- Difficulty
- Intermediate
- Build time
- 60-90 min
- Estimated cost
- $0-$15
- Age range
- 11-17
- Workspace
- A clear table about 90 cm wide
The finish line
What you will build
The winch lifts and holds a 50-gram cup, advances with a consistent click, and releases only when the pawl is deliberately lifted.
Learning goals
- Identify how forward hand-crank rotation produces one-direction drum rotation with holding.
- Construct and explain a rotary-to-indexed one-way rotary system.
- Measure how the return-band tension changes performance.
- Diagnose losses caused by pawl-tooth impact and drum friction.
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 a large cardboard ratchet wheel and laminate three layers around a skewer axle.
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.
- Hold the crank before lifting the pawl, because the load will unwind once the lock is released.
Orient the build
Place the build so forward hand-crank rotation is on your left and one-direction drum rotation with holding 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 winch frame
Brace two drum bearings and leave open access above the ratchet.
Add a stable base wider than the hanging load path.
Step 2
Mount drum and ratchet
Lock both to the same axle and place the crank outside the frame.
Separate string and ratchet so they cannot tangle.
Step 3
Build the pawl lever
Make a stiff lever with a pointed but rounded contact end.
Place its pivot beyond the ratchet radius.
Builder checkpoint: After build the pawl lever, the first subassembly should stay aligned when handled gently.
Step 4
Set the engagement angle
Rest the pawl on a sloped tooth face so forward rotation lifts it.
Check that reverse motion meets the steep face.
Watch for: If this stage binds or drifts, inspect support flex before adding more parts.
Step 5
Add gentle return force
Use gravity or a light band to keep the pawl on the wheel.
Avoid force that makes forward turning unnecessarily hard.
Step 6
Route the lifting string
Anchor and wind three neat wraps on the drum.
Attach an empty cup and keep it over a tray.
Builder checkpoint: After route the lifting string, operate the build slowly and confirm that one-direction drum rotation with holding begins without binding.
Step 7
Test catch positions
Advance one tooth at a time, releasing the crank after each click.
Confirm the frame holds before adding mass.
Step 8
Load and release safely
Increase to 50 grams in steps, then support the crank before lifting the pawl.
Lower the cup slowly instead of letting it drop.
Builder checkpoint: At the final checkpoint, The winch lifts and holds a 50-gram cup, advances with a consistent click, and releases only when the pawl is deliberately lifted.
See the engineering
Why it works
- Input
- forward hand-crank rotation
- Output
- one-direction drum rotation with holding
- Motion
- rotary-to-indexed one-way rotary
- Energy losses
- pawl-tooth impact, drum friction, string rubbing, support flex
Why this works
One-way geometric lock
A sloped tooth face lifts the pawl during forward motion, while a steep face catches the pawl during reverse motion. The pawl converts attempted rollback into compression against the frame.
Look for: Turn forward one tooth, release the crank, and watch the pawl transfer load into its pivot support.
Where the energy goes
Efficiency and losses
The ideal model leaves out pawl-tooth impact, drum friction, string rubbing, support flex. 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 pawl-tooth impact becomes visible or audible.
Math bite
Find holding resolution
Formula: angle per tooth = 360° / tooth count
- Ratchet teeth = 12
- Full circle = 360°
Substitute: angle = 360°/12 = 30°
Result: The winch can hold every 30 degrees of drum rotation.
More teeth create finer holding positions but smaller, weaker tooth faces.
Pawl clearance and tooth shape add positional play.
Make it behave
Test, troubleshoot, and tune
Controlled test
Start here: Advance the empty cup by one tooth and release the crank.
Success looks like: The pawl catches immediately and the drum rolls back less than one tooth.
Measure: Rollback angle and maximum held mass up to 50 grams.
Change: the return-band tension
Keep constant: ratchet, pawl geometry, drum, string, load, and frame
- gravity-only pawl
- light band
- stronger band
| Symptom | Likely cause | Confirm it | Fix |
|---|---|---|---|
| The pawl skips backward | It meets the tooth too shallowly | Hold the load and inspect contact | Move the pivot or lengthen the pawl |
| Forward turning is very hard | Return force or pawl contact is excessive | Lift the pawl slightly while turning | Reduce band tension and smooth the tip |
| The ratchet wobbles away | The axle has side play | Watch alignment from above | Add collars with running clearance |
| The frame bends under load | Pawl and drum supports lack bracing | Release at a low mass and watch the supports | Add cross braces and reduce load |
Choose your tradeoff
The pawl needs enough engagement to catch the steep face but enough freedom to climb forward. More teeth reduce rollback angle while making tooth geometry and frame alignment more demanding.
Keep experimenting
Try another version
Pointer ratchet
Replace the string load with a dial pointer.
Finer ratchet
Compare 12- and 24-tooth holding resolution.
Dual pawls
Offset two pawls to reduce rollback while keeping strong teeth.
Build together
Classroom and access options
Classroom version
Teams can compare the return-band tension while keeping ratchet, pawl geometry, drum, string, load, and frame. 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.
- Extend the pawl release with a large colored tab that can be operated away from the teeth.
Reflect on the design
- How did the return-band tension change the measured result?
- Where did pawl-tooth impact affect the build most strongly?
- What evidence shows that one-way geometric lock explains the motion?
- Which change would improve one-direction drum rotation with holding without creating a new problem?
Glossary
- One-way geometric lock
- A sloped tooth face lifts the pawl during forward motion, while a steep face catches the pawl during reverse motion.
- Input
- The action or energy supplied to a system; here it is forward hand-crank rotation.
- Output
- The useful response produced by a system; here it is one-direction drum rotation with holding.
- Efficiency
- The fraction of input energy that becomes useful output instead of friction, sound, heat, or unwanted motion.
Build your dreams
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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.