Just like a radio-controlled car, a Rumble Robot has four wheels, which are powered by electric motors. As you can see in the picture below, the Rumble Robot has two driving motors, which spin a series of gears to move the robot’s wheels. These motors are housed in the bottom half of the robot.
When the integrated circuit receives the appropriate signal, it sends an electric current to one or both of the motors. Each motor can spin in two directions, depending on the direction of the current. (See How Electric Motors Work for details.)
By reversing the current flowing to either motor, the integrated circuit can change the robot's direction. If both motors receive positive current, all wheels will spin the same way and the robot will move forward. If both receive negative current, the robot will move backward. If one motor receives positive current and the other receives negative current, the wheels on each side will spin in opposite directions, and the robot will turn. If the currents are then switched for both motors, the robot will turn in the opposite direction.
The robot has a third motor in its head that moves the arms back and forth. As you can see in the picture below, this punching mechanism consists of two rack-and-pinion gears. The motor turns the central gear, which turns a connected gear that moves the racks.
In this design, the base of each gear is notched on two sides; that is, it has two sections with teeth separated by two smooth sections. The sections with teeth engage the teeth of the racks, which are attached to the robot's arms. When the teeth are engaged, the gear will slide the rack (and the arm) backward. When the gear revolves around to the smooth section, it releases the rack. The racks are spring-loaded, so they punch forward on release.
This is the particular mechanism at work in "Lug Nut." Other Rumble Robots have different punching styles, with different gear arrangements, but the basic elements are fairly similar.
The object of a Rumble Robot game is to get your robot to land effective blows against your opponent's robot. In the next section, we'll see how Rumble Robots register these hits.