Application Used: Autodesk Maya
Author: Bogdan Amidzic
I am going to show you two ways to do it.
So for starters, create a polygon cylinder with 20 segments, and cap segments to 0. Scale it down.
Then select every second face.
Go to edit mesh/transform component, this will give you a manipulator, scale around x a bit.
Then extrude those faces. If you need some tweaking, in the channel box you can see a list of inputs. Click on them to get options. Or press T key and you will get the manipulator.
So one gear is done.
Create another with 40 segments.
Rotate them to match, so there's no overlapping. Use + and - keys to change the manipulator size.
Then go to animation menu set, and then animate/set driven key/set
A window will pop open. Select the gear you will be rotating, when animating, and click load driver, choose rotateY. Then select the other gear and click load driven, choose rotateY. Press Key button. Don't close this window just yet.
Notice how driven objects rotateY is highlighted in orange - this means that it has a curve as input.
Rotate gears for one step, and then press key in set driven key window. Now there are two keys. If you rotate the driver object, the driven object will rotate also, but only for one step.
Select driven object and go to Graph Editor. Notice the green curve. This curve defines the relation between driver object rotationY and driven object rotationY.
Go to view/infinity
Now you can see how the curve looks before and after keys. So in our case this means that the gear will rotate only between those two keys, and before and after it will remain constant. That's why the second gear rotates only one step.
In the graph editor go to curves/pre infinity/linear and curves/post infinity/linear. Now when you rotate the first gear, the second rotates as well.
That was way #1. Now for way #2 (In Maya, there's at least 5 ways to do the same thing). Select driven object, right click on rotateY, and break connection.
Then in the same menu choose expressions.
Which means that smaller cylinder will rotate twice as slow as the bigger one, and in opposite direction (that's why there's -). We subtract 1.022 because the first frame rotation was -1.022, which basically offsets the gear.
So the cylinders rotate the same as in the first example
Now select all edges on the gear
Shift+RMB choose bevel edge.
Set options for bevel.