Why does the Scribble Bot move?

Your Scribble Bot doesn't have wheels, muscles or even a brain. Its movement starts with the tiny electric motor.

• When electricity from the battery reaches the motor, the motor's shaft spins very quickly.

• Attached to the shaft is a small weight that is off-centre — one side is heavier than the other.

• As this uneven weight spins around, it continually pulls the motor in different directions.

• Those tiny movements travel through the body of the Scribble Bot, making the whole robot vibrate.

You can feel the same kind of idea when a mobile phone buzzes in your hand.

But vibration is only the beginning. Your Scribble Bot still needs something to turn all that shaking into movement across the paper.

What do the textas have to do with it?

The tips of the textas are touching the paper, and that creates friction.

Friction is a force that acts when two surfaces rub or try to slide across each other.

As the Scribble Bot vibrates:

• the texta tips push against the paper

• friction resists their movement

• the bot rocks and shifts slightly

• these tiny movements happen again and again, very quickly

Put them together and your Scribble Bot can wobble, shuffle, spin or travel across the page.

And because the textas are touching the paper, they leave behind a colourful record of that movement — the scribble!

Why does changing the textas change the scribble?

Your three textas aren't just drawing tools. They're also the Scribble Bot's legs.

Changing their angle changes how the robot stands and how the texta tips interact with the paper.

Try making the legs wider, narrower, straighter or more angled and you may change:

• how stable the bot is

• how easily it rocks

• the direction it moves

• how much it spins

• the pattern it draws

That's why two Scribble Bots made from exactly the same materials might create completely different drawings.

Small design changes can produce surprisingly big changes in movement.

Why does the position of the motor matter?

The motor is the source of the vibration, but where you put it can matter too.

Place the motor near the centre and its vibrations act on the robot differently than when the motor is moved towards one side.

An off-centre motor can make one part of the bot shake differently from another. Combined with the position of the textas and the bot's weight, this can change whether your Scribble Bot tends to spin, wobble or travel.

This is why engineers test different designs instead of assuming their first idea will work best.

Build. Test. Observe. Change. Test again.

That's engineering!