- Difficulty
- Beginner
- Build time
- 40-65 min
- Estimated cost
- $0-$12
- Age range
- 10-16
- Workspace
- A clear table about 90 cm wide
The finish line
What you will build
The enclosed robot draws continuously for 30 seconds inside a 60 cm paper boundary without losing a marker or component.
Learning goals
- Identify how rotation of an enclosed eccentric motor mass produces vibration-driven motion and drawn trace.
- Construct and explain a rotary imbalance-to-planar vibration motion system.
- Measure how motor position changes performance.
- Diagnose losses caused by marker friction and body flex.
Before you build
Materials, tools, and safety
Reuse-material cost: Usually under $5 with an existing kit. Supervision: Adult guidance recommended for wiring and cutting.
Tools
- Small screwdriver
- Wire stripper
- Multimeter
- Low-temperature glue gun or tape
Low-cost swaps
- Use alligator-clip leads for a no-solder version.
- Build and test the mechanism manually before adding electronics.
- Use a commercial battery vibration module with an enclosed mass and switch.
Wiring table
| From | To | Purpose |
|---|---|---|
| Battery +3 V | Switch input | Provide controlled supply |
| Switch output | Motor positive | Turn vibration on and off |
| Motor negative | Battery negative | Complete circuit |
Project-specific safety
- Use only the listed low-voltage battery supply; never use mains electricity.
- Disconnect power before changing wires and stop if a motor, wire, or battery becomes warm.
- Use only washable markers and an enclosed motor, secure batteries, run on a protected surface, and stop if parts loosen or warm.
Orient the build
Place the build so rotation of an enclosed eccentric motor mass is on your left and vibration-driven motion and drawn trace 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
Prepare the body
Mark three equally spaced leg positions around the cup rim.
Reinforce each with tape.
Step 2
Attach markers
Band three capped markers at equal angles and heights.
Set the body level on the caps.
Step 3
Mount the motor
Secure the enclosed vibration motor on top with foam tape and a strap.
Keep wires away from motion.
Builder checkpoint: After mount the motor, the first subassembly should stay aligned when handled gently.
Step 4
Wire the switch
Connect the battery through the switch to the motor and insulate joints.
Secure the holder opposite the motor if needed.
Watch for: If this stage binds or drifts, inspect uneven leg stiffness before adding more parts.
Step 5
Build the drawing arena
Tape paper flat and add a low cardboard boundary.
Protect the table beneath.
Step 6
Run a capped test
Switch on for five seconds with caps still fitted.
Inspect all straps and movement.
Builder checkpoint: After run a capped test, operate the build slowly and confirm that vibration-driven motion and drawn trace begins without binding.
Step 7
Draw a baseline
Remove caps, place at center, and run for 30 seconds.
Mark final position and pattern width.
Step 8
Tune one variable
Shift motor position or marker angle and repeat on fresh paper.
Keep voltage and run time fixed.
Builder checkpoint: At the final checkpoint, The enclosed robot draws continuously for 30 seconds inside a 60 cm paper boundary without losing a marker or component.
See the engineering
Why it works
- Input
- rotation of an enclosed eccentric motor mass
- Output
- vibration-driven motion and drawn trace
- Motion
- rotary imbalance-to-planar vibration motion
- Energy losses
- marker friction, body flex, battery movement, uneven leg stiffness
Why this works
Eccentric vibration
An off-center motor mass creates a rotating force. Flexible marker legs alternately grip and slip, so the body wanders while recording its path.
Look for: Move the motor from center toward one edge and compare trace size, direction, and density.
Where the energy goes
Efficiency and losses
The ideal model leaves out marker friction, body flex, battery movement, uneven leg stiffness. 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 marker friction becomes visible or audible.
Math bite
Measure pattern density
Formula: density = line intersections / sampled area
- Intersections = 45
- Area = 100 cm²
Substitute: density = 45 / 100 = 0.45 intersections/cm²
Result: The sampled pattern has 0.45 intersections per square centimetre.
This is a comparison measure rather than a complete description.
Counting intersections by eye introduces uncertainty.
Make it behave
Test, troubleshoot, and tune
Controlled test
Start here: Run five seconds with marker caps on before drawing.
Success looks like: The bot draws 30 seconds inside the boundary with every part secured.
Measure: Pattern width, final offset, intersections, component shift, and battery state.
Change: motor position
Keep constant: body, markers, voltage, paper, run time, and start point
- centered motor
- motor 2 cm off-center
- motor near edge
| Symptom | Likely cause | Confirm it | Fix |
|---|---|---|---|
| It tips | Marker heights or mass balance differ | Stand with caps on | Equalize legs and recenter battery |
| It stays in one spot | Marker friction is high or vibration weak | Test on scrap paper | Change marker angle or replace battery |
| A marker detaches | Band or rim reinforcement is weak | Mark positions before a short run | Add a second strap and tape pad |
| Pattern leaves the paper | Motion has strong direction bias | Run capped and watch drift | Recenter mass or raise the boundary |
Choose your tradeoff
Keep parts secured and the body level before seeking larger patterns. More imbalance can increase movement but also tipping, noise, and attachment stress.
Keep experimenting
Try another version
Single pattern
Build one stable three-marker setup.
Repeatability
Overlay three runs from the same settings.
Color sequence
Run equal times with one marker color changed per trial.
Build together
Classroom and access options
Classroom version
Teams can compare motor position while keeping body, markers, voltage, paper, run time, and start point. Assign builder, tester, recorder, and explainer roles; have each team predict the result before collecting three trials.
Access adaptations
- Color-code and label every wire at both ends.
- Use clip leads, larger controls, and pre-crimped connectors when fine motor work is difficult.
- Use chunky markers, a large slide switch, and clips that hold the robot while caps are removed.
Reflect on the design
- How did motor position change the measured result?
- Where did marker friction affect the build most strongly?
- What evidence shows that eccentric vibration explains the motion?
- Which change would improve vibration-driven motion and drawn trace without creating a new problem?
Glossary
- Eccentric vibration
- An off-center motor mass creates a rotating force.
- Input
- The action or energy supplied to a system; here it is rotation of an enclosed eccentric motor mass.
- Output
- The useful response produced by a system; here it is vibration-driven motion and drawn trace.
- 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 platform-agnostic low-voltage robotics or electronics project with original assembly guidance.
- Low-voltage design review: Battery voltage, polarity, component roles, current paths, and motor or LED protection were editorially checked.
Written and edited by BrickLabClips. Published 2026-07-22; updated 2026-07-22.