A cam is a way of converting rotary motion into reciprocating (back and forth) motion. You can download the parts to make your own cam here. By changing the shape of the cam a variety of different types of motion can be created. Cans are often used in automata to help bring moving characters to life.
Parts of the Cam
This type of cam is known as a snail cam, because it is shaped like a snail shell. As the cam turns, the push rod raises at a steady rate. At the top of the rise the cam follower suddenly drops down and the process starts again.
The graph below shows how the rotation of the cam changes the position of the can follower.
The shape of the cam is known as the cam profile. Change the cam profile and change the story!
Double Snail Cam
By making the cam profile into a double snail profile the cam follower moves twice as fast.
Check out how the output movement changes in the graph.
By carefully shaping the cam profile it is even possible to make make the cam follower pause. In this cam the follower pause for a quarter of a turn at the top and at the bottom. This is known as dwell.
You can see the dwell in the graph below…
Cam Follower Design
As the cam turns it has a tendency to push the cam follower to one side. To overcome this a separate cam follower and push rod can be used as in this mechanism. Here the cam follower drags over the cam surface, accurately tracing the surface of the cam. Any movement of the cam follower is transferred directly to the push rod
Snail Cam video