Grades 3–5 · Machines
How does a turning cam move a follower?
A turning wheel can make a little figure bob up and down instead of simply spinning. One way to do this is a cam: a rotating part whose surface pushes another part, called a follower. A guide keeps the follower moving along its intended straight path.
In the diagramRotation can become an up-and-down motionAxleFollowerGuide keepsmotion vertical0° cam turn0 mm rise10 mm offsetCam shape and contact determine follower height.
The circular cam here turns around a shaft that is not at the circle's center. This offset makes the height of its upper surface change as it rotates. A rising part of the surface pushes the follower upward. As that surface descends, the follower can move down again; gravity or a spring must keep it against the cam if it is to follow the whole motion.
The illustrated offset is 10 millimeters. When the circle's center moves from its lowest position to its highest, the upper surface rises by twice that offset, or 20 millimeters. In the initial pictured position the follower is at its lowest point, marked as zero lift. One complete revolution brings it back to the same position.
A cam therefore builds a repeating movement into a shape. A different profile can produce a longer pause or a differently timed rise. The turning shaft supplies the energy, the cam's surface sets the motion, and the guide prevents the follower from simply moving sideways.
About this explanation
Starting knowledge: Compare positions during a turn and recognize contact between parts.
Sources
- Adafruit Learning System — Cam Follower Basics
- LEGO Education — Teacher’s Notes: Mechanisms — Cam