The first two images show the junkbot drawing the lines and dots on the paper just be using a spinning unbalanced motor.
In the figure below (though you can't see it) the connection between the motor and the power goes through the Crumble to allow the motor to change direction. Some the 'code-clubbers' have played with lowering the power via the Crumble and found below certain values (percentage of the maximum power available through the Crumble) the motor stalls.
The simple code used to control it shown below.
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