+Originally, the \definition{Roomba} is an autonomous vacuum cleaning robot,
+manufactured by the US-based company \definition{iRobot}. The 500 series
+currently represents the third generation of iRobot's cleaning robots, and the
+first generation of robots controllable over an external interface.
+
+\subsection{Hardware design}
+\todo{diagram?}
+\paragraph{Wheels}
+The Roomba lives in a cylindrical case with diameter of about 34~cm and height
+of about 7~cm. It has two main wheels which are positioned slightly behind the
+centerline, so the Roomba leans forward due to gravity, and a small caster on
+the front to prevent it from sliding on the floor. The main wheels can be
+controlled over two independent motors, each one allowing to turn the connected
+wheel with a minimum of 10~mm/s and a maximum of 500~mm/s in each direction.
+One of the main wheel motors consumes about 300~mA in their slowest rotation
+speed, and about 1000~mA when driving with normal speed. Each wheel is also
+equipped with a drop sensor that tells if the respective wheel has dropped into
+a hole or similar, and does not reach the ground anymore. These sensors are
+realized with a spring pushing the wheel towards the ground, with the spring
+force adjusted to the Roomba's weight, and a micro switch which triggers if the
+wheel drops below a specified level. Furthermore, both wheels feature rotating,
+toothed discs, which in conjunction with an LED and a photo-electric resistor
+act as an optical interrupter. This system can be used to measure the wheel's
+current speed by counting the optical interruptions the wheel causes while
+moving.
+
+\paragraph{Brushes}
+In addition to the wheel motors, the Roomba has a motor which operates the
+vacuum brush, and a small motor on the front connected to a side brush, to allow
+cleaning of room corners.
+
+\paragraph{Bumper shield}
+Since the main movement direction in normal operation is forward, the front of
+the Roomba consists of a crecent-shaped bumper shield which contains several
+sensors. This bumper\index{Roomba!bumper} is spring-loaded and on the one
+hand absorbs shock to reduce damage, on the other hand, it allows the Roomba to
+detect obstacles in front of it, both via infrared sensors as well as by
+mechanical means. There are two sensors for mechanical bump detection, located
+30° to the left and to the right of the bumper's center, each implemented as
+photo-electrical interruptors. Additionally, six infrared sensors are unevenly
+distributed over the bumper, facing away from it in a star-like manner. Each one
+of them allows the Roomba to recognize objects in a maxmimum distance of 10~cm.
+Finally, the bumper shield contains four infrared sensors facing downwards,
+acting as cliff sensors \index{Roomba!cliff sensor} to recognize steps or
+similar chasms which could be dangerous for the Roomba to drive towards.
+
+The back part of the Roomba contains the main vacuum brush\index{Roomba!vacuum
+brush}, and the reservoir for holding dirt. Both of them can be removed, though
+the removal of the main brush reduces the Roomba's weight and slightly
+unbalances the Roomba so the springs used for the wheel drop sensors are not in
+balance anymore and push the Roomba upwards, so it tilts more to the front when
+accelerating forwards. There is also a sensor on the underside
+\index{Roomba!dirt sensor} for detecting particularly dirty regions of the
+floor, which is implemented as a capacitive touch sensor.
+
+\paragraph{Battery}
+The battery\index{Roomba!battery} is placed in the front part behind the bumper,
+it is a rechargeable NiMH battery and holds a capacity of 3300~mAh which lasts
+for about 90 to 120 minutes under normal operation. The Roomba can also find its
+home base and charge itself when it has finished cleaning or runs out of energy
+by using a special infrared sensor mounted on top of the Roomba. This sensor can
+see in all directions and is able to detect the home base by looking for a
+special infrared signal the home base\index{Roomba!home base} emits. The same
+principle is used for so-called "`virtual walls"'\index{virtual wall} which can
+be placed by the user in regions the Roomba should not move into.
+
+\subsection{Behaviour}
+\paragraph{Intended Behaviour}
+The Roomba normally follows its own, non-customizable algorithm to detect dirt
+and clean rooms. It is kind of a random walk\index{random walk}, controlled by
+the internal logic, which tries to keep the Roomba away from dangers like
+stairs and walls (by evaluating the cliff and bump sensors), and direct it to
+the more dusty regions of the room (by using the dirt sensor). The random walk
+concept allows a more or less complete coverage of the room, given the time for
+cleaning is large enough, while at the same only needing very little information
+about the environment. Of course, that concept is not very efficient when it
+comes to cleaning rooms, but cleaning time is not neccessarily the constraining
+factor, and the robot still saves the human some time.
+
+\paragraph{Roomba Open Interface}
+However, robots of the Roomba 500 series are also easily controllable over a
+serial port, which provides a two-way communication at 5~V TTL levels over a
+Mini-DIN connector, with a speed of either 19,200 or 115,200 Baud. Over this
+serial port, the Roomba speaks a specified protocol, called the
+\ignoreoutput{\ac{ROI}}\definition{\acl{ROI}} (\acs{ROI})~\cite{irobot-oi},
+which allows the user to interact with the robot's internal logic, reading its
+sensor values, and control its movements and cleaning behaviour.
+
+After starting the communication with the Roomba by sending the \cmd{Start}
+command, the robot is in a state called \definition{Passive mode}. In this mode,
+the user cannot control the robot by himself, but the internal logic defines
+icants behaviour. However, the user is able to read the internal sensors. The
+\ac{ROI} then allows the user to set the Roomba into two different modes:
+\begin{itemize}
+ \item In \definition{Safe mode}, the Roomba monitors the wheel drop, cliff
+ and internal charger sensors, and reverts into Passive mode if safety
+ conditions occur, so the Roomba is not harmed.
+ \item In \definition{Full mode}, the user has full control over the Roomba,
+ and has to take care not to harm the Roomba by evaluating the wheel drop,
+ cliff and internal charger sensors by himself.
+\end{itemize}
+
+In particular, every command is assigned an \ac{opcode} of one byte length,
+followed by a fixed amount of bytes as parameters which depend on the opcode.
+For example, to drive straight with a velocity of 1000~mm, one would send the
+following bytes over the serial interface:
+\begin{verbatim}
+0x80, // start byte
+0x83, // safe mode
+0x89, // drive
+0x03, 0xe8 // drive: parameter velocity: 0x03e8 == 1000
+0x80, 0x00 // drive: parameter radius: special value "straight"
+\end{verbatim}
+
+A little disadvantage of the \ac{ROI} \cmd{Drive} command is that the robot is
+modeled as a state machine. In the previous example, the Roomba would keep on
+driving until it runs out of energy, or a safety condition occurs which causes
+the Roomba to revert into Passive mode, or a new \cmd{Drive} command with the
+velocity parameter set to zero is sent. Thus, if the user wants to drive a
+specific distance, he has to calculate the time interval the robot needs to
+travel that distance, measure the time interval, and stop the robot after that
+time interval has passed.
+
+In our setup, an iRobot Roomba~530 is used as an instance of an autonomous,
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