X-Git-Url: https://git.rohieb.name/bachelor-thesis/written-stuff.git/blobdiff_plain/9a0c63405476423a6f7ca048b38d1c59832ba079..775e6043272712d56c091be5346cf837a754b294:/Ausarbeitung/roomba.tex

diff --git a/Ausarbeitung/roomba.tex b/Ausarbeitung/roomba.tex
index 819d034..f45e31d 100644
--- a/Ausarbeitung/roomba.tex
+++ b/Ausarbeitung/roomba.tex
@@ -5,9 +5,28 @@ currently represents the third generation of iRobot's cleaning robots, and the
 first generation of robots controllable over an external interface.
 
 \subsection{Hardware design}
+\begin{SCfigure}
+  \centering
+  \includegraphics[width=.5\textwidth]{images/Roomba-Diagram.pdf}
+  \caption[Diagram of the Roomba 500 series]{Diagram of the Roomba 500 series,
+    view from below\label{fig:roomba-diagram} \\
+    1:~front~caster, 2:~battery, 3:~side~brush, 4:~main~wheels, 5:~main~brush,
+    6:~vacuum~bin, 7:~front~bumper, 8:~cliff~sensors}
+\end{SCfigure}
+
 The Roomba lives in a cylindrical case with diameter of about 34~cm and height
-of about 7~cm, so it can crawl easily under furniture for cleaning.
-\todo{diagram?}
+of about 8~cm, so it can crawl easily under furniture for cleaning.
+Figure~\ref{fig:roomba-diagram} shows a diagram of the Roomba seen from below.
+
+The top side features several buttons which vary between the different models,
+most notably the ``Clean'' and ``Spot'' buttons for manual control of the
+cleaning routine, and the ``Dock'' button to send the Roomba to its home base.
+The cover on the top side can be removed, and covers the connector for
+the \ac{ROI} which is discussed in Section~\ref{sec:roi}.
+
+On the side, a socket for a coaxial \acs{DC} power connector can be found, which
+is used for external charging.
+
 \paragraph{Wheels}
 The Roomba has two rubberized main wheels which are positioned slightly behind
 the centerline, so the Roomba leans forward due to gravity, and a small caster
@@ -81,14 +100,15 @@ 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}
+\label{sec:roi}
 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, in mode 8N1
-(8 data bits, no parity, 1 stop bit). 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.
+serial port, which provides a two-way communication at 5~V~\acs{TTL} levels over
+a 7-pin mini-\acs{DIN} connector, with a speed of either 19,200 or 115,200 Baud,
+in mode \acused{8N1} \ac{8N1} (\acl{8N1}). Over this serial port, the Roomba
+speaks a specified protocol, called the \acused{ROI}\definition{Roomba Open
+Interface} (\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,
@@ -135,10 +155,10 @@ The velocity is interpreted in mm/s, the value can range from -500~mm/s to
 500~mm/s, with negative values implying backwards movement. The radius is
 interpreted in mm, ranging from -2000~mm to 2000~mm. Negative values make the
 Roomba turn toward the right, whereas positive values make it turn toward the
-left. There are also four special values for the radius: \magicnumber{1} makes
-the Roomba turn on the spot in counter-clockwise direction, \magicnumber{-1}
+left. There are also four special values for the radius: \magicvalue{1} makes
+the Roomba turn on the spot in counter-clockwise direction, \magicvalue{-1}
 makes the Roomba turn on the spot in clockwise direction, and
-\magicnumber{0x7fff} and \magicnumber{0x8000} make it drive straight.
+\magicvalue{0x7fff} and \magicvalue{0x8000} make it drive straight.
 
 For example, to drive straight with a velocity of 1000~mm, one would send the
 following bytes over the serial interface:
@@ -194,15 +214,15 @@ where:
     $\sum_{i=1}^n\left(p_1 + v(p_1)\right) + c + n \equiv 0 \mod 256$
 \end{description}
 Example: The following byte sequence requests data from the left cliff
-signal (packet~ID \magicnumber{0x1d}) and virtual wall sensor (packet~ID
-\magicnumber{0x0d}):
+signal (packet~ID \magicvalue{0x1d}) and virtual wall sensor (packet~ID
+\magicvalue{0x0d}):~\cite{irobot-oi}
 \begin{verbatim}
 0x94,       // Stream command
 0x02,       // parameter: 2 packets following
 0x1d, 0x0d  // parameter: request packets 0x1d and 0x0d
 \end{verbatim}
 The Roomba then would return a packet with the following format every
-15~ms:\label{sec:roi-stream-packet}
+15~ms:\label{sec:roi-stream-packet}~\cite{irobot-oi}
 \begin{verbatim}
 0x13,       // Header byte
 0x05,       // 5 bytes following, except checksum
@@ -213,6 +233,23 @@ The Roomba then would return a packet with the following format every
 0xb6        // checksum: 0x5 + 0x1d + 0x2 + 0x19 + 0xd + 0x0 + 0xb6 = 0x100
 \end{verbatim}
 
+\paragraph{Latency}
+On the connection, there is a certain latency between the time the command is
+sent to the Roomba and the time the Roomba receives this command and carries out
+the motion. At 19,200 baud, mode \ac{8N1}, the transfer of a 5-byte \cmd{Drive}
+command needs $(5 \times 9) \div 19200 = 2.3$~ms. The time the Roomba
+logic needs to process the command is not mentioned in the \ac{ROI}
+Specification, and there was no way to measure it sufficiently. It is however
+short enough that a human would describe it as ``instant''.
+
+The same latency of course also exists in the opposite directions when the
+Roomba is sending sensor data to the user. However, the sensor data are sent by
+the Roomba every 15~ms (which is the internal speed at which the data is
+updated from the sensors) and according to the wheel's maximum velocity of
+500~mm/s (which means that a sensor data packet is received every $0.03$~mm when
+driving at this speed), this is acceptible for real-time evaluation of the data.
+
+
 In our setup, an iRobot Roomba~530 is used as an instance of an autonomous,
 mobile robot to conduct the experiments described afterwards. For that, the
 Roomba's movements are controlled over a netbook mounted on top of the Roomba
