker 1>inward relative to the cylinder, and this stroke is called

0:16:22.160 --> 0:16:25.840
<v Speaker 1>compression because the piston, which is you know, snugly set

0:16:25.840 --> 0:16:29.200
<v Speaker 1>in the cylinder so nothing can escape along the sides

0:16:29.240 --> 0:16:32.280
<v Speaker 1>of the piston. As it moves back into the cylinder,

0:16:32.720 --> 0:16:36.520
<v Speaker 1>the piston compresses this mixture of air and fuel that

0:16:36.640 --> 0:16:40.520
<v Speaker 1>has entered into the cylinder. At the end of this stroke,

0:16:40.960 --> 0:16:43.960
<v Speaker 1>the piston is as far into the cylinder as it goes,

0:16:44.600 --> 0:16:48.320
<v Speaker 1>and both intake and exhaust valves have to be closed, right,

0:16:48.360 --> 0:16:51.720
<v Speaker 1>because if either valve were open, then that would mean

0:16:52.320 --> 0:16:55.880
<v Speaker 1>that you couldn't compress the mixture. The mixture would be

0:16:55.920 --> 0:16:58.400
<v Speaker 1>forced out of the cylinder because one of the valves

0:16:58.400 --> 0:17:01.400
<v Speaker 1>had opened, So these valves have to be shut. The

0:17:01.440 --> 0:17:06.200
<v Speaker 1>next stroke is combustion. This is when the spark plug sparks,

0:17:06.240 --> 0:17:09.200
<v Speaker 1>which ignites the mix of air and fuel. It causes

0:17:09.200 --> 0:17:13.280
<v Speaker 1>the explosion that forces the piston outward again, so the

0:17:13.320 --> 0:17:16.159
<v Speaker 1>piston moves down the length of the cylinder. It's this

0:17:16.240 --> 0:17:19.919
<v Speaker 1>force that provides the rotational force to the crank shaft

0:17:20.240 --> 0:17:24.720
<v Speaker 1>that ultimately makes the car go. As the crank shaft turns,

0:17:25.080 --> 0:17:28.479
<v Speaker 1>it pushes the piston rod as it rotates a one

0:17:28.520 --> 0:17:31.639
<v Speaker 1>full rotation around that therefore makes the piston go back

0:17:31.800 --> 0:17:35.280
<v Speaker 1>into the cylinder. For the fourth and final stroke of

0:17:35.280 --> 0:17:38.840
<v Speaker 1>this process, this is the exhaust stroke. So this is

0:17:38.880 --> 0:17:42.639
<v Speaker 1>when the exhaust valve opens and it allows the spent

0:17:42.960 --> 0:17:46.719
<v Speaker 1>air fuel mixture to escape the cylinder. At the end

0:17:46.760 --> 0:17:49.879
<v Speaker 1>of the stroke, the piston is as far into the

0:17:49.920 --> 0:17:52.720
<v Speaker 1>cylinder as it can be. The whole process is set

0:17:52.760 --> 0:17:56.840
<v Speaker 1>to repeat with the next intake stroke. And we do

0:17:56.880 --> 0:17:59.680
<v Speaker 1>it all again. So let's finally get to the cams,

0:18:00.119 --> 0:18:03.919
<v Speaker 1>because it's the cams that control the opening and closing

0:18:04.080 --> 0:18:07.840
<v Speaker 1>of those intake and exhaust valves. The cams are on

0:18:07.880 --> 0:18:11.640
<v Speaker 1>a cam shaft that ultimately receives its rotational power from

0:18:11.840 --> 0:18:17.040
<v Speaker 1>the crank shaft. As the cams rotate, their surface forces

0:18:17.080 --> 0:18:20.240
<v Speaker 1>their respective valves to open at just the right spot

0:18:20.440 --> 0:18:24.080
<v Speaker 1>during that rotation, and then the valves will close again

0:18:24.200 --> 0:18:27.840
<v Speaker 1>as the cams slopes away from the lever that is

0:18:27.880 --> 0:18:30.840
<v Speaker 1>attached to the valves. The cams are positioned in such

0:18:30.840 --> 0:18:33.080
<v Speaker 1>a way that they will always cause the valves to

0:18:33.119 --> 0:18:36.119
<v Speaker 1>open at just the right part in the stroke process

0:18:37.080 --> 0:18:39.400
<v Speaker 1>as the pistons are moving in and all of the cylinders,

0:18:39.440 --> 0:18:43.120
<v Speaker 1>and then they will remain closed for the other three

0:18:43.200 --> 0:18:48.040
<v Speaker 1>strokes of the four stroke process. Now, cams are used

0:18:48.040 --> 0:18:50.280
<v Speaker 1>in all sorts of mechanical systems, not just cars, And

0:18:50.320 --> 0:18:52.520
<v Speaker 1>the reason I even wanted to touch on these today

0:18:52.640 --> 0:18:54.840
<v Speaker 1>is because again, next week, I should have a new

0:18:54.840 --> 0:18:56.920
<v Speaker 1>episode up in which I'll talk about a theme park

0:18:57.359 --> 0:19:00.399
<v Speaker 1>that used cams in its attractions. Very some alert to

0:19:00.480 --> 0:19:04.080
<v Speaker 1>the gopher example I gave out, but far more complicated,

0:19:04.359 --> 0:19:07.120
<v Speaker 1>and I think it's good to occasionally reflect on mechanical

0:19:07.200 --> 0:19:11.000
<v Speaker 1>systems and get an understanding and appreciation for how humans

0:19:11.000 --> 0:19:14.720
<v Speaker 1>were able to create one and and and create devices

0:19:14.760 --> 0:19:18.679
<v Speaker 1>that could generate forces and also figure out ways to

0:19:18.720 --> 0:19:20.800
<v Speaker 1>harness that force to do work, even if it meant

0:19:20.840 --> 0:19:23.239
<v Speaker 1>having to convert one form of motion into another. It's

0:19:23.280 --> 0:19:26.480
<v Speaker 1>really clever stuff. And with cams, it's also old stuff.

0:19:26.480 --> 0:19:29.639
<v Speaker 1>There are illustrations of Chinese mechanical systems that used cams

0:19:29.640 --> 0:19:33.040
<v Speaker 1>to convert rotational motion like that provided by a water

0:19:33.080 --> 0:19:36.520
<v Speaker 1>wheel into reciprocating motion, so they've been around for a

0:19:36.560 --> 0:19:40.360
<v Speaker 1>really long time. Anyway, I hope you found that interesting

0:19:40.359 --> 0:19:43.760
<v Speaker 1>in this Tech Stuff Tidbits episode, and you know I'm

0:19:43.800 --> 0:19:46.760
<v Speaker 1>looking forward to that episode for next week. Keep an

0:19:46.760 --> 0:19:50.520
<v Speaker 1>ear out for it should be pretty fun and I'll

0:19:50.520 --> 0:20:00.200
<v Speaker 1>talk to you again really soon. Text Stuff is an

0:20:00.200 --> 0:20:03.879
<v Speaker 1>I Heart Radio production. For more podcasts from I Heart Radio,

0:20:04.200 --> 0:20:07.399
<v Speaker 1>visit the i Heart Radio app, Apple Podcasts, or wherever

0:20:07.480 --> 0:20:13.520
<v Speaker 1>you listen to your favorite shows. H