- Difficulty
- Beginner
- Build time
- 45-70 min
- Estimated cost
- $0-$12
- Age range
- 10-16
- Workspace
- A clear table about 90 cm wide
The finish line
What you will build
The follower completes one repeatable lift per cam turn, stays in contact through ten cycles, and reaches a measured rise close to the cam eccentricity.
Learning goals
- Identify how rotation of a shaped cam produces vertical follower lift.
- Construct and explain a rotary-to-reciprocating linear system.
- Measure how the cam profile changes performance.
- Diagnose losses caused by sliding contact and follower side rubbing.
Before you build
Materials, tools, and safety
Reuse-material cost: Usually under $5 with an existing kit. Supervision: Adult help recommended for sharp or heated tools.
Tools
- Ruler
- Removable tape for motion marks
Low-cost swaps
- Use equivalent brick-compatible parts from any kit.
- Use cardboard beams and straw bearings for a larger demonstration model.
- Cut two identical cardboard cam layers, laminate them, and run a skewer axle through the marked center.
Project-specific safety
- Keep fingers, hair, and loose sleeves clear of moving parts.
- Turn the mechanism by hand; do not attach a high-speed motor.
- Use only a light return band; a strongly stretched band can snap or overload the cam axle.
Orient the build
Place the build so rotation of a shaped cam is on your left and vertical follower lift is on your right. Call the side facing you the front, the far side the back, the tabletop the bottom, and the opposite face the top.
Build it
Step-by-step instructions
Step 1
Build the cam frame
Support one horizontal axle in two rigid walls.
Leave the cam face visible from the front.
Step 2
Mount the cam
Place the cam between the walls and mark its largest-radius point.
Add collars that prevent side rubbing.
Step 3
Create the follower
Build a straight vertical slider with a broad foot centered over the cam.
Keep the moving mass low.
Builder checkpoint: After create the follower, the first subassembly should stay aligned when handled gently.
Step 4
Add follower guides
Place upper and lower guides far apart to reduce rocking.
Leave a thin gap on every sliding face.
Watch for: If this stage binds or drifts, inspect insufficient return force before adding more parts.
Step 5
Provide gentle return
Use gravity or a lightly stretched band to keep the follower touching the cam.
Check contact at the smallest radius.
Step 6
Mark the lift scale
Set zero at the low position and add millimeter marks beside the flag.
Rotate to the high point and record rise.
Builder checkpoint: After mark the lift scale, operate the build slowly and confirm that vertical follower lift begins without binding.
Step 7
Turn one slow cycle
Rotate through rise, high point, fall, and low point over four seconds.
Listen for the follower losing contact.
Step 8
Compare profiles
Swap to a round eccentric or a cam with a flat dwell section.
Record timing and peak lift for each.
Builder checkpoint: At the final checkpoint, The follower completes one repeatable lift per cam turn, stays in contact through ten cycles, and reaches a measured rise close to the cam eccentricity.
See the engineering
Why it works
- Input
- rotation of a shaped cam
- Output
- vertical follower lift
- Motion
- rotary-to-reciprocating linear
- Energy losses
- sliding contact, follower side rubbing, cam wobble, insufficient return force
Why this works
Cam profile control
A follower's position is set by the distance from the cam axle to the contact point. Changing that radius around the cam programs rise, dwell, fall, and low intervals.
Look for: Mark the cam high point and watch it align with the follower at maximum lift.
Where the energy goes
Efficiency and losses
The ideal model leaves out sliding contact, follower side rubbing, cam wobble, insufficient return force. These effects turn some input energy into heat, sound, vibration, or unwanted motion, so measured performance will be lower than an ideal calculation.
Look for: Run the build slowly and locate the first place where sliding contact becomes visible or audible.
Math bite
Estimate follower rise
Formula: rise = maximum radius - minimum radius
- Maximum radius = 30 mm
- Minimum radius = 18 mm
Substitute: rise = 30 - 18 = 12 mm
Result: The ideal follower lift is 12 mm.
A flat high-radius section creates a dwell near maximum lift.
Follower clearance and cam flex can reduce measured rise.
Make it behave
Test, troubleshoot, and tune
Controlled test
Start here: Rotate the unloaded cam once over four seconds.
Success looks like: The follower stays in contact and returns to the same zero mark.
Measure: Maximum rise and time spent near the high position.
Change: the cam profile
Keep constant: follower mass, guide gap, return force, axle, and rotation rate
- round eccentric
- pear profile
- profile with a flat dwell
| Symptom | Likely cause | Confirm it | Fix |
|---|---|---|---|
| The follower jumps off the cam | Return force is too low or input is too fast | Turn slower and watch the falling side | Add a small weight or gentler speed |
| The follower sticks | Guides are tight or not parallel | Remove the cam and slide by hand | Realign guides with running clearance |
| Lift changes each cycle | The cam is loose or wobbling | Watch its face from the side | Add collars and secure the cam hub |
| The measured rise is too small | The follower foot misses the widest cam line | Check contact alignment from front | Center the foot over the cam plane |
Choose your tradeoff
A rolling follower lowers friction but changes contact geometry; a flat follower can create sharper transitions. Increase return force only enough to maintain contact because extra force increases wear.
Keep experimenting
Try another version
Round eccentric
Start with an off-center circle and one smooth rise-fall cycle.
Motion sequence
Build a cam with two lobes for two lifts per turn.
Displacement graph
Measure height every 30 degrees and plot follower position.
Build together
Classroom and access options
Classroom version
Teams can compare the cam profile while keeping follower mass, guide gap, return force, axle, and rotation rate. Assign builder, tester, recorder, and explainer roles; have each team predict the result before collecting three trials.
Access adaptations
- Use high-contrast tape to distinguish input and output parts.
- Replace a small crank with a wider handle for an easier grip.
- Add a tall, high-contrast flag to the follower and tactile marks at the high and low positions.
Reflect on the design
- How did the cam profile change the measured result?
- Where did sliding contact affect the build most strongly?
- What evidence shows that cam profile control explains the motion?
- Which change would improve vertical follower lift without creating a new problem?
Glossary
- Cam profile control
- A follower's position is set by the distance from the cam axle to the contact point.
- Input
- The action or energy supplied to a system; here it is rotation of a shaped cam.
- Output
- The useful response produced by a system; here it is vertical follower lift.
- Efficiency
- The fraction of input energy that becomes useful output instead of friction, sound, heat, or unwanted motion.
Build your dreams
One build can start the next.
Share what you learned, change one variable, and help another builder understand what worked.
Explore more guidesSources and build notes
An original BrickLabClips interpretation of a standard mechanical mechanism.
- Mechanism verification: Standard kinematics were checked for motion direction, constraint, clearance, and likely friction points.
Written and edited by BrickLabClips. Published 2026-07-22; updated 2026-07-22.