Unit 3: Bristlebots¶
Tiny buzzing robots, then a race track to crash them in.
Sessions: 1–2 · Cost: ~$15 for a fleet · Badges: Wire Wrangler Prerequisites: Unit 1
The first robots: no brains, all body. They teach motors, wires, and how mechanical design changes behavior.
What we're building¶
- Bristlebot: a toothbrush head, a vibration motor and a coin cell.
- Vibrobot: a bigger body (a scrubbing brush, a plastic cup, or a 3D print) with an AA holder and a switch.
- Arena: a cardboard ring, obstacles, and a race lane.
How it works¶
- A vibration motor spins an off-center weight, so the whole bot shakes.
- Angled bristles turn the shaking into forward hops, each bristle flexing and springing back.
- Change the bristle angle, the weight placement or the motor position, and the bot turns, spins or goes straight.
- This is the whole point: you tune behavior by changing the body.
Parts (per bot)¶
| Qty | Part | Notes |
|---|---|---|
| 1 | Toothbrush head (cut off) | Angled bristles work best |
| 1 | 3 V coin or pager vibration motor | With leads |
| 1 | CR2032 coin cell | |
| — | Double-sided foam tape, thin wire | |
| For the vibrobot | 3 V 1030/1027 or 6×12 mm pager motor, 2×AA holder with switch, scrub brush |
Jobs¶
| Step | 8 y.o. | 11 y.o. | Parent |
|---|---|---|---|
| Cut toothbrush heads | Parent (saw or snips) | ||
| Solder motor leads and wires | Solders their own bot's wires | Solders their own, plus heat-shrink | Supervise |
| Build and decorate | Everything | Everything | |
| Arena | Designs the track | Builds the timing gate (level-up) |
Steps¶
- Solder 3" wire extensions onto the motor leads, add heat-shrink, then shrink it. → Wire Wrangler badge.
- Tape the motor on top of the toothbrush head, with the weight clear of everything.
- Tape one wire to the bottom of the coin cell (−). Press the other wire to the top (+) to start. A small folded tape tab makes an on/off switch.
- Race! Try moving the motor forward or back, and adding weight (a dab of hot glue or a washer).
Experiments (science fair style)¶
Change one thing at a time, time a 30 cm run three times each, and take the average.
| Variable | Try |
|---|---|
| Motor position | front / middle / back |
| Extra weight | 0 / 1 / 2 washers |
| Bristle trim | full / trimmed shorter |
Level-ups¶
- Timing gate (11 y.o., previews Unit 9): an LED plus a phototransistor across the finish line, read by a microcontroller.
- BEAM solar robots: Solarbotics kits, e.g. a "Symet" or a solar photovore. They use a "solar engine" that saves up energy in a capacitor and dumps it into the motor.
- Two-motor vibrobot: one motor on each side with separate switches gives manual steering, which previews differential drive in Unit 5.
Talk about it¶
- The bot has no brain. How does it "decide" which way to go?
- What did changing the body teach you that you couldn't learn from the wiring?