What it shows
Engine valves and sewing machines use cams to give exact timed motion. The project cuts three cam profiles, measures the follower rise at each angle and plots a displacement diagram, which shows why the shape of the profile matters for smooth motion.
The science
As the cam turns, the follower rises according to the profile radius at each angle. A circular cam with offset centre gives simple harmonic motion, a cam with straight flanks gives constant velocity (but with sudden changes, which cause shock), and a cam with cycloidal rise gives smooth acceleration. The displacement diagram plots follower lift against cam angle.
Materials
Cost: under Rs 500. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- 3 mm plywood or acrylic sheet
- A scroll saw or hand saw and sandpaper
- A shaft of 6 mm rod or bolt with a hand crank
- A follower made from a rod in a guide
- A ruler or dial indicator
- A protractor disc
- Graph paper
Safety
For this project: An adult must cut the sheet and drill. Wear a dust mask when sanding.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
10 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Draw the three profiles with a base circle of 3 cm radius and a lift of 1.5 cm: harmonic rise, uniform velocity and dwell-rise-return.
Transfer them to the sheet using tracing paper and cut slowly with a saw.
File and sand each profile smoothly and drill a central hole for the shaft.
Fix a protractor disc on the shaft so you can read angle, and set up the follower guide with the ruler beside it.
Turn the cam in 15 degree steps and record the follower position for each angle.
Repeat for the other two cams and for a full turn.
Plot displacement against angle for each cam on the same graph.
Calculate velocity from the slope between steps and note where the velocity jumps.
Turn each cam quickly by hand and feel the shock at the sharp changes in the uniform-velocity cam.
Write the report with the drawings, graphs and the choice of profile for a given application.
What you should see
The three displacement curves differ clearly: smooth S-shape for harmonic, straight for uniform velocity, and long dwell for the third. The uniform-velocity cam feels jerky at speed, which supports the theory.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is the base circle?
The smallest circle drawn from the cam centre that touches the profile.
2Why does the straight-flank cam give a jerk?
The velocity changes instantly, which needs infinite acceleration in theory.
3What is dwell?
A period during which the follower stays still while the cam rotates.
4Where are cams used?
In engine valve trains, textile machines, toys and printing presses.
Take it further
Drive the cam with a 12 V motor and measure the follower motion with a phone video at 240 frames per second.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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Mini and Major Project Guide
For diploma and BTech students: choose, plan, build, document and present
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Tools, Materials and Safety for Model Making
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