- Difficulty
- Intermediate
- Build time
- 100-160 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 dispenser releases one paper capsule per full handle cycle in at least nine of ten trials without double feeding or crushing the queue.
Learning goals
- Identify how one full handle rotation produces one dispensed lightweight item.
- Construct and explain a rotary input-to-discrete object release system.
- Measure how the pocket width clearance changes performance.
- Diagnose losses caused by item rubbing and pocket flex.
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
- Adult-operated craft knife
- Skewer axle
Low-cost swaps
- Use clean shipping-box cardboard instead of buying sheets.
- Replace hot glue with strong tape and folded tabs.
- Use ping-pong balls and a larger rotating pocket for easier tolerances.
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.
- Dispense only lightweight non-food objects and keep fingers out of the queue while turning.
Orient the build
Place the build so one full handle rotation is on your left and one dispensed lightweight item 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 machine shell
Reinforce side walls around the pocket-wheel axle height.
Leave one removable service panel.
Step 2
Measure the products
Find capsule width and height, then add 2-3 mm running clearance.
Use one sample to check every opening.
Step 3
Laminate the pocket wheel
Glue three disks and cut one cavity sized for a single capsule.
Keep the axle hole centered.
Builder checkpoint: After laminate the pocket wheel, the first subassembly should stay aligned when handled gently.
Step 4
Build the hopper queue
Slope a channel toward the wheel with space for one straight line of products.
Add walls higher than the capsules.
Watch for: If this stage binds or drifts, inspect chute bounce before adding more parts.
Step 5
Set inlet clearance
Position the wheel so one pocket aligns with the queue while its rim blocks the next item.
Turn by hand before securing.
Step 6
Add the outlet chute
Cut a release opening at the lower quarter of the wheel and attach a sloped delivery path.
Raise walls against bounce.
Builder checkpoint: After add the outlet chute, operate the build slowly and confirm that one dispensed lightweight item begins without binding.
Step 7
Add handle and cycle marks
Install the axle, handle, and one full-turn start mark.
Use collars to stop side rubbing.
Step 8
Run ten dispenses
Load the same queue and complete one turn per trial.
Record single, double, missed, or jammed outcomes.
Builder checkpoint: At the final checkpoint, The dispenser releases one paper capsule per full handle cycle in at least nine of ten trials without double feeding or crushing the queue.
See the engineering
Why it works
- Input
- one full handle rotation
- Output
- one dispensed lightweight item
- Motion
- rotary input-to-discrete object release
- Energy losses
- item rubbing, pocket flex, axle friction, chute bounce
Why this works
One-at-a-time singulation
A rotating pocket accepts one object while its solid surface blocks the queue. At the outlet angle, gravity pulls the captured object into a separate delivery chute.
Look for: Watch the second queued item remain supported while the filled pocket leaves the inlet.
Where the energy goes
Efficiency and losses
The ideal model leaves out item rubbing, pocket flex, axle friction, chute bounce. 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 item rubbing becomes visible or audible.
Math bite
Calculate dispensing reliability
Formula: reliability = correct single dispenses / trials × 100%
- Correct singles = 9
- Trials = 10
Substitute: reliability = 9/10 × 100% = 90%
Result: The prototype delivers correctly 90 percent of the time.
The failure type suggests which clearance to adjust.
Ten trials are a short durability sample.
Make it behave
Test, troubleshoot, and tune
Controlled test
Start here: Rotate the empty wheel once and inspect every clearance through the service panel.
Success looks like: At least nine of ten cycles deliver exactly one capsule and reset for the next.
Measure: Single, double, missed, and jammed cycles.
Change: the pocket width clearance
Keep constant: capsules, hopper angle, wheel, outlet, handle rate, and queue length
- 1 mm clearance
- 3 mm clearance
- 5 mm clearance
| Symptom | Likely cause | Confirm it | Fix |
|---|---|---|---|
| Two items dispense | Pocket or inlet gap fits more than one | Pause at the loading angle | Narrow the pocket or add a queue lip |
| Nothing dispenses | Pocket misses inlet or item bridges | Turn slowly with panel open | Realign inlet and widen only the jam point |
| The item stays in the pocket | Outlet is too high or cavity too deep | Stop at release angle and tilt gently | Lower outlet or add an ejector ramp |
| The wheel binds | Side walls squeeze or axle is off-center | Remove products and turn empty | Add side clearance and recenter axle |
Choose your tradeoff
Design around one measured object size. More pocket clearance reduces jams but risks doubles; steeper chutes improve release but increase bounce.
Keep experimenting
Try another version
Ball dispenser
Use ping-pong balls and one large pocket.
Detent stop
Add a ratchet that marks each complete cycle.
Choice machine
Build two independent product columns and selectors.
Build together
Classroom and access options
Classroom version
Teams can compare the pocket width clearance while keeping capsules, hopper angle, wheel, outlet, handle rate, and queue 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.
- Use a large handle, clear viewing window, and tactile start/finish marks.
Reflect on the design
- How did the pocket width clearance change the measured result?
- Where did item rubbing affect the build most strongly?
- What evidence shows that one-at-a-time singulation explains the motion?
- Which change would improve one dispensed lightweight item without creating a new problem?
Glossary
- One-at-a-time singulation
- A rotating pocket accepts one object while its solid surface blocks the queue.
- Input
- The action or energy supplied to a system; here it is one full handle rotation.
- Output
- The useful response produced by a system; here it is one dispensed lightweight item.
- 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.