- Difficulty
- Intermediate
- Build time
- 90-140 min
- Estimated cost
- $0-$10
- Age range
- 11-17
- Workspace
- A clear table about 90 cm wide
The finish line
What you will build
The belt carries five 10-gram boxes across 35 cm without leaving the rollers and runs for twenty crank turns without a jam.
Learning goals
- Identify how hand rotation of a drive roller produces linear transport of objects.
- Construct and explain a rotary-to-continuous linear surface motion system.
- Measure how the left-right idler alignment changes performance.
- Diagnose losses caused by belt slip and roller 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
- Low-temperature glue gun or tape
- Skewers or dowels
- Binder clips
Low-cost swaps
- Use clean shipping-box cardboard instead of buying sheets.
- Replace hot glue with strong tape and folded tabs.
- Use a fabric strip stitched or taped into a loop for better durability.
Project-specific safety
- An adult should handle craft knives and make difficult starter cuts.
- Let hot glue cool before pressing a joint or testing moving parts.
- Keep fingers, hair, and loose sleeves away from roller entry points; use hand speed only.
Orient the build
Place the build so hand rotation of a drive roller is on your left and linear transport of objects 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 parallel side rails
Laminate both rails and join them with equal-width cross braces.
Measure roller openings from one shared end.
Step 2
Make matched rollers
Roll two equal paper tubes around the same form and cap their ends.
Mark exact centers before piercing axles.
Step 3
Install the drive roller
Mount one roller on a fixed axle with a crank outside the rail.
Add a grippy tape strip around its surface.
Builder checkpoint: After install the drive roller, the first subassembly should stay aligned when handled gently.
Step 4
Install the adjustable roller
Mount the second roller in matching horizontal slots.
Use binder clips or bolts to set equal tension on both sides.
Watch for: If this stage binds or drifts, inspect frame twist before adding more parts.
Step 5
Make the belt loop
Join the strip with a thin overlapping seam angled across the width.
Keep the loop flat and untwisted.
Step 6
Set tension and tracking
Slide the adjustable roller until slack disappears while the rollers still turn freely.
Measure left and right center distances.
Builder checkpoint: After set tension and tracking, operate the build slowly and confirm that linear transport of objects begins without binding.
Step 7
Run the empty belt
Turn twenty cycles and mark any sideways drift.
Adjust one side of the idler by 1-2 mm only.
Step 8
Carry test boxes
Place one 10-gram box at a time, then a group of five.
Record travel time and any slip.
Builder checkpoint: At the final checkpoint, The belt carries five 10-gram boxes across 35 cm without leaving the rollers and runs for twenty crank turns without a jam.
See the engineering
Why it works
- Input
- hand rotation of a drive roller
- Output
- linear transport of objects
- Motion
- rotary-to-continuous linear surface motion
- Energy losses
- belt slip, roller friction, edge rubbing, frame twist
Why this works
Friction belt transport
The drive roller's surface friction pulls the endless belt. Parallel rollers and even tension keep the belt centered while static friction carries objects along the top span.
Look for: Mark the belt centerline and watch its position relative to both roller centers over twenty turns.
Where the energy goes
Efficiency and losses
The ideal model leaves out belt slip, roller friction, edge rubbing, frame twist. 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 belt slip becomes visible or audible.
Math bite
Predict belt travel
Formula: travel per roller turn = π × roller diameter
- Roller diameter = 50 mm
- π ≈ 3.14
Substitute: travel = 3.14 × 50 = 157 mm
Result: One ideal roller turn moves the belt about 15.7 cm.
Two and a quarter turns should cross a 35 cm conveyor.
Roller slip and belt stretch reduce real travel.
Make it behave
Test, troubleshoot, and tune
Controlled test
Start here: Run the empty belt for twenty slow crank turns.
Success looks like: The belt stays on both rollers and transports five 10-gram boxes across 35 cm.
Measure: Belt drift, travel time, and successful objects.
Change: the left-right idler alignment
Keep constant: belt, load, drive roller, frame, crank rate, and path length
- idler square
- left side 2 mm forward
- right side 2 mm forward
| Symptom | Likely cause | Confirm it | Fix |
|---|---|---|---|
| The belt walks left | Rollers are not parallel or left tension differs | Measure both side distances | Square the idler in 1 mm steps |
| The belt slips on the driver | Surface grip or tension is low | Mark roller and belt and compare | Add grip tape or slight tension |
| Objects stall | Belt surface is smooth or box drags a rail | Test the object by hand | Add paper cleats or widen rails |
| The seam catches | Overlap is thick or faces backward | Run seam through each roller slowly | Taper and orient the seam |
Choose your tradeoff
Correct tracking with small alignment changes, not high tension. More tension can reduce slip but bends the frame and raises bearing friction; a grippy drive surface is usually safer.
Keep experimenting
Try another version
Short belt
Build a 20 cm conveyor with one test box.
Cleated belt
Add equal paper tabs for steeper transport.
Sorting gate
Trigger a passive diverter based on box width.
Build together
Classroom and access options
Classroom version
Teams can compare the left-right idler alignment while keeping belt, load, drive roller, frame, crank rate, and path length. Assign builder, tester, recorder, and explainer roles; have each team predict the result before collecting three trials.
Access adaptations
- Pre-cut repeated pieces and mark fold lines with high-contrast ink.
- Use large tabs, binder clips, and tape for easier one-handed assembly.
- Add a large crank and raised side rails that help place objects on the belt.
Reflect on the design
- How did the left-right idler alignment change the measured result?
- Where did belt slip affect the build most strongly?
- What evidence shows that friction belt transport explains the motion?
- Which change would improve linear transport of objects without creating a new problem?
Glossary
- Friction belt transport
- The drive roller's surface friction pulls the endless belt.
- Input
- The action or energy supplied to a system; here it is hand rotation of a drive roller.
- Output
- The useful response produced by a system; here it is linear transport of objects.
- 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 cardboard machine with dimensionally specified construction.
- Cardboard design verification: Dimensions, fold allowances, repeated-motion joints, and likely load paths received an editorial geometry review.
Written and edited by BrickLabClips. Published 2026-07-22; updated 2026-07-22.