- Difficulty
- Intermediate
- Build time
- 75-120 min
- Estimated cost
- $0-$10
- Age range
- 10-18
- Workspace
- A clear table about 90 cm wide
The finish line
What you will build
A five-stage sequence starts from one action and completes its final task on at least four of five full runs.
Learning goals
- Identify how one hand release at the first stage produces completion of a visible final task.
- Construct and explain a linked rolling, falling, rotating, and lever motions system.
- Measure how target width at the weakest handoff changes performance.
- Diagnose losses caused by impact misalignment and surface friction.
Before you build
Materials, tools, and safety
Reuse-material cost: $0-$3 with reused materials. Supervision: Adult help recommended for sharp or heated tools.
Tools
- Ruler
- Pencil
- Scissors
- Masking tape
Low-cost swaps
- Use clean recycled packaging whenever it has similar stiffness.
- Substitute paper clips, binder clips, or twist ties for specialty fasteners.
- Use books, blocks, recycled packaging, and rolled paper while avoiding breakable or heavy objects.
Project-specific safety
- Wear eye protection when stretched elastic, magnets, or spinning parts are present.
- Test at floor or tabletop height and keep the path clear of people.
- Keep the machine on the floor or a low table, avoid projectiles and glass, and keep every moving object contained inside the test area.
Orient the build
Place the build so one hand release at the first stage is on your left and completion of a visible final task 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
Choose the final task
Pick a safe visible finish such as raising a paper flag.
Work backward to decide the final trigger.
Step 2
Map five stages
Draw boxes for release, ramp, dominoes, lever, and flag.
Write the required output at each handoff.
Step 3
Build stage five first
Make the final task operate with a deliberate hand trigger.
Measure the motion needed to activate it.
Builder checkpoint: After build stage five first, the first subassembly should stay aligned when handled gently.
Step 4
Add stage four
Build a lever or falling cup that reliably supplies that motion.
Test the two-stage pair five times.
Watch for: If this stage binds or drifts, inspect timing variation before adding more parts.
Step 5
Build the middle stages
Add one rolling and one falling action with containment walls.
Test each new interface before continuing.
Step 6
Create the start
Use a gate or upright block that begins with one clear hand action.
Prevent vibration from triggering later stages early.
Builder checkpoint: After create the start, operate the build slowly and confirm that completion of a visible final task begins without binding.
Step 7
Run interface tests
Trigger each stage immediately before its handoff five times.
Widen targets that miss more than once.
Step 8
Run five complete trials
Reset from a checklist and record the first failed stage each time.
Change only the least reliable interface.
Builder checkpoint: At the final checkpoint, A five-stage sequence starts from one action and completes its final task on at least four of five full runs.
See the engineering
Why it works
- Input
- one hand release at the first stage
- Output
- completion of a visible final task
- Motion
- linked rolling, falling, rotating, and lever motions
- Energy losses
- impact misalignment, surface friction, flexing triggers, timing variation
Why this works
Sequential energy transfer
Each stage receives energy, transforms it, and passes enough useful output to the next trigger. Interfaces between stages usually fail before individual mechanisms do.
Look for: Label every handoff and note whether the incoming motion reaches the center of its intended target.
Where the energy goes
Efficiency and losses
The ideal model leaves out impact misalignment, surface friction, flexing triggers, timing variation. 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 impact misalignment becomes visible or audible.
Math bite
Find system reliability
Formula: system reliability = successful full runs / total runs × 100%
- Successful runs = 4
- Total runs = 5
Substitute: reliability = 4/5 × 100% = 80%
Result: The full machine is 80 percent reliable in this sample.
One weak handoff can dominate the total result.
Five runs are useful for tuning but not a long-term reliability claim.
Make it behave
Test, troubleshoot, and tune
Controlled test
Start here: Test each adjacent pair of stages before the first complete run.
Success looks like: At least four of five complete runs reach the final task from one start action.
Measure: First failed stage, full-run time, and reset errors.
Change: target width at the weakest handoff
Keep constant: stage order, objects, starting energy, surface, and reset checklist
- baseline target
- target 2 cm wider
- target 4 cm wider
| Symptom | Likely cause | Confirm it | Fix |
|---|---|---|---|
| A stage fires early | Vibration reaches an unstable trigger | Tap the table without starting | Widen bases and separate stages |
| The ball misses a lever | Exit direction or target is too narrow | Run only that handoff five times | Add guide walls and enlarge the lever target |
| Dominoes stop midway | Spacing or surface changes | Inspect the first gap after stopping | Use a spacing jig and flat surface |
| Full runs vary | Reset positions are inconsistent | Photograph the ready state | Make a numbered reset checklist and alignment marks |
Choose your tradeoff
Improve the least reliable handoff, not the most dramatic stage. Larger targets and lower trigger thresholds improve reliability but can increase accidental starts.
Keep experimenting
Try another version
Three-stage machine
Use a ramp, lever, and flag.
Ninety-percent target
Reach nine successful runs out of ten.
Timed story
Make each safe stage reveal one part of a message.
Build together
Classroom and access options
Classroom version
Teams can compare target width at the weakest handoff while keeping stage order, objects, starting energy, surface, and reset checklist. Assign builder, tester, recorder, and explainer roles; have each team predict the result before collecting three trials.
Access adaptations
- Offer pre-cut parts and tactile or high-contrast measurement marks.
- Split roles so one builder can hold, another assemble, and another measure.
- Assign each builder one stage, use numbered high-contrast handoff zones, and include a large accessible start control.
Reflect on the design
- How did target width at the weakest handoff change the measured result?
- Where did impact misalignment affect the build most strongly?
- What evidence shows that sequential energy transfer explains the motion?
- Which change would improve completion of a visible final task without creating a new problem?
Glossary
- Sequential energy transfer
- Each stage receives energy, transforms it, and passes enough useful output to the next trigger.
- Input
- The action or energy supplied to a system; here it is one hand release at the first stage.
- Output
- The useful response produced by a system; here it is completion of a visible final task.
- 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
A familiar household engineering activity implemented with original instructions and controlled tests.
- Classroom engineering basis: A common educational challenge implemented with original dimensions, tests, diagrams, and instructions.
Written and edited by BrickLabClips. Published 2026-07-22; updated 2026-07-22.