Our robot performs the magic trick of turning black coffee into "brown" coffee (milk mixed in). There are two wheels controlled by one motor for driving, another motor used to swing the arm in and out of the coffee cup, and a medium motor used to spin our stirrer. Another motor is attached as a counterbalance. Our stirrer was a 3D-printed piece. We used the soft plastic to create a tall, plus sign-shaped gear to make it easier for our robot to stir.

The secret behind the trick is that the milk (or half and half, in our case) is already in the coffee, but it settles to the bottom without mixing in. Our robot stirs up the coffee and milk to mix them together, making the coffee magically change color.