- Difficulty
- Intermediate
- Build time
- 55-80 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 output platform rises and lowers through at least 60 degrees while staying within about 5 degrees of level across the usable range.
Learning goals
- Identify how manual rotation of one side link produces a platform that translates while staying level.
- Construct and explain a oscillating angular-to-guided translation system.
- Measure how the left-right arm length mismatch changes performance.
- Diagnose losses caused by pivot friction and unequal link lengths.
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.
- Build the four bars from identical craft sticks with carefully measured pivot holes.
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.
- Support the platform by its outer edge and keep fingers away from the folding lower pivots.
Orient the build
Place the build so manual rotation of one side link is on your left and a platform that translates while staying level 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 fixed ground
Create a rigid base with two reinforced pivots 8 modules apart.
Mark a horizontal reference line across the front.
Step 2
Match the side links
Select two links with exactly equal pivot-center spacing.
Overlay them to confirm their holes align.
Step 3
Attach both arms
Mount one side link at each ground pivot with free rotation.
Use equal spacers so the arms lie in parallel planes.
Builder checkpoint: After attach both arms, the first subassembly should stay aligned when handled gently.
Step 4
Join the output bar
Connect the upper pivots using a bar equal to the ground spacing.
Keep the linkage uncrossed during assembly.
Watch for: If this stage binds or drifts, inspect frame twist before adding more parts.
Step 5
Add the platform
Center a lightweight tray or pointer on the output bar.
Avoid overhang that twists one arm more than the other.
Step 6
Mark level references
Add a second horizontal line to the output platform.
Align both marks at the lowest test position.
Builder checkpoint: After mark level references, operate the build slowly and confirm that a platform that translates while staying level begins without binding.
Step 7
Sweep the range
Raise one arm slowly through 60 degrees and stop at three positions.
Measure the angle between the two reference lines.
Step 8
Load symmetrically
Place a 20-gram mass at the platform center and repeat.
Watch whether one side droops or pivots spread.
Builder checkpoint: At the final checkpoint, The output platform rises and lowers through at least 60 degrees while staying within about 5 degrees of level across the usable range.
See the engineering
Why it works
- Input
- manual rotation of one side link
- Output
- a platform that translates while staying level
- Motion
- oscillating angular-to-guided translation
- Energy losses
- pivot friction, unequal link lengths, joint play, frame twist
Why this works
Parallelogram constraint
Opposite sides of a true parallelogram remain parallel when all pivots are free and opposite links have equal center-to-center lengths. The output link therefore keeps the same orientation as the ground link.
Look for: Place matching level marks on the base and output, then compare them at low, middle, and high positions.
Where the energy goes
Efficiency and losses
The ideal model leaves out pivot friction, unequal link lengths, joint play, 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 pivot friction becomes visible or audible.
Math bite
Check opposite link equality
Formula: length error = |left arm - right arm|
- Left arm = 80 mm
- Right arm = 78 mm
Substitute: error = |80 - 78| = 2 mm
Result: A 2 mm mismatch prevents an exact parallelogram.
Smaller mismatch should reduce platform tilt across the range.
Pivot clearance and frame twist can still add angular error.
Make it behave
Test, troubleshoot, and tune
Controlled test
Start here: Move the unloaded platform to low, middle, and high positions.
Success looks like: Its reference line stays within 5 degrees of the base line at all three positions.
Measure: Platform angle and vertical height.
Change: the left-right arm length mismatch
Keep constant: ground spacing, output length, platform mass, and test positions
- matched arms
- one arm 1 module longer
- matched arms with centered load
| Symptom | Likely cause | Confirm it | Fix |
|---|---|---|---|
| The platform tilts through the range | Opposite links are unequal | Overlay arms and compare pivot centers | Replace them with matched lengths |
| One arm binds | Pivot collars are tight or planes are offset | Disconnect the output and test each arm | Add side clearance and equal spacers |
| The linkage twists out of plane | The base or output bar lacks torsional stiffness | Push the platform front to back | Add a second parallel linkage or cross brace |
| The platform flips through the base | The linkage crossed its intended branch | Compare the arm order with the start view | Return to the uncrossed parallelogram assembly |
Choose your tradeoff
Matched dimensions matter more than tight joints. Reduce side play enough to control tilt, but preserve free pivots; for heavier loads, use two parallel linkages rather than squeezing one.
Keep experimenting
Try another version
Level pointer
Replace the platform with one paper arrow.
Twin linkage lift
Add a second parallelogram behind the first for stiffness.
Error map
Measure platform angle every 10 degrees and graph deviation from level.
Build together
Classroom and access options
Classroom version
Teams can compare the left-right arm length mismatch while keeping ground spacing, output length, platform mass, and test positions. 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 tactile horizontal stripes to both base and output so parallel orientation can be checked while stopped.
Reflect on the design
- How did the left-right arm length mismatch change the measured result?
- Where did pivot friction affect the build most strongly?
- What evidence shows that parallelogram constraint explains the motion?
- Which change would improve a platform that translates while staying level without creating a new problem?
Glossary
- Parallelogram constraint
- Opposite sides of a true parallelogram remain parallel when all pivots are free and opposite links have equal center-to-center lengths.
- Input
- The action or energy supplied to a system; here it is manual rotation of one side link.
- Output
- The useful response produced by a system; here it is a platform that translates while staying level.
- 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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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.