# An Introduction to Mechanisms

## 1 Cams

### Learn It

• A mechanism is a device that takes an input motion or force and outputs a different motion or force.
• Gears trains, for instance, are a type of mechanism.
• This gear train takes rotary motion as input, and outputs rotary motion. The difference between the input and output is the speed and direction of the motion.
• In this project you're going to be looking at different type mechanism called a Cam Mechanism.

### Learn It

• Cam mechanisms turn rotary motion (round and round) into reciprocating motion (up and down)

### Learn It

• A cam mechanism is made up of three main parts: cam, slide and follower. In the image below, the slide (or guide) is the red ring.
• The cam rotates continually. The follower is a rod that rests on the edge of the turning cam.
• The follower moves up and down, but can't move to the side because of the slide or guide.
• This means the cam follower can only:
• Rise
• Fall
• Dwell

### Learn It

• We can draw what are know as `displacement graphs` for any cam mechanism.
• A displacement graph shows how the follower moves as the cam rotates.
• Follow these steps to create your own displacement graphs. This one is for a pear cam.

• Click on the following link to complete the quiz on different types of cams and displacement graphs.

### Try It

• Let's try and make one of the Cams in SolidWorks
• We'll make a pear-shaped Cam.
• If you've forgotten how to get started in SolidWorks, then ask your teacher for some help.
• First we'll need a couple of circles, as shown below
• Notice the little symbol between the circles like this.
• This means they have a tangential relationship (look up the word tangent if you don't know what that means)
• You can give sketch elements a tangential relationship by shift-clicking both elements and choosing `tangent` from the menu on the left
• The centre of the two circles also have a `horizontal` relationship
• Now draw two straight lines as shown below. Don't let them touch the circles yet.
• We can now give the lines a tangential relationship with each of the circles.

-Then use thew trim tool to cut away the lines you don't want

• Lastly you can add a small circle in the cam, where doweling would go.
• Once completed, you can extrude the sketch.
• Note that this is just practice and not your actual cam, which will need to have a different center cut-out.

• Using SolidWorks, produce either a heart, drop, irregular or ratchet cam.
• The Cam's diameter must not exceed 60mm.
• Screenshot your finished sketches including the part where it states your sketch is fully defined.

### Try It

• We can animate cams in SolidWorks as well.
• Create a new assembly and import in one of your cams.
• Now select `New Motion Study` from the tool bar.
• Near the bottom of the screen, the motion study will appear. In it's tool bar is the symbol for a motor - click it.
• Now you'll need to select the inner face of the cam, to choose what part the motor will turn.
• You should see it populated in the menu on the left. You can make other changes here as well, such as the speed of rotation.
• Once you're done, watch the animation using the play buttons.