Commit b611290e471d55d39054c1cadc1674f597873bb4 - droidcopter

Merge branch 'master' of github.com:haldean/droidcopter Benjamin Bardin 9 years ago

10 changed file(s) with 467 addition(s) and 60 deletion(s). Raw diff Collapse all Expand all

-0

.gitignore less more

8	8	*.dvi
9	9	*.dex
10	10	*.apk
	11	*.so
11	12	video
12	13	Pilot/bin
13	14	PilotTest/bin

jars/commons-math3-3.1.1.jar less more

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org/haldean/chopper/server/PidExperiment.java less more

	0	package org.haldean.chopper.server;
	1
	2	import java.util.ArrayList;
	3
	4	/**
	5	* Note: this class has a natural ordering that is inconsistent with equals.
	6	*/
	7	public class PidExperiment implements Comparable<PidExperiment> {
	8	public static final long MAX_TIME_MILLIS = 10000;
	9	public static final double THRESHOLD_ANGLE = 20.0;
	10	public static final double THRESHOLD_MULTIPLIER = 10000; // Exact value unimportant.
	11
	12	private double mP;
	13	private double mI;
	14	private double mD;
	15	private ArrayList<Double> mErrors;
	16	private long mStartTime;
	17	private double mScore;
	18
	19	public PidExperiment(double p, double i, double d) {
	20	mP = p;
	21	mI = i;
	22	mD = d;
	23	mErrors = new ArrayList<Double>();
	24	mScore = -1;
	25	mStartTime = 0;
	26	}
	27
	28	public double getP() {
	29	return mP;
	30	}
	31
	32	public double getI() {
	33	return mI;
	34	}
	35
	36	public double getD() {
	37	return mD;
	38	}
	39
	40	public void addError(double newError) {
	41	if (mErrors.isEmpty()) {
	42	mStartTime = System.currentTimeMillis();
	43	}
	44	mErrors.add(newError);
	45	}
	46
	47	public boolean isDone() {
	48	// True if time limit expired, or two full sin curves are complete.
	49	if (isTimeUp()) return true;
	50
	51	int first = getNextCycle(0);
	52	if (first == -1) return false;
	53
	54	int second = getNextCycle(first);
	55	if (second == -1) return false;
	56
	57	int third = getNextCycle(second);
	58	if (third == -1) return false;
	59
	60	return true;
	61	}
	62
	63	public double getScore() {
	64	// mScore saved once processed (lazy evaluation)
	65	if (mScore != -1) return mScore;
	66
	67	// If we don't get to the start of a third cycle, this experiment
	68	// was really bad. Return MAX_VALUE.
	69	if (isTimeUp()) {
	70	mScore = Integer.MAX_VALUE;
	71	return mScore;
	72	}
	73
	74	int first = getNextCycle(0);
	75	if (first == -1) {
	76	mScore = Integer.MAX_VALUE;
	77	return mScore;
	78	}
	79	int second = getNextCycle(first);
	80	if (second == -1) {
	81	mScore = Integer.MAX_VALUE;
	82	return mScore;
	83	}
	84	int third = getNextCycle(second);
	85	if (third == -1) {
	86	mScore = Integer.MAX_VALUE;
	87	return mScore;
	88	}
	89
	90	double score = 0.0;
	91	for (int i = first; i < third; i++) {
	92	if (mErrors.get(i) < THRESHOLD_ANGLE) {
	93	score += Math.abs(mErrors.get(i));
	94	} else {
	95	score += Math.abs(mErrors.get(i)) * THRESHOLD_MULTIPLIER;
	96	}
	97	}
	98	mScore = score;
	99	return mScore;
	100	}
	101
	102	private int getNextCycle(int fromPos) {
	103	int truncateStart = fromPos;
	104	if (fromPos == 0) {
	105	// Cycle a bit longer, to compensate for the weird start.
	106	for (; mErrors.get(truncateStart) <= 0; truncateStart++) {
	107	// If value at index is nonpositive, continue until positive.
	108	if (truncateStart == mErrors.size()) return -1;
	109	}
	110	}
	111	int negativeIndex = truncateStart;
	112	for (; mErrors.get(negativeIndex) >= 0; negativeIndex++) {
	113	// If value at index nonnegative, continue until negative.
	114	if (negativeIndex == mErrors.size()) return -1;
	115	}
	116	int cycleStart = negativeIndex;
	117	for (; mErrors.get(cycleStart) <= 0; cycleStart++) {
	118	// If value at index is nonpositive, continue until positive.
	119	if (negativeIndex == mErrors.size()) return -1;
	120	}
	121	return cycleStart;
	122	}
	123
	124	private boolean isTimeUp() {
	125	if (mStartTime == 0) return false;
	126
	127	if (System.currentTimeMillis() - mStartTime > MAX_TIME_MILLIS) {
	128	return true;
	129	} else {
	130	return false;
	131	}
	132	}
	133
	134	/** Does not compare scores, only PID values. */
	135	public boolean equals(PidExperiment other) {
	136	return (getP() == other.getP()) && (getI() == other.getI()) && (getD() == other.getD());
	137	}
	138
	139	public int hashCode() {
	140	return new Double(getP()).hashCode() ^
	141	new Double(getI()).hashCode() ^
	142	new Double(getD()).hashCode();
	143	}
	144
	145	public int compareTo(PidExperiment other) {
	146	if (getScore() == other.getScore()) return 0;
	147	if (getScore() < other.getScore()) return -1;
	148	// if (getScore() > other.getScore())
	149	return 1;
	150	}
	151
	152	public String gnuplotLine() {
	153	return getP() + " " + getI() + " " + getD() + " " + getScore();
	154	}
	155
	156	public static void main(String args[]) {
	157	// Tests.
	158	PidExperiment pe = new PidExperiment(0.0, 0.0, 0.0);
	159	pe.addError(1);
	160	pe.addError(-1);
	161	pe.addError(1);
	162	pe.addError(-1);
	163	if (2 != pe.getNextCycle(0)) {
	164	System.out.println("TEST #1 FAILED. Expected 2, got " + pe.getNextCycle(0));
	165	System.exit(1);
	166	}
	167
	168	pe = new PidExperiment(0.0, 0.0, 0.0);
	169	pe.addError(-1);
	170	pe.addError(1);
	171	pe.addError(-1);
	172	pe.addError(1);
	173	pe.addError(-1);
	174	if (3 != pe.getNextCycle(0)) {
	175	System.out.println("TEST #2 FAILED. Expected 3, got " + pe.getNextCycle(0));
	176	System.exit(1);
	177	}
	178
	179	System.out.println("SUCCESS");
	180	}
	181	}

-2

org/haldean/chopper/server/PidLogger.java less more

45	45
46	46	public String[] processablePrefixes() {
47	47	if (activated) {
48		return new String[] {"ACCEL", "MOTORSPEED", "GUID:PID:SET", "GUID:PID:VALUE"};
	48	return new String[] {"GUID:ERROR", "MOTORSPEED", "GUID:PID:SET", "GUID:PID:VALUE"};
49	49	} else {
50	50	return new String[0];
51	51	}

76	76	}
77	77	}
78	78	}
79		}⏎
	79	}

+176

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org/haldean/chopper/server/PidTuner.java less more

	0	package org.haldean.chopper.server;
	1
	2	import org.apache.commons.math3.distribution.MultivariateNormalDistribution;
	3
	4	import java.io.BufferedWriter;
	5	import java.io.FileWriter;
	6	import java.io.IOException;
	7	import java.io.OutputStreamWriter;
	8
	9	import java.text.SimpleDateFormat;
	10	import java.util.ArrayList;
	11	import java.util.Date;
	12	import java.util.PriorityQueue;
	13	import java.util.Random;
	14	import java.util.HashSet;
	15
	16	public class PidTuner implements Updatable {
	17	private static enum TuningAxis { DX, DY, DZ, DT };
	18	// Axis to tune. Either DX or DY.
	19	private TuningAxis mAxis;
	20
	21	// Search Parameters
	22
	23	// StDev for expanding nodes.
	24	private static final double expStdev = 2.0e-6;
	25	// Uniform distribution for creating initial nodes
	26	private static final double initRangeStart = 0;
	27	private static final double initRangeEnd = 1.0e-4;
	28	// Number of nodes to select from fringe.
	29	private static final int SELECT_NUM = 3;
	30	// Number of children to expand from each selected node.
	31	private static final int EXPAND_NUM = 3;
	32
	33	private static SimpleDateFormat dateFormat =
	34	new SimpleDateFormat("EEE, d MMM yyyy HH:mm:ss");
	35
	36	private ArrayList<PidExperiment> mFringe;
	37	private HashSet<PidExperiment> mHistory;
	38	private int mFringeIndex;
	39	// Covariance matrix for expanding nodes.
	40	private double[][] mExpCovar;
	41	private Random rn;
	42	private BufferedWriter output;
	43
	44	private boolean mEnabled = false;
	45
	46	public PidTuner() {
	47	try {
	48	String axis = ServerCreator.getArgument("pidTuning");
	49	mEnabled = true;
	50	if (axis.equals("dx")) {
	51	mAxis = TuningAxis.DX;
	52	} else if (axis.equals("dy")) {
	53	mAxis = TuningAxis.DY;
	54	} else if (axis.equals("dt")) {
	55	mAxis = TuningAxis.DT;
	56	} else {
	57	mEnabled = false;
	58	}
	59	} catch (IllegalArgumentException e) {
	60	// Default state; no tuning.
	61	return;
	62	}
	63	mFringe = new ArrayList<PidExperiment>();
	64	mHistory = new HashSet<PidExperiment>();
	65	mFringeIndex = 0;
	66	rn = new Random();
	67	try {
	68	output = new BufferedWriter(new FileWriter("tuning_" + mAxis + ".txt", true));
	69	output.write("# "+ dateFormat.format(new Date()));
	70	output.newLine();
	71	output.write("# tuning " + mAxis + " select_num " + SELECT_NUM + " expand_num " +
	72	EXPAND_NUM);
	73	output.newLine();
	74	} catch (IOException e) {
	75	Debug.log("WARNING: PID TUNING LOGGING FAILED.");
	76	e.printStackTrace();
	77	}
	78	mExpCovar = new double[3][3];
	79	for (int i = 0; i < 3; i++) {
	80	for (int j = 0; j < 3; j++) {
	81	if (i == j) {
	82	mExpCovar[i][j] = expStdev;
	83	} else {
	84	mExpCovar[i][j] = 0.0;
	85	}
	86	}
	87	}
	88
	89	// Create list of PidExperiments
	90	double initRange = initRangeEnd - initRangeStart;
	91	for (int j = 0; j < SELECT_NUM * EXPAND_NUM; j++) {
	92	double p = rn.nextDouble() * initRange + initRangeStart;
	93	double i = rn.nextDouble() * initRange + initRangeStart;
	94	double d = rn.nextDouble() * initRange + initRangeStart;
	95	mFringe.add(new PidExperiment(p, i, d));
	96	}
	97	}
	98
	99	public void update(String message) {
	100	if (!mEnabled) return;
	101	if (!message.startsWith("GUID:ERROR")) return;
	102	// retrieve error for my axis
	103	String parts[] = message.split(":");
	104	Double error = new Double(parts[2 + mAxis.ordinal()]);
	105	// Add error to current PidE
	106	PidExperiment currentExp = mFringe.get(mFringeIndex);
	107	currentExp.addError(error);
	108	// If PidE not done, return;
	109	if (!currentExp.isDone()) return;
	110	// PidE done: record result, increment index
	111	try {
	112	if (output != null) {
	113	output.write(currentExp.gnuplotLine());
	114	output.newLine();
	115	output.flush();
	116	}
	117	} catch (IOException e) {
	118	Debug.log("WARNING: PID TUNING LOGGING FAILED");
	119	e.printStackTrace();
	120	}
	121	mFringeIndex++;
	122	// If index <= mFringe.size(), send new PID values, return;
	123	if (mFringeIndex <= mFringe.size()) {
	124	PidExperiment newExp = mFringe.get(mFringeIndex);
	125	EnsignCrusher.tunePid(mAxis.ordinal(), 0, newExp.getP());
	126	EnsignCrusher.tunePid(mAxis.ordinal(), 1, newExp.getI());
	127	EnsignCrusher.tunePid(mAxis.ordinal(), 2, newExp.getD());
	128	return;
	129	}
	130	// Fringe done: copy into history.
	131	mHistory.addAll(mFringe);
	132	mFringeIndex = 0;
	133
	134	// stochastically choose the nodes to expand.
	135	ArrayList<PidExperiment> nodesToExpand = new ArrayList<PidExperiment>();
	136	for (int i = 0; i < SELECT_NUM; i++) {
	137	// the usual method of drawing a random element probabilistically.
	138	double scoreSum = 0.0;
	139	for (PidExperiment p : mFringe) {
	140	scoreSum += p.getScore();
	141	}
	142	double pos = rn.nextDouble() * scoreSum;
	143	double runningSum = 0.0;
	144	for (int j = 0; j < mFringe.size(); j++) {
	145	runningSum += mFringe.get(j).getScore();
	146	if (runningSum >= pos) {
	147	nodesToExpand.add(mFringe.get(j));
	148	mFringe.remove(mFringe.get(j)); // To avoid duplicates.
	149	break;
	150	}
	151	}
	152	}
	153	// Expand the selected nodes into new Fringe, checking against history.
	154	mFringe.clear();
	155	for (PidExperiment parent : nodesToExpand) {
	156	double[] mean = new double[3];
	157	mean[0] = parent.getP();
	158	mean[1] = parent.getI();
	159	mean[2] = parent.getD();
	160	MultivariateNormalDistribution dist =
	161	new MultivariateNormalDistribution(mean, mExpCovar);
	162	for (int i = 0; i < EXPAND_NUM; i++) {
	163	double[] sample = dist.sample();
	164	PidExperiment child = new PidExperiment(sample[0], sample[1], sample[2]);
	165	while (mHistory.contains(child)) {
	166	// Extraordinarily unlikely under this implementation of expansion,
	167	// but we'll check anyway in case the expansion implementation changes.
	168	sample = dist.sample();
	169	child = new PidExperiment(sample[0], sample[1], sample[2]);
	170	}
	171	mFringe.add(child);
	172	}
	173	}
	174	}
	175	}

-5

org/haldean/chopper/server/ServerCreator.java less more

41	41
42	42	public static String getArgument(String argumentName) throws IllegalArgumentException {
43	43	if (! arguments.containsKey(argumentName)) {
44		throw new IllegalArgumentException(argumentName +
	44	throw new IllegalArgumentException(argumentName +
45	45	" was not specified on the command line.");
46	46	}
47	47
48	48	return arguments.get(argumentName);
49	49	}
50	50
51		/** Run the chopper host
	51	/** Run the chopper host
52	52	* @param args -d enables printing debug information to the command line,
53		* and -h followed by a hostname specifies the hostname to connect to
	53	* and -h followed by a hostname specifies the hostname to connect to
54	54	* @throws Exception if the provided host name is invalid */
55	55	public static void main(String args[]) {
56	56	/* Parse command line arguments */

63	63	arguments.put(argparts[0], value);
64	64	}
65	65	}
66
	66
67	67	if (arguments.containsKey("debug")) {
68	68	Debug.setEnabled(true);
69	69	if (arguments.containsKey("debuglog")) {

105	105
106	106	serverHost.accept();
107	107	}
108		}⏎
	108	}

+10

-6

org/haldean/chopper/server/ServerHost.java less more

9	9	import javax.swing.event.*;
10	10
11	11	/** The superclass! This is the frame that encompasses everything
12		* else.
	12	* else.
13	13	* @author William Brown */
14	14	public class ServerHost extends JFrame {
15	15	/** The chopper name. We've been changing it enough that

23	23	/** The component that displays the globe with tracking
24	24	* data and location selection */
25	25	final WorldWindComponent globeComponent;
26		/** The component that displays a 3D rendering of the
	26	/** The component that displays a 3D rendering of the
27	27	* current orientation of the chopper */
28	28	final OrientationComponent orientationComponent;
29	29	/** The component that displays telemetry and allows for

34	34	/** The component that displays error values from the four PID
35	35	* loops on the chopper. */
36	36	final PidErrorComponent pidComponent;
	37	final PidTuner pidTuner;
37	38	/** An Updatable that receives all messages from the chopper
38	39	* @see EchoUpdatable */
39	40	final Updatable status;

77	78	imagePanel = new ImagePanel();
78	79	accelerationComponent = new AccelerationComponent();
79	80	pidComponent = new PidErrorComponent();
	81	pidTuner = new PidTuner();
80	82	sensorComponent = new SensorComponent();
81	83	status = new EchoUpdatable();
82	84	motorComponent = new MotorComponent();

98	100	dataReceiver.tie(PidTuningComponent.getInstance());
99	101	dataReceiver.tieImage(imagePanel);
100	102
	103	dataReceiver.tie(pidTuner);
	104
101	105	MessageHookManager.addHook(motorComponent);
102	106	MessageHookManager.addHook(sp);
103	107

146	150
147	151	/** Initialize operating system specific stuff */
148	152	public void osInit() {
149		Debug.log("Running on " + System.getProperty("os.name") + " " +
	153	Debug.log("Running on " + System.getProperty("os.name") + " " +
150	154	System.getProperty("os.arch"));
151	155	if (System.getProperty("os.name").startsWith("Mac"))
152	156	System.setProperty("apple.laf.useScreenMenuBar", "true");

156	160	public void start() {
157	161	/* Update the Look and Feel of components created
158	162	* in the constructor */
159
	163
160	164	/* The right/left pane creator */
161	165	JPanel horizontalPanel = new JPanel(new GridLayout(1,2));
162	166

197	201	disconnectButton.addActionListener(new ActionListener() {
198	202	private boolean connected = true;
199	203	public void actionPerformed(ActionEvent e) {
200		/* If connected, stop the DataReceiver and switch the
	204	/* If connected, stop the DataReceiver and switch the
201	205	* text of the button. If not connected, restart the
202	206	* DataReceiver thread */
203	207	if (connected) {

247	251	new Thread(pad).start();
248	252	}
249	253	}
250		}⏎
	254	}

-3

run less more

11	11	fi
12	12
13	13	export ANDROIDPATH="$ANDROID_ROOT/platforms/android-8/android.jar"
14		export CLASSPATH=$ANDROIDPATH:$CLASSPATH:./lib/simplegraph/:`ls -1 jars/.jar jars/worldwind/.jar \| xargs \| sed "s/ /:/g"`:/usr/share/java/j3dcore.jar:/usr/share/java/j3dutils.jar:/usr/share/java/vecmath.jar:.
	14	export CLASSPATH=$ANDROIDPATH:$CLASSPATH:./lib/simplegraph/:`ls -1 jars/.jar jars/worldwind/.jar \| xargs \| sed "s/ /:/g"`:/usr/share/java/j3dcore.jar:/usr/share/java/j3dutils.jar:/usr/share/java/vecmath.jar:.:/usr/lib/jvm/java-7-openjdk/jre/lib/ext/j3dcore.jar:/usr/lib/jvm/java-7-openjdk/jre/lib/ext/j3dutils.jar:/usr/lib/jvm/java-7-openjdk/jre/lib/ext/vecmath.jar:
15	15	export PORT=7000
16	16
17	17	if [ 'heartless' == "$1" ] \|\| [ 'heartless' == "$2" ]; then

36	36	CMD="java -Djava.library.path=/lib/:jars/worldwind/:jars/ -Xmx512m
37	37	-Dsun.java2d.noddraw=true $DOCK org.haldean.chopper.server.ServerCreator
38	38	host=$HOST port=$PORT $DEBUG $HEARTLESS pidlog=pidlog.txt imgdir=video/
39		debuglog=debug.txt"
	39	debuglog=debug.txt pidTuning=dx"
40	40	echo $CMD
41	41	exec $CMD
42	42	}

52	52	}
53	53
54	54	build() {
55		javac org/haldean/chopper/server/ServerCreator.java -Xlint:deprecation
	55	javac org/haldean/chopper/server/ServerCreator.java -Xlint:deprecation -encoding ISO-8859-1
56	56	}
57	57
58	58	keyboard() {

text/spring/essay-spring.pdf less more

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text/spring/essay-spring.tex less more

0		\input{latex_template.tex}
	0	\documentclass[letterpaper]{article}
	1	\usepackage{amsmath,amssymb,appendix,color,etoolbox,
	2	graphicx,index,listings,lscape,natbib,url}
	3
	4	\usepackage{mathpazo} % math & rm
	5	\linespread{1.05} % Palatino needs more leading (space between lines)
	6	\usepackage[scaled]{helvet} % ss
	7	\normalfont
	8	\usepackage[T1]{fontenc}
	9
	10	\newcommand\figref[1]{Figure \ref{fig:#1}}
	11	\newcommand\tabref[1]{Table \ref{tab:#1}}
	12	\newcommand\code[1]{\texttt{#1}}
	13	\newcommand\pipe[0]{\;\|\;}
	14	\newcommand\st[0]{\;\mathrm{s.t.}\;}
	15	\newcommand\startappendix{\appendix\appendixpage\addappheadtotoc}
	16
	17	\newcommand\imgfig[4]{
	18	\begin{figure}[h]
	19	\centering
	20	\includegraphics[scale=#2]{figures/#1}
	21	\caption{#3}
	22	\label{fig:#4}
	23	\end{figure}}
	24
	25	\definecolor{gray}{gray}{0.95}
	26
	27	\lstset{
	28	language=Python,
	29	basicstyle=\footnotesize\ttfamily,
	30	numbersep=5pt,
	31	tabsize=2,
	32	extendedchars=true,
	33	breaklines=true,
	34	stringstyle=\ttfamily,
	35	showspaces=false,
	36	showtabs=false,
	37	xleftmargin=17pt,
	38	framexleftmargin=17pt,
	39	framexrightmargin=5pt,
	40	framexbottommargin=4pt,
	41	backgroundcolor=\color{gray},
	42	showstringspaces=false
	43	}
	44
1	45	\title{Stable Flight and Object Tracking with a Quadricopter using an
2	46	Android Device}
3	47	\author{Benjamin Bardin \and William Brown
4	48	\and Dr. Paul Blaer}
5	49
6	50	\begin{document}
7		\todolist
8	51
9	52	\maketitle
10	53

18	61	platform on our first hardware iteration, named Jabberwock.
19	62	\end{abstract}
20	63	\tableofcontents
	64	\pagebreak
21	65
22	66	\section{Motivation}
23	67	\subsection{Objectives}

76	120
77	121	\section{Pilot Android Application}
78	122	\label{sec:pilot}
79		The Pilot program has two core functionalities.‭ ‬The first is the
80		actual robotic control of the quadrocopter itself‭; ‬the second is
81		communication with the control server.‭ ‬The parallel processing
	123	The Pilot program has two core functionalities. The first is the
	124	actual robotic control of the quadrocopter itself; the second is
	125	communication with the control server. The parallel processing
82	126	required in these distinct tasks is complicated by the performance
83		requirements of the program.‭ ‬Flight control processing must take place
84		in real time -- or an extremely close approximation.‭ ‬Communication
	127	requirements of the program. Flight control processing must take place
	128	in real time -- or an extremely close approximation. Communication
85	129	with the control server, on the other hand, yields priority to flight
86		control.‭ ‬Consequently,‭ ‬a great deal of effort went into prioritizing
87		inter-thread communications and access of shared data.‭ ‬For flight
88		control algorithms,‭ ‬blocking on locked data is unacceptable,‭ ‬since
89		timely performance is essential‭; ‬instead of blocking,‭ ‬they will use
90		the most recent,‭ ‬locally stored version of the data requested.‭ ‬For
91		communication algorithms,‭ ‬accessing flawed data is unacceptable‭; ‬the
	130	control. Consequently, a great deal of effort went into prioritizing
	131	inter-thread communications and access of shared data. For flight
	132	control algorithms, blocking on locked data is unacceptable, since
	133	timely performance is essential; instead of blocking, they will use
	134	the most recent, locally stored version of the data requested. For
	135	communication algorithms, accessing flawed data is unacceptable; the
92	136	control server must not receive out-of-date information portrayed as
93	137	current.
94	138
95	139	\subsection{Flight Control}
96		Flight control itself is divided into two main components:‭ ‬navigation
	140	Flight control itself is divided into two main components: navigation
97	141	and guidance.
98	142
99	143	\subsubsection{Navigation}
100		Navigation determines a desired velocity vector for the quadrocopter.‭
101		‬In‭ “‬manual‭” ‬mode,‭ ‬it simply accepts this vector from the control
102		server.‭ ‬In‭ “‬autopilot‭” ‬mode,‭ ‬or when the connection is lost,‭ ‬autopilot
103		subroutines determine the desired velocity vector.‭ ‬It's determination
104		is based on two factors.‭ ‬The first is its current location.‭ ‬The second
105		is either previously transmitted autopilot instructions,‭ ‬or
106		pre-programmed safeties‭ (‬for low power,‭ ‬bad network,‭ ‬etc.‭).
	144	Navigation determines a desired velocity vector for the quadrocopter.
	145	In ``manual'' mode, it simply accepts this vector from the control
	146	server. In ``autopilot'' mode, or when the connection is lost, autopilot
	147	subroutines determine the desired velocity vector. It's determination
	148	is based on two factors. The first is its current location. The second
	149	is either previously transmitted autopilot instructions, or
	150	pre-programmed safeties (for low power, bad network, etc.).
107	151
108	152	\subsubsection{Guidance}
109		Guidance takes the desired velocity from Navigation,‭ ‬and uses PID
	153	Guidance takes the desired velocity from Navigation, and uses PID
110	154	loops to adjust individual motor speeds to achieve and maintain that
111		vector.‭ ‬To improve the performance of the PID loop,‭ ‬the system is
112		transformed into an approximately linear one.‭ ‬The transformation
	155	vector. To improve the performance of the PID loop, the system is
	156	transformed into an approximately linear one. The transformation
113	157	accounts both for the quadratic relationship between motor speed and
114		thrust,‭ ‬and for changing effects of motor thrust as its orientation
	158	thrust, and for changing effects of motor thrust as its orientation
115	159	changes.
116	160
117	161	\section{Server Software}

201	245	color from red to green, denoting the current speed of the motor.
202	246
203	247	\section{Communication}
204		Communication is composed of two main components:‭ ‬telemetry and
205		commands/data.‭ ‬Each is relayed on separate ports,‭ ‬since commands must
	248	Communication is composed of two main components: telemetry and
	249	commands/data. Each is relayed on separate ports, since commands must
206	250	be relayed as synchronously as possible and telemetry will be
207	251	asynchronous.
208	252
209	253	\subsection{Telemetry}
210	254	The telemetry modules continuously run the Android's preview
211		functionality,‭ ‬at‭ ‬5fps.‭ ‬Each frame is saved to a buffer as it is
212		available,‭ ‬overwriting the previous frame.‭ ‬When the Android has
213		finished sending one frame to the control server,‭ ‬it immediately
214		copies the buffer and starts sending the frame.‭ ‬The result is real
215		time telepresence,‭ ‬at approximately two to four fps and a lag of
	255	functionality, at 5fps. Each frame is saved to a buffer as it is
	256	available, overwriting the previous frame. When the Android has
	257	finished sending one frame to the control server, it immediately
	258	copies the buffer and starts sending the frame. The result is real
	259	time telepresence, at approximately two to four fps and a lag of
216	260	less than one second.
217	261
218	262	\subsection{Commands and Data}
219	263	Commands and data are relayed in the form of strings over standard
220		Java sockets.‭ ‬When the connection is lost,‭ ‬the Android device
221		immediately tries to reconnect,‭ ‬continuing to do so indefinitely.‭
222		‬While the connection is lost, autopilot is enabled and the‭
223		``‬communication lost‭'' pre-programmed instruction set is engaged.
	264	Java sockets. When the connection is lost, the Android device
	265	immediately tries to reconnect, continuing to do so indefinitely.
	266	While the connection is lost, autopilot is enabled and the
	267	``communication lost'' pre-programmed instruction set is engaged.
224	268
225	269	\subsection{Message Formats}
226	270	\label{sec:msgs}
227	271	‏Messages between the Android and the control server are sent as
228		strings,‭ ‬delimited by colons.‭ ‬The strings from the control server --
229		commands -- contain the instruction itself,‭ ‬prefixed by a sequence of
230		meta-data describing the instruction.‭ ‬Similarly,‭ ‬data from the Android
231		device contain not just the data,‭ ‬but also a prefix tag describing the
232		data.‭ ‬This enables somewhat efficient analysis on each end:‭ ‬messages can
	272	strings, delimited by colons. The strings from the control server --
	273	commands -- contain the instruction itself, prefixed by a sequence of
	274	meta-data describing the instruction. Similarly, data from the Android
	275	device contain not just the data, but also a prefix tag describing the
	276	data. This enables somewhat efficient analysis on each end: messages can
233	277	be routed only to those components that are registered to process a
234	278	given prefix tag. Messages are not transmitted directly between the
235		Android device and the control server.‭ ‬Instead,‭ ‬they are routed through
236		a separate,‭ ‬dedicated broker server.‭ ‬This enables the control server
237		itself to operate easily from different IP addresses,‭ ‬and hence from
	279	Android device and the control server. Instead, they are routed through
	280	a separate, dedicated broker server. This enables the control server
	281	itself to operate easily from different IP addresses, and hence from
238	282	various locations. It also allows for easy logging and playback of
239	283	sessions -- the broker server logs all data and commands, and can replay
240	284	a session later for analysis.